Overview on Linux

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Overview of Unix
Activity Guide 1
[Edition 1]
[Last Update 130815]
For any issues/help contact : support@k21technologies.com

Sno Topics
1 IntroductiontoUnix,History,Versions,Features.FileSystems
2 LoggingIn,Password,CreatingFilesandDir.Removingfilesanddir.
3 Additional commands (uname,mv,date,,lsoptions,finger,who,cal.
Copyingusing(absolute,relative)method,
Wild characters, redirection(?, *,[] ),(stdin, stdout, stderr)
4 Fileaccesspermissionschmod(absolute,symbolic),umask.Simplefilters(more,less,wc,sort,
cut,paste,tr)
5 Editors-vi(advance)-3modes-escape,insert,colon
6 Searchingfilesusingfindcommandbyusingvariousoptions,communicationstools-using
write,talk, mail, wall commands
7 Advancefilters(grep,sed,awk)
8 Linkingfilesusinghardlinkandshortlink,processscheduling-backgroundprocess,killing
process

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CompaniesthatlaunchedMULTICS

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IBM Mainframe Computers

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KenThompson

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Linus Torvolds

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General Operating SystemDiagram

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FileSystemofUnix

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Directory Structure & its contents
OrdinaryFiles

Devi ces
Directories
Links

Basic Commands
Creating,Removing,Copying,Moving files& directories
Creatinga file inLinux
Usingcat command:
 Cat (concatenate) commandisusedtocreate a file andto displayandmodifythe contents
of a file.
 To create a file.
#cat > filename(sayktfile)
HelloWorld
Ctrl+d (to save the file)
 To Displaythe contentof the file
#cat filename (sayktfile)
 To append (edit)thedatainthe alreadyexistingfile
#cat >> <filename>
#cat >> ktfile
Ctrl+d (tosave the changes)

Creatingmultiplefilesatsame time usingtouchcommand andto checkthe fileswith“ls”command
#touch <filename1><filename><filename>
Creatinga Directory
#mkdir<dir name>
Making multipledirectoriesinside adirectory
Checkit byusingtree command or ls –R command

CopyingfilesintoDirectory
#cp <source filename><destinationdirectoryinwhichtopaste the file>
#cp file1ktdir

Copyingdirectoriesfromone locationtoother
#cp –rvfp<dir name><destinationname>
Movingfilesfromone locationtoother(cutand Paste)
#mv <filename><Destinationdirectory>
MovingDirectoryfromone locationto other
#mv <filename><Destinationdirname>
#mv ktdirktdir2
RenamingaFile

#mv <oldname> <newname>
RenamingaDirectory
The procedure andcommand forrenamingthe directoryisexactlysame asrenamingafile.
#mv <oldname><newname>
#mv ktdirkerneldir
RemovingaFile
#rm filename or#rm –f filename(withoutprompting)

RemovinganEmptyDirectory
#rmdir dirname
Removingadirectorywithfilesordirectoriesinside:
A di wichis havingsome contentsinsideitcannotbe removedbyrmdir command.There are two
waysto delete the direcotywithcontents.
Remove the contentsinsidethe directoryandthenrunrmdircommand
#rmdir –rf dirname( where rstandsforrecursive andf stands forforcefully).

VIMEDITOR
VIVisual Displayeditor
VIMVisual Displayeditorimproved
Thisis commandmode editorforfiles.OthereditorsinLinux are emacs,gedit.Vi editorismost
popularithas 3 modes(1 CommandMode,2 InsertMode,3 extendedcommandmode)
Note:whenyouopenthe vimeditor,itwill be inthe commandmode bydefault.
In the commandmode the cursor’scan be usedas h/l/k/j tomove cursorleft/right/up/down
Insert mode
i To begininsertmode atthe cursor position
I To insertat the beginningof line
a To appendto the nextword’sletter
A To appendat the endof the line
o To inserta newline belowthe cursorposition
O To inserta newline above the cursorposition
Command Mode
gg To go to the beginningof the page

G To go to the endof the page
w To move the cursor forward,wordby word
b To move the cursor backward,wordby word
nw To move the cursor forwardto n words(5W)
nb To move the cusor backwardto n words(5B)
u To undolast change (word)
U To undothe previouschanges(entire line)
Ctrl+R To redothe changes
Yy To copy a line
Nyy To copy n lines(5yyor4yy)
p To paste line belowthe cursorposition
P To paste line above the cursorposition
dw To delete the wordletterbyletter(like Backspace)
x To delete the worldletterbyletter(like DEL Key)
dd To delete the entire line
ndd To delete nno.Of linesfromcursor position(5dd)
/ To search a wordin the file
ExtendedMode:(ColonMode)
ExtendedMode isusedforsave and quitor save withoutquitusing“Esc” keywith“:”
Esc+:w To Save the changes
Esc+:q To quit(Withoutsaving)
Esc+:wq To save and quit
Esc+:w! To save forcefully
Esc+wq! To save and quitforcefully
Esc+:x To save and quit
Esc+:X To give passwordtothe file andremove password
Esc+:20(n) To go to line no.20 or n
Esc+: se nu To setthe line numberstothe file
Esc+:se nonu To Remove the setline numbers
To openmultiple filesinvimeditor
#vim–o file1file2
To Switchbetweenfilesuse Ctrl+w
ListingfilesandDirectories

