Introductionto Linux(RHEL8)
LinuxHistoryandBasics
1.InitialRelease:LinusTorvaldsreleasedthefirstLinuxkernel(0.02) inOctober1991.Currentversion:2.6(major-minor-release).
2.Versioning:Evenminorversions(2.6)indicatestablereleases, whileoddversions(2.5)signifydevelopmentreleases.
LinuxBootSequence
1.Hardwareinitialization
2.Kernelloading
3.GUI(Gnome3/KDE)+shell(CLI)
ShellBasics
1.Shelltypes:Bourne(sh),Bash(bash),Korn(ksh),C(csh),Z(zsh)
2.Defaultshell:Bash
3.Promptformat:username@machinename:currentdirectory(# forroot,$forusers) CommandStructure
1.Commandname 2.Options(-/+)
3.Arguments
BasicLinuxCommands
#cal:Displaycalendar(e.g.,cal2020)
#who:Displayloggedusers
#whoami:Displaycurrentloggeduser
#mkdir:Createdirectory(e.g.,mkdirtest)
#date:Displaydate/time
#date+%x:10/03/2021
#date+%R:08:20
#date+%r:08:14:30AM
#date:Customformat:date+"nowis%A,%B%d,%y,%nitis%r"
#su:Switchuser(e.g.,su,suahmed)
#history:Displaylastcommands
#!!:Repeatlastcommand
#!32or!date:Executespecificcommands
#clear:Clearscreen
#passwd:Changepassword
#uptime:Displaysystemrunningtime
#du-hs/etc:Aggregatesizesofobjectswithin/etc
FileTypes
Ordinaryfiles(txt,jpg…..) (ls-l -)
1. Configurationfiles(/etc/passwd containsusrinfo) (/etc/shadowcontainencryptedpasswords)(-) 2. Devicefiles(/dev)(blockdevfile(harddesk),chardevfile( serialinterfaceRS232)(corb) 3. Directoryfile(containsinfoaboutinsidefiles) (d) 4. Linkfiles(symboliclink/softlink) (l) 5. Namedpipe 6 Socketfile 7.
FileTypeContents:
Static
Dynamicorvariable modifiedorappendedbyactiveprocess)
Persistent configurationremainsafterreboot)
Runtime systemspecificcontentsthatclearedduringreboot)
FileSystem
/ slashorrootdirectory
/root homedirectoryofrootuser
/home homedirs.Ofallusersexceptroot
/home/Mohamedhomedir.OfMohameduser
/home/sara homedirofsarauser
/etc alldifferentconfigurationfiles
/usr/bin normalcommands(executablefiles,binaryfiles)
/usr/sbin systemadmincommands
/bin,/sbin linkto/usr/bin,/usr/sbin
/dev devicefiles(driversfiles)
/media,/mntmounteddevices(cdorusb)
/var,/srv variablefiles(DB,ftp,web,log….)
/boot bootingfiles(bootloader(grub)runkernel)
/opt applicationsfiles
/proc infoaboutsystem
/tmp removedafter10days
/var/tmp removedafter30days(/usr/tmplinkedto/var/tmp)
/run runtimefilesforprocesses(processedIDandlockfiles)
Paths:absolutepathsstartwith/, relativepaths(dependonyour currentlocation)
#cdchangedirectorytohomedir
#cd-lastdir
#pwdprintworkingdir
#cd..stepup
#cd/home/studentmovetothisdir
#cd~alihomedirofuser
#filedeterminefiletype
#file/etc/passwd
#file/home
#file/dev/sda1
#file/bin/passwd
#cat/etc/passwdtextviewer
#cat-b/etc/passwdaddlinenumber
#head/etc/passwdview10lines(head)
#tail-n2/etc/passwdviewlasttwolines(or-2)
#tail-n+2/etc/passwdfromline2toend(or+2)
#tail-f/var/log/messagesfollowtheendoffile
#less/etc/passwdviewer(linebylineorpage)andcansearch (/,nnext,Nprevious)qforexit
#morenearlysamelikeless(notclearthescreenafterexit,
thefile
Filenamerules:upto255char.,connotuse(*,$,&,”,#)
#wc-l-w-c/etc/passwdcountlines,characters,wordsoftext files
#mkdircreatenewdir
#mkdir-p/dir1/dir2/dir3(pparent)
#rmdirremoveemptydir
#cpsourcedestinationcopyfiles/direct(-roption)
#mvsourcedestinationcut/movefile/dir(-roption)
#rm-rargumentdeletefiles/dir(-roption)
#rm-i/test/testinteractiveconfirmation
#\rmpreventaliase
#rm-rffwillnotpromptforconfirmation
#aliasviewaliaes
#aliasmm=”ls-l”
#unaliasmm
lab:createtwodiron/(dir1,dir2),touchabc,alfa,beta,d123indir1 copyabcalfatodir2 movebeta,d123todir2 renamed123to123 removeabcfromdir2
Help
1.
