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Linux for professional

B
BennethObilor

The document provides an overview of getting started with GNU/Linux. It covers useful terminal shortcuts, file management commands like navigating directories, listing files, and copying/removing files. It also discusses detecting the Linux distribution, getting system information, and using common commands like ls, tar, ssh and more. The document is intended as a reference for Linux professionals.

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Linux Notes for Professionals Linux ® Notes for Professionals GoalKicker.com Free Programming Books Disclaimer This is an unocial free book created for educational purposes and is not aliated with ocial Linux® group(s) or company(s). All trademarks and registered trademarks are the property of their respective owners 50+ pages of professional hints and tricks
Contents About 1 ................................................................................................................................................................................... Chapter 1: Getting started with GNU/Linux 2 ..................................................................................................... Section 1.1: Useful shortcuts 2 .......................................................................................................................................... Section 1.2: File Management Commands 3 .................................................................................................................. Section 1.3: Hello World 5 ................................................................................................................................................. Section 1.4: Basic Linux Utilities 5 .................................................................................................................................... Section 1.5: Searching for files by patterns in name/contents 6 ................................................................................. Section 1.6: File Manipulation 7 ........................................................................................................................................ Section 1.7: File/Directory details 8 ................................................................................................................................. Chapter 2: Detecting Linux distribution name and version 11 .................................................................. Section 2.1: Detect what debian-based distribution you are working in 11 ............................................................... Section 2.2: Detect what systemd-based distribution you are using 11 .................................................................... Section 2.3: Detect what RHEL / CentOS / Fedora distribution you are working in 12 ............................................ Section 2.4: Uname - Print information about the current system 13 ........................................................................ Section 2.5: Detect basic informations about your distro 13 ...................................................................................... Section 2.6: using GNU coreutils 13 ................................................................................................................................ Section 2.7: find your linux os (both debian & rpm) name and release number 14 ................................................. Chapter 3: Getting information on a running Linux kernel 15 ................................................................... Section 3.1: Getting details of Linux kernel 15 ................................................................................................................ Chapter 4: Shell 16 ........................................................................................................................................................... Section 4.1: Changing default shell 16 ............................................................................................................................ Section 4.2: Basic Shell Utilities 17 .................................................................................................................................. Section 4.3: Create Your Own Command Alias 18 ........................................................................................................ Section 4.4: Locate a file on your system 18 ................................................................................................................. Chapter 5: Check Disk Space 19 ................................................................................................................................ Section 5.1: Investigate Directories For Disk Usage 19 ................................................................................................. Section 5.2: Checking Disk Space 21 .............................................................................................................................. Chapter 6: Getting System Information 23 ......................................................................................................... Section 6.1: Statistics about CPU, Memory, Network and Disk (I/O operations) 23 .................................................. Section 6.2: Using tools like lscpu and lshw 23 .............................................................................................................. Section 6.3: List Hardware 24 .......................................................................................................................................... Section 6.4: Find CPU model/speed information 25 ..................................................................................................... Section 6.5: Process monitoring and information gathering 26 .................................................................................. Chapter 7: ls command 28 ........................................................................................................................................... Section 7.1: Options for ls command 28 ......................................................................................................................... Section 7.2: ls command with most used options 28 .................................................................................................... Chapter 8: File Compression with 'tar' command 30 ...................................................................................... Section 8.1: Compress a folder 30 ................................................................................................................................... Section 8.2: Extract a folder from an archive 30 .......................................................................................................... Section 8.3: List contents of an archive 30 .................................................................................................................... Section 8.4: List archive content 31 ................................................................................................................................ Section 8.5: Compress and exclude one or multiple folder 31 .................................................................................... Section 8.6: Strip leading components 31 ...................................................................................................................... Chapter 9: Services 32 .................................................................................................................................................... Section 9.1: List running service on Ubuntu 32 .............................................................................................................. Section 9.2: Systemd service management 32 .............................................................................................................
Chapter 10: Managing Services 33 ........................................................................................................................... Section 10.1: Diagnosing a problem with a service 33 .................................................................................................. Section 10.2: Starting and Stopping Services 33 ........................................................................................................... Section 10.3: Getting the status of a service 34 ............................................................................................................. Chapter 11: Modifying Users 35 .................................................................................................................................. Section 11.1: Setting your own password 35 ................................................................................................................... Section 11.2: Setting another user's password 35 .......................................................................................................... Section 11.3: Adding a user 35 .......................................................................................................................................... Section 11.4: Removing a user 35 .................................................................................................................................... Section 11.5: Removing a user and its home folder 35 ................................................................................................. Section 11.6: Listing groups the current user is in 35 ..................................................................................................... Section 11.7: Listing groups a user is in 35 ...................................................................................................................... Chapter 12: LAMP Stack 36 ........................................................................................................................................... Section 12.1: Installing LAMP on Arch Linux 36 ............................................................................................................... Section 12.2: Installing LAMP on Ubuntu 37 ................................................................................................................... Section 12.3: Installing LAMP stack on CentoOS 38 ....................................................................................................... Chapter 13: tee command 40 ...................................................................................................................................... Section 13.1: Write output to stdout, and also to a file 40 ............................................................................................. Section 13.2: Write output from the middle of a pipe chain to a file and pass it back to the pipe 40 ..................... Section 13.3: write the output to multiple files 40 .......................................................................................................... Section 13.4: Instruct tee command to append to the file 40 ....................................................................................... Chapter 14: Secure Shell (SSH) 42 ............................................................................................................................ Section 14.1: Connecting to a remote server 42 ............................................................................................................. Section 14.2: Installing OpenSSH suite 42 ....................................................................................................................... Section 14.3: Configuring an SSH server to accept connections 43 ............................................................................ Section 14.4: Passwordless connection (using a key pair) 43 ...................................................................................... Section 14.5: Generate public and private key 43 ......................................................................................................... Section 14.6: Disable ssh service 43 ................................................................................................................................ Chapter 15: SCP 45 ............................................................................................................................................................ Section 15.1: Secure Copy 45 ............................................................................................................................................ Section 15.2: Basic Usage 45 ........................................................................................................................................... Chapter 16: GnuPG (GPG) 46 ........................................................................................................................................ Section 16.1: Exporting your public key 46 ...................................................................................................................... Section 16.2: Create and use a GnuPG key quickly 46 .................................................................................................. Chapter 17: Network Configuration 47 .................................................................................................................. Section 17.1: Local DNS resolution 47 .............................................................................................................................. Section 17.2: Configure DNS servers for domain name resolution 47 ........................................................................ Section 17.3: See and manipulate routes 47 .................................................................................................................. Section 17.4: Configure a hostname for some other system on your network 48 .................................................... Section 17.5: Interface details 49 ..................................................................................................................................... Section 17.6: Adding IP to an interface 50 ...................................................................................................................... Chapter 18: Midnight Commander 52 ..................................................................................................................... Section 18.1: Midnight Commander function keys in browsing mode 52 .................................................................... Section 18.2: Midnight Commander function keys in file editing mode 52 ................................................................. Chapter 19: Change root (chroot) 54 ...................................................................................................................... Section 19.1: Requirements 54 ......................................................................................................................................... Section 19.2: Manually changing root in a directory 54 ............................................................................................... Section 19.3: Reasons to use chroot 55 .......................................................................................................................... Chapter 20: Package Managers 56 ..........................................................................................................................
Section 20.1: How to update packages with the apt package manager 56 .............................................................. Section 20.2: How to install a package with the pacman package manager 56 ...................................................... Section 20.3: How to update packages with the pacman package manager 56 ..................................................... Section 20.4: How to update packages with yum 57 ................................................................................................... Chapter 21: Compiling the Linux kernel 58 ........................................................................................................... Section 21.1: Compilation of Linux Kernel on Ubuntu 58 ............................................................................................... Credits 59 .............................................................................................................................................................................. You may also like 61 ........................................................................................................................................................
Linux® Notes for Professionals 1 About Please feel free to share this PDF with anyone for free, latest version of this book can be downloaded from: http://GoalKicker.com/LinuxBook This Linux® Notes for Professionals book is compiled from Stack Overflow Documentation, the content is written by the beautiful people at Stack Overflow. Text content is released under Creative Commons BY-SA, see credits at the end of this book whom contributed to the various chapters. Images may be copyright of their respective owners unless otherwise specified This is an unofficial free book created for educational purposes and is not affiliated with official Linux® group(s) or company(s) nor Stack Overflow. All trademarks and registered trademarks are the property of their respective company owners The information presented in this book is not guaranteed to be correct nor accurate, use at your own risk Please send feedback and corrections to web@petercv.com
Linux® Notes for Professionals 2 Chapter 1: Getting started with GNU/Linux Section 1.1: Useful shortcuts Using The Terminal The examples in this document assume that you are using a POSIX-compliant (such as bash, sh, zsh, ksh) shell. Large portions of GNU/Linux functionality are achieved using the terminal. Most distributions of Linux include terminal emulators that allow users to interact with a shell from their desktop environment. A shell is a command- line interpreter that executes user inputted commands. Bash (Bourne Again SHell) is a common default shell among many Linux distributions and is the default shell for macOS. These shortcuts will work if you are using Bash with the emacs keybindings (set by default): Open terminal Ctrl + Alt + T or Super + T Cursor movement Ctrl + A Go to the beginning of the line you are currently typing on. Ctrl + E Go to the end of the line you are currently typing on. Ctrl + XX Move between the beginning of the line and the current position of the cursor. Alt + F Move cursor forward one word on the current line. Alt + B Move cursor backward one word on the current line. Ctrl + F Move cursor forward one character on the current line. Ctrl + B Move cursor backward one character on the current line. Text manipulation Ctrl + U Cut the line from the current position to the beginning of the line, adding it to the clipboard. If you are at the end of the line, cut the entire line. Ctrl + K Cut the line from the current position to the end of the line, adding it to the clipboard. If you are at the beginning of the line, cut the entire line. Ctrl + W Delete the word before the cursor, adding it to the clipboard. Ctrl + Y Paste the last thing from the clipboard that you cut recently (undo the last delete at the current cursor position). Alt + T Swap the last two words before the cursor. Alt + L Make lowercase from cursor to end of word. Alt + U Make uppercase from cursor to end of word. Alt + C Capitalize to end of word starting at cursor (whole word if cursor is at the beginning of word). Alt + D Delete to end of word starting at cursor (whole word if cursor is at the beginning of word). Alt + . Prints the last word written in previous command. Ctrl + T Swap the last two characters before the cursor. History access Ctrl + R Lets you search through previously used commands. Ctrl + G Leave history searching mode without running a command. Ctrl + J Lets you copy current matched command to command line without running it, allowing you to
Linux® Notes for Professionals 3 make modifications before running the command. Alt + R Revert any changes to a command you’ve pulled from your history, if you’ve edited it. Ctrl + P Shows last executed command, i.e. walk back through the command history (Similar to up arrow). Ctrl + N Shows next executed command, i.e. walk forward through the command history (Similar to down arrow). Terminal control Ctrl + L Clears the screen, similar to the clear command. Ctrl + S Stop all output to the screen. This is useful when running commands with lots of long output. But this doesn't stop the running command. Ctrl + Q Resume output to the screen after stopping it with Ctrl+S. Ctrl + C End currently running process and return the prompt. Ctrl + D Log out of the current shell session, similar to the exit or logout command. In some commands, acts as End of File signal to indicate that a file end has been reached. Ctrl + Z Suspends (pause) currently running foreground process, which returns shell prompt. You can then use bg command allowing that process to run in the background. To again bring that process to foreground, use fg command. To view all background processes, use jobs command. Tab Auto-complete files and directory names. Tab Tab Shows all possibilities, when typed characters doesn't uniquely match to a file or directory name. Special characters Ctrl + H Same as Backspace. Ctrl + J Same as Return (historically Line Feed). Ctrl + M Same as Return (historically Carriage Return). Ctrl + I Same as Tab. Ctrl + G Bell Character. Ctrl + @ Null Character. Esc Deadkey equivalent to the Alt modifier. Close Terminal Ctrl + Shift + W To close terminal tab. Ctrl + Shift + Q To close entire terminal. Alternatively, you can switch to the vi keybindings in bash using set -o vi. Use set -o emacs to switch back to the emacs keybindings. Section 1.2: File Management Commands Linux uses some conventions for present and parent directories. This can be a little confusing for beginners. Whenever you are in a terminal in Linux, you will be in what is called the current working directory. Often your command prompt will display either the full working directory, or just the last part of that directory. Your prompt could look like one of the following: user@host ~/somedir $ user@host somedir $ user@host /home/user/somedir $ which says that your current working directory is /home/user/somedir.
Linux® Notes for Professionals 4 In Linux .. represents the parent directory and . represents the current directory. Therefore, if the current directory is /home/user/somedir, then cd ../somedir will not change the working directory. The table below lists some of the most used file management commands Directory navigation Command Utility pwd Get the full path of the current working directory. cd - Navigate to the last directory you were working in. cd ~ or just cd Navigate to the current user's home directory. cd .. Go to the parent directory of current directory (mind the space between cd and ..) Listing files inside a directory Command Utility ls -l List the files and directories in the current directory in long (table) format (It is recommended to use -l with ls for better readability). ls -ld dir-name List information about the directory dir-name instead of its contents. ls -a List all the files including the hidden ones (File names starting with a . are hidden files in Linux). ls -F Appends a symbol at the end of a file name to indicate its type (* means executable, / means directory, @ means symbolic link, = means socket, | means named pipe, > means door). ls -lt List the files sorted by last modified time with most recently modified files showing at the top (remember -l option provides the long format which has better readability). ls -lh List the file sizes in human readable format. ls -lR Shows all subdirectories recursively. tree Will generate a tree representation of the file system starting from the current directory. File/directory create, copy and remove Command Utility cp -p source destination Will copy the file from source to destination. -p stands for preservation. It preserves the original attributes of file while copying like file owner, timestamp, group, permissions etc. cp -R source_dir destination_dir Will copy source directory to specified destination recursively. mv file1 file2 In Linux there is no rename command as such. Hence mv moves/renames the file1 to file2. rm -i filename Asks you before every file removal for confirmation. IF YOU ARE A NEW USER TO LINUX COMMAND LINE, YOU SHOULD ALWAYS USE rm -i. You can specify multiple files. rm -R dir-name Will remove the directory dir-name recursively. rm -rf dir-name Will remove the directory dir recursively, ignoring non-existent files and will never prompt for anything. BE CAREFUL USING THIS COMMAND! You can specify multiple directories. rmdir dir-name Will remove the directory dir-name, if it's empty. This command can only remove empty directories. mkdir dir-name Create a directory dir-name. mkdir -p dir-name/dir-name Create a directory hierarchy. Create parent directories as needed, if they don't exist. You can specify multiple directories. touch filename Create a file filename, if it doesn't exist, otherwise change the timestamp of the file to current time. File/directory permissions and groups Command Utility chmod <specification> filename Change the file permissions. Specifications = u user, g group, o other, + add permission, - remove, r read, w write,x execute. chmod -R <specification> dir- name Change the permissions of a directory recursively. To change permission of a directory and everything within that directory, use this command. chmod go=+r myfile Add read permission for the owner and the group. chmod a +rwx myfile Allow all users to read, write or execute myfile.
Linux® Notes for Professionals 5 chmod go -r myfile Remove read permission from the group and others. chown owner1 filename Change ownership of a file to user owner1. chgrp grp_owner filename Change primary group ownership of file filename to group grp_owner. chgrp -R grp_owner dir-name Change primary group ownership of directory dir-name to group grp_owner recursively. To change group ownership of a directory and everything within that directory, use this command. Section 1.3: Hello World Type the following code into your terminal, then press Enter : echo "Hello World" This will produce the following output: Hello World Section 1.4: Basic Linux Utilities Linux has a command for almost any tasks and most of them are intuitive and easily interpreted. Getting Help in Linux Command Usability man <name> Read the manual page of <name>. man <section> <name> Read the manual page of <name>, related to the given section. man -k <editor> Output all the software whose man pages contain <editor> keyword. man -K <keyword> Outputs all man pages containing <keyword> within them. apropos <editor> Output all the applications whose one line description matches the word editor. When not able to recall the name of the application, use this command. help In Bash shell, this will display the list of all available bash commands. help <name> In Bash shell, this will display the info about the <name> bash command. info <name> View all the information about <name>. dpkg -l Output a list of all installed packages on a Debian-based system. dpkg -L packageName Will list out the files installed and path details for a given package on Debian. dpkg -l | grep -i <edit> Return all .deb installed packages with <edit> irrespective of cases. less /var/lib/dpkg/available Return descriptions of all available packages. whatis vim List a one-line description of vim. <command-name> --help Display usage information about the <tool-name>. Sometimes command -h also works, but not for all commands. User identification and who is who in Linux world Command Usability hostname Display hostname of the system. hostname -f Displays Fully Qualified Domain Name (FQDN) of the system. passwd Change password of current user. whoami Username of the users logged in at the terminal. who List of all the users currently logged in as a user. w Display current system status, time, duration, list of users currently logged in on system and other user information. last Who recently used the system. last root When was the last time root logged in as user. lastb Shows all bad login attempts into the system. chmod Changing permissions - read,write,execute of a file or directory.
Linux® Notes for Professionals 6 Process related information Command Usability top List all processes sorted by their current system resource usage. Displays a continually updated display of processes (By default 3 seconds). Use q key to exit top. ps List processes currently running on current shell session ps -u root List all of the processes and commands root is running ps aux List all the processes by all users on the current system Section 1.5: Searching for files by patterns in name/contents A common and task of someone using the Linux Command Line (shell) is to search for files/directories with a certain name or containing certain text. There are 2 commands you should familiarise yourself with in order to accomplish this: Find files by name find /var/www -name '*.css' This will print out the full path/filename to all files under /var/www that end in .css. Example output: /var/www/html/text-cursor.css /var/www/html/style.css For more info: man find Find files containing text grep font /var/www/html/style.css This will print all lines containing the pattern font in the specified file. Example output: font-weight: bold; font-family: monospace; Another example: grep font /var/www/html/ This doesn't work as you'd hoped. You get: grep: /var/www/html/: Is a directory You need to grep recursively to make it work, using the -R option: grep -R font /var/www/html/ Hey nice! Check out the output of this one: /var/www/html/admin/index.php: echo '<font color=red><b>Error: no dice</b></font><br/>'; /var/www/html/admin/index.php: echo '<font color=red><b>Error: try again</b></font><br/>'; /var/www/html/style.css: font-weight: bold; /var/www/html/style.css: font-family: monospace; Notice that when grep is matching multiple files, it prefixes the matched lines with the filenames. You can use the -
Linux® Notes for Professionals 7 h option to get rid of that, if you want. For more info: man grep Section 1.6: File Manipulation Files and directories (another name for folders) are at the heart of Linux, so being able to create, view, move, and delete them from the command line is very important and quite powerful. These file manipulation commands allow you to perform the same tasks that a graphical file explorer would perform. Create an empty text file called myFile: touch myFile Rename myFile to myFirstFile: mv myFile myFirstFile View the contents of a file: cat myFirstFile View the content of a file with pager (one screenful at a time): less myFirstFile View the first several lines of a file: head myFirstFile View the last several lines of a file: tail myFirstFile Edit a file: vi myFirstFile See what files are in your current working directory: ls Create an empty directory called myFirstDirectory: mkdir myFirstDirectory Create multi path directory: (creates two directories, src and myFirstDirectory) mkdir -p src/myFirstDirectory Move the file into the directory:
Linux® Notes for Professionals 8 mv myFirstFile myFirstDirectory/ You can also rename the file: user@linux-computer:~$ mv myFirstFile secondFileName Change the current working directory to myFirstDirectory: cd myFirstDirectory Delete a file: rm myFirstFile Move into the parent directory (which is represented as ..): cd .. Delete an empty directory: rmdir myFirstDirectory Delete a non-empty directory (i.e. contains files and/or other directories): rm -rf myFirstDirectory Make note that when deleting directories, that you delete ./ not / that will wipe your whole filesystem. Section 1.7: File/Directory details The ls command has several options that can be used together to show more information. Details/Rights The l option shows the file permissions, size, and last modified date. So if the root directory contained a dir called test and a file someFile the command: user@linux-computer:~$ ls -l Would output something like -rw-r--r-- 1 user users 70 Jul 22 13:36 someFile.txt drwxrwxrwx 2 user users 4096 Jul 21 07:18 test The permissions are in format of drwxrwxrwx. The first character represents the file type d if it's a directory - otherwise. The next three rwx are the permissions the user has over the file, the next three are the permissions the group has over the file, and the last three are the permissions everyone else has over the file. The r of rwx stands for if a file can be read, the w represents if the file can be modified, and the x stands for if the file can be executed. If any permission isn't granted a - will be in place of r, w, or x. So from above user can read and modify someFile.txt but the group has only read-only rights. To change rights you can use the chmod ### fileName command if you have sudo rights. r is represented by a
Linux® Notes for Professionals 9 value of 4, w is represented by 2, and x is represented by a 1. So if only you want to be able to modify the contents to the test directory Owner rwx = 4+2+1 = 7 Group r-x = 4+0+1 = 5 Other r-x = 4+0+1 = 5 So the whole command is chmod 755 test Now doing a ls -l would show something like drwxr-xr-x 2 user users 4096 Jul 21 07:20 test Readable Size Used in conjunction with the l option the h option shows file sizes that are human readable. Running user@linux-computer:~$ ls -lh Would output: total 4166 -rw-r--r-- 1 user users 70 Jul 22 13:36 someFile.txt drwxrwxrwx 2 user users 4.0K Jul 21 07:18 test Hidden To view hidden files use the a option. For example user@linux-computer:~$ ls -a Might list .profile someFile.txt test Total Directory Size To view the size of the current directory use the s option (the h option can also be used to make the size more readable). user@linux-computer:~$ ls -s Outputs total 4166 someFile.txt test Recursive View Lets say test directory had a file anotherFile and you wanted to see it from the root folder, you could use the R option which would list the recursive tree.
