Linux Basic Command and Options with Example

1.Shell :

            Operating system to User intermediate

            #cat /etc/shells

                 /bin/sh         => Shell

                 /bin/bash     => Bourn Again Shell

                 /bin/tcsh      =>

                 /bin/csh        => C Shell

                 /bin/nologin   =>  NoLogin shell

2. Kernel :

            Hardware to Operating system monitoring

3. [Root@Server6 ~]#  or $ :

            Root        => Indicate to which User

            Server6   => Indicate to Hostname

            ~    => Indicate to Home Directory

            #    => Indicate to Root Privilege

            $     => Indicate to Normal User Privilege

4. F.S.H  ( File System Hierarchy ) :

            /root     => Root Home Directory

            /boot    => Only stored Boot files

            /home  => Normal users Home Directory

            /bin       => Stored in Binary files or Executions files

            /lib        => Library files or Documentations

            /etc       => All Configuration files stored in this directory

            /var       => Variable Directory. Used to share the contents ( FTP, HTTP…)

            /mnt     => Used to default mount point for Disk Partitions

            /media => Mount Point for External Devices ( CD/DVD, USB, Pendrive…)

5. Help and Information for Commands :

            MAN  =>  Format and Display online manual copy.

                 # man ls        

                 # man mkdir

            INFO  =>  Read full Documentations.

                 # info ls

                 # info cd

            PINFO  =>  Small Graphical Page.

                 # pinfo ls

                 # pinfo cd

            --HELP or  -?   =>  Small Information.

                 # ls –help

                 # ls -?

            WEBPAGE  =>  It display webpage Documentations.

                  File:///usr/share/doc

6.  LS Command :

            Options :       -l => Long List

    -a => Display All Files.

    -d => Display Present Directory Information

    -h => Human Readable.

    -f  => Display File Type.

    -R => Display sub directory to recurs.

            # ls –alh

            # ls –R

            # ls –d .

7.  PWD Command : ( Present Working Directory )

            # pwd

               /root.

8.  WHOAMI Command :  ( To identify which user login for Terminal)

            # whoami                   # whoami

               Root.                           Shyam.

9.  LOGNAME Command : (The real user who logs in initially)

            # logname                      # su - shyam

               Root.                             # logname

             # whoami                         Root.

                root                              $ whoami

                                                          shyam

10.  HOSTNAME Command : ( to check the computer name )

            # hostname

               Server6.

11.  UNAME Command : (to check  OS, Version, Architecture, Hostname etc..)

            Options  :  -a, -s, -n, -r, -v, -m, -p, -I, -o

           

            # uname

               Linux.

            #uname –a  ( all )

              Linux server6.example.com 2-6.32-131.0.15.el6.x86_64 ……………………

           

12.  CD Command : ( to use Change Directory )

            # cd       => go to home directory

            #cd ~     => go to home directory

            # cd /var/www/html/       => go to html directory

            #cd ..                         =>  back to one directory

            #cd -                          => forword to directory

13   ID Command : ( Identification, to check UID and GID )

            # id

               Uid=0(root) gid=0(root)  groups=0(root)

            # id shyam

               Uid=500(shyam) gid=500(shyam) groups=500(shyam)

14.   TTY Command : (Psuedo Terminal, to check the user login and terminal)

            Terminal 0 :

            # tty

              /dev/pts/0

            Terminal 1 :

            #tty

              /dev/pts/1

15.   CLEAR Command : ( to clear the terminal screen )

            # clear

16.   DATE Command : ( Display the Date and Time )

            # date     => to display date and time

            # date –s   2011-12-05  => change only date

            # date –s   5:30:20         =>  change only time

17. CAL Command : ( Display the Calendar )

            # cal    => to display current month

            # cal 2011  => to display 2011 an all month

            # cal 12 2011   => to display month 12, year2011

18.   WHICH Command : ( Show the full path of commands/shell)

            # which ls

               /bin/ls

            #which  chown

              /bin/chown

19.   WHATIS Command : ( Search the full database for complete words )

            # whatis w

              Who is logged on and what they are doing

            #whatis ls

20.   WHEREIS Command : ( Locate the Binary, Source, Manual page for all commands)

            # whereis ls

               Ls: /bin/ls   /usr/share/man/ma1/ls.1.gz   /usr/share/man/man1p/ls.lp.gz

21.   WALL Command : ( Broadcast on the message send to all logged in user on the system)

            # wall

               Hai Pls reboot.  => type the msg.

