Unix Commands Tutorial

Unix commands are the first thing needed by a unix sysadmin who are starting to work in unix operating system . Unix operating systems comes with online manual system which can be used to see the command details , syntax options and examples on while working on a unix system. Unix manual can be accessed using man and it requires the man package installed and MANPATH set to man directories. The manual page directories may differ in different unix operating systems and man package may not be installed in all systems .

Following is a unix command tutorial with some of the most popular and useful commands used in unix operating system arranged by functionality .

The * wildcard character substitutes for one or more characters in a filename. For instance, to list all the files in your directory that end with .c, enter the command
ls *.c
? (question mark) serves as wildcard character for any one character in a filename. For instance, if you have files named prog1, prog2, prog3 , and prog3 in your directory, the Unix command:
ls prog?
Change cd dir Change to directory d
Make mkdir dir Create new directory d
Move mv dir1 dir2 Rename directory d1 as d2
Remove rmdir dir Remove directory d
list , no details only names ls filename , filename with wildcard character/s.
list , details ls -1 filename , filename with wildcard character/s.
move to directory mv filename dirname (wildcard character/s supported)
copy file to other/current directory cp file directory/newfile or cp directory/oldfile .
Delete the file rm file , rm -rf directory – Recursively remove files & directly without any warning.
file file filename , file command tries to determine the file type , text , executable etc after comparing the values in /etc/magic .
File edit/create/view
vi – vi full screen editor vi filename , Opens a existing file or creates
ed – Line Text editor ed filename
count – Line, word, & char wc filename
Text content display – List contents of file at once cat filename
Text content display by screen : List contents of file screen by screen more filename
Concatenate – file1 & file2 into file3 cat file1 file2 >file3
File operation
Change read/write/execute mode of fil chmod mode file
chown chown [-R] [-h] owner[:group] file
move (rename ) file mv file1 file2 Rename file file1 as file2
Remove rm file Delete (remove) file f
Compare two files cmp file1 file2
Copy file file1 into file2 cp file1 file2
Sort Alphabetically sort file
Sort Numerically sort -n file
Split f into n-line pieces split [-n] f
match pattern grep pattern file Outputs lines that
Lists file differences diff file1 file2
head f Output beginning of file head file
Output end of file tail file
Suspend current process CTRL/z *
Interrupt processes CTRL/c *
Stop screen scrolling CTRL/s *
Resume screen scrolling CTRL/q *
Sleep for n seconds sleep n
Print list of jobs jobs
Kill job n kill %
Remove process n kill -9 n
status process status stats ps
Resume background job n bg [%n]
Resume foreground job n fg [%n]
Exit from shell exit
User admin
add a new user login to the system # useradd -u 655 -g 20 -d /home/ttes testlogin loginname

-u is userid , if not specified system takes highest available .
-g group id should be existing in /etc/group , if not specified other or user is assigned.
-d home directory , default is to use user as the directory name under the home directory.
loginname – new login name to be created .

#useradd testlogin will create a user by the name ‘testlogin’ with all default values .

password Change passwd <user>
alias (csh/tcsh) – Create command alias name1 name2
alias (ksh/bash) – Create alias command alias name1=”name2″
alias – Remove alias unalias name1[na2…]
Output file f to line printer p -d printer file
System Status
Display disk quota quota
Print date & time date
List logged in users who
Display current user whoami
Output user information finger [username]
Display recent commands history
Environment Variable
set set command alone displays the environment variables, it is used to set options in ksh like set -o vi
export export variable , export makes variable visible in sub shells.
Set environment variable (csh/tcsh) to value v sentenv name v
Set environment variable (ksh/bash) to value v export name=v example : export TERM=vt100
Connecting to a remote host $telnet hostname/ip address or $telnetTelnet brings up the login prompt of remote host and expects you to enter your user name & password .Without argument it enters command mode (telnet>) and accepts command listed by ? at telnet> prompt. Communication is not encrypted between two hosts.
Securely connecting to a remote host
ssh [email protected] or ssh -l username hostname
Depending on ssh setting for your account you may or may not be asked a password to login. Your login/passwd will be same login password as you would use with telnet connection.
Communication is encrypted between two hosts so if someone intercepts your communication he will not be able to use it.
Copy files from/to remote host
ftp hostname
ftp expects you to enter your username/passwd or if it is ftp only account it will require ftp account password .
put , mput ( multiple put ) command is used to transfer files to remote host.
get , mget ( multiple put) command is used to transfer files from remote host.
ftp allows some limited number of commands to be executed at ftp> prompt & summary of ftp command can be found by using ? at ftp> prompt
Securely copy files from/to remote host sftp [email protected]:remotefile localfile Communication is encrypted between two hosts.
Test the tcp/ip connectivity between two hosts
ping hostname
If you can ping a host the host is reachable from the machine that you are using .
Router/firewall configuration may prevent ping to succeed .
Backup and Restore
backup and restore using tar , TApeaRchive
tar tvf filename.tarView the table of content of a tar archive
tar xvf filename.tar Extract content of a tar archive
tar cvf filename.tar file1 file2 file3Create a tar archive called filename.tar using file1, file2,file3 .
tar can’t copy the special files , device files .Not suitable for taking root backup.
backup and restore using cpio , CopyInputOutput
cpio is mostly used in conjunction with other commands to generate a list of files to be copied :
#ls | cpio -o > /dev/rmt/c0t0d0 — Copy the contents of a directory into a tape archive:
#find . -depth -print | cpio -pd newdir — copy entire directory to other place:
#find . -cpio /dev/rmt/c0t0d0 — Copy files in current directory to a tape
cpio can copy special files and hence useful in taking root backup containing device file.
Find files , directories
find files , directories
Find command is used to find the files , directories and to run commands on the list of files thus generated .By default, find does not follow symbolic links.
find . -name *.log -print — Simple find to list log files
find . -name ‘*.log’ -exec rm {} ; — Simple find to find log files and delete them .
find accepts a long list of options to find the files based on different parameters such as create time , modified time , of certain size etc. Please refer to man find for more option.

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