Linux® Notes for Professionals 10 user@linux-computer:~$ ls -R Outputs .: someFile.txt test ./test: anotherFile
Linux® Notes for Professionals 11 Chapter 2: Detecting Linux distribution name and version Section 2.1: Detect what debian-based distribution you are working in Just execute lsb_release -a. On Debian: $ lsb_release -a No LSB modules are available. Distributor ID: Debian Description: Debian GNU/Linux testing (stretch) Release: testing Codename: stretch On Ubuntu: $ lsb_release -a No LSB modules are available. Distributor ID: Ubuntu Description: Ubuntu 14.04.4 LTS Release: 14.04 Codename: trusty In case when you don't have lsb_release installed you may want to try some guessing, for example, there is a file /etc/issue that often contains distribution name. For example, on ubuntu: $ cat /etc/issue Ubuntu 12.04.5 LTS n l Don't use file /etc/debian_version because its contents do not match distribution name! Note that this will also work on non-Debian-family distributions like Fedora, RHEL, or openSUSE — but that lsb_release may not be installed. Section 2.2: Detect what systemd-based distribution you are using This method will work on modern versions of Arch, CentOS, CoreOS, Debian, Fedora, Mageia, openSUSE, Red Hat Enterprise Linux, SUSE Linux Enterprise Server, Ubuntu, and others. This wide applicability makes it an ideal as a first approach, with fallback to other methods if you need to also identify older systems. Look at /etc/os-release. In specific, look at variables NAME, VERSION, ID, VERSION_ID, and PRETTY_NAME. On Fedora, this file might look like: NAME=Fedora VERSION="24 (Workstation Edition)" ID=fedora VERSION_ID=24 PRETTY_NAME="Fedora 24 (Workstation Edition)" ANSI_COLOR="0;34"
Linux® Notes for Professionals 12 CPE_NAME="cpe:/o:fedoraproject:fedora:24" HOME_URL="https://fedoraproject.org/" BUG_REPORT_URL="https://bugzilla.redhat.com/" REDHAT_BUGZILLA_PRODUCT="Fedora" REDHAT_BUGZILLA_PRODUCT_VERSION=24 REDHAT_SUPPORT_PRODUCT="Fedora" REDHAT_SUPPORT_PRODUCT_VERSION=24 PRIVACY_POLICY_URL=https://fedoraproject.org/wiki/Legal:PrivacyPolicy VARIANT="Workstation Edition" VARIANT_ID=workstation On CentOS, this file might look like this: NAME="CentOS Linux" VERSION="7 (Core)" ID="centos" ID_LIKE="rhel fedora" VERSION_ID="7" PRETTY_NAME="CentOS Linux 7 (Core)" ANSI_COLOR="0;31" CPE_NAME="cpe:/o:centos:centos:7" HOME_URL="https://www.centos.org/" BUG_REPORT_URL="https://bugs.centos.org/" CENTOS_MANTISBT_PROJECT="CentOS-7" CENTOS_MANTISBT_PROJECT_VERSION="7" REDHAT_SUPPORT_PRODUCT="centos" REDHAT_SUPPORT_PRODUCT_VERSION="7" This file is documented on the freedesktop web site; in principle, it is not systemd specific — but it will exist on all systemd-based distributions. From the bash shell, one can source the /etc/os-release file and then use the various variables directly, like this: $ ( source /etc/os-release && echo "$PRETTY_NAME" ) Fedora 24 (Workstation Edition) Section 2.3: Detect what RHEL / CentOS / Fedora distribution you are working in Look at the contents of /etc/redhat-release cat /etc/redhat-release Here is the output from a Fedora 24 machine: Fedora release 24 (Twenty Four) As mentioned in the debian-based response, you can also use the lsb_release -a command, which outputs this from a Fedora 24 machine: LSB Version: :core-4.1-amd64:core-4.1-noarch:cxx-4.1-amd64:cxx-4.1-noarch:desktop-4.1- amd64:desktop-4.1-noarch:languages-4.1-amd64:languages-4.1-noarch:printing-4.1-amd64:printing-4.1- noarch Distributor ID: Fedora Description: Fedora release 24 (Twenty Four) Release: 24 Codename: TwentyFour
Linux® Notes for Professionals 13 Section 2.4: Uname - Print information about the current system Uname is the short name for unix name. Just type uname in console to get information about your operating system. uname [OPTION] If no OPTION is specified, uname assumes the -s option. -a or --all - Prints all information, omitting -p and -i if the information is unknown. Example: > uname -a SunOS hope 5.7 Generic_106541-08 sun4m sparc SUNW,SPARCstation-10 All the options: -s, --kernel-name Print the kernel name. -n, --nodename Print the network node hostname. -r, --kernel-release Print the kernel release. -v, --kernel-version Print the kernel version. -m, --machine Print the machine hardware name. -p, --processor Print the processor type, or "unknown". -i, --hardware-platform Print the hardware platform, or "unknown". -o, --operating-system Print the operating system. --help Display a help message, and exit. --version Display version information, and exit. Section 2.5: Detect basic informations about your distro just execute uname -a. On Arch: $ uname -a Linux nokia 4.6.4-1-ARCH #1 SMP PREEMPT Mon Jul 11 19:12:32 CEST 2016 x86_64 GNU/Linuxenter code here Section 2.6: using GNU coreutils So the GNU coreutils should be avaialable on all linux based systems (please correct me if I am wrong here). If you do not know what system you are using you may not be able to directly jump to one of the examples above, hence this may be your first port of call. `$ uname -a On my system this gives me the following... `Linux Scibearspace 3.16.0-4-amd64 #1 SMP Debian 3.16.7-ckt25-2+deb8u3 (2016-07-02) x86_64 GNU/Linux Here you can see the following :
Linux® Notes for Professionals 14 Scibearspace : the name of my pc Scibearspace : the name of my pc 3.16.0-4-amd64 : the kernel and architecture SMP Debian 3.16.7-CKT25-2+deb8u3 : tells me I am running debian with the 3.16 kernel Finaly the last part I am running debian 8 (update 3). I would welcome any others to add in results for RHEL, and SuSe systems. Section 2.7: find your linux os (both debian & rpm) name and release number Most of linux distros stores its version info in the /etc/lsb-release (debian) or /etc/redhat-release (RPM based) file. Using below generic command should get you past most of the Debian and RPM derivatives as Linux Mint and Cent-Os. Example on Ubuntu Machine: cat /etc/*release DISTRIB_ID=Ubuntu DISTRIB_RELEASE=14.04 DISTRIB_CODENAME=trusty DISTRIB_DESCRIPTION="Ubuntu 14.04 LTS"
Linux® Notes for Professionals 15 Chapter 3: Getting information on a running Linux kernel Section 3.1: Getting details of Linux kernel We can use command uname with various options to get complete details of running kernel. uname -a Linux df1-ws-5084 4.4.0-64-generic #85-Ubuntu SMP Mon Feb 20 11:50:30 UTC 2017 x86_64 x86_64 x86_64 GNU/Linux As per man page here few more options Usage: uname [OPTION]... Print certain system information. With no OPTION, same as -s. -a, --all print all information, in the following order, except omit -p and -i if unknown: -s, --kernel-name print the kernel name -n, --nodename print the network node hostname -r, --kernel-release print the kernel release -v, --kernel-version print the kernel version -m, --machine print the machine hardware name -p, --processor print the processor type (non-portable) -i, --hardware-platform print the hardware platform (non-portable) -o, --operating-system print the operating system --help display this help and exit --version output version information and exit
Linux® Notes for Professionals 16 Chapter 4: Shell The shell executes a program in response to its prompt. When you give a command, the shell searches for the program, and then executes it. For example, when you give the command ls, the shell searches for the utility/program named ls, and then runs it in the shell. The arguments and the options that you provide with the utilities can impact the result that you get. The shell is also known as a CLI, or command line interface. Section 4.1: Changing default shell Most modern distributions will come with BASH (Bourne Again SHell) pre-installed and configured as a default shell. The command (actually an executable binary, an ELF) that is responsible for changing shells in Linux is chsh (change shell). We can first check which shells are already installed and configured on our machine by using the chsh -l command, which will output a result similar to this: [user@localhost ~]$ chsh -l /bin/sh /bin/bash /sbin/nologin /usr/bin/sh /usr/bin/bash /usr/sbin/nologin /usr/bin/fish In some Linux distributions, chsh -l is invalid. In this case, the list of all available shells can be found at /etc/shells file. You can show the file contents with cat: [user@localhost ~]$ cat /etc/shells # /etc/shells: valid login shells /bin/sh /bin/bash /sbin/nologin /usr/bin/sh /usr/bin/bash /usr/sbin/nologin /usr/bin/fish Now we can choose our new default shell, e.g. fish, and configure it by using chsh -s, [user@localhost ~]$ chsh -s /usr/bin/fish Changing shell for user. Password: Shell changed. Now all that is left to do is preform a logoff-logon cycle, and enjoy our new default shell. If you wish to change the default shell for a different user, and you have administrative privileges on the machine, you'll be able to accomplish this by using chsh as root. So assuming we want to change user_2's default shell to fish, we will use the same command as before, but with the addition of the other user's username, chsh -s /usr/bin/fish user_2. In order to check what the current default shell is, we can view the $SHELL environment variable, which points to the path to our default shell, so after our change, we would expect to get a result similar to this,
Linux® Notes for Professionals 17 ~ ? echo $SHELL /usr/bin/fish chsh options: -s shell Sets shell as the login shell. -l, --list-shells Print the list of shells listed in /etc/shells and exit. -h, --help Print a usage message and exit. -v, --version Print version information and exit. Section 4.2: Basic Shell Utilities Customizing the Shell prompt Default command prompt can be changed to look different and short. In case the current directory is long default command prompt becomes too large. Using PS1 becomes useful in these cases. A short and customized command pretty and elegant. In the table below PS1 has been used with a number of arguments to show different forms of shell prompts. Default command prompt looks something like this: user@host ~ $ in my case it looks like this: bruce@gotham ~ $. It can changed as per the table below: Command Utility PS1='w $ ' ~ $ shell prompt as directory name. In this case root directory is Root. PS1='h $ ' gotham $ shell prompt as hostname PS1='u $ ' bruce $ shell prompt as username PS1='t $ ' 22:37:31 $ shell prompt in 24 hour format PS1='@ $ ' 10:37 PM shell prompt in 12 hour time format PS1='! $ ' 732 will show the history number of command in place of shell prompt PS1='dude $ ' dude $ will show the shell prompt the way you like Some basic shell commands Command Utility Ctrl-k cut/kill Ctrl-y yank/paste Ctrl-a will take cursor to the start of the line Ctrl-e will take cursor to the end of the line Ctrl-d will delete the character after/at the cursor Ctrl-l will clear the screen/terminal Ctrl-u will clear everything between prompt and the cursor Ctrl-_ will undo the last thing typed on the command line Ctrl-c will interrupt/stop the job/process running in the foreground Ctrl-r reverse search in history ~/.bash_history stores last 500 commands/events used on the shell history will show the command history history | grep <key-word> will show all the commands in history having keyword <key-word> (useful in cases when you remember part of the command used in the past)
Linux® Notes for Professionals 18 Section 4.3: Create Your Own Command Alias If you are tired of using long commands in bash you can create your own command alias. The best way to do this is to modify (or create if it does not exist) a file called .bash_aliases in your home folder. The general syntax is: alias command_alias='actual_command' where actual_command is the command you are renaming and command_alias is the new name you have given it. For example alias install='sudo apt-get -y install' maps the new command alias install to the actual command sudo apt-get -y install. This means that when you use install in a terminal this is interpreted by bash as sudo apt-get -y install. Section 4.4: Locate a file on your system Using bash you can easily locate a file with the locate command. For example say you are looking for the file mykey.pem: locate mykey.pem Sometimes files have strange names for example you might have a file like random7897_mykey_0fidw.pem. Let's say you're looking for this file but you only remember the mykey and pem parts. You could combine the locate command with grep using a pipe like this: locate pem | grep mykey Which would bring up all results which contain both of these pieces. Note that not all systems have the locate utility installed, and many that do have not enabled it. locate is fast and efficient because it periodically scans your system and caches the names and locations for every file on it, but if that data collection is not enabled then it cannot tell you anything. You can use updatedb to manually initiate the filesystem scan in order to update the cached info about files on your filesystem. Should you not have a working locate, you can fall back on the find utility: find / -name mykey.pem -print is roughly equivalent to locate mykey.pem but has to scan your filesystem(s) each time you run it for the file in question, rather than using cached data. This is obviously slower and less efficient, but more real-time. The find utility can do much more than find files, but a full description of its capabilities is beyond the scope of this example.
Linux® Notes for Professionals 19 Chapter 5: Check Disk Space Section 5.1: Investigate Directories For Disk Usage Sometimes it may be required to find out which directory consuming how much disk space especially when you are used df -h and realized your available disk space is low. du: du command summarizes disk usage of the set of FILEs, recursively for directories. It's often uses with -sh option: -s, --summarize display only a total for each argument -h, --human-readable print sizes in human readable format (e.g., 1K 234M 2G) For summarizing disk usages of the files in the current directory we use: du -sh * Example output: 572K Documents 208M Downloads 4,0K Music 724K Pictures 4,0K Public 4,0K Templates 4,0K Videos We can also include hidden files with using: du -sh .[!.]* * Example output: 6,3M .atom 4,0K .bash_history 4,0K .bash_logout 8,0K .bashrc 350M .cache 195M .config 12K .dbus 4,0K .dmrc 44K .gconf 60K .gem 520K .gimp-2.8 28K .gnome 4,0K .ICEauthority 8,3M .local 8,0K .nano 404K .nv 36K .pki 4,0K .profile
Linux® Notes for Professionals 20 8,0K .ssh 0 .sudo_as_admin_successful 4,0K .Xauthority 4,0K .xsession-errors 4,0K .xsession-errors.old 572K Documents 208M Downloads 4,0K Music 724K Pictures 4,0K Public 4,0K Templates 4,0K Videos Thirdly, you can add total to the output by adding ,-c, option: du -sch .[!.]* * Result: . . . 4,0K Templates 4,0K Videos 769M total Most importantly using du command properly on the root directory is a life saving action to find out what application/service or user is consuming your disk space wildly. For example, in case of a ridiculously low level of disk space availability for a web and mail server, the reason could be a spam attack to your mail service and you can diagnose it just by using du command. Investigate root directory for disk usage: sudo du -sch /.[!.]* /* Example output: 16K /.VolumeIcon.icns 24K /.VolumeIcon.png 13M /bin 57M /boot 4,0K /cdrom 620K /dev 13M /etc 779M /home 0 /initrd.img 406M /lib 3,9M /lib32 4,0K /lib64 16K /lost+found 4,0K /media 4,0K /mnt 367M /opt du: cannot access '/proc/18221/task/18221/fd/4': No such file or directory du: cannot access '/proc/18221/task/18221/fdinfo/4': No such file or directory du: cannot access '/proc/18221/fd/4': No such file or directory du: cannot access '/proc/18221/fdinfo/4': No such file or directory
Linux® Notes for Professionals 21 0 /proc 20K /root du: cannot access '/run/user/1000/gvfs': Permission denied 9,4M /run 13M /sbin 4,0K /srv 0 /sys 72K /tmp 3,5G /usr 639M /var 0 /vmlinuz 5,8G total Lastly, the best method forms when you add a threshold size value for directories to ignore small ones. This command will only show folders with more than 1GB in size which located under root directory up to the farthermost branch of the whole directory tree in your file system: sudo du --threshold=1G -ch /.[!.]* /* Example output: 1,4G /usr/lib 1,8G /usr/share 3,5G /usr 5,8G total Section 5.2: Checking Disk Space It's quite common to want to check the status of the various partitions/drives on your server/computer to see how full they are. The following command is the one you'll want to run: df -h This will produce output similar to the following: [root@mail ~]# df -h Filesystem Size Used Avail Use% Mounted on /dev/mapper/VolGroup-lv_root 19G 1.6G 16G 9% / tmpfs 245M 0 245M 0% /dev/shm /dev/sda1 485M 47M 413M 11% /boot In this basic example, we can see that the / partition only has 9% used. For a more complex example that also covers using df to see various mountpoints, see below: [root@mail ~]# df -h Filesystem Size Used Avail Use% Mounted on /dev/mapper/VG-root 1.9T 1.7T 89G 95% / /dev/mapper/VG-var 431G 145G 264G 36% /var devtmpfs 7.8G 204K 7.8G 1% /dev tmpfs 7.8G 4.0K 7.8G 1% /dev/shm /dev/md1 495M 126M 344M 27% /boot ku.example.com:9421 2.5T 487G 2.0T 20% /mnt/test tmpfs 500M 86M 415M 18% /var/ngx_pagespeed_cache
Linux® Notes for Professionals 22 In this example, we have a / partition that's 95% full along with an additional /var partition that's only 36% full. It's got an external network mount of 2T that's mounted on /mnt/test and a ramdisk/tmpfs mount of 500M mounted on /var/ngx_pagespeed_cache.
