Useful commands for Linux normal users and administrators

Recently, CLI is mostly used by Linux/Unix administrators since most popular linux distros come with a complete set of GUI applications that make the user use less and less the command line. In our previous post, we saw 11 useful commands for Linux/Unix administrators, in this post we will see a list of useful commands useful for both administrators and normal Linux users.

  •  For Linux/Unix administrators:

1- Compare a remote dir with a local dir

 $ diff -y <(ssh user@host find /boot|sort) <(find /boot|sort)

2- Trace and view network traffic

tcpdump -s 0 -w - port <port> | tcpdump -r - -A

3- Check if a machine is online

ping -c 1 -q MACHINE_IP_OR_NAME >/dev/null 2>&1 && echo ONLINE || echo OFFLINE

c 1 limits to 1 pinging attempt
q makes the command quiet (or silent mode)
/dev/null 2>&1 is to remove the display
&& echo ONLINE is executed if previous command is successful (return value 0)
|| echo OFFLINE is executed otherwise (return value of 1 if unreachable or 2 if you’re offline yourself).
I personally use this command as an alias with a predefined machine name but there are at least 2 improvements that may be done.
Asking for the machine name or IP
Escaping the output so that it displays ONLINE in green and OFFLINE in red (for instance).

4-  Reverse SSH

ssh -f -N -R 8888:localhost:22

Reverse SSH
this command from the source server and this follow in the destination server:

 ssh user@localhost -p 8888

5- Show mounted volumes in a table (Thanks to Shawn):

mount | column -t

6- The fastest way to kill tcp or udp port is to run the following command (Thanks to Sriram):

fuser -k PORT-NUMBER-HERE/tcp
fuser -k PORT-NUMBER-HERE/udp

7- edit a file on a remote server using vim from your Linux / Unix / OS X desktop:

vim scp://sriram@server1/etc/http/httpd.conf
  • Commands for Both Normal users and Linux admins

8- Grep your command history (Thanks to Shawn)

history | grep /pattern/

9- Extract audio from Flash video (*.flv) as mp3 file

 ffmpeg -i video.flv -vn -ar 44100 -ac 2 -ab 192k -f mp3 audio.mp3

10- copy hybrid iso images to USB key for booting from it, progress bar and remaining time are displayed while copying

time (pv file.iso | dd bs=1M oflag=sync of=/dev/sdX 2>/dev/null)

11- what model of computer I’m using?

sudo dmidecode | grep Product