            CTRL + D   => Exit

22.   WC Command : ( Word Count, word counting cmd)

            Options  :   -l => line count ,    -w => word count,     -c => byte count,     -m => character count

            # wc –l /etc/passwd

            # ls | wc –l

23.  TOUCH Command :  ( to create Empty File or 0byte file )

            # touch file1

            # touch /home/shyam/shyam.txt

            # touch file{1..5}.txt

            # touch file1 file2 file3 file4 file5

24.   CAT Command :  ( Canonical system )

            # cat file1 => show the file1

            # cat > newfile1.txt             => create new file.

            # cat >> newfile1.txt          => overwrite new content

25.  HISTORY Command : ( to shows the all typed commands )

            # history

            # ! serv                     => to run service httpd restart

            # !55                          => to run 55 command

26.   MKDIR Command : ( Make Directory )

           

            # mkdir test            => create directory under the PWD

            # mkdir /var/www/html/pc1.linux.com/   => create to directory under the html.

27.   MORE Command : ( It shows small paragraph )

            # more /etc/httpd/conf/httpd

            #more /etc/passwd

28.   LESS Command : ( it display simple method, scrolling function available)

            # less /etc/httpd/conf/httpd

            # less /etc/passwd

29.   HEAD Command : ( it shows 1^st few lines of the text, By default 10 line )

            # head /etc/passwd           => By default 1^st 10 line

            # head -5 /etc/passwd      => to display 1^st 5 lines

            # head -20 /etc/passwd => to display 1^st 20 lines

30.    TAIL Command : ( it display last few lines of text, By default last 10 line )

            # tail /etc/passwd                => By default last 10 lines

            # tail -15 /etc/passwd        => to display last 15 lines

           

            # tailf /var/log/httpd/access_log   => view log files while it is being updates

31.    UNIQ Command : ( Identify any duplicate line entries in a file or input provider )

           

            Options  :  -d , -i

            # vim shyam.txt  => type any content

            # uniq shyam.txt =. To check

32.    STRING Command : (Find and Display legible information embedded within a non-text or binary file)

            # string /bin/cat

            # string /bin/mkdir

33.    CP Command : ( Copy File, Copy the file/Directory one location to another location as same copy )

           

            Options  :  -I, -r, -p

            # cp shyam.txt   shyam.txt.back  => take the copy and change the name

            # cp shyam.txt   /var/ftp/pub/shyam.txt  => copy to another location

            # cp /root/shyam.txt   /var/ftp/pub/shyam.txt  => same as above, it is another method

            # cp –I /root/abc.txt   /tmp/abc.txt  => copy time ask Yes or No

            # cp –p /root /abc.tcxt   /tmp/abc.txt  => permission, time, ownership copy to same

            # cp /root/*   /tmp/  =>  copy all

            # cp /root/.txt  /tmp/  => only copy .txt contents

            # cp –r /root/*   /tmp/  => copy at recursive  

34.   MV Command : ( Used to Move / Rename the file or directory )

            # mv /root/shyam.txt   /root/aaa.txt  => rename the file

            # mv /root/shyam.txt   /var/ftp/pub/shyam.txt  => move the file to another location

35.   RF Command : ( Remove the File / Directory )

            Option  :  -f => Force,    -r => Recursive

            # rm shyam.txt  => Remove the file

            # rm –f shyam.txt => Remove the file forcibly

            # rm –r shyam.txt => Remove the file and ask the Yes or No

            # rm –rf shyam.txt  => Forcibly removing

36.   STAT Command : ( File/Directory Statistics or Properties)

            # stat /root

            # stat/root/shyam.txt

37.   File / Directory Attribute Settings :

            lsattr  => Listing ,     chattr  => Modifying    ( + set the value,   - Unset the value )

            Options  :  -a, -i,….