Linux® Notes for Professionals 23 Chapter 6: Getting System Information Collection of commands to fetch system related information. Section 6.1: Statistics about CPU, Memory, Network and Disk (I/O operations) To get general statistics about main components of Linux family of stat commands are extremely useful CPU To get processors related statistics you can use mpstat command but with some options it will provide better visibility: $ mpstat 2 10 Memory We all know command free to show amount of (remaining) RAM but to see all statistic including I/O operations: $ vmstat 2 10 Disk To get general information about your disk operations in real time you can utilise iostat. $ iostat -kx 2 Network To be able to see what is happening with your network services you can use netstat $ netstat -ntlp # open TCP sockets $ netstat -nulp # open UDP sockets $ netstat -nxlp # open Unix sockets But you can find useful monitoring to see network traffic in real time: $ sudo iftop Optional To generate statistics in real time related to I/O operations across all components you can use dstat. That tool that is a versatile replacement for vmstat, iostat and ifstat Section 6.2: Using tools like lscpu and lshw By using tools like lscpu as lscpu is an easy way to get CPU information. $ lscpu Architecture: x86_64 CPU op-mode(s): 32-bit, 64-bit Byte Order: Little Endian CPU(s): 4 On-line CPU(s) list: 0-3 Thread(s) per core: 1 Core(s) per socket: 4 Socket(s): 1
Linux® Notes for Professionals 24 NUMA node(s): 1 Vendor ID: GenuineIntel CPU family: 6 Model: 23 Stepping: 10 CPU MHz: 1998.000 BogoMIPS: 5303.14 Virtualization: VT-x L1d cache: 32K L1i cache: 32K L2 cache: 2048K NUMA node0 CPU(s): 0-3 By using tool lshw $ lshw | grep cpu df1-ws-5084 description: Computer width: 64 bits capabilities: vsyscall32 *-core description: Motherboard physical id: 0 *-memory description: System memory physical id: 0 size: 5881MiB *-cpu product: Intel(R) Pentium(R) CPU G3220 @ 3.00GHz vendor: Intel Corp. physical id: 1 bus info: cpu@0 size: 3GHz capacity: 3GHz width: 64 bits Section 6.3: List Hardware Ubuntu: lshw is a small tool to extract detailed information on the hardware configuration of the machine. It can report exact memory configuration, firmware version, mainboard configuration, CPU version and speed, cache configuration, bus speed, etc. $ sudo lshw | less (or more) $ sudo lshw -html > myhardware.html $ sudo lshw -xml > myhardware.xml To show PCI info $ lspci -tv To see USB info $ lsusb -tv To display BIOS informations
Linux® Notes for Professionals 25 $ dmidecode -q | less To see specific information about disk (disk sda in example) you can use: $ hdparm -i /dev/sda Few additional utilities/commands will help gather some extra information: $ smartctl -A /dev/sda | grep Power_On_Hours # How long has this disk (system) been powered on in total $ hdparm -tT /dev/sda # Do a read speed test on disk sda $ badblocks -s /dev/sda # Test for unreadable blocks on disk sda Section 6.4: Find CPU model/speed information Ubuntu: $ cat /proc/cpuinfo Sample Output: processor : 0 vendor_id : GenuineIntel cpu family : 6 model : 15 model name : Intel(R) Core(TM)2 Quad CPU Q6600 @ 2.40GHz stepping : 11 cpu MHz : 1596.000 cache size : 4096 KB physical id : 0 siblings : 4 core id : 0 cpu cores : 4 apicid : 0 initial apicid : 0 fpu : yes fpu_exception : yes cpuid level : 10 wp : yes flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx lm constant_tsc arch_perfmon pebs bts rep_good pni dtes64 monitor ds_cpl vmx est tm2 ssse3 cx16 xtpr pdcm lahf_lm tpr_shadow vnmi flexpriority bogomips : 4800.18 clflush size : 64 cache_alignment : 64 address sizes : 36 bits physical, 48 bits virtual power management: .... .. processor : 3 vendor_id : GenuineIntel cpu family : 6 model : 15 model name : Intel(R) Core(TM)2 Quad CPU Q6600 @ 2.40GHz stepping : 11 cpu MHz : 1596.000 cache size : 4096 KB physical id : 0 siblings : 4
Linux® Notes for Professionals 26 core id : 3 cpu cores : 4 apicid : 3 initial apicid : 3 fpu : yes fpu_exception : yes cpuid level : 10 wp : yes flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx lm constant_tsc arch_perfmon pebs bts rep_good pni dtes64 monitor ds_cpl vmx est tm2 ssse3 cx16 xtpr pdcm lahf_lm tpr_shadow vnmi flexpriority bogomips : 4800.30 clflush size : 64 cache_alignment : 64 address sizes : 36 bits physical, 48 bits virtual power management: count processor (including cores): $ grep -c processor /proc/cpuinfo Section 6.5: Process monitoring and information gathering Overall you have two ways to monitor processes at linux host Static monitoring Most widely used command is ps (i.e., process status) command is used to provide information about the currently running processes, including their process identification numbers (PIDs). Here few useful options to gather specific informations. List processes in a hierarchy $ ps -e -o pid,args --forest List processes sorted by % cpu usage $ ps -e -o pcpu,cpu,nice,state,cputime,args --sort pcpu | sed '/^ 0.0 /d' List processes sorted by mem (KB) usage. $ ps -e -orss=,args= | sort -b -k1,1n | pr -TW$COLUMNS List all threads for a particular process ("firefox-bin" process in example ) $ ps -C firefox-bin -L -o pid,tid,pcpu,state After finding specific process you can gather information related to it using lsof to list paths that process id has open $ lsof -p $$ Or based on path find out list processes that have specified path open
Linux® Notes for Professionals 27 $ lsof ~ Interactive monitoring Most commonly known tool for dynamic monitoring is: $ top That mostly default command that have huge amount options to filter and represent information in real time (in comparison to ps command. Still there are more advance options that can be considered and installed as top replacement $ htop -d 5 or $ atop Which has ability to log all the activities into log file (default atop will log all the activity on every 600 seconds) To this list there are few specialised commands as iotop or iftop $ sudo iotop
Linux® Notes for Professionals 28 Chapter 7: ls command Section 7.1: Options for ls command Full list of options: ls -a list all files including hidden file starting with '.' ls --color colored list [=always/never/auto] ls -d list directories - with ' */' ls -F add one char of */=>@| to enteries ls -i list file's inode index number ls -l list with long format - show permissions ls -la list long format including hidden files ls -lh list long format with readable file size ls -ls list with long format with file size ls -r list in reverse order ls -R list recursively directory tree ls -s list file size ls -S sort by file size ls -t sort by time & date ls -X sort by extension name Section 7.2: ls command with most used options ls shows files and directories in present working directory. (if no arguments are passed.) (It doesn't show hidden files which starts with . by default.) user@ubuntu14:/usr$ ls bin games include lib lib32 local sbin share src To see all files (hidden files/folders also). Use ls -a OR ls -all user@ubuntu14:/usr$ ls -a . .. bin games include lib lib32 local sbin share src To differentiate between files and folders and symbolic links and other, use ls -F OR ls --classify user@ubuntu14:~$ ls -F bash_profile_course chat_apps/ Desktop/ Downloads/ foxitsoftware/ Public/ test/ bin/ ClionProjects/ Documents/ IDE/ Music/ Pictures/ Templates/ Videos/
Linux® Notes for Professionals 29 Here, ending characters are used to distinguish files and folders. “/” suggest directory. “*”suggest executables. “@” suggest symbolic links. To get more details about the files and directories, use ls -l user@ubuntu14:~/example$ ls -l total 6464 -rw-r--r-- 1 dave dave 41 Dec 24 12:19 Z.txt drwxr-xr-x 2 user group 4096 Dec 24 12:00 a_directory -rw-r--r-- 1 user group 6 Dec 24 12:01 a_file lrwxrwxrwx 1 user group 6 Dec 24 12:04 a_link -> a_file -rw-r--r-- 1 user group 6 Dec 24 12:03 a_newer_file -rw-r----- 1 user group 6586816 Dec 24 12:07 big.zip In this example, the total size of the contents is 6460KB. Then there is an entry for each file/directory in alphabetical order with upper case before lower case. The first character is the type (e.g. d - directory, l - link). The next 9 characters show the permissions for the user, group and other. This is followed by the number of hard links, then the owner's name and group. The next field is the size in bytes. This can be displayed in a human friendly form by adding the -h option e.g. 6586816 is displayed as 6.3M There then follows a timestamp (usually the modification time). The final field is the name. Note: links also show the target of the link.
Linux® Notes for Professionals 30 Chapter 8: File Compression with 'tar' command Common Options - -c --create Create a new archive. -x --extract Extract files from an archive. -t --list List the contents of an archive. -f --file=ARCHIVE Use archive file or dir ARCHIVE. -v --verbose Verbosely list files processed. Compression Options - -a --auto-compress Use archive suffix to determine the compression program. -j --bzip2 Filter the archive through bzip2. -J --xz --lzma Filter the archive through xz. -z --gzip Filter the archive through gzip. Section 8.1: Compress a folder This creates a simple archive of a folder : tar -cf ./my-archive.tar ./my-folder/ Verbose output shows which files and directories are added to the archive, use the -v option: tar -cvf ./my-archive.tar ./my-folder/ For archiving a folder compressed 'gzip', you have to use the -z option : tar -czf ./my-archive.tar.gz ./my-folder/ You can instead compress the archive with 'bzip2', by using the -j option: tar -cjf ./my-archive.tar.bz2 ./my-folder/ Or compress with 'xz', by using the -J option: tar -cJf ./my-archive.tar.xz ./my-folder/ Section 8.2: Extract a folder from an archive There is an example for extract a folder from an archive in the current location : tar -xf archive-name.tar If you want to extract a folder from an archive to a specfic destination : tar -xf archive-name.tar -C ./directory/destination Section 8.3: List contents of an archive List the contents of an archive file without extracting it: tar -tf archive.tar.gz
Linux® Notes for Professionals 31 Folder-In-Archive/ Folder-In-Archive/file1 Folder-In-Archive/Another-Folder/ Folder-In-Archive/Another-Folder/file2 Section 8.4: List archive content There is an example of listing content : tar -tvf archive.tar The option -t is used for the listing. For listing the content of a tar.gz archive, you have to use the -z option anymore : tar -tzvf archive.tar.gz Section 8.5: Compress and exclude one or multiple folder If you want to extract a folder, but you want to exclude one or several folders during the extraction, you can use the --exclude option. tar -cf archive.tar ./my-folder/ --exclude="my-folder/sub1" --exclude="my-folder/sub3" With this folder tree : my-folder/ sub1/ sub2/ sub3/ The result will be : ./archive.tar my-folder/ sub2/ Section 8.6: Strip leading components To strip any number of leading components, use the --strip-components option: --strip-components=NUMBER strip NUMBER leading components from file names on extraction For example to strip the leading folder, use: tar -xf --strip-components=1 archive-name.tar
Linux® Notes for Professionals 32 Chapter 9: Services Section 9.1: List running service on Ubuntu To get a list of the service on your system, you may run: service --status-all The output of service --status-all lists the state of services controlled by System V. The + indicates the service is running, - indicates a stopped service. You can see this by running service SERVICENAME status for a + and - service. Some services are managed by Upstart. You can check the status of all Upstart services with sudo initctl list. Any service managed by Upstart will also show in the list provided by service --status-all but will be marked with a ?. ref: https://askubuntu.com/questions/407075/how-to-read-service-status-all-results Section 9.2: Systemd service management Listing services systemctl To list running services systemctl --failed To list failed services Managing Targets (Similar to Runlevels in SysV) systemctl get-default To find the default target for your system systemctl set-default <target-name> To set the default target for your system Managing services at runtime systemctl start [service-name] To start a service systemctl stop [service-name] To stop a service systemctl restart [service-name] To restart a service systemctl reload [service-name] To request service to reload its configuration systemctl status [service-name] To show current status of a service Managing autostart of services systemctl is-enabled [service-name] To show whether a service is enabled on system boot systemctl is-active [service-name] To show whether a service is currently active(running) systemctl enable [service-name] To enable a service on system boot systemctl disable [service-name] To disable a service on system boot Masking services systemctl mask [service-name] To mask a service (Makes it hard to start a service by mistake) systemctl unmask [service-name] To unmask a service Restarting systemd systemctl daemon-reload
Linux® Notes for Professionals 33 Chapter 10: Managing Services Section 10.1: Diagnosing a problem with a service On systems using systemd, such as Fedora => 15, Ubuntu (Server and Desktop) >= 15.04, and RHEL/CentOS >= 7: systemctl status [servicename] ...where [servicename] is the service in question; for example, systemctl status sshd. This will show basic status information and any recent errors logged. You can see further errors with journalctl. For example,journalctl -xe will load the last 1000 logged into a pager (like less), jumping to the end. You can also use journalctl -f, which will follow log messages as they come in. To see logs for a particular service, use the -t flag, like this: journalctl -f -t sshd Other handy options include -p for priority (-p warnings to see only warnings and above), -b for "since last boot", and -S for "since" — putting that together, we might do journalctl -p err -S yesterday to see all items logged as errors since yesterday. If journalctl is not available, or if you are following application error logs which do not use the system journal, the tail command can be used to show the last few lines of a file. A useful flag for tail is -f (for "follow"), which causes tail continue showing data as it gets appended to the file. To see messages from most services on the system: tail -f /var/log/messages Or, if the service is privileged, and may log sensitive data: tail -f /var/log/secure Some services have their own log files, a good example is auditd, the linux auditing daemon, which has its logs stored in /var/log/audit/. If you do not see output from your service in /var/log/messages try looking for service specific logs in /var/log/ Section 10.2: Starting and Stopping Services On systems that use the System-V style init scripts, such as RHEL/CentOS 6: service <service> start service <service> stop On systems using systemd, such as Ubuntu (Server and Desktop) >= 15.04, and RHEL/CentOS >= 7: systemctl <service> dnsmasq systemctl <service> dnsmasq
Linux® Notes for Professionals 34 Section 10.3: Getting the status of a service On systems that use the System-V style init scripts, such as RHEL/CentOS 6: service <service> status On systems using systemd, such as Ubuntu (Server and Desktop) >= 15.04, and RHEL/CentOS >= 7.0: systemctl status <service>
Linux® Notes for Professionals 35 Chapter 11: Modifying Users Parameter Details username The name of the user. Do not use capital letters, do not use dots, do not end it in dash, it must not include colons, no special characters. Cannot start with a number. Section 11.1: Setting your own password passwd Section 11.2: Setting another user's password Run the following as root: passwd username Section 11.3: Adding a user Run the following as root: useradd username Section 11.4: Removing a user Run the following as root: userdel username Section 11.5: Removing a user and its home folder Run the following as root: userdel -r username Section 11.6: Listing groups the current user is in groups More detailed information about user and group numerical IDs can be found with the id command. Section 11.7: Listing groups a user is in groups username More detailed information about user and group numerical IDs can be found with id username.
Linux® Notes for Professionals 36 Chapter 12: LAMP Stack LAMP (Linux Apache MySQL PHP) consists of the Linux operating system as development environment, the Apache HTTP Server as web server, the MySQL relational database management system (RDBMS) as DB(Data Base) system, and the PHP programming language as Server side (Back End) programming language. LAMP is used as a Open Source stack of technologies solution to web development area. Windows version of this stack is called WAMP(Windows Apache MySQL PHP) Section 12.1: Installing LAMP on Arch Linux With this line we will install all the necessary packages in one step, and the last update: pacman -Syu apache php php-apache mariadb HTTP Edit /etc/httpd/conf/httpd.conf Change ServerAdmin you@example.com as you need. The folder of the WEB Pages by default is ServerRoot "/etc/httpd". Directory must be set to the same folder, so change the line <Directory "/etc/httpd"> This folder must have read and execution access, so chmod o+x /etc/httpd Change AllowOverride from none (default) to All so .htaccess will works. Now you need the ~/public_html folder for each user. (to get the root page of each user as http://localhost/~yourusername/. Unremark this line: Include conf/extra/httpd-userdir.conf Now as root you need to create the ~/public_html for each user and change the access to (755) of each one. chmod 755 /home chmod 755 /home/username chmod 755 /home/username/public_html You can comment out this line if you want to use SSL: LoadModule ssl_module modules/mod_ssl.so If you need to use virtual domains, uncomment the line: Include conf/extra/httpd-vhosts.conf and in /etc/httpd/conf/extra/httpd-vhosts.conf you must to add all the virtual domains. (plus into /etc/hosts if you want to test those virtuals domains) Edit /etc/httpd/conf/extra/httpd-default.conf and change ServerSignature to Off and ServerToken to Prod
Linux® Notes for Professionals 37 for hiding critical data PHP Edit: /etc/httpd/conf/httpd.conf Comment out: LoadModule mpm_event_module modules/mod_mpm_event.so Uncomment: LoadModule mpm_prefork_module modules/mod_mpm_prefork.so As last item in the LoadModule list, add LoadModule php7_module modules/libphp7.so As last item in the include list, add Include conf/extra/php7_module.conf Edit /etc/php/php.ini Uncomment extension=mysqli.so and extension=pdo_mysql.so Change the timezone as you need, for example: date.timezone = America/Argentina/Buenos_Aires, date.default_latitude = 0.0, date.default_longitude = 0.0 MySQL Run as root: mysql_install_db --user=mysql --basedir=/usr --datadir=/var/lib/mysql Now you have the root of the MySQL Server. Start MySQL daemon: systemctl enable mysqld systemctl start mysqld At last, run: sh /usr/bin/mysql_secure_installation That all to get a web server ready to be customized as you need. Section 12.2: Installing LAMP on Ubuntu Install apache: sudo apt-get install apache2 Install MySql: sudo apt-get install mysql-server Install PHP: sudo apt-get install php5 libapache2-mod-php5 Restart system:
Linux® Notes for Professionals 38 sudo systemctl restart apache2 Check PHP installation: php -r 'echo "nnYour PHP installation is working fine.nnn";' Section 12.3: Installing LAMP stack on CentoOS Install Apache Web Server First step is to install web server Apache. sudo yum -y install httpd Once it is installed, enable (to run on startup) and start Apache web server service. sudo systemctl enable --now httpd Point your browser to: http://localhost You will see the default Apache web server page. Install MariaDB Server Second step is to install MariaDB: sudo yum -y install mariadb-server Then start and enable (on startup) the MariaDB server: sudo systemctl enable --now mariadb As needed, use mysql_secure_installation to secure your database. This script will allow you to do the following: Change the root user's password Remove test databases Disable remote access Install PHP sudo yum -y install php php-common Then restart Apache's httpd service. sudo systemctl restart httpd To test PHP, create a file called index.php in /var/www/html. Then add the following line to the file: Then point your browser to: http://localhost/index.php
Linux® Notes for Professionals 39 You should see information related to your server. If you do not, ensure that php is for sure installed correctly by running the following command: php --version If you receive something like: PHP 5.4.16 (cli) (built: Nov 6 2016 00:29:02) Copyright (c) 1997-2013 The PHP Group Then PHP is installed correctly. If this is the case, please ensure that you've restarted your web server.
Linux® Notes for Professionals 40 Chapter 13: tee command Options Description -a, --append Append to the given FILEs. Do not overwrite. -i, --ignore-interrupts Ignore interrupt signals. --help Display a help message, and exit. --version Display version information, and exit. tee - read from standard input and write to standard output and files. The tee command is named after the T-splitter in plumbing, which splits water into two directions and is shaped like an uppercase T. tee copies data from standard input to each FILE, and also to standard output. In effect, tee duplicates its input, routing it to multiple outputs at once. Section 13.1: Write output to stdout, and also to a file The following command displays output only on the screen (stdout). $ ls The following command writes the output only to the file and not to the screen. $ ls > file The following command (with the help of tee command) writes the output both to the screen (stdout) and to the file. $ ls | tee file Section 13.2: Write output from the middle of a pipe chain to a file and pass it back to the pipe You can also use tee command to store the output of a command in a file and redirect the same output to another command. The following command will write current crontab entries to a file crontab-backup.txt and pass the crontab entries to sed command, which will do the substituion. After the substitution, it will be added as a new cron job. $ crontab -l | tee crontab-backup.txt | sed 's/old/new/' | crontab – Section 13.3: write the output to multiple files You can pipe your output to multiple files (including your terminal) by using tee like this: $ ls | tee file1 file2 file3 Section 13.4: Instruct tee command to append to the file By default tee command overwrites the file. You can instruct tee to append to the file using the –a option as shown below.