#whatispasswd (#makewhatis)
man commandname (in/usr/share/man) 2.
man-kkeyword (mustrun#mandbfirst)searchontitleand description
1pinfocommandname . 2sharedocuments(/usr/share/doc) .
3internetsites .
#ls -a all
#ls -d directory
#ls-l longlisting(includehardlinkcounts)
#ls -R recursive
#ls-s listsizeinblocks(block=512B)
#ls -r reverse
#ls-t sortbylastmodificationtime(-ltrreverse)
#ls-F (/dir,*exec,@symbolic,noneplaintext)
#ls-ullastaccesstimeinsteadoflastmodification(catorlesson files)
#ls-n uid&gidoffiles
#dircmpdisplayuniquefilesineachdir&commonfiles
#dircmp-s-ddir1dir2(ssuppressidenticalfiles,ddifference operationbetweentwofiles)
#echo“testfile“>/dir1/link
#lnfilehardlink-file
#ln-sfilesoftlink-file
#ls-il/showinodenumberoffiles,hardlinkedfileshavethesame inode
#dflistfilesystems(-bfreespace,-tusedblocksandtotal)
######hardlinkcountfieldindirectoriesindicatenumberof directoriesinside
#whichnanoexecutablefilelocation
#whereispasswdexecutablefile,manual,configurationfiles locations
##lab
Createhiddenfilenamed.filein/dir2
Listallfilesin/dir2
Createsoftlinknamed/softin/to/dir1/link
Createhardlink/hardto/dir1/link
Viewhardlinkcountof/hard&/dir1/link
Removeonelinkandcheckhardlinkcount
Bashexpansion
PatternMatching
-lsb*-zeroormorecharacters
-lsb??-listfilesstartingwith"b"andendingwithanytwo characters
-ls[abc]??-listfilesstartingwith"a","b",or"c"andendingwith anytwocharacters
-ls[!abc]??-listfilesnotstartingwith"a","b",or"c"andending withanytwocharacters([^abc])
-ls[[:alpha:]]-startwithanyalphabeticcharacter
-ls[[:digit:]]-startwithanynumber(0-9)
-ls[[:upper:]]*
-ls[[:lower:]]*
BraceExpansion
-touch{alfa,b,c,d,1,2}.log -echofile{a{1,2,3},b,c}.txt
CommandSubstitution
-echo"todayis$(date+%x)"
-echo"linenumbersofpasswordfileare`wc-l/etc/passwd"
HomeDirectoryExpansion
-cd~user-user'shomedirectory -ls~/mm
VariableSubstitution
-echo"executablepathsare$PATH"
PreventingExpansion
-\beforethepattern -\*,\?,"*"-preventsomeexpansions
''-preventallexpansions
Redirection
->file-overwrite
->>file-appendmode
-2>file-redirectstandarderror
-2>/dev/null-discardstandarderror
-&>file-redirectbothoutputanderror
-&>>file-appendbothoutputanderror
Piping
-|-passoutputasinputtoanothercommand
-tee-takesnapshotofoutputandsendcopytonextcommand
Tasks
-Countfiles:ls-R|wc-l
-Redirecterror/output:ls//zxy2>/err>/out
-Countfiles/sizes:ls-l|wc-l>/count;du-sh/etc>>/count;date +%x>>/count
TextfileEditing
1.nano
2.vim (vi ->vim)
speed,mostunix/linux,difficult searchasless(/dogsearchdown,?dogsearchupword) searchandreplaceassed(:%s/dog/cat/g alllines) 4modes
Commandmode(yycopyline,ppaste,ddcutline,uundolast changeUlastchangesontheline,ctrl+rredo,wmoveword……..,: extendedmode,Iinsertmode)
Insertmode (editmode)(A-appendendofline,I-appendbegin oflight,o–insertnewline)
Extendedmode(wq saveandquit,q! quitwithoutsave,w save, searchandreplace)
Visualmode(v,Vlines,^vblocks)selectmultiple 3.gedit
4.streameditor(sed)
##sed‘s/cat/dog/’file #onechangeinline
##sed‘s/cat/dog/gi’file#global(multiplechangeinline)case insensitive
##sed‘1,50s/cat/dog/g’file
##sed-e‘s/cat/dog/g’-e‘s/cow/goat/g’file