#ls List the file names
#ls –l Long listof the file
#ls –l filename To see the permissionsof aparticularfile
#ls –al Showsthe filesinascendingorderof modification.
#ls p* All the filesstartwithp.
#ls ?ample Fileswithanyfirstcharacterand has ample
#ls –ldl* Directorylistingonly
#ls –lddirectoryname To see the permissionsof aparticulardirectory
#ls [ae]* Firstcharacter of the filename mustbe aor e.
#ls [!ae]* ! Symbol complementsthe conditionthatfollows.The charactersmust
not be a or e.
Typesof Files
Symbol Type of File
- Normal file
d Directory
l Linkfile (shortcut)
b Blockfile (Harddisk,Floppydisk)
c Character file (Keyboard,Mouse)
P A namedpipedfile isusedforinterprocesscommunication
S Its isa socketfile usedforinterprocesscommunication
D A doorfile .it isa special file forinterprocesscommunication (sunsolaris)
SymbolicLink
There are twotypesof Links:-
S.No. SoftLink Hard Link
1 Size of linkfile isequal tono.Of characters inthe name
of the original file.
Size of bothfile issame
2 Can be createdacross the partition Can’tbe createdacross the
partition.
3 inode no.Of source and linkfile isdifferent inode no.Of both file issame
4 If original file isdeleted,linkisbrokenanddataislost If original file isdeletedthen
alsolinkwill containdata
5 SHORCUT FILE BACKUPFILE

Creatinga softlink:
#ln -s<source file><destination>
CreatingHard Link
#ln <source file><Destination>
Grep:
Grep standsfor Global RegularExpression Print.It isusedto pickout the requiredexpressionfrom
the file andprintthe output.If grep iscombinedwithanothercommanditcan be usedto pickout
the selectedword,phrase fromthe outputof the firstcommandand printit.
Examplesof Grep
Let uspick the informationaboutrootfromthe file /etc/passwd(/etc/passwdconatainsinformation
aboutall the userspresentinthe system)
#grep root/etc/passwd

To avoidcase sensitivityof the word(i.e the wordmaybe uppercase of lowercase) use -i
#grep -i IT ktfile (letsgrepthe word IT whetherupperof lowercase inthe file ktfile)
To displayaword and 2 linesafterthe word
To displayaword and 2 linesafterthe word
To displaythe things exceptthe givenword
To displaythe searchedwordincolor

Combininggrepwithothercommands
FilterCommands:
filtercommandsare usedtofilterthe outputsothat the requiredthingscaneasilybe pickedup.The
commandswhichare used to filterthe outputare
 #less
 #more
 #head
 #tail
 #sort
 #cut
 #sed

less:- The lesscommand is usedto see the output line wise or page wise.
Note:-
pressEnterkeyto scroll downline byline (or)
Use d to go to nextpage
Use b to go to previouspage
use / to searchfor a wordin the file
Use v to go vi mode where youcan editthe file andonce yousave it youwill backto lesscommand
more: more isexactlysame like less

Ex: #more /etc/passwd
Note:-
pressEnter keyto scroll downline byline (or)
use d to go to nextpage
use / to searchfor a wordin the file
Use v to go vi mode where youcan editthe file andonce yousave ityou will backtomore command
head: it is usedto displaythe top 10 linesof the file.
ex:# head/etc/passwd
To display the custom lines
#head -n /etc/passwd (where n can be any number)
tail: It is usedto displaythe last 10 linesofthe file
#tail /etc/passwd

To display the custom lines
#tail -n /etc/passwd(where n can be any number)
sort: It is usedto sort the output in numeric or alphabeticorder
#sort filename

To sort the file accordingto numbers
#sort -dktfile
To remove the duplicate entriesfrom the output
#sort -uktfile

cut command:
The cut commandisusedto pick the givenexpression(incolumns) anddisplaythe output.
#cut -d -f filename(where dstandsfordelimiterex.:," "etcand f standsfor field)

To delimitspacesandprintthe field
#cut -d "" -f1 filename
To delimitcommasandprintthe field
#cut -d, f1 filename
sedcommand
sedstands forstreameditor,whichisusedtosearch a word inthe file andreplace itwiththe word
requiredtobe inthe output.
Note:- itwill onlymodifythe output,butthere will be nochange inthe original file.
sed's/searchfor/replacewith/g' filename
Redirection:Redirectionisaprocesswhere we cancopy the outputof anycommand(s),file(s) intoa
newfile.There are twowaysof redirectingthe outputintoafile.
Using> or >> filename afterthe command,and usingtee command
Note:if the givenname of the file isnotavilable anew file will be createdautomatically.If the file
alreadyexiststhenitwill overwrite contentsof thatfile.