Linux® Notes for Professionals 41 $ ls | tee –a file
Linux® Notes for Professionals 42 Chapter 14: Secure Shell (SSH) A secure shell is used to remotely access a server from a client over an encrypted connection. OpenSSH is used as an alternative to Telnet connections that achieve remote shell access but are unencrypted. The OpenSSH Client is installed on most GNU/Linux distributions by default and is used to connect to a server. These examples show use how to use the SSH suite to for accept SSH connections and connecting to another host. Section 14.1: Connecting to a remote server To connect to a server we must use SSH on the client as follows, # ssh -p port user@server-address port - The listening ssh port of the server (default port 22). user - Must be an existing user on the server with SSH privileges. server address - The IP/Domain of the server. For a real world example lets pretend that you're making a website. The company you chose to host your site tells you that the server is located at web-servers.com on a custom port of 2020 and your account name usr1 has been chosen to create a user on the server with SSH privileges. In this case the SSH command used would be as such # ssh -p 2020 usr1@web-servers.com If account name on the remote system is the same as the one one the local client you may leave the user name off. So if you are usr1 on both systems then you my simply use web-servers.com instead of usr1@web-servers.com. When a server you want to connect to is not directly accessible to you, you can try using ProxyJump switch to connect to it through another server which is accessible to you and can connect to the desired server. # ssh -J usr1@10.0.0.1:2020 usr2@10.0.0.2 -p 2222 This will let you connect to the server 10.0.0.2 (running ssh on port 2222) through server at 10.0.0.1 (running ssh on port 2020). You will need to have accounts on both servers of course. Also note that the -J switch is introduced in OpenSSH version 7.3. Section 14.2: Installing OpenSSH suite Both connecting to a remove SSH server and accepting SSH connections require installation of openssh Debian: # apt-get install openssh Arch Linux: # pacman -S openssh Yum: # yum install openssh
Linux® Notes for Professionals 43 Section 14.3: Configuring an SSH server to accept connections First we must edit the SSH daemon config file. Though under different Linux distributions this may be located in different directories, usually it is stored under /etc/ssh/sshd_config Use your text editor to change the values set in this file, all lines starting with # are commented out and must have this character removed to take any effect. A list of recommendations follow as such. Port (chose a number between 0 - 65535, normaly greater than four digits) PasswordAuthentication yes AllowUsers user1 user2 ...etc Note that it is preferable to disable password logins all together and use SSH Keys for improved security as explained in this document. Section 14.4: Passwordless connection (using a key pair) First of all you'll need to have a key pair. If you don't have one yet, take a look at the 'Generate public and private key topic'. Your key pair is composed by a private key (id_rsa) and a public key (id_rsa.pub). All you need to do is to copy the public key to the remote host and add its contents to the ~/.ssh/authorized_keys file. One simple way to do that is: ssh <user>@<ssh-server> 'cat >> ~/.ssh/authorized_keys' < id_rsa.pub Once the public key is properly placed in your user's home directory, you just need to login using the respective private key: ssh <user>@<ssh-server> -i id_rsa Section 14.5: Generate public and private key To generate keys for SSH client: ssh-keygen [-t rsa | rsa1 | dsa ] [-C <comment>] [-b bits] For example: ssh-keygen -t rsa -b 4096 - C myemail@email.com Default location is ~/.ssh/id_rsa for private and ~/.ssh/id_rsa.pub for public key. For more info, please visit man.openbsd.org Section 14.6: Disable ssh service This will disable the SSH server side service, as if needed this will insure that clients cannot connect via ssh Ubuntu sudo service ssh stop sudo systemctl disable sshd.service
Linux® Notes for Professionals 44 Debian sudo /etc/init.d/ssh stop sudo systemctl disable sshd.service Arch Linux sudo killall sshd sudo systemctl disable sshd.service
Linux® Notes for Professionals 45 Chapter 15: SCP Section 15.1: Secure Copy scp command is used to securely copy a file to or from a remote destination. If the file is in current working directly only filename is sufficient else full path is required which included the remote hostname e.g. remote_user@some_server.org:/path/to/file Copy local file in your CWD to new directory scp localfile.txt /home/friend/share/ Copy remote file to you current working directory scp rocky@arena51.net:/home/rocky/game/data.txt ./ Copy file from one remote location to another remote location scp mars@universe.org:/beacon/light/bitmap.conf jupiter@universe.org:/beacon/night/ To copy directory and sub-directories use '-r' recursive option to scp scp -r user@192.168.0.4:~/project/* ./workspace/ Section 15.2: Basic Usage # Copy remote file to local dir scp user@remotehost.com:/remote/path/to/foobar.md /local/dest # Copy local file to remote dir scp foobar.md user@remotehost.com:/remote/dest # Key files can be used (just like ssh) scp -i my_key.pem foobar.md user@remotehost.com:/remote/dest
Linux® Notes for Professionals 46 Chapter 16: GnuPG (GPG) GnuPG is a sophisticated key management system which allows for secure signing or encrypting data. GPG is a command-line tool used to create and manipulate GnuPG keys. GnuPG is most widely used for having SSH (Secure Shell) connections without password or any means of interactive authentication, which improves security level significantly. Following sections describe ways to create, use, and maintain security of GnuPG keys. Section 16.1: Exporting your public key In order for your public-private keypair to be of use, you must make your public key freely available to others. Be sure that you are working with your public key here since you should never share your private key. You can export your public key with the following command: gpg —armor —export EMAIL_ADDRESS > public_key.asc where EMAIL_ADDRESS is the email address associated with the key Alternately, you can upload your public key to a public key server such as keys.gnupg.net so that others can use it. To do so, enter the following in a terminal: gpg —list-keys Then, search for the 8-digit string (the primary ID) associated with the key you want to export. Then, issue the command: gpg —send-keys PRIMARY_ID where PRIMARY_ID is the actual ID of that key. Now, the public key has been uploaded to the key server and is publicly available. Section 16.2: Create and use a GnuPG key quickly Install haveged (example sudo apt-get install haveged) to speed up the random byte process. Then: gpg --gen-key gpg --list-keys outputs: pub 2048R/NNNNNNNN 2016-01-01 uid Name <name@example.com> sub 2048R/xxxxxxxx 2016-01-01 Then publish: gpg --keyserver pgp.mit.edu --send-keys NNNNNNNN Then plan to revoke: https://www.hackdiary.com/2004/01/18/revoking-a-gpg-key/
Linux® Notes for Professionals 47 Chapter 17: Network Configuration This document covers TCP/IP networking, network administration and system configuration basics. Linux can support multiple network devices. The device names are numbered and begin at zero and count upwards. For example, a computer with two NICs will have two devices labeled eth0 and eth1. Section 17.1: Local DNS resolution File: /etc/hosts contains a list of hosts that are to be resolved locally(not by DNS) Sample contents of the file: 127.0.0.1 your-node-name.your-domain.com localhost.localdomain localhost XXX.XXX.XXX.XXX node-name The file format for the hosts file is specified by RFC 952 Section 17.2: Configure DNS servers for domain name resolution File: /etc/resolv.conf contains a list of DNS servers for domain name resolution Sample contents of the file: nameserver 8.8.8.8 # IP address of the primary name server nameserver 8.8.4.4 # IP address of the secondary name server In case internal DNS server you can validate if this server resolve DNS names properly using dig command: $ dig google.com @your.dns.server.com +short Section 17.3: See and manipulate routes Manipulate the IP routing table using route Display routing table $ route # Displays list or routes and also resolves host names $ route -n # Displays list of routes without resolving host names for faster results Add/Delete route Option Description add or del Add or delete a route -host x.x.x.x Add route to a single host identified by the IP address -net x.x.x.x Add route to a network identified by the network address gw x.x.x.x Specify the network gateway netmask x.x.x.x Specify the network netmask default Add a default route Examples: add route to a host $ route add -host x.x.x.x eth1
Linux® Notes for Professionals 48 add route to a network $ route add -net 2.2.2.0 netmask 255.255.255.0 eth0 Alternatively, you could also use cidr format to add a route to network route add -net 2.2.2.0/24 eth0 add default gateway $ route add default gw 2.2.2.1 eth0 delete a route $ route del -net 2.2.2.0/24 Manipulate the IP routing table using ip Display routing table $ ip route show # List routing table Add/Delete route Option Description add or del or change or append or replace Change a route show or flush the command displays the contents of the routing tables or remove it restore restore routing table information from stdin get this command gets a single route to a destination and prints its contents exactly as the kernel sees it Examples: Set default gateway to 1.2.3.254 $ ip route add default via 1.2.3.254 Adds a default route (for all addresses) via the local gateway 192.168.1.1 that can be reached on device eth0 $ ip route add default via 192.168.1.1 dev eth0 Section 17.4: Configure a hostname for some other system on your network You can configure your Linux (or macOS) system in order to tie in an identifier <hostname> to some other system's IP address in your network. You can configure it: Systemwide. You should modify the /etc/hosts file. You just have to add to that file a new line containing: the remote system's IP address <ip_rem>, 1. one or more blank spaces, and 2. the identifier <hostname>. 3. For a single user. You should modify the ~/.hosts file --- you-d have to create it. It is not as simple as for systemwide. Here you can see an explanation. For instance, you could add this line using the cat Unix tool. Suppose that you want to make a ping to a PC in yout local network whose IP address is 192.168.1.44 and you want to refer to that IP address just by remote_pc. Then you must write on your shell: $ sudo cat 192.168.1.44 remote_pc Then you can make that ping just by: $ ping remote_pc
Linux® Notes for Professionals 49 Section 17.5: Interface details Ifconfig List all the interfaces available on the machine $ ifconfig -a List the details of a specific interface Syntax: $ ifconfig <interface> Example: $ ifconfig eth0 eth0 Link encap:Ethernet HWaddr xx:xx:xx:xx:xx:xx inet addr:x.x.x.x Bcast:x.x.x.x Mask:x.x.x.x inet6 addr: xxxx::xxx:xxxx:xxxx:xxxx/64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:4426618 errors:0 dropped:1124 overruns:0 frame:0 TX packets:189171 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:382611580 (382.6 MB) TX bytes:36923665 (36.9 MB) Interrupt:16 Memory:fb5e0000-fb600000 Ethtool - query the network driver and hardware settings Syntax: $ ethtool <interface> Example: $ ethtool eth0 Settings for eth0: Supported ports: [ TP ] Supported link modes: 10baseT/Half 10baseT/Full 100baseT/Half 100baseT/Full 1000baseT/Full Supported pause frame use: No Supports auto-negotiation: Yes Advertised link modes: 10baseT/Half 10baseT/Full 100baseT/Half 100baseT/Full 1000baseT/Full Advertised pause frame use: No Advertised auto-negotiation: Yes Speed: 1000Mb/s Duplex: Full Port: Twisted Pair PHYAD: 1 Transceiver: internal Auto-negotiation: on MDI-X: on (auto) Supports Wake-on: pumbg Wake-on: g Current message level: 0x00000007 (7) drv probe link Link detected: yes ip - show / manipulate routing, devices, policy routing and tunnels
Linux® Notes for Professionals 50 Syntax: $ ip { link | ... | route | macsec } (please see man ip for full list of objects) Examples List network interfaces $ ip link show Rename interface eth0 to wan $ ip link set dev eth0 name wan Bring interface eth0 up (or down) $ ip link set dev eth0 up List addresses for interfaces $ ip addr show Add (or del) ip and mask (255.255.255.0) $ ip addr add 1.2.3.4/24 brd + dev eth0 Section 17.6: Adding IP to an interface An IP address to an interface could be obtained via DHCP or Static assignment DHCP If you are connected to a network with a DHCP server running, dhclient command can get an IP address for your interface $ dhclient <interface> or alternatively, you could make a change to the /etc/network/interfaces file for the interface to be brought up on boot and obtain DHCP IP auto eth0 iface eth0 inet dhcp Static configuration(Permanent Change) using /etc/network/interfaces file If you want to statically configure the interface settings(permanent change), you could do so in the /etc/network/interfaces file. Example: auto eth0 # Bring up the interface on boot iface eth0 inet static address 10.10.70.10 netmask 255.255.0.0 gateway 10.10.1.1 dns-nameservers 10.10.1.20 dns-nameservers 10.10.1.30 These changes persist even after system reboot.
Linux® Notes for Professionals 51 Static configuration(Temporary change) using ifconfig utility A static IP address could be added to an interface using the ifconfig utility as follows $ ifconfig <interface> <ip-address>/<mask> up Example: $ ifconfig eth0 10.10.50.100/16 up
Linux® Notes for Professionals 52 Chapter 18: Midnight Commander Midnight Commander or mc is a console file manager. This topic includes the descripton of it's functionalities and examples and tips of how to use it to it's full potential. Section 18.1: Midnight Commander function keys in browsing mode Here is a list of actions which can be triggered in the Midnight Commander filesystem browsing mode by using function keys on your keyboard. F1 Displays help F2 Opens user menu F3 Displays the contents of the selected file F4 Opens the selected file in the internal file editor F5 Copies the selected file to the directory open in the second panel F6 Moves the selected file to the directory open in the second panel F7 Makes a new directory in the directory open in the current panel F8 Deletes the selected file or directory F9 Focuses to the main menu on the top of the screen F10 Exits mc Section 18.2: Midnight Commander function keys in file editing mode Midnight Commander has a built in editor which is started by F4 function key when over the desired file in the browse mode. It can also be invoked in standalone mode by executing mcedit <filename> Here is a list of actions which can be triggered in the edit mode. F1 Displays help F2 Saves current file F3 Marks the start of the text selection. Move cursor any direction to select. Second hit marks the end of the selection. F4 Brings up the text search/replace dialog F5 Copies selected text to the cursor location (copy/paste) F6 Moves selected text to the cursor location (cut/paste) F7 Brings up the text search dialog
Linux® Notes for Professionals 53 F8 Deletes selected text F9 Focuses to the main menu on the top of the screen F10 Exits the editor
Linux® Notes for Professionals 54 Chapter 19: Change root (chroot) Change root (chroot) is an operation that changes the apparent root directory for the current running process and their children. A program that is run in such a modified environment cannot access files and commands outside that environmental directory tree. Section 19.1: Requirements root privileges another working Linux environment,such as Live CD boot or an existing distribution matching environment architectures of chroot source and destination (check current environment architecture with uname -m) kernel modules which you may need in chroot environment must be loaded (for example, with modprobe) Section 19.2: Manually changing root in a directory Ensure you met all requirements, as per Requirements 1. Mount the temporary API filesystems: 2. cd /location/of/new/root mount -t proc proc proc/ mount --rbind /sys sys/ mount --rbind /dev dev/ mount --rbind /run run/ (optionally) If you need to use an internet connection in the chroot environment, copy over the DNS details: 3. cp /etc/resolv.conf etc/resolv.conf Change root into /location/of/new/root, specifying the shell (/bin/bash in this example): 4. chroot /location/of/new/root /bin/bash After chrooting it may be necessary to load the local bash configuration: 5. source /etc/profile source ~/.bashrc Optionally, create a unique prompt to be able to differentiate your chroot environment: 6. export PS1="(chroot) $PS1" When finished with the chroot, you can exit it via: 7. exit Unmount the temporary file systems: 8. cd / umount --recursive /location/of/new/root
Linux® Notes for Professionals 55 Section 19.3: Reasons to use chroot Changing root is commonly done for performing system maintenance on systems where booting and/or logging in is no longer possible. Common examples are: reinstalling the bootloader rebuilding the initramfs image upgrading or downgrading packages resetting a forgotten password building software in a clean root environment
Linux® Notes for Professionals 56 Chapter 20: Package Managers Section 20.1: How to update packages with the apt package manager The Advanced Package Tool, aptly named the 'apt' package manager can handle the installation and removal of software on the Debian, Slackware, and other Linux Distributions. Below are some simple examples of use: update This option retrieves and scans the Packages.gz files, so that information about new and updated packages is available. To do so, enter the following command: sudo apt-get update upgrade This option is used to install the newest versions of all packages currently installed on the system. Packages currently installed with new versions available are retrieved and upgraded; under no circumstances are currently installed packages removed, or packages not already installed retrieved and installed. To upgrade, enter the following command: sudo apt-get upgrade dist-upgrade In addition to performing the function of upgrade, dist-upgrade also intelligently handles changing dependencies with new versions of packages. It will attempt to upgrade the most important packages at the expense of less important ones if necessary. To do so, enter the following command: sudo apt-get dist-upgrade Section 20.2: How to install a package with the pacman package manager In order to search for packages in the databse, searching both in packages' names and descriptions: pacman -Ss string1 string2 ... To install a single package or list of packages (including dependencies), issue the following command: sudo pacman -S package_name1 package_name2 ... source Section 20.3: How to update packages with the pacman package manager To update a specific program: sudo pacman -S <programName> To update entire the system: sudo pacman -Syu
Linux® Notes for Professionals 57 Section 20.4: How to update packages with yum Yellowdog Updater, Modified, one of the last remaining vestiges of Yellow Dog Linux, is the package manager used by Red Hat, Fedora, and CentOS systems and their derivatives. It can handle the installation and removal of software packaged as rpms for these Linux distributions. Below are some simple examples of use: search This command will attempt to locate software packages in the configured software repositories that match the given search criteria, and display the name / version / repository location of the matches it finds. To use it, enter the following command: yum search <queryString> install This command will attempt to locate and install the named software from the configured software repositories, recursively locating and installing any needed prerequisite software as well. To use it, enter the following command: sudo yum install <packageName> update This option is used to install the newest versions of all packages currently installed on the system. Packages currently installed with new versions available are retrieved and upgraded; new prerequisites are also retrieved and installed as necessary, and replaced or obsoleted packages are removed. To upgrade, enter the following command: sudo yum update Unlike apt, most yum commands will also automatically check for updates to repository metadata if a check has not been done recently (or if forced to do so) and will retrieve and scan updated metadata so that information about new and updated packages is available before the requested operation is performed.
Linux® Notes for Professionals 58 Chapter 21: Compiling the Linux kernel Section 21.1: Compilation of Linux Kernel on Ubuntu Warning: be sure you have at least 15 GB of free disk space. Compilation in Ubuntu >=13.04 Option A) Use Git Use git if you want to stay in sync with the latest Ubuntu kernel source. Detailed instructions can be found in the Kernel Git Guide. The git repository does not include necessary control files, so you must build them by: fakeroot debian/rules clean Option B) Download the source archive Download the source archive - This is for users who want to rebuild the standard Ubuntu packages with additional patches. Use a follow command to install the build dependencies and extract the source (to the current directory): Install the following packages: 1. sudo apt-get build-dep linux-image-`uname -r` Option C) Download the source package and build This is for users who want to modify, or play around with, the Ubuntu-patched kernel source. Retrieve the latest kernel source from kernel.org. 1. Extract the archive to a directory and cd into it: 2. tar xf linux-*.tar.xz cd linux-* Build the ncurses configuration interface: 3. make menuconfig To accept the default configuration, press ? to highlight < Exit > and then Return . 4. Press Return again to save the configuration. 5. Use make to build the kernel: 6. make Note that you can use the -jem> flag to compile files in parallel and take advantage of multiple cores. The compressed kernel image can be found at arch/[arch]/boot/bzImage, where [arch] is equal to uname -a.
