50 Basic Linux Commands
1. tar command
examples
Create a new tar
archive.
$
tar cvf archive_name.tar dirname/
Extract from an
existing tar archive.
$
tar xvf archive_name.tar
View an existing tar
archive.
$
tar tvf archive_name.tar
2. grep command
examples
Search for a given string
in a file (case in-sensitive search).
$
grep -i "the" demo_file
Print the matched
line, along with the 3 lines after it.
$
grep -A 3 -i "example" demo_text
Search for a given
string in all files recursively
3. find command
examples
Find files using
file-name ( case in-sensitve find)
#
find -iname "MyCProgram.c"
Execute commands on
files found by the find command
$
find -iname "MyCProgram.c" -exec md5sum {} \;
Find all empty files
in home directory
4. ssh command
examples
Login to remote host
ssh
-l jsmith remotehost.example.com
Debug ssh client
ssh
-v -l jsmith remotehost.example.com
Display ssh client
version
$
ssh -V
OpenSSH_3.9p1,
OpenSSL 0.9.7a Feb 19 2003
5. sed command
examples
When you copy a DOS
file to Unix, you could find \r\n in the end of each line. This example
converts the DOS file format to Unix file format using sed command.
Print file content in
reverse order
$
sed -n '1!G;h;$p' thegeekstuff.txt
Add line number for
all non-empty-lines in a file
$
sed '/./=' thegeekstuff.txt | sed 'N; s/\n/ /'
6. awk command
examples
Remove duplicate lines
using awk
$
awk '!($0 in array) { array[$0]; print }' temp
Print all lines from
/etc/passwd that has the same uid and gid
$awk
-F ':' '$3==$4' passwd.txt
Print only specific
field from a file.
$
awk '{print $2,$5;}' employee.txt
7. vim command
examples
Go to the 143rd line
of file
Go to the first match
of the specified
$
vim +/search-term filename.txt
Open the file in read
only mode.
8. diff command
examples
Ignore white space
while comparing.
#
diff -w name_list.txt name_list_new.txt
2c2,3
<
John Doe --- > John M Doe
>
Jason Bourne
9. sort command
examples
Sort a file in ascending
order
Sort a file in
descending order
Sort passwd file by
3rd field.
$
sort -t: -k 3n /etc/passwd | more
10. export command
examples
To view oracle related
environment variables.
$
export | grep ORACLE
declare
-x ORACLE_BASE="/u01/app/oracle"
declare
-x ORACLE_HOME="/u01/app/oracle/product/10.2.0"
declare
-x ORACLE_SID="med"
declare
-x ORACLE_TERM="xterm"
To export an
environment variable:
$
export ORACLE_HOME=/u01/app/oracle/product/10.2.0
11. xargs command examples
Copy all images to
external hard-drive
#
ls *.jpg | xargs -n1 -i cp {} /external-hard-drive/directory
Search all jpg images
in the system and archive it.
#
find / -name *.jpg -type f -print | xargs tar -cvzf images.tar.gz
Download all the URLs mentioned
in the url-list.txt file
#
cat url-list.txt | xargs wget –c
12. ls command
examples
Display filesize in
human readable format (e.g. KB, MB etc.,)
$
ls -lh
-rw-r-----
1 ramesh team-dev 8.9M Jun 12 15:27 arch-linux.txt.gz
Order Files Based on
Last Modified Time (In Reverse Order) Using ls -ltr
Visual Classification
of Files With Special Characters Using ls -F
13. pwd command
pwd is Print working
directory. What else can be said about the good old pwd who has been printing
the current directory name for ages.