Appendinganotheroutputinsame the same file
Likewise thereare manyoptionswhere we canuse redirections
Ex: copyingcontentsof twofilesinanew file
#cat file1file2>file3
Usingtee
The above optionsof redirectionswill notdisplayanyoutput,butdirectlysave the outputinafile.
usingtee commandwill notonlyredirectthe outputtonew file butitwill alsodisplaythe output.
Syntax:cat <filename>|tee <newfile name>
Note:If the givenof the file (newfile)isnotavailable anew file will be createdautomatically.If the
file alreadyexiststhenitwill overwrite contentsof the file.
#cat ktfile |tee ktf1

Appendingdatainthe same file usingtee command
Syntax: cat filname | tee -a filename2
#cat ktfile1| tee -a ktf1
FindCommand
findcommandis usedto findthe filesordirectory'spath, itisexactlylike the findoptioninwindows
where youcan searchfor a file.
Syntax: find / (underroot) - option filename
optionsthatcan be usedwithfindcommand:
Option Usage
-name For searchinga file withitsname
-inum For searchinga file withparticularinodenumber
-type For searchinga particulartype of file.
-user For fileswhose owner
-group For filesbelongingtoparticulargroup

Findingafile withname
#find/ -name test
#find/ -num5934
Findingthe files,whose ownerisausercalled"abc"
Findingthe fileswhose groupis"abc"

File Permissions
Permissionsare appliedonthree levels:-
 Owneror User level
 Group level
 Otherslevel
Accessmodesare of three types:-
 r readonly
 w write/edit/delete/append
 x execute/runacommand
Accessmodesare differentonfile anddirectory.
PERMISSIONS FILES DIRECTORY
r Openthe file 'ls' the contentsof dir
w Write,edit,append,deletefile Add/Del/Renamecontentsof
dir
x To run a command/shell script To enterintodirusing'cd'
r : For normal or directoryfile - viewthe contents
w: Editthe contentsof a normal or directoryfile

x: Runan executable file /Enterintodirectoryfile
Permissionscanbe seton any file/dirbytwomethods:-
1. Symbolicmethod (ugo)
2. Absolute method(numbers)
SymbolicMethod
Symbolicmode:General formof symbolicmode is
#chmod [who] [+/-/=] [permissions] file
who> to whomthe permissionstobe assigned
user/owner(u);group(g);others(o)
Example:- Assigndifferrentpermissionstothe file (user=rwx,group=rw andothers=r)
#chmod u=rwx,g=rw,o=r ktfile(where ktfileisthe name of the file)

Assigningfullpermissiontothe file i.e rwx toall
#chmod ugo=rwx <file name>
likewise youcanaddor remove permissionsfromanyfile foranyone(usergrouporother)
 #chmod u+x ktfile (addingexecutepermissionstouseronly)
 #chmod go-wx ktfile(Removingwrite andexecutepermissionsfromgroupandother)
 #chmod go+wx ktfile (Addingwriteandexecute permissionsfromgroupandother)
 #chmod go=r ktfile (Givingonlyreadpermissiontogroupandother)
ABSOLUTE METHOD(NUMBERS)
In Absolute methodwe use numbersinsteadof usingsymbolsi.e
 Read = 4
 Write = 2
 Execute = 1
Assigningdifferentpermissionstothe file (user=rwx,group=rw andothers=r)
#chmod 764 ktfile (where 7 means rwx i.e 4+2+1, rw=6 i.e 4+2 and 1 indicatesx)

Assigningfullpermissionstothe file i.e rwx toall
#chmod 777 ktfile
likewise youcangive differentpermissionsaccordingtoyour requirement
Removingall permissionsfromothers
#chmod 770 ktfile (where 0 indicatesno permissions)
Note:All the above permissionsandprocedure issame forfilesanddirectories
Umask
Whenwe create any file usingtouch,cator vi commandstheygetcreatedwithdefaultfile
permissionsasstoredinumask(userfilecreationmask).umaskisa4 digitoctal numberwhichtells
unix whichof the three permissionsare tobe deniedratherthangranted.Umask will decidethat
whatshouldbe the defaultpermissionsforafile anddirectorywhenitiscreated.
the defaultumask value is 0022

calculationof defaultpermissionsforfile anddirectory,basinguponthe umaskvalue
Note:For a file bydefaultitcannothave the execute permissions,sothe maximumfull permission
for a file atthe time of creationcan be 666 (i.e 777 -111 = 666), whereasadirectorycan have full
permissionsi.e777
The full permissionsforthe file 666
Minusthe umaskvalue -022
The defaultpermissionforfile is 644 (rw-,r--,r--)
The full permissionsforthe directory 777
Minusthe umaskvalue -022
The defaultpermissionforfile is 755 (rwx,r-x,r-x)
#umask002
The modifieddefaultpermissionforafile will be 666-002=664 i.e.rw,rw,r,andforthe directoryit
will be 777-002=775 i.e.rwx,rwx,r-x

Note:Create a file anda directoryandcheckfor the defaultpermissions.
These were the fewthings amongst the basics; keepworkingto furnishyour basics. After all,if the
foundationis good thenonly the buildingcan stand still"
=============End of the Activity 1 Guide========

Overview on Linux

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Overview on Linux