Linux® Notes for Professionals 59 Credits Thank you greatly to all the people from Stack Overflow Documentation who helped provide this content, more changes can be sent to web@petercv.com for new content to be published or updated 7heo.tk Chapter 1 Aaron Skomra Chapter 16 Ajay Sangale Chapters 1 and 9 Anagh Hegde Chapters 4 and 14 Ani Menon Chapters 2 and 4 Arden Shackelford Chapter 12 Armali Chapter 1 Baard Kopperud Chapter 8 BrightOne Chapters 9, 14, 13 and 19 C.W.Holeman II Chapter 14 caped114 Chapters 1 and 4 colelemonz Chapter 1 ctafur Chapter 17 DaveM Chapter 2 depperm Chapter 1 e.dan Chapter 1 embedded Chapter 8 Emmanuel Mathi Chapter 4 EsmaeelE Chapter 1 fdeslaur Chapter 3 Federico Ponzi Chapter 9 Filipe Chapter 14 Flamewires Chapter 10 FOP Chapter 12 foxtrot9 Chapter 7 geek1011 Chapter 11 Jarryd Chapter 1 Jensd Chapters 1 and 4 KerDam Chapter 1 Kiran Vemuri Chapters 17 and 6 kuldeep mishra Chapter 13 Léo Léopold Hertz 준영 Chapter 21 lardenn Chapters 2 and 4 leeor Chapter 9 likewhoa Chapter 1 manav m Chapter 15 Manuel Chapter 14 Marsso Chapter 8 Mateusz Piotrowski Chapter 1 mattdm Chapters 2, 10 and 11 mertyildiran Chapter 5 Mike P Chapter 1 Mohammad Chapter 1 Nathan Osman Chapter 21 Naveen Chakravarthy Chapter 1 Nikhil Raj Chapter 2 Not22 Chapter 8 oznek Chapter 4 Paradox Chapters 16 and 20
Linux® Notes for Professionals 60 parkydr Chapter 7 Philip Kirkbride Chapters 4, 20, 7 and 12 Quaker Chapter 4 Rajesh Rengaraj Chapter 14 Riley Guerin Chapter 15 Rubio Chapters 1, 4 and 20 S.Rohit Chapters 3, 12 and 6 Sergey Stolyarov Chapter 2 Sudip Bhandari Chapter 1 Teddy Chapter 2 Tejus Prasad Chapter 1 TiansHUo Chapter 1 Todd Chapters 1 and 14 user Chapters 1, 4, 14 and 18 vishram0709 Chapter 1 Whoami Chapter 1 Y4Rv1K Chapters 17 and 6 Zumo de Vidrio Chapter 1 zyio Chapter 5
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Linux for professional

  • 1. Linux Notes for Professionals Linux ® Notes for Professionals GoalKicker.com Free Programming Books Disclaimer This is an unocial free book created for educational purposes and is not aliated with ocial Linux® group(s) or company(s). All trademarks and registered trademarks are the property of their respective owners 50+ pages of professional hints and tricks
  • 2. Contents About 1 ................................................................................................................................................................................... Chapter 1: Getting started with GNU/Linux 2 ..................................................................................................... Section 1.1: Useful shortcuts 2 .......................................................................................................................................... Section 1.2: File Management Commands 3 .................................................................................................................. Section 1.3: Hello World 5 ................................................................................................................................................. Section 1.4: Basic Linux Utilities 5 .................................................................................................................................... Section 1.5: Searching for files by patterns in name/contents 6 ................................................................................. Section 1.6: File Manipulation 7 ........................................................................................................................................ Section 1.7: File/Directory details 8 ................................................................................................................................. Chapter 2: Detecting Linux distribution name and version 11 .................................................................. Section 2.1: Detect what debian-based distribution you are working in 11 ............................................................... Section 2.2: Detect what systemd-based distribution you are using 11 .................................................................... Section 2.3: Detect what RHEL / CentOS / Fedora distribution you are working in 12 ............................................ Section 2.4: Uname - Print information about the current system 13 ........................................................................ Section 2.5: Detect basic informations about your distro 13 ...................................................................................... Section 2.6: using GNU coreutils 13 ................................................................................................................................ Section 2.7: find your linux os (both debian & rpm) name and release number 14 ................................................. Chapter 3: Getting information on a running Linux kernel 15 ................................................................... Section 3.1: Getting details of Linux kernel 15 ................................................................................................................ Chapter 4: Shell 16 ........................................................................................................................................................... Section 4.1: Changing default shell 16 ............................................................................................................................ Section 4.2: Basic Shell Utilities 17 .................................................................................................................................. Section 4.3: Create Your Own Command Alias 18 ........................................................................................................ Section 4.4: Locate a file on your system 18 ................................................................................................................. Chapter 5: Check Disk Space 19 ................................................................................................................................ Section 5.1: Investigate Directories For Disk Usage 19 ................................................................................................. Section 5.2: Checking Disk Space 21 .............................................................................................................................. Chapter 6: Getting System Information 23 ......................................................................................................... Section 6.1: Statistics about CPU, Memory, Network and Disk (I/O operations) 23 .................................................. Section 6.2: Using tools like lscpu and lshw 23 .............................................................................................................. Section 6.3: List Hardware 24 .......................................................................................................................................... Section 6.4: Find CPU model/speed information 25 ..................................................................................................... Section 6.5: Process monitoring and information gathering 26 .................................................................................. Chapter 7: ls command 28 ........................................................................................................................................... Section 7.1: Options for ls command 28 ......................................................................................................................... Section 7.2: ls command with most used options 28 .................................................................................................... Chapter 8: File Compression with 'tar' command 30 ...................................................................................... Section 8.1: Compress a folder 30 ................................................................................................................................... Section 8.2: Extract a folder from an archive 30 .......................................................................................................... Section 8.3: List contents of an archive 30 .................................................................................................................... Section 8.4: List archive content 31 ................................................................................................................................ Section 8.5: Compress and exclude one or multiple folder 31 .................................................................................... Section 8.6: Strip leading components 31 ...................................................................................................................... Chapter 9: Services 32 .................................................................................................................................................... Section 9.1: List running service on Ubuntu 32 .............................................................................................................. Section 9.2: Systemd service management 32 .............................................................................................................
  • 3. Chapter 10: Managing Services 33 ........................................................................................................................... Section 10.1: Diagnosing a problem with a service 33 .................................................................................................. Section 10.2: Starting and Stopping Services 33 ........................................................................................................... Section 10.3: Getting the status of a service 34 ............................................................................................................. Chapter 11: Modifying Users 35 .................................................................................................................................. Section 11.1: Setting your own password 35 ................................................................................................................... Section 11.2: Setting another user's password 35 .......................................................................................................... Section 11.3: Adding a user 35 .......................................................................................................................................... Section 11.4: Removing a user 35 .................................................................................................................................... Section 11.5: Removing a user and its home folder 35 ................................................................................................. Section 11.6: Listing groups the current user is in 35 ..................................................................................................... Section 11.7: Listing groups a user is in 35 ...................................................................................................................... Chapter 12: LAMP Stack 36 ........................................................................................................................................... Section 12.1: Installing LAMP on Arch Linux 36 ............................................................................................................... Section 12.2: Installing LAMP on Ubuntu 37 ................................................................................................................... Section 12.3: Installing LAMP stack on CentoOS 38 ....................................................................................................... Chapter 13: tee command 40 ...................................................................................................................................... Section 13.1: Write output to stdout, and also to a file 40 ............................................................................................. Section 13.2: Write output from the middle of a pipe chain to a file and pass it back to the pipe 40 ..................... Section 13.3: write the output to multiple files 40 .......................................................................................................... Section 13.4: Instruct tee command to append to the file 40 ....................................................................................... Chapter 14: Secure Shell (SSH) 42 ............................................................................................................................ Section 14.1: Connecting to a remote server 42 ............................................................................................................. Section 14.2: Installing OpenSSH suite 42 ....................................................................................................................... Section 14.3: Configuring an SSH server to accept connections 43 ............................................................................ Section 14.4: Passwordless connection (using a key pair) 43 ...................................................................................... Section 14.5: Generate public and private key 43 ......................................................................................................... Section 14.6: Disable ssh service 43 ................................................................................................................................ Chapter 15: SCP 45 ............................................................................................................................................................ Section 15.1: Secure Copy 45 ............................................................................................................................................ Section 15.2: Basic Usage 45 ........................................................................................................................................... Chapter 16: GnuPG (GPG) 46 ........................................................................................................................................ Section 16.1: Exporting your public key 46 ...................................................................................................................... Section 16.2: Create and use a GnuPG key quickly 46 .................................................................................................. Chapter 17: Network Configuration 47 .................................................................................................................. Section 17.1: Local DNS resolution 47 .............................................................................................................................. Section 17.2: Configure DNS servers for domain name resolution 47 ........................................................................ Section 17.3: See and manipulate routes 47 .................................................................................................................. Section 17.4: Configure a hostname for some other system on your network 48 .................................................... Section 17.5: Interface details 49 ..................................................................................................................................... Section 17.6: Adding IP to an interface 50 ...................................................................................................................... Chapter 18: Midnight Commander 52 ..................................................................................................................... Section 18.1: Midnight Commander function keys in browsing mode 52 .................................................................... Section 18.2: Midnight Commander function keys in file editing mode 52 ................................................................. Chapter 19: Change root (chroot) 54 ...................................................................................................................... Section 19.1: Requirements 54 ......................................................................................................................................... Section 19.2: Manually changing root in a directory 54 ............................................................................................... Section 19.3: Reasons to use chroot 55 .......................................................................................................................... Chapter 20: Package Managers 56 ..........................................................................................................................
  • 4. Section 20.1: How to update packages with the apt package manager 56 .............................................................. Section 20.2: How to install a package with the pacman package manager 56 ...................................................... Section 20.3: How to update packages with the pacman package manager 56 ..................................................... Section 20.4: How to update packages with yum 57 ................................................................................................... Chapter 21: Compiling the Linux kernel 58 ........................................................................................................... Section 21.1: Compilation of Linux Kernel on Ubuntu 58 ............................................................................................... Credits 59 .............................................................................................................................................................................. You may also like 61 ........................................................................................................................................................
  • 5. Linux® Notes for Professionals 1 About Please feel free to share this PDF with anyone for free, latest version of this book can be downloaded from: http://GoalKicker.com/LinuxBook This Linux® Notes for Professionals book is compiled from Stack Overflow Documentation, the content is written by the beautiful people at Stack Overflow. Text content is released under Creative Commons BY-SA, see credits at the end of this book whom contributed to the various chapters. Images may be copyright of their respective owners unless otherwise specified This is an unofficial free book created for educational purposes and is not affiliated with official Linux® group(s) or company(s) nor Stack Overflow. All trademarks and registered trademarks are the property of their respective company owners The information presented in this book is not guaranteed to be correct nor accurate, use at your own risk Please send feedback and corrections to web@petercv.com
  • 6. Linux® Notes for Professionals 2 Chapter 1: Getting started with GNU/Linux Section 1.1: Useful shortcuts Using The Terminal The examples in this document assume that you are using a POSIX-compliant (such as bash, sh, zsh, ksh) shell. Large portions of GNU/Linux functionality are achieved using the terminal. Most distributions of Linux include terminal emulators that allow users to interact with a shell from their desktop environment. A shell is a command- line interpreter that executes user inputted commands. Bash (Bourne Again SHell) is a common default shell among many Linux distributions and is the default shell for macOS. These shortcuts will work if you are using Bash with the emacs keybindings (set by default): Open terminal Ctrl + Alt + T or Super + T Cursor movement Ctrl + A Go to the beginning of the line you are currently typing on. Ctrl + E Go to the end of the line you are currently typing on. Ctrl + XX Move between the beginning of the line and the current position of the cursor. Alt + F Move cursor forward one word on the current line. Alt + B Move cursor backward one word on the current line. Ctrl + F Move cursor forward one character on the current line. Ctrl + B Move cursor backward one character on the current line. Text manipulation Ctrl + U Cut the line from the current position to the beginning of the line, adding it to the clipboard. If you are at the end of the line, cut the entire line. Ctrl + K Cut the line from the current position to the end of the line, adding it to the clipboard. If you are at the beginning of the line, cut the entire line. Ctrl + W Delete the word before the cursor, adding it to the clipboard. Ctrl + Y Paste the last thing from the clipboard that you cut recently (undo the last delete at the current cursor position). Alt + T Swap the last two words before the cursor. Alt + L Make lowercase from cursor to end of word. Alt + U Make uppercase from cursor to end of word. Alt + C Capitalize to end of word starting at cursor (whole word if cursor is at the beginning of word). Alt + D Delete to end of word starting at cursor (whole word if cursor is at the beginning of word). Alt + . Prints the last word written in previous command. Ctrl + T Swap the last two characters before the cursor. History access Ctrl + R Lets you search through previously used commands. Ctrl + G Leave history searching mode without running a command. Ctrl + J Lets you copy current matched command to command line without running it, allowing you to
  • 7. Linux® Notes for Professionals 3 make modifications before running the command. Alt + R Revert any changes to a command you’ve pulled from your history, if you’ve edited it. Ctrl + P Shows last executed command, i.e. walk back through the command history (Similar to up arrow). Ctrl + N Shows next executed command, i.e. walk forward through the command history (Similar to down arrow). Terminal control Ctrl + L Clears the screen, similar to the clear command. Ctrl + S Stop all output to the screen. This is useful when running commands with lots of long output. But this doesn't stop the running command. Ctrl + Q Resume output to the screen after stopping it with Ctrl+S. Ctrl + C End currently running process and return the prompt. Ctrl + D Log out of the current shell session, similar to the exit or logout command. In some commands, acts as End of File signal to indicate that a file end has been reached. Ctrl + Z Suspends (pause) currently running foreground process, which returns shell prompt. You can then use bg command allowing that process to run in the background. To again bring that process to foreground, use fg command. To view all background processes, use jobs command. Tab Auto-complete files and directory names. Tab Tab Shows all possibilities, when typed characters doesn't uniquely match to a file or directory name. Special characters Ctrl + H Same as Backspace. Ctrl + J Same as Return (historically Line Feed). Ctrl + M Same as Return (historically Carriage Return). Ctrl + I Same as Tab. Ctrl + G Bell Character. Ctrl + @ Null Character. Esc Deadkey equivalent to the Alt modifier. Close Terminal Ctrl + Shift + W To close terminal tab. Ctrl + Shift + Q To close entire terminal. Alternatively, you can switch to the vi keybindings in bash using set -o vi. Use set -o emacs to switch back to the emacs keybindings. Section 1.2: File Management Commands Linux uses some conventions for present and parent directories. This can be a little confusing for beginners. Whenever you are in a terminal in Linux, you will be in what is called the current working directory. Often your command prompt will display either the full working directory, or just the last part of that directory. Your prompt could look like one of the following: user@host ~/somedir $ user@host somedir $ user@host /home/user/somedir $ which says that your current working directory is /home/user/somedir.
  • 8. Linux® Notes for Professionals 4 In Linux .. represents the parent directory and . represents the current directory. Therefore, if the current directory is /home/user/somedir, then cd ../somedir will not change the working directory. The table below lists some of the most used file management commands Directory navigation Command Utility pwd Get the full path of the current working directory. cd - Navigate to the last directory you were working in. cd ~ or just cd Navigate to the current user's home directory. cd .. Go to the parent directory of current directory (mind the space between cd and ..) Listing files inside a directory Command Utility ls -l List the files and directories in the current directory in long (table) format (It is recommended to use -l with ls for better readability). ls -ld dir-name List information about the directory dir-name instead of its contents. ls -a List all the files including the hidden ones (File names starting with a . are hidden files in Linux). ls -F Appends a symbol at the end of a file name to indicate its type (* means executable, / means directory, @ means symbolic link, = means socket, | means named pipe, > means door). ls -lt List the files sorted by last modified time with most recently modified files showing at the top (remember -l option provides the long format which has better readability). ls -lh List the file sizes in human readable format. ls -lR Shows all subdirectories recursively. tree Will generate a tree representation of the file system starting from the current directory. File/directory create, copy and remove Command Utility cp -p source destination Will copy the file from source to destination. -p stands for preservation. It preserves the original attributes of file while copying like file owner, timestamp, group, permissions etc. cp -R source_dir destination_dir Will copy source directory to specified destination recursively. mv file1 file2 In Linux there is no rename command as such. Hence mv moves/renames the file1 to file2. rm -i filename Asks you before every file removal for confirmation. IF YOU ARE A NEW USER TO LINUX COMMAND LINE, YOU SHOULD ALWAYS USE rm -i. You can specify multiple files. rm -R dir-name Will remove the directory dir-name recursively. rm -rf dir-name Will remove the directory dir recursively, ignoring non-existent files and will never prompt for anything. BE CAREFUL USING THIS COMMAND! You can specify multiple directories. rmdir dir-name Will remove the directory dir-name, if it's empty. This command can only remove empty directories. mkdir dir-name Create a directory dir-name. mkdir -p dir-name/dir-name Create a directory hierarchy. Create parent directories as needed, if they don't exist. You can specify multiple directories. touch filename Create a file filename, if it doesn't exist, otherwise change the timestamp of the file to current time. File/directory permissions and groups Command Utility chmod <specification> filename Change the file permissions. Specifications = u user, g group, o other, + add permission, - remove, r read, w write,x execute. chmod -R <specification> dir- name Change the permissions of a directory recursively. To change permission of a directory and everything within that directory, use this command. chmod go=+r myfile Add read permission for the owner and the group. chmod a +rwx myfile Allow all users to read, write or execute myfile.
  • 9. Linux® Notes for Professionals 5 chmod go -r myfile Remove read permission from the group and others. chown owner1 filename Change ownership of a file to user owner1. chgrp grp_owner filename Change primary group ownership of file filename to group grp_owner. chgrp -R grp_owner dir-name Change primary group ownership of directory dir-name to group grp_owner recursively. To change group ownership of a directory and everything within that directory, use this command. Section 1.3: Hello World Type the following code into your terminal, then press Enter : echo "Hello World" This will produce the following output: Hello World Section 1.4: Basic Linux Utilities Linux has a command for almost any tasks and most of them are intuitive and easily interpreted. Getting Help in Linux Command Usability man <name> Read the manual page of <name>. man <section> <name> Read the manual page of <name>, related to the given section. man -k <editor> Output all the software whose man pages contain <editor> keyword. man -K <keyword> Outputs all man pages containing <keyword> within them. apropos <editor> Output all the applications whose one line description matches the word editor. When not able to recall the name of the application, use this command. help In Bash shell, this will display the list of all available bash commands. help <name> In Bash shell, this will display the info about the <name> bash command. info <name> View all the information about <name>. dpkg -l Output a list of all installed packages on a Debian-based system. dpkg -L packageName Will list out the files installed and path details for a given package on Debian. dpkg -l | grep -i <edit> Return all .deb installed packages with <edit> irrespective of cases. less /var/lib/dpkg/available Return descriptions of all available packages. whatis vim List a one-line description of vim. <command-name> --help Display usage information about the <tool-name>. Sometimes command -h also works, but not for all commands. User identification and who is who in Linux world Command Usability hostname Display hostname of the system. hostname -f Displays Fully Qualified Domain Name (FQDN) of the system. passwd Change password of current user. whoami Username of the users logged in at the terminal. who List of all the users currently logged in as a user. w Display current system status, time, duration, list of users currently logged in on system and other user information. last Who recently used the system. last root When was the last time root logged in as user. lastb Shows all bad login attempts into the system. chmod Changing permissions - read,write,execute of a file or directory.
  • 10. Linux® Notes for Professionals 6 Process related information Command Usability top List all processes sorted by their current system resource usage. Displays a continually updated display of processes (By default 3 seconds). Use q key to exit top. ps List processes currently running on current shell session ps -u root List all of the processes and commands root is running ps aux List all the processes by all users on the current system Section 1.5: Searching for files by patterns in name/contents A common and task of someone using the Linux Command Line (shell) is to search for files/directories with a certain name or containing certain text. There are 2 commands you should familiarise yourself with in order to accomplish this: Find files by name find /var/www -name '*.css' This will print out the full path/filename to all files under /var/www that end in .css. Example output: /var/www/html/text-cursor.css /var/www/html/style.css For more info: man find Find files containing text grep font /var/www/html/style.css This will print all lines containing the pattern font in the specified file. Example output: font-weight: bold; font-family: monospace; Another example: grep font /var/www/html/ This doesn't work as you'd hoped. You get: grep: /var/www/html/: Is a directory You need to grep recursively to make it work, using the -R option: grep -R font /var/www/html/ Hey nice! Check out the output of this one: /var/www/html/admin/index.php: echo '<font color=red><b>Error: no dice</b></font><br/>'; /var/www/html/admin/index.php: echo '<font color=red><b>Error: try again</b></font><br/>'; /var/www/html/style.css: font-weight: bold; /var/www/html/style.css: font-family: monospace; Notice that when grep is matching multiple files, it prefixes the matched lines with the filenames. You can use the -
  • 11. Linux® Notes for Professionals 7 h option to get rid of that, if you want. For more info: man grep Section 1.6: File Manipulation Files and directories (another name for folders) are at the heart of Linux, so being able to create, view, move, and delete them from the command line is very important and quite powerful. These file manipulation commands allow you to perform the same tasks that a graphical file explorer would perform. Create an empty text file called myFile: touch myFile Rename myFile to myFirstFile: mv myFile myFirstFile View the contents of a file: cat myFirstFile View the content of a file with pager (one screenful at a time): less myFirstFile View the first several lines of a file: head myFirstFile View the last several lines of a file: tail myFirstFile Edit a file: vi myFirstFile See what files are in your current working directory: ls Create an empty directory called myFirstDirectory: mkdir myFirstDirectory Create multi path directory: (creates two directories, src and myFirstDirectory) mkdir -p src/myFirstDirectory Move the file into the directory:
  • 12. Linux® Notes for Professionals 8 mv myFirstFile myFirstDirectory/ You can also rename the file: user@linux-computer:~$ mv myFirstFile secondFileName Change the current working directory to myFirstDirectory: cd myFirstDirectory Delete a file: rm myFirstFile Move into the parent directory (which is represented as ..): cd .. Delete an empty directory: rmdir myFirstDirectory Delete a non-empty directory (i.e. contains files and/or other directories): rm -rf myFirstDirectory Make note that when deleting directories, that you delete ./ not / that will wipe your whole filesystem. Section 1.7: File/Directory details The ls command has several options that can be used together to show more information. Details/Rights The l option shows the file permissions, size, and last modified date. So if the root directory contained a dir called test and a file someFile the command: user@linux-computer:~$ ls -l Would output something like -rw-r--r-- 1 user users 70 Jul 22 13:36 someFile.txt drwxrwxrwx 2 user users 4096 Jul 21 07:18 test The permissions are in format of drwxrwxrwx. The first character represents the file type d if it's a directory - otherwise. The next three rwx are the permissions the user has over the file, the next three are the permissions the group has over the file, and the last three are the permissions everyone else has over the file. The r of rwx stands for if a file can be read, the w represents if the file can be modified, and the x stands for if the file can be executed. If any permission isn't granted a - will be in place of r, w, or x. So from above user can read and modify someFile.txt but the group has only read-only rights. To change rights you can use the chmod ### fileName command if you have sudo rights. r is represented by a
  • 13. Linux® Notes for Professionals 9 value of 4, w is represented by 2, and x is represented by a 1. So if only you want to be able to modify the contents to the test directory Owner rwx = 4+2+1 = 7 Group r-x = 4+0+1 = 5 Other r-x = 4+0+1 = 5 So the whole command is chmod 755 test Now doing a ls -l would show something like drwxr-xr-x 2 user users 4096 Jul 21 07:20 test Readable Size Used in conjunction with the l option the h option shows file sizes that are human readable. Running user@linux-computer:~$ ls -lh Would output: total 4166 -rw-r--r-- 1 user users 70 Jul 22 13:36 someFile.txt drwxrwxrwx 2 user users 4.0K Jul 21 07:18 test Hidden To view hidden files use the a option. For example user@linux-computer:~$ ls -a Might list .profile someFile.txt test Total Directory Size To view the size of the current directory use the s option (the h option can also be used to make the size more readable). user@linux-computer:~$ ls -s Outputs total 4166 someFile.txt test Recursive View Lets say test directory had a file anotherFile and you wanted to see it from the root folder, you could use the R option which would list the recursive tree.
