20 Advanced Commands for Middle Level Linux Users

You might have found the first article very much useful, this article is an extension of the 20 Useful Commands for Linux Newbies. The first article was intended for newbies and this article is for Middle-Level-User and Advanced Users. Here you will find how to customise search, know the processes running guide to kill them, how to make your Linux terminal productive is an important aspect and how to compile c, c++, java programs in nix.

Linux Advanced & Expert Commands
20 Linux Advanced & Expert Commands

21. Command: Find

Search for files in the given directory, hierarchically starting at the parent directory and moving to sub-directories.

root@tecmint:~# find -name *.sh 


Note: The `-name‘ option makes the search case sensitive. You can use the `-iname‘ option to find something regardless of case. (* is a wildcard and searches all the file having extension ‘.sh‘ you can use filename or a part of file name to customise the output).

root@tecmint:~# find -iname *.SH ( find -iname *.Sh /  find -iname *.sH)

root@tecmint:~# find -name *.tar.gz 


Note: The above command searches for all the file having extension ‘tar.gz‘ in root directory and all the sub-directories including mounted devices.

Read more examples of Linux ‘find‘ command at 35 Find Command Examples in Linux

22. Command: grep

The ‘grep‘ command searches the given file for lines containing a match to the given strings or words. Search ‘/etc/passwd‘ for ‘tecmint‘ user.

root@tecmint:~# grep tecmint /etc/passwd 


Ignore word case and all other combination with ‘-i‘ option.

root@tecmint:~# grep -i TECMINT /etc/passwd 


Search recursively (-r) i.e. read all files under each directory for a string ““.

root@tecmint:~# grep -r "" /etc/ 

/etc/speech-dispatcher/modules/ivona.conf:#IvonaServerHost ""
/etc/mysql/my.cnf:bind-address		=
/etc/apache2/mods-available/status.conf:    Allow from ::1
/etc/apache2/mods-available/ldap.conf:    Allow from ::1
/etc/apache2/mods-available/info.conf:    Allow from ::1
/etc/apache2/mods-available/proxy_balancer.conf:#    Allow from ::1
/etc/security/access.conf:#+ : root :
/etc/dhcp/dhclient.conf:#prepend domain-name-servers;
/etc/dhcp/dhclient.conf:#  option domain-name-servers;
/etc/init/network-interface.conf:	ifconfig lo up || true
/etc/java-6-openjdk/net.properties:# localhost &
/etc/java-6-openjdk/net.properties:# http.nonProxyHosts=localhost|
/etc/java-6-openjdk/net.properties:# localhost &
/etc/java-6-openjdk/net.properties:# ftp.nonProxyHosts=localhost|
/etc/hosts:	localhost

Note: You can use these following options along with grep.

  1. -w for word (egrep -w ‘word1|word2‘ /path/to/file).
  2. -c for count (i.e., total number of times the pattern matched) (grep -c ‘word‘ /path/to/file).
  3. –color for coloured output (grep –color server /etc/passwd).

23. Command: man

The ‘man‘ is the system’s manual pager. Man provides online documentation for all the possible options with a command and its usages. Almost all the command comes with their corresponding manual pages. For example,

root@tecmint:~# man man

MAN(1)                                                               Manual pager utils                                                              MAN(1)

       man - an interface to the on-line reference manuals

       man  [-C  file]  [-d]  [-D]  [--warnings[=warnings]]  [-R  encoding]  [-L  locale]  [-m  system[,...]]  [-M  path]  [-S list] [-e extension] [-i|-I]
       [--regex|--wildcard] [--names-only] [-a] [-u] [--no-subpages] [-P pager] [-r prompt] [-7] [-E encoding] [--no-hyphenation] [--no-justification]  [-p
       string] [-t] [-T[device]] [-H[browser]] [-X[dpi]] [-Z] [[section] page ...] ...
       man -k [apropos options] regexp ...
       man -K [-w|-W] [-S list] [-i|-I] [--regex] [section] term ...
       man -f [whatis options] page ...
       man -l [-C file] [-d] [-D] [--warnings[=warnings]] [-R encoding] [-L locale] [-P pager] [-r prompt] [-7] [-E encoding] [-p string] [-t] [-T[device]]
       [-H[browser]] [-X[dpi]] [-Z] file ...
       man -w|-W [-C file] [-d] [-D] page ...
       man -c [-C file] [-d] [-D] page ...
       man [-hV]

Manual page for man page itself, similarly ‘man cat‘ (Manual page for cat command) and ‘man ls‘ (Manual page for command ls).

