Linux Fundamentals - Extra.pdf

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Prepared by: Eng. Anwar Fouad
Linux Fundamentals

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What is Linux?
A fully-networked 32/64-Bit Unix-like Operating System
 Unix Tools Like sed, awk , find, and grep (explained later)
 Compilers Like C, C++, Fortran, …etc.
 Network Tools Like telnet, ftp, ping, traceroute
Multi-user, Multitasking, Multiprocessor
Has the X Windows GUI
Coexists with other Operating Systems
Runs on multiple hardware platforms
Includes the Source Code

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How do you get it?
Download it from the Internet
From a “Distribution” (e.g. Red Hat)
 Linux kernel
 X Windows system and GUI
 Web, e-mail, FTP servers
 Installation & configuration support
 3rd party apps
 Hardware support

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Popular Linux Distributions

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Why is it significant?
Growing popularity
Powerful
 Runs on multiple hardware platforms
 Users like its speed and stability
 No requirement for latest hardware
It’s “free”
 Licensed under GPL
 Vendors are distributors who package Linux

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Linux’s place in the market
Impacts:
 Applications:
 Web servers (65%)
 Web Infrastructure (mail, DNS) (15%)
 File/Print (15%)
 DB & DB Applications (2%)
 Observations
 Linux/Apache share of Web serving high
 Many SMB and small ISP
 Strong mindshare among developers

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Linux Fundamentals
Using the system

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Linux Fundamentals
Linux Command Basics
Working with files and directories

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Syntax Of Basic Commands
<command name> [<options>] [<arg1> <arg2> ... <arg n>]
Expressions between brackets [ ] are optional.
<options>: sequence of letters preceded by ‘-’ character.
each letter represents one option.
the order of the options has no importance.
<arg i>: string of characters
its meaning depends on the current command
(usually, they are file pathnames)
<command name>: command name
usually an executable filename.
Different command elements are delimited by at least one space
character.
Linux/Unix is case-sensitive.

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Execute a command line
To execute a command, type its name and arguments at the command line
ls -l /etc
Command name
Options
(flags)
Arguments

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File System Finding

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Finding and Processing Files
● Use locate
● Use find

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locate
● Queries a pre-built database of paths to files on the system
 Database must be updated by administrator
 Full path is searched, not just filename
● May only search directories where the user has read and execute
permission

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locate Examples
● locate file1
 Search for files with “file1" in the name or path
● Useful options
 -i performs a case-insensitive search
 -n X lists only the first X matches

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find
● find [directory...] [criteria...]
● Searches directory trees in real-time
 Slower but more accurate than locate
 CWD is used if no starting directory given
 All files are matched if no criteria given
● May only search directories where the user has read and execute
permission

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Basic find Examples
● find -name snow.png
 Search for files named snow.png
● find -iname snow.png
 Case-insensitive search for files named snow.png,Snow.png, SNOW.PNG, etc
● find -user joe -group joe
 Search for files owned by the user joe and the group joe

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find and Logical Operators
● Criteria are ANDed together by default.
● Can be OR'd or negated with -o and -not
● Parentheses can be used to determine logic order, but must be escaped
in bash.
 find -user joe -not -group joe
 find -user joe -o -user jane
 find -not ( -user joe -o -user jane )

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find and Numeric Criteria
● Many find criteria take numeric values
● find -size 1024k
 Files with a size of exactly 1 megabyte
● find -size +1024k
 Files with a size over 1 megabyte
● find -size -1024k
 Files with a size less than 1 megabyte

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find and Access Times
● find can match by inode timestamps
 -atime when file was last read
 -mtime when file data last changed
 -ctime when file data or metadata last changed
● Value given is in days
 find -ctime -10
Files modified less than 10 days ago
● Value given is in minutes
 find -cmin -60
Files modified less than 1 hour ago

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Storage Management

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What is Software RAID?
● Multiple disks grouped together into "arrays” to provide better
performance, redundancy or both.
● mdadm - provides the administration interface to software RAID.
● Many "RAID Levels" supported, including RAID O, 1 and 5.
● Spare disks add extra redundancy
● RAID devices are named, /dev/md0, /dev/md1, /dev/md2, /dev/md3 and
so on.

