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
$ grep -r "ramesh" *
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
# find ~ -empty
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.
$sed 's/.$//' filename
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
$ vim +143 filename.txt
Go to the first match of
the specified
$ vim +/search-term filename.txt
Open the file in read only
mode.
$ vim -R /etc/passwd
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 names.txt
Sort a file in descending
order
$ sort -r names.txt
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
$ ls -ltr
Visual Classification of
Files With Special Characters Using ls -F
$ 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:
$ gzip test.txt
To uncompress a *.gz file:
$ gzip -d test.txt.gz
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:
$ bzip2 test.txt
To uncompress a *.bz2
file:
bzip2 -d test.txt.bz2
17. unzip command examples
To extract a *.zip
compressed file:
$ unzip test.zip
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 -h now
Shutdown the system after
10 minutes.
# shutdown -h +10
Reboot the system using
shutdown command.
# shutdown -r now
Force the filesystem check
during reboot.
# shutdown -Fr now
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
# crontab -u john -l
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:
# service ssh status
Check the steatus of all
the services.
service --status-all
Restart a service.
# service ssh restart
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.
$ ps -ef | more
To view current running
processes in a tree structure. H option stands for process hierarchy.
$ ps -efH | more
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.
$ top -u oracle
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.
$ rm -i filename.txt
It is very useful while
giving shell metacharacters in the file name argument.
Print the filename and get
confirmation before removing the file.
$ rm -i file*
Following example
recursively removes all files and directories under the example directory. This
also removes the example directory itself.
$ rm -r example
28. cp command examples
Copy file1 to file2
preserving the mode, ownership and timestamp.
$ cp -p file1 file2
Copy file1 to file2. if
file2 exists prompt for confirmation before overwritting it.
$ cp -i file1 file2
29. mv command examples
Rename file1 to file2. if
file2 exists prompt for confirmation before overwritting it.
$ mv -i file1 file2
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.
$ mv -v file1 file2
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.
$ cat file1 file2
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.
$ chmod ug+rwx file.txt
Revoke all access for the
group (i.e read, write and execute ) on a specific file.
$ chmod g-rwx file.txt
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.
$ passwd
Super user can use passwd
command to reset others password. This will not prompt for current password of
the user.
# passwd USERNAME
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.
# passwd -d USERNAME
35. mkdir command examples
Following example creates
a directory called temp under your home directory.
$ mkdir ~/temp
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.
$ ifconfig -a
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.
$ man crontab
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.
$ tail filename.txt
Print N number of lines
from the file named filename.txt
$ tail -n N 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.
$ tail -f log-file
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.
$ less huge-log-file.log
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.
$ su - USERNAME
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.
$ mysql -u root -p
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
(works on RH environment)
To install apache using
yum.
$ yum install httpd
To upgrade apache using
yum.
$ yum update httpd
To uninstall/remove apache
using yum.
$ yum remove httpd
47. rpm command
examples (works on RH environment)
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.
# rpm -ev httpd
48. ping command examples
Ping a remote host by
sending only 5 packets.
$ ping -c 5 gmail.com
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
NOTE: For any command specific usage, use <command-name> --help, e.g. "ls --help" or you can use "man ls" so see the manuals:
No comments:
Post a Comment