14. cd command
examples
Use “cd -” to toggle
between the last two directories
Use “shopt -s cdspell”
to automatically correct mistyped directory names on cd
15. gzip command
examples
To create a *.gz
compressed file:
To uncompress a *.gz
file:
Display compression
ratio of the compressed file using gzip -l
$
gzip -l *.gz
compressed uncompressed ratio uncompressed_name
23709 97975 75.8% asp-patch-rpms.txt
16. bzip2 command
examples
To create a *.bz2
compressed file:
To uncompress a *.bz2
file:
17. unzip command
examples
To extract a *.zip
compressed file:
View the contents of
*.zip file (Without unzipping it):
$
unzip -l jasper.zip
Archive: jasper.zip
Length
Date Time Name
--------
---- ---- ----
40995
11-30-98 23:50
META-INF/MANIFEST.MF
32169
08-25-98 21:07 classes_
15964
08-25-98 21:07 classes_names
10542
08-25-98 21:07 classes_ncomp
18. shutdown command
examples
Shutdown the system
and turn the power off immediately.
Shutdown the system
after 10 minutes.
Reboot the system
using shutdown command.
Force the filesystem
check during reboot.
19. ftp command
examples
Both ftp and secure
ftp (sftp) has similar commands. To connect to a remote server and download
multiple files, do the following.
$
ftp IP/hostname
ftp>
mget *.html
To view the file names
located on the remote server before downloading, mls ftp command as shown
below.
ftp>
mls *.html -
/ftptest/features.html
/ftptest/index.html
/ftptest/othertools.html
/ftptest/samplereport.html
/ftptest/usage.html
20. crontab command
examples
View crontab entry for
a specific user
Schedule a cron job
every 10 minutes.
*/10
* * * * /home/ramesh/check-disk-space
21. service command
examples
Service command is
used to run the system V init scripts. i.e Instead of calling the scripts
located in the /etc/init.d/ directory with their full path, you can use the
service command.
Check the status of a
service:
Check the status of
all the services.
Restart a service.
22. ps command
examples
ps command is used to
display information about the processes that are running in the system.
While there are lot of
arguments that could be passed to a ps command, following are some of the
common ones.
To view current
running processes.
To view current
running processes in a tree structure. H option stands for process hierarchy.
23. free command
examples
This command is used
to display the free, used, swap memory available in the system.
Typical free command
output. The output is displayed in bytes.
$
free
total used free
shared buffers cached
Mem: 3566408 1580220
1986188 0
203988 902960
-/+
buffers/cache: 473272 3093136
Swap: 4000176 0
4000176
If you want to quickly
check how many GB of RAM your system has use the -g option. -b option displays
in bytes, -k in kilo bytes, -m in mega bytes.
$
free -g
total used free
shared buffers cached
Mem: 3 1 1 0 0 0
-/+
buffers/cache: 0 2
Swap: 3 0 3
If you want to see a
total memory ( including the swap), use the -t switch, which will display a
total line as shown below.
ramesh@ramesh-laptop:~$
free -t
total used free
shared buffers cached
Mem: 3566408 1592148
1974260 0 204260
912556
-/+
buffers/cache: 475332 3091076
Swap: 4000176 0
4000176
Total: 7566584
1592148 5974436
24. top command
examples
top command displays
the top processes in the system ( by default sorted by cpu usage ). To sort top
output by any column, Press O (upper-case O) , which will display all the
possible columns that you can sort by as shown below.
Current
Sort Field: P for window 1:Def
Select
sort field via field letter, type any other key to return
a: PID
= Process Id v:
nDRT = Dirty Pages count
d: UID
= User Id y:
WCHAN = Sleeping in Function
e: USER
= User Name z:
Flags = Task Flags
........
To displays only the
processes that belong to a particular user use -u option. The following will
show only the top processes that belongs to oracle user.
25. df command
examples
Displays the file
system disk space usage. By default df -k displays output in bytes.
$
df -k
Filesystem 1K-blocks Used Available Use% Mounted on
/dev/sda1 29530400 3233104
24797232 12% /
/dev/sda2 120367992 50171596
64082060 44% /home
df -h displays output
in human readable form. i.e size will be displayed in GB’s.
ramesh@ramesh-laptop:~$
df -h
Filesystem Size Used Avail Use% Mounted on
/dev/sda1 29G 3.1G
24G 12% /
/dev/sda2 115G 48G
62G 44% /home
Use -T option to
display what type of file system.
ramesh@ramesh-laptop:~$
df -T
Filesystem Type
1K-blocks Used Available Use%
Mounted on
/dev/sda1 ext4
29530400 3233120 24797216
12% /
/dev/sda2 ext4
120367992 50171596 64082060
44% /home
26. kill command
examples
Use kill command to
terminate a process. First get the process id using ps -ef command, then use
kill -9 to kill the running Linux process as shown below. You can also use
killall, pkill, xkill to terminate a unix process.