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Software RAID Configuration
● Create and define RAID devices using mdadm
mdadm -C /dev/md0 -l 1 -n 2 -x 1 /dev/sda1 /dev/sdb1 /dev/sdc1
● Format each RAID device with a filesystem
mke2fs -j /dev/md0
● Test the RAID devices
● mdadm allows you to check the status of your RAID devices
mdadm --detail /dev/md0

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Software RAID Testing and Recovery
● Simulating disk failures
mdadm /dev/md0 -f /dev/sda1
● Recovering from a software RAID disk failure
 replace the failed hard drive and power on
 reconstruct partitions on the replacement drive
 mdadm /dev/md0 -a /dev/sda1
● mdadm, /proc/mdstat, and syslog messages

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What is Logical Volume Manager (LVM)?
● A layer of abstraction that allows easy manipulation of
volumes. Including resizing of filesystems
● Allows reorganization of filesystems across multiple
physical devices

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LVM

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Creating Logical Volumes
● Create physical volumes
pvcreate /dev/hda3
● Assign physical volumes to volume groups
vgcreate vg0 /dev/hda3
● Create logical volumes from volume groups
lvcreate -L 256M -n data vg0
mke2fs -j /dev/vg0/data

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Resizing Logical Volumes
Growing Volumes
 lvextend can grow logical volumes
 vgextend adds new physical volumes to an existing volume group.
● Shrinking volumes
 lvreduce can then reduce the volume.
 Volume Groups can be reduced with:
pvmove /dev/hda3
vgreduce vg0 /dev/hda3

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Logical Volume Manager Snapshots
● Snapshots are special Logical Volumes that are an exact copy of an
existing Logical Volume at the time the snapshot is created
● Snapshots are perfect for backups and other operations
where a temporary copy of an existing dataset is needed
● Snapshots only consume space where they are
different from the original Logical Volume

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Using LVM Snapshots
● Create Snapshot of existing Logical Volume
# lvcreate -l 64 -s -n databackup /dev/vg0/data
● Mount Snapshot
# mkdir -p /mnt/databackup
# mount -o ro /dev/vg0/databackup /mnt/databackup
● Remove Snapshot
# umount /mnt/databackup
# lvremove /dev/vg0/databackup

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Linux Fundamentals
Backup and restore

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Importance of Regular File System Backups
Backing up file systems is one of the most crucial system
administration functions.
Backups should be performed on a regularly scheduled basis to
prevent loss of data due to:
• Accidental deletion of files
• Hardware failures
• Problems when reinstalling or upgrading a system
• System crashes
• System break-in by an unauthorized user compromising data integrity
• Natural disasters

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Overview of Backup Methods
 The backup process involves copying data from one
computer to some other reliable storage medium for
safekeeping.
 Once the data has been archived, the system administrator
can then restore data to the system from any previously
recorded backup.
 Considerations that are relevant for storage devices:
 Cost
 Size
 Manageability
 Reliability

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Overview of Backup Methods
There are many types of backup procedures that define how the
backup will take place:
 Full - will backup everything on the hard drive at the scheduled point in
the day
 Partial - backs up selected files
 Incremental - only the files that have changed since the last backup

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Archiving Tools: tar
● tar can backup to a file or tape device
● supports GZIP and BZIP2 compression
● can preserve file permissions, ownership and timestamps
● supports extended attributes
● uses rmt to write to a remote tape device

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Archiving Tools: dump/restore
● Back up and restore ext2/3/4 filesystems
 Does not work with other filesystems
 dump should only be used on unmounted filesystems or filesystems
that are read-only.
● Can do full or incremental backups
● Examples:
dump -0uf /dev/nst0 /dev/hda2
restore -rf /dev/nst0

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The /etc/dumpdates File
Each line in /etc/dumpdates file shows the file system backed up, the level
of the last backup, and the day, date, and time of the backup.
The following is an example of a typical /etc/dumpdates file:
# cat /etc/dumpdates
/dev/sda3 0 Fri Jun 2 19:12:27 2000
/dev/sda1 0 Fri Jun 2 20:44:02 2000
/dev/sda3 5 Thu Jun 8 19:42:21 2000

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Backing Up to Tape
1. Become root to bring the system to single-user mode and unmount the file
systems.
# shutdown -v -g30 “System is being shutdown for backup”
Shutdown started. Mon Jun 5 14:05:46 MdT 2000
Broadcast Message from root (pts/1) on host1 Mon Jun 5 14:05:46...
The system host1 will be shut down in 30 minutes
System is being shutdown for backup
2. Unmount all file systems (except / and /usr)
# umount /home
3. Check the integrity of the file system data with the fsck
command, but only if the file system has been unmounted.
# fsck /home
4. Perform a full level 0 backup of the /home file system.
# dump -0uf /dev/rmt/0 /home
DUMP: Writing 32 Kilobyte records
DUMP: Date of this level 0 dump: Mon Jun 5 2000 14:10:15 PM MDT
DUMP: Date of last level 0 dump: the epoch
DUMP: Dumping / dev/sda3 (host1:/home) to /dev/rmt/0.
….
DUMP: DUMP IS DONE
DUMP: Level 0 dump on Mon Jun 5 2000 14:10:15 PM MDT
#