Note: man page is intended for command reference and learning.

24. Command: ps

ps (Process) gives the status of running processes with a unique Id called PID.

root@tecmint:~# ps

 PID TTY          TIME CMD
 4170 pts/1    00:00:00 bash
 9628 pts/1    00:00:00 ps

To list status of all the processes along with process id and PID, use option ‘-A‘.

root@tecmint:~# ps -A

 PID TTY          TIME CMD
    1 ?        00:00:01 init
    2 ?        00:00:00 kthreadd
    3 ?        00:00:01 ksoftirqd/0
    5 ?        00:00:00 kworker/0:0H
    7 ?        00:00:00 kworker/u:0H
    8 ?        00:00:00 migration/0
    9 ?        00:00:00 rcu_bh

Note: This command is very useful when you want to know which processes are running or may need PID sometimes, for process to be killed. You can use it with ‘grep‘ command to find customised output. For example,

root@tecmint:~# ps -A | grep -i ssh

 1500 ?        00:09:58 sshd
 4317 ?        00:00:00 sshd

Here ‘ps‘ is pipelined with ‘grep‘ command to find customised and relevant output of our need.

25. Command: kill

OK, you might have understood what this command is for, from the name of the command. This command is used to kill process which is not relevant now or is not responding. It is very useful command, rather a very very useful command. You might be familiar with frequent windows restarting because of the fact that most of the time a running process can’t be killed, and if killed it needs windows to get restart so that changes could be taken into effect but in the world of Linux, there is no such things. Here you can kill a process and start it without restarting the whole system.

You need a process’s pid (ps) to kill it.

Let suppose you want to kill program ‘apache2‘ that might not be responding. Run ‘ps -A‘ along with grep command.

root@tecmint:~# ps -A | grep -i apache2

1285 ?        00:00:00 apache2

Find process ‘apache2‘, note its pid and kill it. For example, in my case ‘apache2‘ pid is ‘1285‘.

root@tecmint:~# kill 1285 (to kill the process apache2)

Note: Every time you re-run a process or start a system, a new pid is generated for each process and you can know about the current running processes and its pid using command ‘ps‘.

Another way to kill the same process is.

root@tecmint:~# pkill apache2

Note: Kill requires job id / process id for sending signals, where as in pkill, you have an option of using pattern, specifying process owner, etc.

26. Command: whereis

The ‘whereis‘ command is used to locate the Binary, Sources and Manual Pages of the command. For example, to locate the Binary, Sources and Manual Pages of the command ‘ls‘ and ‘kill‘.

root@tecmint:~# whereis ls 

ls: /bin/ls /usr/share/man/man1/ls.1.gz
root@tecmint:~# whereis kill

kill: /bin/kill /usr/share/man/man2/kill.2.gz /usr/share/man/man1/kill.1.gz

Note: This is useful to know where the binaries are installed for manual editing sometimes.

27. Command: service

The ‘service‘ command controls the Starting, Stopping or Restarting of a ‘service‘. This command make it possible to start, restart or stop a service without restarting the system, for the changes to be taken into effect.

Startting an apache2 server on Ubuntu

root@tecmint:~# service apache2 start

 * Starting web server apache2                                                                                                                                 apache2: Could not reliably determine the server's fully qualified domain name, using for ServerName
httpd (pid 1285) already running						[ OK ]

Restarting a apache2 server on Ubuntu

root@tecmint:~# service apache2 restart

* Restarting web server apache2                                                                                                                               apache2: Could not reliably determine the server's fully qualified domain name, using for ServerName
 ... waiting .apache2: Could not reliably determine the server's fully qualified domain name, using for ServerName  [ OK ]

Stopping a apache2 server on Ubuntu

root@tecmint:~# service apache2 stop

 * Stopping web server apache2                                                                                                                                 apache2: Could not reliably determine the server's fully qualified domain name, using for ServerName
 ... waiting                                                           		[ OK ]

Note: All the process script lies in ‘/etc/init.d‘, and the path might needs to be included on certain system, i.e., in spite of running “service apache2 start” you would be asked to run “/etc/init.d/apache2 start”.

28. Command: alias

alias is a built in shell command that lets you assign name for a long command or frequently used command.