$
ps -ef | grep vim
ramesh 7243
7222 9 22:43 pts/2 00:00:00 vim
$
kill -9 7243
27. rm command
examples
Get confirmation
before removing the file.
It is very useful
while giving shell metacharacters in the file name argument.
Print the filename and
get confirmation before removing the file.
Following example
recursively removes all files and directories under the example directory. This
also removes the example directory itself.
28. cp command
examples
Copy file1 to file2
preserving the mode, ownership and timestamp.
Copy file1 to file2.
if file2 exists prompt for confirmation before overwritting it.
29. mv command
examples
Rename file1 to file2.
if file2 exists prompt for confirmation before overwritting it.
Note: mv -f is just
the opposite, which will overwrite file2 without prompting.
mv -v will print what
is happening during file rename, which is useful while specifying shell
metacharacters in the file name argument.
30. cat command
examples
You can view multiple
files at the same time. Following example prints the content of file1 followed
by file2 to stdout.
While displaying the
file, following cat -n command will prepend the line number to each line of the
output.
$
cat -n /etc/logrotate.conf
1 /var/log/btmp
{
2 missingok
3 monthly
4 create 0660 root utmp
5 rotate 1
6 }
31. mount command
examples
To mount a file
system, you should first create a directory and mount it as shown below.
#
mkdir /u01
#
mount /dev/sdb1 /u01
You can also add this
to the fstab for automatic mounting. i.e Anytime system is restarted, the
filesystem will be mounted.
/dev/sdb1
/u01 ext2 defaults 0 2
32. chmod command
examples
chmod command is used
to change the permissions for a file or directory.
Give full access to
user and group (i.e read, write and execute ) on a specific file.
Revoke all access for
the group (i.e read, write and execute ) on a specific file.
Apply the file
permissions recursively to all the files in the sub-directories.
$
chmod -R ug+rwx file.txt
33. chown command
examples
chown command is used
to change the owner and group of a file. \
To change owner to
oracle and group to db on a file. i.e Change both owner and group at the same
time.
$
chown oracle:dba dbora.sh
Use -R to change the
ownership recursively.
$
chown -R oracle:dba /home/oracle
34. passwd command
examples
Change your password
from command line using passwd. This will prompt for the old password followed
by the new password.
Super user can use
passwd command to reset others password. This will not prompt for current
password of the user.
Remove password for a
specific user. Root user can disable password for a specific user. Once the
password is disabled, the user can login without entering the password.
35. mkdir command
examples
Following example
creates a directory called temp under your home directory.
Create nested
directories using one mkdir command. If any of these directories exist already,
it will not display any error. If any of these directories doesn’t exist, it
will create them.
$
mkdir -p dir1/dir2/dir3/dir4/
36. ifconfig command
examples
Use ifconfig command
to view or configure a network interface on the Linux system.
View all the
interfaces along with status.
Start or stop a
specific interface using up and down command as shown below.
$
ifconfig eth0 up
$
ifconfig eth0 down
37. uname command
examples
Uname command displays
important information about the system such as — Kernel name, Host name, Kernel
release number,
Processor type, etc.,
Sample uname output
from a Ubuntu laptop is shown below.
$
uname -a
Linux
john-laptop 2.6.32-24-generic #41-Ubuntu SMP Thu Aug 19 01:12:52 UTC 2010 i686
GNU/Linux
38. whereis command
examples
When you want to find
out where a specific Unix command exists (for example, where does ls command
exists?), you can execute the following command.
$
whereis ls
ls:
/bin/ls /usr/share/man/man1/ls.1.gz /usr/share/man/man1p/ls.1p.gz
When you want to
search an executable from a path other than the whereis default path, you can
use -B option and give path as argument to it. This searches for the executable
lsmk in the /tmp directory, and displays it, if it is available.