            # lsattr /root/shyam.txt

               -----------e- shyam.txt

            #chattr +ia shyam.txt

               ------ia----e- shyam.txt

#chattr -ia shyam.txt

               ------ia----e- shyam.txt

38.   Pattern Matching : GREP  ( Global Regular Expression Print )

            # grep “shyam” /etc/passwd

               Shyam:X:500:500: :/home/shyam:/bin/bash

            # grep “shyam” - -color /etc/passwd            

           

            # grep “root” /etc/passwd  /etc/shadow

               /etc/passwd => root:X:0:0:root:/bin/bash

              /etc/shadow => root: :15253:0:9999:7: : :

            # grep ^root /etc/passwd  => ( to display startins word for root all entries )

            # grep bash$ /etc/passwd  => ( to display last word or sentence )

            # grep ^root$ /etc/passwd

            # grep –i shyam /etc/passwd  => ( to ignore all letters)

            # cut –f2 –d “ : “ /etc/shadow       

            # grep “shyam” /etc/shadow

            # grep “shyam” /etc/shadow | cut –f2 –d “ : “

39.   Symbols :

Ø     => Overwrite the file’s

>>      => Appending the file’s

|        => Pipe

&&    => AND Option 1^st is true then go to 2^nd option

||      => OR any one condition is true

40.    USER Administration :

            UID :  0 => root,     1 to 499 => System Services,      500 above => Normal Users

           

           User Account file and Directory :

            /etc/passwd,    /etc/shadow,    /etc/groups,    /etc/gshadow,    /home/users,    /var/mail

1.       /etc/passwd :  user1: X: 500: 500: Regular Comments: /home/user1: /bin/bash

User 1                  => User name

X                            => Password place holder

500:500               => UID and GID

Comments        =>  Use any Comments, Hai welcome etc…

/home/user1   => User Home Directory

/bin/bahs           => User Shell

        

2.       /etc/shadow :  user1: $6$BY$JKJJ9789N…: 15265: 0: 99999: 7:  :  :

User1                   => User name

$6$jhvjh….         => Encrypted Password

15265                   => Last changes day ( Epoch time Jan 01 1970 )

0                                           => Minimum days

99999                   => Maximum days

7                            => Warning days

:                             => Inactive days

:                             => Disabled day

:                             => Feature use

3.       /etc/group  :   user1: X: 500:  :

User                     => User name

X                            => Password place holder ( /etc/gshadow)

500                        => GID (Privet GID )

:                             => Group members

42.   USERADD Command :  ( Add a new user )

         Option :      -c => Comments

                                -o => non-unique (  to use duplicate UID in normal user )

                                -u => UID ( we have to prefer UID )

                                -s => Shell ( to change shell )

                                - r => system account ( to use system service accounts )

                                -g => GID ( to use duplicate GID in normal users )

                                -e => Expire date ( given to the account expire date )

                                -p => Password ( given to the Encrypted password )

                                -d => Home Directory ( change to home directory)          

         # useradd user1  => Normal creation

         # userad  –c Hai  –o  –u 605  –s /bin/csh user2  => Add Comments, UID, Shell

         # useradd –r user3  => Encrypted Password

         # useradd  –g 700   -e 2011-11-01  -d  /var/www/html/user4  user4  => Add GID, Expir date, Home                                                                                                                         directory

         # useradd  -s /sbin/nologin   user5  => Use nologin

         # passwd user1

1.       User Login Information :

# vim /etc/login.defs

2.       Default Useradd Functions :

# vim /etc/default/useradd