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Unix Commands Reference
A Quick Reference
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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
<command name> 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 are a few of the most popular and useful commands used in unix
operating system |
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wildcard characters
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* |
- 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
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? |
- ? (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? |
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dir |
| Change |
cd dir
Change to directory d |
| Make |
mkdir dir
Create new directory d |
| Move |
mv dir1 dir2 Rename directory d1 as d2
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| Remove |
rmdir dir Remove directory d
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| file |
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| 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 |
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| vi - vi full screen editor |
vi filename , Opens a existing file or creates
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| 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 |
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File operation |
| Change read/write/execute mode of fil |
chmod mode file |
| chown
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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 |
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PROCESS |
| 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 |
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User admin |
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| 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 .
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| 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...] |
| printer |
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| Output file f to line printer |
lp -d printer file |
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| System Status |
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| 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 |
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| 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
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| Set environment variable (ksh/bash) to value v |
export name=v
example : export TERM=vt100 |
| Connectivity |
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| Connecting to a remote host |
$telnet hostname/ip address or $telnet Telnet 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 username@hostname 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.
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| 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 (multipleput) command is used to transfer files to remote host.
- get , mget (multipleput)
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
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| Securely copy files from/to remote host |
sftp username@hostname: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 .
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| Backup and Restore |
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| backup and restore using tar , TApeaRchive |
- tar tvf filename.tar --- View the table of content of a tar archive
- tar xvf filename.tar --- Extract content of a tar archive
- tar cvf filename.tar file1 file2 file3 --- Create 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.
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| 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.
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| 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.
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- 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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by by Æleen Frisch