$
whereis -u -B /tmp -f lsmk
lsmk:
/tmp/lsmk
39. whatis command
examples
Whatis command displays
a single line description about a command.
$
whatis ls
ls (1)
- list directory contents
$
whatis ifconfig
ifconfig
(8) - configure a network
interface
40. locate command
examples
Using locate command
you can quickly search for the location of a specific file (or group of files).
Locate command uses the database created by updatedb.
The example below
shows all files in the system that contains the word crontab in it.
$
locate crontab
/etc/anacrontab
/etc/crontab
/usr/bin/crontab
/usr/share/doc/cron/examples/crontab2english.pl.gz
/usr/share/man/man1/crontab.1.gz
/usr/share/man/man5/anacrontab.5.gz
/usr/share/man/man5/crontab.5.gz
/usr/share/vim/vim72/syntax/crontab.vim
41. man command
examples
Display the man page
of a specific command.
When a man page for a
command is located under more than one section, you can view the man page for
that command from a specific section as shown below.
$
man SECTION-NUMBER commandname
Following 8 sections
are available in the man page.
1. General commands
2. System calls
3. C library functions
4. Special files (usually devices, those found in
/dev) and drivers
5. File formats and conventions
6. Games and screensavers
7. Miscellaneous
8. System administration commands and daemons
For example, when you
do whatis crontab, you’ll notice that crontab has two man pages (section 1 and
section 5). To view section 5 of crontab man page, do the following.
$
whatis crontab
crontab
(1) - maintain crontab files for
individual users (V3)
crontab
(5) - tables for driving cron
$
man 5 crontab
42. tail command
examples
Print the last 10
lines of a file by default.
Print N number of
lines from the file named filename.txt
View the content of
the file in real time using tail -f. This is useful to view the log files, that
keeps growing. The command can be terminated using CTRL-C.
43. less command
examples
less is very efficient
while viewing huge log files, as it doesn’t need to load the full file while
opening.
One you open a file
using less command, following two keys are very helpful.
CTRL+F
– forward one window
CTRL+B
– backward one window
44. su command
examples
Switch to a different
user account using su command. Super user can switch to any other user without
entering their password.
Execute a single
command from a different account name. In the following example, john can
execute the ls command as raj username. Once the command is executed, it will
come back to john’s account.
[john@dev-server]$
su - raj -c 'ls'
[john@dev-server]$
Login to a specified
user account, and execute the specified shell instead of the default shell.
$
su -s 'SHELLNAME' USERNAME
45. mysql command
examples
mysql is probably the
most widely used open source database on Linux. Even if you don’t run a mysql
database on your server, you might end-up using the mysql command ( client ) to
connect to a mysql database running on the remote server.
To connect to a remote
mysql database. This will prompt for a password.
$
mysql -u root -p -h 192.168.1.2
To connect to a local
mysql database.
If you want to specify
the mysql root password in the command line itself, enter it immediately after
-p (without any space).
46. yum command
examples
To install apache
using yum.
To upgrade apache
using yum.
To uninstall/remove
apache using yum.
47. rpm command
examples
To install apache
using rpm.
#
rpm -ivh httpd-2.2.3-22.0.1.el5.i386.rpm
To upgrade apache
using rpm.
#
rpm -uvh httpd-2.2.3-22.0.1.el5.i386.rpm
To uninstall/remove
apache using rpm.
48. ping command
examples
Ping a remote host by
sending only 5 packets.
49. date command
examples
Set the system date:
#
date -s "01/31/2010 23:59:53"
Once you’ve changed
the system date, you should syncronize the hardware clock with the system date
as shown below.
#
hwclock –systohc
#
hwclock --systohc –utc
50. wget command
examples
The quick and
effective method to download software, music, video from internet is using wget
command.
$
wget http://prdownloads.sourceforge.net/sourceforge/nagios/nagios-3.2.1.tar.gz
Download and store it
with a different name.
$
wget -O taglist.zip http://www.vim.org/scripts/download_script.php?src_id=7701