  • 14. Linux® Notes for Professionals 10 user@linux-computer:~$ ls -R Outputs .: someFile.txt test ./test: anotherFile
  • 15. Linux® Notes for Professionals 11 Chapter 2: Detecting Linux distribution name and version Section 2.1: Detect what debian-based distribution you are working in Just execute lsb_release -a. On Debian: $ lsb_release -a No LSB modules are available. Distributor ID: Debian Description: Debian GNU/Linux testing (stretch) Release: testing Codename: stretch On Ubuntu: $ lsb_release -a No LSB modules are available. Distributor ID: Ubuntu Description: Ubuntu 14.04.4 LTS Release: 14.04 Codename: trusty In case when you don't have lsb_release installed you may want to try some guessing, for example, there is a file /etc/issue that often contains distribution name. For example, on ubuntu: $ cat /etc/issue Ubuntu 12.04.5 LTS n l Don't use file /etc/debian_version because its contents do not match distribution name! Note that this will also work on non-Debian-family distributions like Fedora, RHEL, or openSUSE — but that lsb_release may not be installed. Section 2.2: Detect what systemd-based distribution you are using This method will work on modern versions of Arch, CentOS, CoreOS, Debian, Fedora, Mageia, openSUSE, Red Hat Enterprise Linux, SUSE Linux Enterprise Server, Ubuntu, and others. This wide applicability makes it an ideal as a first approach, with fallback to other methods if you need to also identify older systems. Look at /etc/os-release. In specific, look at variables NAME, VERSION, ID, VERSION_ID, and PRETTY_NAME. On Fedora, this file might look like: NAME=Fedora VERSION="24 (Workstation Edition)" ID=fedora VERSION_ID=24 PRETTY_NAME="Fedora 24 (Workstation Edition)" ANSI_COLOR="0;34"
  • 16. Linux® Notes for Professionals 12 CPE_NAME="cpe:/o:fedoraproject:fedora:24" HOME_URL="https://fedoraproject.org/" BUG_REPORT_URL="https://bugzilla.redhat.com/" REDHAT_BUGZILLA_PRODUCT="Fedora" REDHAT_BUGZILLA_PRODUCT_VERSION=24 REDHAT_SUPPORT_PRODUCT="Fedora" REDHAT_SUPPORT_PRODUCT_VERSION=24 PRIVACY_POLICY_URL=https://fedoraproject.org/wiki/Legal:PrivacyPolicy VARIANT="Workstation Edition" VARIANT_ID=workstation On CentOS, this file might look like this: NAME="CentOS Linux" VERSION="7 (Core)" ID="centos" ID_LIKE="rhel fedora" VERSION_ID="7" PRETTY_NAME="CentOS Linux 7 (Core)" ANSI_COLOR="0;31" CPE_NAME="cpe:/o:centos:centos:7" HOME_URL="https://www.centos.org/" BUG_REPORT_URL="https://bugs.centos.org/" CENTOS_MANTISBT_PROJECT="CentOS-7" CENTOS_MANTISBT_PROJECT_VERSION="7" REDHAT_SUPPORT_PRODUCT="centos" REDHAT_SUPPORT_PRODUCT_VERSION="7" This file is documented on the freedesktop web site; in principle, it is not systemd specific — but it will exist on all systemd-based distributions. From the bash shell, one can source the /etc/os-release file and then use the various variables directly, like this: $ ( source /etc/os-release && echo "$PRETTY_NAME" ) Fedora 24 (Workstation Edition) Section 2.3: Detect what RHEL / CentOS / Fedora distribution you are working in Look at the contents of /etc/redhat-release cat /etc/redhat-release Here is the output from a Fedora 24 machine: Fedora release 24 (Twenty Four) As mentioned in the debian-based response, you can also use the lsb_release -a command, which outputs this from a Fedora 24 machine: LSB Version: :core-4.1-amd64:core-4.1-noarch:cxx-4.1-amd64:cxx-4.1-noarch:desktop-4.1- amd64:desktop-4.1-noarch:languages-4.1-amd64:languages-4.1-noarch:printing-4.1-amd64:printing-4.1- noarch Distributor ID: Fedora Description: Fedora release 24 (Twenty Four) Release: 24 Codename: TwentyFour
  • 17. Linux® Notes for Professionals 13 Section 2.4: Uname - Print information about the current system Uname is the short name for unix name. Just type uname in console to get information about your operating system. uname [OPTION] If no OPTION is specified, uname assumes the -s option. -a or --all - Prints all information, omitting -p and -i if the information is unknown. Example: > uname -a SunOS hope 5.7 Generic_106541-08 sun4m sparc SUNW,SPARCstation-10 All the options: -s, --kernel-name Print the kernel name. -n, --nodename Print the network node hostname. -r, --kernel-release Print the kernel release. -v, --kernel-version Print the kernel version. -m, --machine Print the machine hardware name. -p, --processor Print the processor type, or "unknown". -i, --hardware-platform Print the hardware platform, or "unknown". -o, --operating-system Print the operating system. --help Display a help message, and exit. --version Display version information, and exit. Section 2.5: Detect basic informations about your distro just execute uname -a. On Arch: $ uname -a Linux nokia 4.6.4-1-ARCH #1 SMP PREEMPT Mon Jul 11 19:12:32 CEST 2016 x86_64 GNU/Linuxenter code here Section 2.6: using GNU coreutils So the GNU coreutils should be avaialable on all linux based systems (please correct me if I am wrong here). If you do not know what system you are using you may not be able to directly jump to one of the examples above, hence this may be your first port of call. `$ uname -a On my system this gives me the following... `Linux Scibearspace 3.16.0-4-amd64 #1 SMP Debian 3.16.7-ckt25-2+deb8u3 (2016-07-02) x86_64 GNU/Linux Here you can see the following :
  • 18. Linux® Notes for Professionals 14 Scibearspace : the name of my pc Scibearspace : the name of my pc 3.16.0-4-amd64 : the kernel and architecture SMP Debian 3.16.7-CKT25-2+deb8u3 : tells me I am running debian with the 3.16 kernel Finaly the last part I am running debian 8 (update 3). I would welcome any others to add in results for RHEL, and SuSe systems. Section 2.7: find your linux os (both debian & rpm) name and release number Most of linux distros stores its version info in the /etc/lsb-release (debian) or /etc/redhat-release (RPM based) file. Using below generic command should get you past most of the Debian and RPM derivatives as Linux Mint and Cent-Os. Example on Ubuntu Machine: cat /etc/*release DISTRIB_ID=Ubuntu DISTRIB_RELEASE=14.04 DISTRIB_CODENAME=trusty DISTRIB_DESCRIPTION="Ubuntu 14.04 LTS"
  • 19. Linux® Notes for Professionals 15 Chapter 3: Getting information on a running Linux kernel Section 3.1: Getting details of Linux kernel We can use command uname with various options to get complete details of running kernel. uname -a Linux df1-ws-5084 4.4.0-64-generic #85-Ubuntu SMP Mon Feb 20 11:50:30 UTC 2017 x86_64 x86_64 x86_64 GNU/Linux As per man page here few more options Usage: uname [OPTION]... Print certain system information. With no OPTION, same as -s. -a, --all print all information, in the following order, except omit -p and -i if unknown: -s, --kernel-name print the kernel name -n, --nodename print the network node hostname -r, --kernel-release print the kernel release -v, --kernel-version print the kernel version -m, --machine print the machine hardware name -p, --processor print the processor type (non-portable) -i, --hardware-platform print the hardware platform (non-portable) -o, --operating-system print the operating system --help display this help and exit --version output version information and exit
  • 20. Linux® Notes for Professionals 16 Chapter 4: Shell The shell executes a program in response to its prompt. When you give a command, the shell searches for the program, and then executes it. For example, when you give the command ls, the shell searches for the utility/program named ls, and then runs it in the shell. The arguments and the options that you provide with the utilities can impact the result that you get. The shell is also known as a CLI, or command line interface. Section 4.1: Changing default shell Most modern distributions will come with BASH (Bourne Again SHell) pre-installed and configured as a default shell. The command (actually an executable binary, an ELF) that is responsible for changing shells in Linux is chsh (change shell). We can first check which shells are already installed and configured on our machine by using the chsh -l command, which will output a result similar to this: [user@localhost ~]$ chsh -l /bin/sh /bin/bash /sbin/nologin /usr/bin/sh /usr/bin/bash /usr/sbin/nologin /usr/bin/fish In some Linux distributions, chsh -l is invalid. In this case, the list of all available shells can be found at /etc/shells file. You can show the file contents with cat: [user@localhost ~]$ cat /etc/shells # /etc/shells: valid login shells /bin/sh /bin/bash /sbin/nologin /usr/bin/sh /usr/bin/bash /usr/sbin/nologin /usr/bin/fish Now we can choose our new default shell, e.g. fish, and configure it by using chsh -s, [user@localhost ~]$ chsh -s /usr/bin/fish Changing shell for user. Password: Shell changed. Now all that is left to do is preform a logoff-logon cycle, and enjoy our new default shell. If you wish to change the default shell for a different user, and you have administrative privileges on the machine, you'll be able to accomplish this by using chsh as root. So assuming we want to change user_2's default shell to fish, we will use the same command as before, but with the addition of the other user's username, chsh -s /usr/bin/fish user_2. In order to check what the current default shell is, we can view the $SHELL environment variable, which points to the path to our default shell, so after our change, we would expect to get a result similar to this,
  • 21. Linux® Notes for Professionals 17 ~ ? echo $SHELL /usr/bin/fish chsh options: -s shell Sets shell as the login shell. -l, --list-shells Print the list of shells listed in /etc/shells and exit. -h, --help Print a usage message and exit. -v, --version Print version information and exit. Section 4.2: Basic Shell Utilities Customizing the Shell prompt Default command prompt can be changed to look different and short. In case the current directory is long default command prompt becomes too large. Using PS1 becomes useful in these cases. A short and customized command pretty and elegant. In the table below PS1 has been used with a number of arguments to show different forms of shell prompts. Default command prompt looks something like this: user@host ~ $ in my case it looks like this: bruce@gotham ~ $. It can changed as per the table below: Command Utility PS1='w $ ' ~ $ shell prompt as directory name. In this case root directory is Root. PS1='h $ ' gotham $ shell prompt as hostname PS1='u $ ' bruce $ shell prompt as username PS1='t $ ' 22:37:31 $ shell prompt in 24 hour format PS1='@ $ ' 10:37 PM shell prompt in 12 hour time format PS1='! $ ' 732 will show the history number of command in place of shell prompt PS1='dude $ ' dude $ will show the shell prompt the way you like Some basic shell commands Command Utility Ctrl-k cut/kill Ctrl-y yank/paste Ctrl-a will take cursor to the start of the line Ctrl-e will take cursor to the end of the line Ctrl-d will delete the character after/at the cursor Ctrl-l will clear the screen/terminal Ctrl-u will clear everything between prompt and the cursor Ctrl-_ will undo the last thing typed on the command line Ctrl-c will interrupt/stop the job/process running in the foreground Ctrl-r reverse search in history ~/.bash_history stores last 500 commands/events used on the shell history will show the command history history | grep <key-word> will show all the commands in history having keyword <key-word> (useful in cases when you remember part of the command used in the past)
  • 22. Linux® Notes for Professionals 18 Section 4.3: Create Your Own Command Alias If you are tired of using long commands in bash you can create your own command alias. The best way to do this is to modify (or create if it does not exist) a file called .bash_aliases in your home folder. The general syntax is: alias command_alias='actual_command' where actual_command is the command you are renaming and command_alias is the new name you have given it. For example alias install='sudo apt-get -y install' maps the new command alias install to the actual command sudo apt-get -y install. This means that when you use install in a terminal this is interpreted by bash as sudo apt-get -y install. Section 4.4: Locate a file on your system Using bash you can easily locate a file with the locate command. For example say you are looking for the file mykey.pem: locate mykey.pem Sometimes files have strange names for example you might have a file like random7897_mykey_0fidw.pem. Let's say you're looking for this file but you only remember the mykey and pem parts. You could combine the locate command with grep using a pipe like this: locate pem | grep mykey Which would bring up all results which contain both of these pieces. Note that not all systems have the locate utility installed, and many that do have not enabled it. locate is fast and efficient because it periodically scans your system and caches the names and locations for every file on it, but if that data collection is not enabled then it cannot tell you anything. You can use updatedb to manually initiate the filesystem scan in order to update the cached info about files on your filesystem. Should you not have a working locate, you can fall back on the find utility: find / -name mykey.pem -print is roughly equivalent to locate mykey.pem but has to scan your filesystem(s) each time you run it for the file in question, rather than using cached data. This is obviously slower and less efficient, but more real-time. The find utility can do much more than find files, but a full description of its capabilities is beyond the scope of this example.
  • 23. Linux® Notes for Professionals 19 Chapter 5: Check Disk Space Section 5.1: Investigate Directories For Disk Usage Sometimes it may be required to find out which directory consuming how much disk space especially when you are used df -h and realized your available disk space is low. du: du command summarizes disk usage of the set of FILEs, recursively for directories. It's often uses with -sh option: -s, --summarize display only a total for each argument -h, --human-readable print sizes in human readable format (e.g., 1K 234M 2G) For summarizing disk usages of the files in the current directory we use: du -sh * Example output: 572K Documents 208M Downloads 4,0K Music 724K Pictures 4,0K Public 4,0K Templates 4,0K Videos We can also include hidden files with using: du -sh .[!.]* * Example output: 6,3M .atom 4,0K .bash_history 4,0K .bash_logout 8,0K .bashrc 350M .cache 195M .config 12K .dbus 4,0K .dmrc 44K .gconf 60K .gem 520K .gimp-2.8 28K .gnome 4,0K .ICEauthority 8,3M .local 8,0K .nano 404K .nv 36K .pki 4,0K .profile
  • 24. Linux® Notes for Professionals 20 8,0K .ssh 0 .sudo_as_admin_successful 4,0K .Xauthority 4,0K .xsession-errors 4,0K .xsession-errors.old 572K Documents 208M Downloads 4,0K Music 724K Pictures 4,0K Public 4,0K Templates 4,0K Videos Thirdly, you can add total to the output by adding ,-c, option: du -sch .[!.]* * Result: . . . 4,0K Templates 4,0K Videos 769M total Most importantly using du command properly on the root directory is a life saving action to find out what application/service or user is consuming your disk space wildly. For example, in case of a ridiculously low level of disk space availability for a web and mail server, the reason could be a spam attack to your mail service and you can diagnose it just by using du command. Investigate root directory for disk usage: sudo du -sch /.[!.]* /* Example output: 16K /.VolumeIcon.icns 24K /.VolumeIcon.png 13M /bin 57M /boot 4,0K /cdrom 620K /dev 13M /etc 779M /home 0 /initrd.img 406M /lib 3,9M /lib32 4,0K /lib64 16K /lost+found 4,0K /media 4,0K /mnt 367M /opt du: cannot access '/proc/18221/task/18221/fd/4': No such file or directory du: cannot access '/proc/18221/task/18221/fdinfo/4': No such file or directory du: cannot access '/proc/18221/fd/4': No such file or directory du: cannot access '/proc/18221/fdinfo/4': No such file or directory
  • 25. Linux® Notes for Professionals 21 0 /proc 20K /root du: cannot access '/run/user/1000/gvfs': Permission denied 9,4M /run 13M /sbin 4,0K /srv 0 /sys 72K /tmp 3,5G /usr 639M /var 0 /vmlinuz 5,8G total Lastly, the best method forms when you add a threshold size value for directories to ignore small ones. This command will only show folders with more than 1GB in size which located under root directory up to the farthermost branch of the whole directory tree in your file system: sudo du --threshold=1G -ch /.[!.]* /* Example output: 1,4G /usr/lib 1,8G /usr/share 3,5G /usr 5,8G total Section 5.2: Checking Disk Space It's quite common to want to check the status of the various partitions/drives on your server/computer to see how full they are. The following command is the one you'll want to run: df -h This will produce output similar to the following: [root@mail ~]# df -h Filesystem Size Used Avail Use% Mounted on /dev/mapper/VolGroup-lv_root 19G 1.6G 16G 9% / tmpfs 245M 0 245M 0% /dev/shm /dev/sda1 485M 47M 413M 11% /boot In this basic example, we can see that the / partition only has 9% used. For a more complex example that also covers using df to see various mountpoints, see below: [root@mail ~]# df -h Filesystem Size Used Avail Use% Mounted on /dev/mapper/VG-root 1.9T 1.7T 89G 95% / /dev/mapper/VG-var 431G 145G 264G 36% /var devtmpfs 7.8G 204K 7.8G 1% /dev tmpfs 7.8G 4.0K 7.8G 1% /dev/shm /dev/md1 495M 126M 344M 27% /boot ku.example.com:9421 2.5T 487G 2.0T 20% /mnt/test tmpfs 500M 86M 415M 18% /var/ngx_pagespeed_cache
  • 26. Linux® Notes for Professionals 22 In this example, we have a / partition that's 95% full along with an additional /var partition that's only 36% full. It's got an external network mount of 2T that's mounted on /mnt/test and a ramdisk/tmpfs mount of 500M mounted on /var/ngx_pagespeed_cache.