I uses ‘ls -l‘ command frequently, which includes 5 characters including space. Hence I created an alias for this to ‘l‘.

root@tecmint:~# alias l='ls -l'

check if it works or not.

root@tecmint:~# l

total 36 
drwxr-xr-x 3 tecmint tecmint 4096 May 10 11:14 Binary 
drwxr-xr-x 3 tecmint tecmint 4096 May 21 11:21 Desktop 
drwxr-xr-x 2 tecmint tecmint 4096 May 21 15:23 Documents 
drwxr-xr-x 8 tecmint tecmint 4096 May 20 14:56 Downloads 
drwxr-xr-x 2 tecmint tecmint 4096 May  7 16:58 Music 
drwxr-xr-x 2 tecmint tecmint 4096 May 20 16:17 Pictures 
drwxr-xr-x 2 tecmint tecmint 4096 May  7 16:58 Public 
drwxr-xr-x 2 tecmint tecmint 4096 May  7 16:58 Templates 
drwxr-xr-x 2 tecmint tecmint 4096 May  7 16:58 Videos

To remove alias ‘l‘, use the following ‘unalias‘ command.

root@tecmint:~# unalias l

check, if ‘l‘ still is alias or not.

root@tecmint:~# l

bash: l: command not found

Making a little fun out of this command. Make alias of certain important command to some other important command.

alias cd='ls -l' (set alias of ls -l to cd)
alias su='pwd' (set alias of pwd to su)
(You can create your own)

Now when your friend types ‘cd‘, just think how funny it would be when he gets directory listing and not directory changing. And when he tries to be ‘su‘ the all he gets is the location of working directory. You can remove the alias later using command ‘unalias‘ as explained above.

29. Command: df

Report disk usages of file system. Useful for user as well as System Administrator to keep track of their disk usages. ‘df‘ works by examining directory entries, which generally are updated only when a file is closed.

root@tecmint:~# df

Filesystem     1K-blocks    Used Available Use% Mounted on
/dev/sda1       47929224 7811908  37675948  18% /
none                   4       0         4   0% /sys/fs/cgroup
udev             1005916       4   1005912   1% /dev
tmpfs             202824     816    202008   1% /run
none                5120       0      5120   0% /run/lock
none             1014120     628   1013492   1% /run/shm
none              102400      44    102356   1% /run/user
/dev/sda5         184307   79852     94727  46% /boot
/dev/sda7       95989516   61104  91045676   1% /data
/dev/sda8       91953192   57032  87218528   1% /personal

For more examples of ‘df‘ command, read the article 12 df Command Examples in Linux.

30. Command: du

Estimate file space usage. Output the summary of disk usages by ever file hierarchically, i.e., in recursive manner.

root@tecmint:~# du

8       ./Daily Pics/wp-polls/images/default_gradient
8       ./Daily Pics/wp-polls/images/default
32      ./Daily Pics/wp-polls/images
8       ./Daily Pics/wp-polls/tinymce/plugins/polls/langs
8       ./Daily Pics/wp-polls/tinymce/plugins/polls/img
28      ./Daily Pics/wp-polls/tinymce/plugins/polls
32      ./Daily Pics/wp-polls/tinymce/plugins
36      ./Daily Pics/wp-polls/tinymce
580     ./Daily Pics/wp-polls
1456    ./Daily Pics
36      ./Plugins/wordpress-author-box
16180   ./Plugins
12      ./May Articles 2013/Xtreme Download Manager
4632    ./May Articles 2013/XCache

Note: ‘df‘ only reports usage statistics on file systems, while ‘du‘, on the other hand, measures directory contents. For more ‘du‘ command examples and usage, read 10 du (Disk Usage) Commands.

31. Command: rm

The command ‘rm‘ stands for remove. rm is used to remove files (s) and directories.

Removing a directory

root@tecmint:~# rm PassportApplicationForm_Main_English_V1.0

rm: cannot remove `PassportApplicationForm_Main_English_V1.0': Is a directory

The directory can’t be removed simply by ‘rm‘ command, you have to use ‘-rf‘ switch along with ‘rm‘.

root@tecmint:~# rm -rf PassportApplicationForm_Main_English_V1.0

Warning: “rm -rf” command is a destructive command if accidently you make it to the wrong directory. Once you ‘rm -rf‘ a directory all the files and the directory itself is lost forever, all of a sudden. Use it with caution.

32. Command: echo

echo as the name suggest echoes a text on the standard output. It has nothing to do with shell, nor does shell reads the output of echo command. However in an interactive script, echo passes the message to the user through terminal. It is one of the command that is commonly used in scripting, interactive scripting.

root@tecmint:~# echo "Tecmint.com is a very good website" 

Tecmint.com is a very good website
creating a small interactive script

1. create a file, named ‘interactive_shell.sh‘ on desktop. (Remember ‘.sh‘ extension is must).
2. copy and paste the below script, exactly same, as below.

echo "Please enter your name:" 
   read name 
   echo "Welcome to Linux $name"

Next, set execute permission and run the script.

root@tecmint:~# chmod 777 interactive_shell.sh
root@tecmint:~# ./interactive_shell.sh

Please enter your name:
Ravi Saive
Welcome to Linux Ravi Saive

Note: ‘#!/bin/bash‘ tells the shell that it is an script an it is always a good idea to include it at the top of script. ‘read‘ reads the given input.