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Restoring File Systems
Command Format
restore options [ arguments ] [ filesystem ]
restore options [ arguments ] [ filenames . . . ]
Common Options
The following describes the some options for the restore command:
• t – Lists the table of contents of the backup media.
• r – Restores the entire file system from the backup media.
• x – Restores only the files named on the command line.
• i – Invokes an interactive restore.
• v – Specifies Verbose mode. Displays pathnames to the terminal
screen as each file is being restored.
• f – Specifies the tape device name.

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Restoring Regular File Systems
To restore a regular file system, (for example, /home, or /opt) back to
disk.
Example
# mkfs /dev/sda#
# mount /dev/sda# /mnt
# cd /mnt
# restore -rf /dev/rmt/#
# rm restoresymtable
# cd /
# umount /mnt
# fsck /dev/sda#
# dump -0uf /dev/rmt/# /dev/sda#
# mount /dev/sda# /home

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Command: at
at -f script [m] <arg_hour> [<arg_date>] [+arg_increment>]
 Executes a command file at a given date
<arg_temps> : hh:mm | now | noon | midnight
<arg_date> : <month> <day> or today | tomorrow
<arg_increment> : <number> minutes | hours | days | weeks | months
$ at -f myscript.sh 17:30 mar 22 2014 +2 hours
job 24 at 2014-03-22 19:30
at –l / atq : list the number of registered commands
at -d / atrm : cancels a registered command
Authorized users (respectively non-authorized users ) to use
this command are declared in a system file at.allow
(respectively at.deny).

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Disk Quota

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Configuring the Quota System
● Overview
 Implemented within the kernel
 Enabled on a per-filesystem basis
 Individual policies for groups or users
■ Limit by the number of blocks or inodes
■ Implement both soft and hard limits
● Initialization
 Partition mount options: usrquota, grpquota
 Initialize database: quotacheck
 Create these files
#touch aquota.group
#touch aquota.user

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Setting Quotas for Users
● Implementation
 Start or stop quotas: quotaon, quotaoff
 Edit quotas directly: edquota username
 From a shell:
 setquota username 4096 5120 40 50 /Data
 Define prototypical users:
 edquota -p user1 user2

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Reporting Quota Status
● Reporting
 User inspection: quota
 Quota overviews: repquota

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Linux Fundamentals
Network File Sharing Services

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File Transfer Protocol(FTP)
● vsftpd - the default Red Hat Enterprise Linux ftp server
● No longer managed by xinetd
● Allows system, anonymous or virtual (FTPonly)user access
● The anonymous directory hierarchy is provided by the
vsftpd RPM
● /etc/vsftpd/vsftpd.conf is the main configuration file

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Service Profile: FTP
● Type: SystemV-managed service
● Package: vsftpd
● Daemon: /usr/sbin/vsftpd
● Script: /etc/init.d/vsftpd
● Ports: 21 (ftp), 20 (ftp-data)
● Configuration: /etc/vsftpd/vsftpd.conf /etc/vsftpd/ftpusers
/etc/vsftpd/user_list /etc/pam.d/vsftpd
● Log: /var/log/xferlog

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Network File Service (NFS)
● The Red Hat Enterprise Linux NFS service is similar to
other BSD and UNIX variants
 Exports are listed in /etc/exports
 Server notified of changes to exports list with
exportfs -r or service nfs restart
 Shared directories are accessed through the mount command

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Service Profile: NFS
● Type: System V-managed service
● Package: nfs-utils
● Daemons: rpc.nfsd, rpc.lockd, rpciod, rpc.
mountd, rpc.rquotad, rpc.statd
● Scripts: /etc/init.d/nfs, /etc/init.d/nfslock
● Ports: 2049(nfsd), Others assigned by portmap (111)
● Configuration: /etc/sysconfig/nfs , /etc/exports ,
/var/lib/nfs/rmtab

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NFS Server
● Exported directories are defined in /etc/exports
NFS utilities
● exportfs –v from server-side
● showmount -e hostname from client-side

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