  • 27. Linux® Notes for Professionals 23 Chapter 6: Getting System Information Collection of commands to fetch system related information. Section 6.1: Statistics about CPU, Memory, Network and Disk (I/O operations) To get general statistics about main components of Linux family of stat commands are extremely useful CPU To get processors related statistics you can use mpstat command but with some options it will provide better visibility: $ mpstat 2 10 Memory We all know command free to show amount of (remaining) RAM but to see all statistic including I/O operations: $ vmstat 2 10 Disk To get general information about your disk operations in real time you can utilise iostat. $ iostat -kx 2 Network To be able to see what is happening with your network services you can use netstat $ netstat -ntlp # open TCP sockets $ netstat -nulp # open UDP sockets $ netstat -nxlp # open Unix sockets But you can find useful monitoring to see network traffic in real time: $ sudo iftop Optional To generate statistics in real time related to I/O operations across all components you can use dstat. That tool that is a versatile replacement for vmstat, iostat and ifstat Section 6.2: Using tools like lscpu and lshw By using tools like lscpu as lscpu is an easy way to get CPU information. $ lscpu Architecture: x86_64 CPU op-mode(s): 32-bit, 64-bit Byte Order: Little Endian CPU(s): 4 On-line CPU(s) list: 0-3 Thread(s) per core: 1 Core(s) per socket: 4 Socket(s): 1
  • 28. Linux® Notes for Professionals 24 NUMA node(s): 1 Vendor ID: GenuineIntel CPU family: 6 Model: 23 Stepping: 10 CPU MHz: 1998.000 BogoMIPS: 5303.14 Virtualization: VT-x L1d cache: 32K L1i cache: 32K L2 cache: 2048K NUMA node0 CPU(s): 0-3 By using tool lshw $ lshw | grep cpu df1-ws-5084 description: Computer width: 64 bits capabilities: vsyscall32 *-core description: Motherboard physical id: 0 *-memory description: System memory physical id: 0 size: 5881MiB *-cpu product: Intel(R) Pentium(R) CPU G3220 @ 3.00GHz vendor: Intel Corp. physical id: 1 bus info: cpu@0 size: 3GHz capacity: 3GHz width: 64 bits Section 6.3: List Hardware Ubuntu: lshw is a small tool to extract detailed information on the hardware configuration of the machine. It can report exact memory configuration, firmware version, mainboard configuration, CPU version and speed, cache configuration, bus speed, etc. $ sudo lshw | less (or more) $ sudo lshw -html > myhardware.html $ sudo lshw -xml > myhardware.xml To show PCI info $ lspci -tv To see USB info $ lsusb -tv To display BIOS informations
  • 29. Linux® Notes for Professionals 25 $ dmidecode -q | less To see specific information about disk (disk sda in example) you can use: $ hdparm -i /dev/sda Few additional utilities/commands will help gather some extra information: $ smartctl -A /dev/sda | grep Power_On_Hours # How long has this disk (system) been powered on in total $ hdparm -tT /dev/sda # Do a read speed test on disk sda $ badblocks -s /dev/sda # Test for unreadable blocks on disk sda Section 6.4: Find CPU model/speed information Ubuntu: $ cat /proc/cpuinfo Sample Output: processor : 0 vendor_id : GenuineIntel cpu family : 6 model : 15 model name : Intel(R) Core(TM)2 Quad CPU Q6600 @ 2.40GHz stepping : 11 cpu MHz : 1596.000 cache size : 4096 KB physical id : 0 siblings : 4 core id : 0 cpu cores : 4 apicid : 0 initial apicid : 0 fpu : yes fpu_exception : yes cpuid level : 10 wp : yes flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx lm constant_tsc arch_perfmon pebs bts rep_good pni dtes64 monitor ds_cpl vmx est tm2 ssse3 cx16 xtpr pdcm lahf_lm tpr_shadow vnmi flexpriority bogomips : 4800.18 clflush size : 64 cache_alignment : 64 address sizes : 36 bits physical, 48 bits virtual power management: .... .. processor : 3 vendor_id : GenuineIntel cpu family : 6 model : 15 model name : Intel(R) Core(TM)2 Quad CPU Q6600 @ 2.40GHz stepping : 11 cpu MHz : 1596.000 cache size : 4096 KB physical id : 0 siblings : 4
  • 30. Linux® Notes for Professionals 26 core id : 3 cpu cores : 4 apicid : 3 initial apicid : 3 fpu : yes fpu_exception : yes cpuid level : 10 wp : yes flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx lm constant_tsc arch_perfmon pebs bts rep_good pni dtes64 monitor ds_cpl vmx est tm2 ssse3 cx16 xtpr pdcm lahf_lm tpr_shadow vnmi flexpriority bogomips : 4800.30 clflush size : 64 cache_alignment : 64 address sizes : 36 bits physical, 48 bits virtual power management: count processor (including cores): $ grep -c processor /proc/cpuinfo Section 6.5: Process monitoring and information gathering Overall you have two ways to monitor processes at linux host Static monitoring Most widely used command is ps (i.e., process status) command is used to provide information about the currently running processes, including their process identification numbers (PIDs). Here few useful options to gather specific informations. List processes in a hierarchy $ ps -e -o pid,args --forest List processes sorted by % cpu usage $ ps -e -o pcpu,cpu,nice,state,cputime,args --sort pcpu | sed '/^ 0.0 /d' List processes sorted by mem (KB) usage. $ ps -e -orss=,args= | sort -b -k1,1n | pr -TW$COLUMNS List all threads for a particular process ("firefox-bin" process in example ) $ ps -C firefox-bin -L -o pid,tid,pcpu,state After finding specific process you can gather information related to it using lsof to list paths that process id has open $ lsof -p $$ Or based on path find out list processes that have specified path open
  • 31. Linux® Notes for Professionals 27 $ lsof ~ Interactive monitoring Most commonly known tool for dynamic monitoring is: $ top That mostly default command that have huge amount options to filter and represent information in real time (in comparison to ps command. Still there are more advance options that can be considered and installed as top replacement $ htop -d 5 or $ atop Which has ability to log all the activities into log file (default atop will log all the activity on every 600 seconds) To this list there are few specialised commands as iotop or iftop $ sudo iotop
  • 32. Linux® Notes for Professionals 28 Chapter 7: ls command Section 7.1: Options for ls command Full list of options: ls -a list all files including hidden file starting with '.' ls --color colored list [=always/never/auto] ls -d list directories - with ' */' ls -F add one char of */=>@| to enteries ls -i list file's inode index number ls -l list with long format - show permissions ls -la list long format including hidden files ls -lh list long format with readable file size ls -ls list with long format with file size ls -r list in reverse order ls -R list recursively directory tree ls -s list file size ls -S sort by file size ls -t sort by time & date ls -X sort by extension name Section 7.2: ls command with most used options ls shows files and directories in present working directory. (if no arguments are passed.) (It doesn't show hidden files which starts with . by default.) user@ubuntu14:/usr$ ls bin games include lib lib32 local sbin share src To see all files (hidden files/folders also). Use ls -a OR ls -all user@ubuntu14:/usr$ ls -a . .. bin games include lib lib32 local sbin share src To differentiate between files and folders and symbolic links and other, use ls -F OR ls --classify user@ubuntu14:~$ ls -F bash_profile_course chat_apps/ Desktop/ Downloads/ foxitsoftware/ Public/ test/ bin/ ClionProjects/ Documents/ IDE/ Music/ Pictures/ Templates/ Videos/
  • 33. Linux® Notes for Professionals 29 Here, ending characters are used to distinguish files and folders. “/” suggest directory. “*”suggest executables. “@” suggest symbolic links. To get more details about the files and directories, use ls -l user@ubuntu14:~/example$ ls -l total 6464 -rw-r--r-- 1 dave dave 41 Dec 24 12:19 Z.txt drwxr-xr-x 2 user group 4096 Dec 24 12:00 a_directory -rw-r--r-- 1 user group 6 Dec 24 12:01 a_file lrwxrwxrwx 1 user group 6 Dec 24 12:04 a_link -> a_file -rw-r--r-- 1 user group 6 Dec 24 12:03 a_newer_file -rw-r----- 1 user group 6586816 Dec 24 12:07 big.zip In this example, the total size of the contents is 6460KB. Then there is an entry for each file/directory in alphabetical order with upper case before lower case. The first character is the type (e.g. d - directory, l - link). The next 9 characters show the permissions for the user, group and other. This is followed by the number of hard links, then the owner's name and group. The next field is the size in bytes. This can be displayed in a human friendly form by adding the -h option e.g. 6586816 is displayed as 6.3M There then follows a timestamp (usually the modification time). The final field is the name. Note: links also show the target of the link.
  • 34. Linux® Notes for Professionals 30 Chapter 8: File Compression with 'tar' command Common Options - -c --create Create a new archive. -x --extract Extract files from an archive. -t --list List the contents of an archive. -f --file=ARCHIVE Use archive file or dir ARCHIVE. -v --verbose Verbosely list files processed. Compression Options - -a --auto-compress Use archive suffix to determine the compression program. -j --bzip2 Filter the archive through bzip2. -J --xz --lzma Filter the archive through xz. -z --gzip Filter the archive through gzip. Section 8.1: Compress a folder This creates a simple archive of a folder : tar -cf ./my-archive.tar ./my-folder/ Verbose output shows which files and directories are added to the archive, use the -v option: tar -cvf ./my-archive.tar ./my-folder/ For archiving a folder compressed 'gzip', you have to use the -z option : tar -czf ./my-archive.tar.gz ./my-folder/ You can instead compress the archive with 'bzip2', by using the -j option: tar -cjf ./my-archive.tar.bz2 ./my-folder/ Or compress with 'xz', by using the -J option: tar -cJf ./my-archive.tar.xz ./my-folder/ Section 8.2: Extract a folder from an archive There is an example for extract a folder from an archive in the current location : tar -xf archive-name.tar If you want to extract a folder from an archive to a specfic destination : tar -xf archive-name.tar -C ./directory/destination Section 8.3: List contents of an archive List the contents of an archive file without extracting it: tar -tf archive.tar.gz
  • 35. Linux® Notes for Professionals 31 Folder-In-Archive/ Folder-In-Archive/file1 Folder-In-Archive/Another-Folder/ Folder-In-Archive/Another-Folder/file2 Section 8.4: List archive content There is an example of listing content : tar -tvf archive.tar The option -t is used for the listing. For listing the content of a tar.gz archive, you have to use the -z option anymore : tar -tzvf archive.tar.gz Section 8.5: Compress and exclude one or multiple folder If you want to extract a folder, but you want to exclude one or several folders during the extraction, you can use the --exclude option. tar -cf archive.tar ./my-folder/ --exclude="my-folder/sub1" --exclude="my-folder/sub3" With this folder tree : my-folder/ sub1/ sub2/ sub3/ The result will be : ./archive.tar my-folder/ sub2/ Section 8.6: Strip leading components To strip any number of leading components, use the --strip-components option: --strip-components=NUMBER strip NUMBER leading components from file names on extraction For example to strip the leading folder, use: tar -xf --strip-components=1 archive-name.tar
  • 36. Linux® Notes for Professionals 32 Chapter 9: Services Section 9.1: List running service on Ubuntu To get a list of the service on your system, you may run: service --status-all The output of service --status-all lists the state of services controlled by System V. The + indicates the service is running, - indicates a stopped service. You can see this by running service SERVICENAME status for a + and - service. Some services are managed by Upstart. You can check the status of all Upstart services with sudo initctl list. Any service managed by Upstart will also show in the list provided by service --status-all but will be marked with a ?. ref: https://askubuntu.com/questions/407075/how-to-read-service-status-all-results Section 9.2: Systemd service management Listing services systemctl To list running services systemctl --failed To list failed services Managing Targets (Similar to Runlevels in SysV) systemctl get-default To find the default target for your system systemctl set-default <target-name> To set the default target for your system Managing services at runtime systemctl start [service-name] To start a service systemctl stop [service-name] To stop a service systemctl restart [service-name] To restart a service systemctl reload [service-name] To request service to reload its configuration systemctl status [service-name] To show current status of a service Managing autostart of services systemctl is-enabled [service-name] To show whether a service is enabled on system boot systemctl is-active [service-name] To show whether a service is currently active(running) systemctl enable [service-name] To enable a service on system boot systemctl disable [service-name] To disable a service on system boot Masking services systemctl mask [service-name] To mask a service (Makes it hard to start a service by mistake) systemctl unmask [service-name] To unmask a service Restarting systemd systemctl daemon-reload
  • 37. Linux® Notes for Professionals 33 Chapter 10: Managing Services Section 10.1: Diagnosing a problem with a service On systems using systemd, such as Fedora => 15, Ubuntu (Server and Desktop) >= 15.04, and RHEL/CentOS >= 7: systemctl status [servicename] ...where [servicename] is the service in question; for example, systemctl status sshd. This will show basic status information and any recent errors logged. You can see further errors with journalctl. For example,journalctl -xe will load the last 1000 logged into a pager (like less), jumping to the end. You can also use journalctl -f, which will follow log messages as they come in. To see logs for a particular service, use the -t flag, like this: journalctl -f -t sshd Other handy options include -p for priority (-p warnings to see only warnings and above), -b for "since last boot", and -S for "since" — putting that together, we might do journalctl -p err -S yesterday to see all items logged as errors since yesterday. If journalctl is not available, or if you are following application error logs which do not use the system journal, the tail command can be used to show the last few lines of a file. A useful flag for tail is -f (for "follow"), which causes tail continue showing data as it gets appended to the file. To see messages from most services on the system: tail -f /var/log/messages Or, if the service is privileged, and may log sensitive data: tail -f /var/log/secure Some services have their own log files, a good example is auditd, the linux auditing daemon, which has its logs stored in /var/log/audit/. If you do not see output from your service in /var/log/messages try looking for service specific logs in /var/log/ Section 10.2: Starting and Stopping Services On systems that use the System-V style init scripts, such as RHEL/CentOS 6: service <service> start service <service> stop On systems using systemd, such as Ubuntu (Server and Desktop) >= 15.04, and RHEL/CentOS >= 7: systemctl <service> dnsmasq systemctl <service> dnsmasq
  • 38. Linux® Notes for Professionals 34 Section 10.3: Getting the status of a service On systems that use the System-V style init scripts, such as RHEL/CentOS 6: service <service> status On systems using systemd, such as Ubuntu (Server and Desktop) >= 15.04, and RHEL/CentOS >= 7.0: systemctl status <service>
  • 39. Linux® Notes for Professionals 35 Chapter 11: Modifying Users Parameter Details username The name of the user. Do not use capital letters, do not use dots, do not end it in dash, it must not include colons, no special characters. Cannot start with a number. Section 11.1: Setting your own password passwd Section 11.2: Setting another user's password Run the following as root: passwd username Section 11.3: Adding a user Run the following as root: useradd username Section 11.4: Removing a user Run the following as root: userdel username Section 11.5: Removing a user and its home folder Run the following as root: userdel -r username Section 11.6: Listing groups the current user is in groups More detailed information about user and group numerical IDs can be found with the id command. Section 11.7: Listing groups a user is in groups username More detailed information about user and group numerical IDs can be found with id username.
  • 40. Linux® Notes for Professionals 36 Chapter 12: LAMP Stack LAMP (Linux Apache MySQL PHP) consists of the Linux operating system as development environment, the Apache HTTP Server as web server, the MySQL relational database management system (RDBMS) as DB(Data Base) system, and the PHP programming language as Server side (Back End) programming language. LAMP is used as a Open Source stack of technologies solution to web development area. Windows version of this stack is called WAMP(Windows Apache MySQL PHP) Section 12.1: Installing LAMP on Arch Linux With this line we will install all the necessary packages in one step, and the last update: pacman -Syu apache php php-apache mariadb HTTP Edit /etc/httpd/conf/httpd.conf Change ServerAdmin you@example.com as you need. The folder of the WEB Pages by default is ServerRoot "/etc/httpd". Directory must be set to the same folder, so change the line <Directory "/etc/httpd"> This folder must have read and execution access, so chmod o+x /etc/httpd Change AllowOverride from none (default) to All so .htaccess will works. Now you need the ~/public_html folder for each user. (to get the root page of each user as http://localhost/~yourusername/. Unremark this line: Include conf/extra/httpd-userdir.conf Now as root you need to create the ~/public_html for each user and change the access to (755) of each one. chmod 755 /home chmod 755 /home/username chmod 755 /home/username/public_html You can comment out this line if you want to use SSL: LoadModule ssl_module modules/mod_ssl.so If you need to use virtual domains, uncomment the line: Include conf/extra/httpd-vhosts.conf and in /etc/httpd/conf/extra/httpd-vhosts.conf you must to add all the virtual domains. (plus into /etc/hosts if you want to test those virtuals domains) Edit /etc/httpd/conf/extra/httpd-default.conf and change ServerSignature to Off and ServerToken to Prod
  • 41. Linux® Notes for Professionals 37 for hiding critical data PHP Edit: /etc/httpd/conf/httpd.conf Comment out: LoadModule mpm_event_module modules/mod_mpm_event.so Uncomment: LoadModule mpm_prefork_module modules/mod_mpm_prefork.so As last item in the LoadModule list, add LoadModule php7_module modules/libphp7.so As last item in the include list, add Include conf/extra/php7_module.conf Edit /etc/php/php.ini Uncomment extension=mysqli.so and extension=pdo_mysql.so Change the timezone as you need, for example: date.timezone = America/Argentina/Buenos_Aires, date.default_latitude = 0.0, date.default_longitude = 0.0 MySQL Run as root: mysql_install_db --user=mysql --basedir=/usr --datadir=/var/lib/mysql Now you have the root of the MySQL Server. Start MySQL daemon: systemctl enable mysqld systemctl start mysqld At last, run: sh /usr/bin/mysql_secure_installation That all to get a web server ready to be customized as you need. Section 12.2: Installing LAMP on Ubuntu Install apache: sudo apt-get install apache2 Install MySql: sudo apt-get install mysql-server Install PHP: sudo apt-get install php5 libapache2-mod-php5 Restart system:
  • 42. Linux® Notes for Professionals 38 sudo systemctl restart apache2 Check PHP installation: php -r 'echo "nnYour PHP installation is working fine.nnn";' Section 12.3: Installing LAMP stack on CentoOS Install Apache Web Server First step is to install web server Apache. sudo yum -y install httpd Once it is installed, enable (to run on startup) and start Apache web server service. sudo systemctl enable --now httpd Point your browser to: http://localhost You will see the default Apache web server page. Install MariaDB Server Second step is to install MariaDB: sudo yum -y install mariadb-server Then start and enable (on startup) the MariaDB server: sudo systemctl enable --now mariadb As needed, use mysql_secure_installation to secure your database. This script will allow you to do the following: Change the root user's password Remove test databases Disable remote access Install PHP sudo yum -y install php php-common Then restart Apache's httpd service. sudo systemctl restart httpd To test PHP, create a file called index.php in /var/www/html. Then add the following line to the file: Then point your browser to: http://localhost/index.php
  • 43. Linux® Notes for Professionals 39 You should see information related to your server. If you do not, ensure that php is for sure installed correctly by running the following command: php --version If you receive something like: PHP 5.4.16 (cli) (built: Nov 6 2016 00:29:02) Copyright (c) 1997-2013 The PHP Group Then PHP is installed correctly. If this is the case, please ensure that you've restarted your web server.
  • 44. Linux® Notes for Professionals 40 Chapter 13: tee command Options Description -a, --append Append to the given FILEs. Do not overwrite. -i, --ignore-interrupts Ignore interrupt signals. --help Display a help message, and exit. --version Display version information, and exit. tee - read from standard input and write to standard output and files. The tee command is named after the T-splitter in plumbing, which splits water into two directions and is shaped like an uppercase T. tee copies data from standard input to each FILE, and also to standard output. In effect, tee duplicates its input, routing it to multiple outputs at once. Section 13.1: Write output to stdout, and also to a file The following command displays output only on the screen (stdout). $ ls The following command writes the output only to the file and not to the screen. $ ls > file The following command (with the help of tee command) writes the output both to the screen (stdout) and to the file. $ ls | tee file Section 13.2: Write output from the middle of a pipe chain to a file and pass it back to the pipe You can also use tee command to store the output of a command in a file and redirect the same output to another command. The following command will write current crontab entries to a file crontab-backup.txt and pass the crontab entries to sed command, which will do the substituion. After the substitution, it will be added as a new cron job. $ crontab -l | tee crontab-backup.txt | sed 's/old/new/' | crontab – Section 13.3: write the output to multiple files You can pipe your output to multiple files (including your terminal) by using tee like this: $ ls | tee file1 file2 file3 Section 13.4: Instruct tee command to append to the file By default tee command overwrites the file. You can instruct tee to append to the file using the –a option as shown below.
