Useful Commands For The Linux Command Line

This short guide shows some important commands for your daily work on the Linux command line.

With the command:

tail -f /path/to/logfile

Enter the command line and hit the keys:

[CTRL] + [#]

This will put a # in front of the command and execute it. The shell will take it as comment.

Use the commad:

clear

or the keyboard shortcut:

[CTRL] + [L]

The command is:

convert -border 2x2 old.jpg new.jpg

This creates a new image (new.jpg) with a 2 pixel border from the image old.jpg.

To set the bordercolor to red, use this command:

convert -border 2x2 -bordercolor "#FF0000" old.jpg new.jpg

To get a list of the installed services on the shell, you may use this command (on Fedora, RedHat, CentOS, SuSE, and Mandriva):

chkconfig --list

To view only the processes owned by a specific user, use the following command:

top -U [USERNAME]

and replace [USERNAME] with the name of the user.

To make a snapshot of the current process table, use the following command:

top -n 1 -b > /tmp/processtable.txt

You can now view the textfile with any text editor, e.g. pico or vi.

With the grep command.

If you want to find out if the term user is in /etc/httpd/conf/httpd.conf, you would run

grep -i user /etc/httpd/conf/httpd.conf

(-i makes the search case-insensitive).

Normally grep does not tell you the line number where it finds the term. If you want to find out the line number, run

grep -n -i user /etc/httpd/conf/httpd.conf

You can find out about logged in users either by running

who

(Sample output:

server:~# who
root     pts/0        Nov 12 11:28 (192.168.0.202)

)

or

w

which gives more detailed output:

server:~# w
 11:29:49 up  2:19,  1 user,  load average: 0.02, 0.01, 0.00
USER     TTY      FROM              LOGIN@   IDLE   JCPU   PCPU WHAT
root     pts/0    192.168.0.202    11:28    0.00s  0.08s  0.01s w