  • 45. Linux® Notes for Professionals 41 $ ls | tee –a file
  • 46. Linux® Notes for Professionals 42 Chapter 14: Secure Shell (SSH) A secure shell is used to remotely access a server from a client over an encrypted connection. OpenSSH is used as an alternative to Telnet connections that achieve remote shell access but are unencrypted. The OpenSSH Client is installed on most GNU/Linux distributions by default and is used to connect to a server. These examples show use how to use the SSH suite to for accept SSH connections and connecting to another host. Section 14.1: Connecting to a remote server To connect to a server we must use SSH on the client as follows, # ssh -p port user@server-address port - The listening ssh port of the server (default port 22). user - Must be an existing user on the server with SSH privileges. server address - The IP/Domain of the server. For a real world example lets pretend that you're making a website. The company you chose to host your site tells you that the server is located at web-servers.com on a custom port of 2020 and your account name usr1 has been chosen to create a user on the server with SSH privileges. In this case the SSH command used would be as such # ssh -p 2020 usr1@web-servers.com If account name on the remote system is the same as the one one the local client you may leave the user name off. So if you are usr1 on both systems then you my simply use web-servers.com instead of usr1@web-servers.com. When a server you want to connect to is not directly accessible to you, you can try using ProxyJump switch to connect to it through another server which is accessible to you and can connect to the desired server. # ssh -J usr1@10.0.0.1:2020 usr2@10.0.0.2 -p 2222 This will let you connect to the server 10.0.0.2 (running ssh on port 2222) through server at 10.0.0.1 (running ssh on port 2020). You will need to have accounts on both servers of course. Also note that the -J switch is introduced in OpenSSH version 7.3. Section 14.2: Installing OpenSSH suite Both connecting to a remove SSH server and accepting SSH connections require installation of openssh Debian: # apt-get install openssh Arch Linux: # pacman -S openssh Yum: # yum install openssh
  • 47. Linux® Notes for Professionals 43 Section 14.3: Configuring an SSH server to accept connections First we must edit the SSH daemon config file. Though under different Linux distributions this may be located in different directories, usually it is stored under /etc/ssh/sshd_config Use your text editor to change the values set in this file, all lines starting with # are commented out and must have this character removed to take any effect. A list of recommendations follow as such. Port (chose a number between 0 - 65535, normaly greater than four digits) PasswordAuthentication yes AllowUsers user1 user2 ...etc Note that it is preferable to disable password logins all together and use SSH Keys for improved security as explained in this document. Section 14.4: Passwordless connection (using a key pair) First of all you'll need to have a key pair. If you don't have one yet, take a look at the 'Generate public and private key topic'. Your key pair is composed by a private key (id_rsa) and a public key (id_rsa.pub). All you need to do is to copy the public key to the remote host and add its contents to the ~/.ssh/authorized_keys file. One simple way to do that is: ssh <user>@<ssh-server> 'cat >> ~/.ssh/authorized_keys' < id_rsa.pub Once the public key is properly placed in your user's home directory, you just need to login using the respective private key: ssh <user>@<ssh-server> -i id_rsa Section 14.5: Generate public and private key To generate keys for SSH client: ssh-keygen [-t rsa | rsa1 | dsa ] [-C <comment>] [-b bits] For example: ssh-keygen -t rsa -b 4096 - C myemail@email.com Default location is ~/.ssh/id_rsa for private and ~/.ssh/id_rsa.pub for public key. For more info, please visit man.openbsd.org Section 14.6: Disable ssh service This will disable the SSH server side service, as if needed this will insure that clients cannot connect via ssh Ubuntu sudo service ssh stop sudo systemctl disable sshd.service
  • 48. Linux® Notes for Professionals 44 Debian sudo /etc/init.d/ssh stop sudo systemctl disable sshd.service Arch Linux sudo killall sshd sudo systemctl disable sshd.service
  • 49. Linux® Notes for Professionals 45 Chapter 15: SCP Section 15.1: Secure Copy scp command is used to securely copy a file to or from a remote destination. If the file is in current working directly only filename is sufficient else full path is required which included the remote hostname e.g. remote_user@some_server.org:/path/to/file Copy local file in your CWD to new directory scp localfile.txt /home/friend/share/ Copy remote file to you current working directory scp rocky@arena51.net:/home/rocky/game/data.txt ./ Copy file from one remote location to another remote location scp mars@universe.org:/beacon/light/bitmap.conf jupiter@universe.org:/beacon/night/ To copy directory and sub-directories use '-r' recursive option to scp scp -r user@192.168.0.4:~/project/* ./workspace/ Section 15.2: Basic Usage # Copy remote file to local dir scp user@remotehost.com:/remote/path/to/foobar.md /local/dest # Copy local file to remote dir scp foobar.md user@remotehost.com:/remote/dest # Key files can be used (just like ssh) scp -i my_key.pem foobar.md user@remotehost.com:/remote/dest
  • 50. Linux® Notes for Professionals 46 Chapter 16: GnuPG (GPG) GnuPG is a sophisticated key management system which allows for secure signing or encrypting data. GPG is a command-line tool used to create and manipulate GnuPG keys. GnuPG is most widely used for having SSH (Secure Shell) connections without password or any means of interactive authentication, which improves security level significantly. Following sections describe ways to create, use, and maintain security of GnuPG keys. Section 16.1: Exporting your public key In order for your public-private keypair to be of use, you must make your public key freely available to others. Be sure that you are working with your public key here since you should never share your private key. You can export your public key with the following command: gpg —armor —export EMAIL_ADDRESS > public_key.asc where EMAIL_ADDRESS is the email address associated with the key Alternately, you can upload your public key to a public key server such as keys.gnupg.net so that others can use it. To do so, enter the following in a terminal: gpg —list-keys Then, search for the 8-digit string (the primary ID) associated with the key you want to export. Then, issue the command: gpg —send-keys PRIMARY_ID where PRIMARY_ID is the actual ID of that key. Now, the public key has been uploaded to the key server and is publicly available. Section 16.2: Create and use a GnuPG key quickly Install haveged (example sudo apt-get install haveged) to speed up the random byte process. Then: gpg --gen-key gpg --list-keys outputs: pub 2048R/NNNNNNNN 2016-01-01 uid Name <name@example.com> sub 2048R/xxxxxxxx 2016-01-01 Then publish: gpg --keyserver pgp.mit.edu --send-keys NNNNNNNN Then plan to revoke: https://www.hackdiary.com/2004/01/18/revoking-a-gpg-key/
  • 51. Linux® Notes for Professionals 47 Chapter 17: Network Configuration This document covers TCP/IP networking, network administration and system configuration basics. Linux can support multiple network devices. The device names are numbered and begin at zero and count upwards. For example, a computer with two NICs will have two devices labeled eth0 and eth1. Section 17.1: Local DNS resolution File: /etc/hosts contains a list of hosts that are to be resolved locally(not by DNS) Sample contents of the file: 127.0.0.1 your-node-name.your-domain.com localhost.localdomain localhost XXX.XXX.XXX.XXX node-name The file format for the hosts file is specified by RFC 952 Section 17.2: Configure DNS servers for domain name resolution File: /etc/resolv.conf contains a list of DNS servers for domain name resolution Sample contents of the file: nameserver 8.8.8.8 # IP address of the primary name server nameserver 8.8.4.4 # IP address of the secondary name server In case internal DNS server you can validate if this server resolve DNS names properly using dig command: $ dig google.com @your.dns.server.com +short Section 17.3: See and manipulate routes Manipulate the IP routing table using route Display routing table $ route # Displays list or routes and also resolves host names $ route -n # Displays list of routes without resolving host names for faster results Add/Delete route Option Description add or del Add or delete a route -host x.x.x.x Add route to a single host identified by the IP address -net x.x.x.x Add route to a network identified by the network address gw x.x.x.x Specify the network gateway netmask x.x.x.x Specify the network netmask default Add a default route Examples: add route to a host $ route add -host x.x.x.x eth1
  • 52. Linux® Notes for Professionals 48 add route to a network $ route add -net 2.2.2.0 netmask 255.255.255.0 eth0 Alternatively, you could also use cidr format to add a route to network route add -net 2.2.2.0/24 eth0 add default gateway $ route add default gw 2.2.2.1 eth0 delete a route $ route del -net 2.2.2.0/24 Manipulate the IP routing table using ip Display routing table $ ip route show # List routing table Add/Delete route Option Description add or del or change or append or replace Change a route show or flush the command displays the contents of the routing tables or remove it restore restore routing table information from stdin get this command gets a single route to a destination and prints its contents exactly as the kernel sees it Examples: Set default gateway to 1.2.3.254 $ ip route add default via 1.2.3.254 Adds a default route (for all addresses) via the local gateway 192.168.1.1 that can be reached on device eth0 $ ip route add default via 192.168.1.1 dev eth0 Section 17.4: Configure a hostname for some other system on your network You can configure your Linux (or macOS) system in order to tie in an identifier <hostname> to some other system's IP address in your network. You can configure it: Systemwide. You should modify the /etc/hosts file. You just have to add to that file a new line containing: the remote system's IP address <ip_rem>, 1. one or more blank spaces, and 2. the identifier <hostname>. 3. For a single user. You should modify the ~/.hosts file --- you-d have to create it. It is not as simple as for systemwide. Here you can see an explanation. For instance, you could add this line using the cat Unix tool. Suppose that you want to make a ping to a PC in yout local network whose IP address is 192.168.1.44 and you want to refer to that IP address just by remote_pc. Then you must write on your shell: $ sudo cat 192.168.1.44 remote_pc Then you can make that ping just by: $ ping remote_pc
  • 53. Linux® Notes for Professionals 49 Section 17.5: Interface details Ifconfig List all the interfaces available on the machine $ ifconfig -a List the details of a specific interface Syntax: $ ifconfig <interface> Example: $ ifconfig eth0 eth0 Link encap:Ethernet HWaddr xx:xx:xx:xx:xx:xx inet addr:x.x.x.x Bcast:x.x.x.x Mask:x.x.x.x inet6 addr: xxxx::xxx:xxxx:xxxx:xxxx/64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:4426618 errors:0 dropped:1124 overruns:0 frame:0 TX packets:189171 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:382611580 (382.6 MB) TX bytes:36923665 (36.9 MB) Interrupt:16 Memory:fb5e0000-fb600000 Ethtool - query the network driver and hardware settings Syntax: $ ethtool <interface> Example: $ ethtool eth0 Settings for eth0: Supported ports: [ TP ] Supported link modes: 10baseT/Half 10baseT/Full 100baseT/Half 100baseT/Full 1000baseT/Full Supported pause frame use: No Supports auto-negotiation: Yes Advertised link modes: 10baseT/Half 10baseT/Full 100baseT/Half 100baseT/Full 1000baseT/Full Advertised pause frame use: No Advertised auto-negotiation: Yes Speed: 1000Mb/s Duplex: Full Port: Twisted Pair PHYAD: 1 Transceiver: internal Auto-negotiation: on MDI-X: on (auto) Supports Wake-on: pumbg Wake-on: g Current message level: 0x00000007 (7) drv probe link Link detected: yes ip - show / manipulate routing, devices, policy routing and tunnels
  • 54. Linux® Notes for Professionals 50 Syntax: $ ip { link | ... | route | macsec } (please see man ip for full list of objects) Examples List network interfaces $ ip link show Rename interface eth0 to wan $ ip link set dev eth0 name wan Bring interface eth0 up (or down) $ ip link set dev eth0 up List addresses for interfaces $ ip addr show Add (or del) ip and mask (255.255.255.0) $ ip addr add 1.2.3.4/24 brd + dev eth0 Section 17.6: Adding IP to an interface An IP address to an interface could be obtained via DHCP or Static assignment DHCP If you are connected to a network with a DHCP server running, dhclient command can get an IP address for your interface $ dhclient <interface> or alternatively, you could make a change to the /etc/network/interfaces file for the interface to be brought up on boot and obtain DHCP IP auto eth0 iface eth0 inet dhcp Static configuration(Permanent Change) using /etc/network/interfaces file If you want to statically configure the interface settings(permanent change), you could do so in the /etc/network/interfaces file. Example: auto eth0 # Bring up the interface on boot iface eth0 inet static address 10.10.70.10 netmask 255.255.0.0 gateway 10.10.1.1 dns-nameservers 10.10.1.20 dns-nameservers 10.10.1.30 These changes persist even after system reboot.
  • 55. Linux® Notes for Professionals 51 Static configuration(Temporary change) using ifconfig utility A static IP address could be added to an interface using the ifconfig utility as follows $ ifconfig <interface> <ip-address>/<mask> up Example: $ ifconfig eth0 10.10.50.100/16 up
  • 56. Linux® Notes for Professionals 52 Chapter 18: Midnight Commander Midnight Commander or mc is a console file manager. This topic includes the descripton of it's functionalities and examples and tips of how to use it to it's full potential. Section 18.1: Midnight Commander function keys in browsing mode Here is a list of actions which can be triggered in the Midnight Commander filesystem browsing mode by using function keys on your keyboard. F1 Displays help F2 Opens user menu F3 Displays the contents of the selected file F4 Opens the selected file in the internal file editor F5 Copies the selected file to the directory open in the second panel F6 Moves the selected file to the directory open in the second panel F7 Makes a new directory in the directory open in the current panel F8 Deletes the selected file or directory F9 Focuses to the main menu on the top of the screen F10 Exits mc Section 18.2: Midnight Commander function keys in file editing mode Midnight Commander has a built in editor which is started by F4 function key when over the desired file in the browse mode. It can also be invoked in standalone mode by executing mcedit <filename> Here is a list of actions which can be triggered in the edit mode. F1 Displays help F2 Saves current file F3 Marks the start of the text selection. Move cursor any direction to select. Second hit marks the end of the selection. F4 Brings up the text search/replace dialog F5 Copies selected text to the cursor location (copy/paste) F6 Moves selected text to the cursor location (cut/paste) F7 Brings up the text search dialog
  • 57. Linux® Notes for Professionals 53 F8 Deletes selected text F9 Focuses to the main menu on the top of the screen F10 Exits the editor
  • 58. Linux® Notes for Professionals 54 Chapter 19: Change root (chroot) Change root (chroot) is an operation that changes the apparent root directory for the current running process and their children. A program that is run in such a modified environment cannot access files and commands outside that environmental directory tree. Section 19.1: Requirements root privileges another working Linux environment,such as Live CD boot or an existing distribution matching environment architectures of chroot source and destination (check current environment architecture with uname -m) kernel modules which you may need in chroot environment must be loaded (for example, with modprobe) Section 19.2: Manually changing root in a directory Ensure you met all requirements, as per Requirements 1. Mount the temporary API filesystems: 2. cd /location/of/new/root mount -t proc proc proc/ mount --rbind /sys sys/ mount --rbind /dev dev/ mount --rbind /run run/ (optionally) If you need to use an internet connection in the chroot environment, copy over the DNS details: 3. cp /etc/resolv.conf etc/resolv.conf Change root into /location/of/new/root, specifying the shell (/bin/bash in this example): 4. chroot /location/of/new/root /bin/bash After chrooting it may be necessary to load the local bash configuration: 5. source /etc/profile source ~/.bashrc Optionally, create a unique prompt to be able to differentiate your chroot environment: 6. export PS1="(chroot) $PS1" When finished with the chroot, you can exit it via: 7. exit Unmount the temporary file systems: 8. cd / umount --recursive /location/of/new/root
  • 59. Linux® Notes for Professionals 55 Section 19.3: Reasons to use chroot Changing root is commonly done for performing system maintenance on systems where booting and/or logging in is no longer possible. Common examples are: reinstalling the bootloader rebuilding the initramfs image upgrading or downgrading packages resetting a forgotten password building software in a clean root environment
  • 60. Linux® Notes for Professionals 56 Chapter 20: Package Managers Section 20.1: How to update packages with the apt package manager The Advanced Package Tool, aptly named the 'apt' package manager can handle the installation and removal of software on the Debian, Slackware, and other Linux Distributions. Below are some simple examples of use: update This option retrieves and scans the Packages.gz files, so that information about new and updated packages is available. To do so, enter the following command: sudo apt-get update upgrade This option is used to install the newest versions of all packages currently installed on the system. Packages currently installed with new versions available are retrieved and upgraded; under no circumstances are currently installed packages removed, or packages not already installed retrieved and installed. To upgrade, enter the following command: sudo apt-get upgrade dist-upgrade In addition to performing the function of upgrade, dist-upgrade also intelligently handles changing dependencies with new versions of packages. It will attempt to upgrade the most important packages at the expense of less important ones if necessary. To do so, enter the following command: sudo apt-get dist-upgrade Section 20.2: How to install a package with the pacman package manager In order to search for packages in the databse, searching both in packages' names and descriptions: pacman -Ss string1 string2 ... To install a single package or list of packages (including dependencies), issue the following command: sudo pacman -S package_name1 package_name2 ... source Section 20.3: How to update packages with the pacman package manager To update a specific program: sudo pacman -S <programName> To update entire the system: sudo pacman -Syu
  • 61. Linux® Notes for Professionals 57 Section 20.4: How to update packages with yum Yellowdog Updater, Modified, one of the last remaining vestiges of Yellow Dog Linux, is the package manager used by Red Hat, Fedora, and CentOS systems and their derivatives. It can handle the installation and removal of software packaged as rpms for these Linux distributions. Below are some simple examples of use: search This command will attempt to locate software packages in the configured software repositories that match the given search criteria, and display the name / version / repository location of the matches it finds. To use it, enter the following command: yum search <queryString> install This command will attempt to locate and install the named software from the configured software repositories, recursively locating and installing any needed prerequisite software as well. To use it, enter the following command: sudo yum install <packageName> update This option is used to install the newest versions of all packages currently installed on the system. Packages currently installed with new versions available are retrieved and upgraded; new prerequisites are also retrieved and installed as necessary, and replaced or obsoleted packages are removed. To upgrade, enter the following command: sudo yum update Unlike apt, most yum commands will also automatically check for updates to repository metadata if a check has not been done recently (or if forced to do so) and will retrieve and scan updated metadata so that information about new and updated packages is available before the requested operation is performed.
  • 62. Linux® Notes for Professionals 58 Chapter 21: Compiling the Linux kernel Section 21.1: Compilation of Linux Kernel on Ubuntu Warning: be sure you have at least 15 GB of free disk space. Compilation in Ubuntu >=13.04 Option A) Use Git Use git if you want to stay in sync with the latest Ubuntu kernel source. Detailed instructions can be found in the Kernel Git Guide. The git repository does not include necessary control files, so you must build them by: fakeroot debian/rules clean Option B) Download the source archive Download the source archive - This is for users who want to rebuild the standard Ubuntu packages with additional patches. Use a follow command to install the build dependencies and extract the source (to the current directory): Install the following packages: 1. sudo apt-get build-dep linux-image-`uname -r` Option C) Download the source package and build This is for users who want to modify, or play around with, the Ubuntu-patched kernel source. Retrieve the latest kernel source from kernel.org. 1. Extract the archive to a directory and cd into it: 2. tar xf linux-*.tar.xz cd linux-* Build the ncurses configuration interface: 3. make menuconfig To accept the default configuration, press ? to highlight < Exit > and then Return . 4. Press Return again to save the configuration. 5. Use make to build the kernel: 6. make Note that you can use the -jem> flag to compile files in parallel and take advantage of multiple cores. The compressed kernel image can be found at arch/[arch]/boot/bzImage, where [arch] is equal to uname -a.
  • 63. Linux® Notes for Professionals 59 Credits Thank you greatly to all the people from Stack Overflow Documentation who helped provide this content, more changes can be sent to web@petercv.com for new content to be published or updated 7heo.tk Chapter 1 Aaron Skomra Chapter 16 Ajay Sangale Chapters 1 and 9 Anagh Hegde Chapters 4 and 14 Ani Menon Chapters 2 and 4 Arden Shackelford Chapter 12 Armali Chapter 1 Baard Kopperud Chapter 8 BrightOne Chapters 9, 14, 13 and 19 C.W.Holeman II Chapter 14 caped114 Chapters 1 and 4 colelemonz Chapter 1 ctafur Chapter 17 DaveM Chapter 2 depperm Chapter 1 e.dan Chapter 1 embedded Chapter 8 Emmanuel Mathi Chapter 4 EsmaeelE Chapter 1 fdeslaur Chapter 3 Federico Ponzi Chapter 9 Filipe Chapter 14 Flamewires Chapter 10 FOP Chapter 12 foxtrot9 Chapter 7 geek1011 Chapter 11 Jarryd Chapter 1 Jensd Chapters 1 and 4 KerDam Chapter 1 Kiran Vemuri Chapters 17 and 6 kuldeep mishra Chapter 13 Léo Léopold Hertz 준영 Chapter 21 lardenn Chapters 2 and 4 leeor Chapter 9 likewhoa Chapter 1 manav m Chapter 15 Manuel Chapter 14 Marsso Chapter 8 Mateusz Piotrowski Chapter 1 mattdm Chapters 2, 10 and 11 mertyildiran Chapter 5 Mike P Chapter 1 Mohammad Chapter 1 Nathan Osman Chapter 21 Naveen Chakravarthy Chapter 1 Nikhil Raj Chapter 2 Not22 Chapter 8 oznek Chapter 4 Paradox Chapters 16 and 20
  • 64. Linux® Notes for Professionals 60 parkydr Chapter 7 Philip Kirkbride Chapters 4, 20, 7 and 12 Quaker Chapter 4 Rajesh Rengaraj Chapter 14 Riley Guerin Chapter 15 Rubio Chapters 1, 4 and 20 S.Rohit Chapters 3, 12 and 6 Sergey Stolyarov Chapter 2 Sudip Bhandari Chapter 1 Teddy Chapter 2 Tejus Prasad Chapter 1 TiansHUo Chapter 1 Todd Chapters 1 and 14 user Chapters 1, 4, 14 and 18 vishram0709 Chapter 1 Whoami Chapter 1 Y4Rv1K Chapters 17 and 6 Zumo de Vidrio Chapter 1 zyio Chapter 5
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