33. Command: passwd

This is an important command that is useful for changing own password in terminal. Obviously you need to know your current passowrd for Security reason.

root@tecmint:~# passwd 

Changing password for tecmint. 
(current) UNIX password: ******** 
Enter new UNIX password: ********
Retype new UNIX password: ********
Password unchanged   [Here was passowrd remians unchanged, i.e., new password=old password]
Enter new UNIX password: #####
Retype new UNIX password:#####

34. Command: lpr

This command print files named on command line, to named printer.

root@tecmint:~# lpr -P deskjet-4620-series 1-final.pdf

Note: The ‘lpq‘ command lets you view the status of a printer (whether it’s up or not), and the jobs (files) waiting to be printed.

35. Command: cmp

compare two files of any type and writes the results to the standard output. By default, ‘cmp‘ Returns 0 if the files are the same; if they differ, the byte and line number at which the first difference occurred is reported.

To provide examples for this command, lets consider two files:

root@tecmint:~# cat file1.txt

Hi My name is Tecmint
root@tecmint:~# cat file2.txt

Hi My name is tecmint [dot] com

Now, let’s compare two files and see output of the command.

root@tecmint:~# cmp file1.txt file2.txt 

file1.txt file2.txt differ: byte 15, line 1

36. Command: wget

Wget is a free utility for non-interactive (i.e., can work in background) download of files from the Web. It supports HTTP, HTTPS, FTP protocols and HTTP proxies.

Download ffmpeg using wget

root@tecmint:~# wget http://downloads.sourceforge.net/project/ffmpeg-php/ffmpeg-php/0.6.0/ffmpeg-php-0.6.0.tbz2

--2013-05-22 18:54:52--  http://downloads.sourceforge.net/project/ffmpeg-php/ffmpeg-php/0.6.0/ffmpeg-php-0.6.0.tbz2
Resolving downloads.sourceforge.net (downloads.sourceforge.net)...
Connecting to downloads.sourceforge.net (downloads.sourceforge.net)||:80... connected.
HTTP request sent, awaiting response... 302 Found
Location: http://kaz.dl.sourceforge.net/project/ffmpeg-php/ffmpeg-php/0.6.0/ffmpeg-php-0.6.0.tbz2 [following]
--2013-05-22 18:54:54--  http://kaz.dl.sourceforge.net/project/ffmpeg-php/ffmpeg-php/0.6.0/ffmpeg-php-0.6.0.tbz2
Resolving kaz.dl.sourceforge.net (kaz.dl.sourceforge.net)...
Connecting to kaz.dl.sourceforge.net (kaz.dl.sourceforge.net)||:80... connected.
HTTP request sent, awaiting response... 200 OK
Length: 275557 (269K) [application/octet-stream]
Saving to: ‘ffmpeg-php-0.6.0.tbz2’

100%[===========================================================================>] 2,75,557    67.8KB/s   in 4.0s   

2013-05-22 18:55:00 (67.8 KB/s) - ‘ffmpeg-php-0.6.0.tbz2’ saved [275557/275557]

37. Command: mount

Mount is an important command which is used to mount a filesystem that don’t mount itself. You need root permission to mount a device.

First run ‘lsblk‘ after plugging-in your filesystem and identify your device and note down you device assigned name.

root@tecmint:~# lsblk 

sda      8:0    0 931.5G  0 disk 
├─sda1   8:1    0 923.6G  0 part / 
├─sda2   8:2    0     1K  0 part 
└─sda5   8:5    0   7.9G  0 part [SWAP] 
sr0     11:0    1  1024M  0 rom  
sdb      8:16   1   3.7G  0 disk 
└─sdb1   8:17   1   3.7G  0 part

From this screen it was clear that I plugged in a 4 GB pendrive thus ‘sdb1‘ is my filesystem to be mounted. Become a root to perform this operation and change to /dev directory where all the file system is mounted.

root@tecmint:~# su
root@tecmint:~# cd /dev

Create a directory named anything but should be relevent for reference.

root@tecmint:~# mkdir usb

Now mount filesystem ‘sdb1‘ to directory ‘usb‘.

root@tecmint:~# mount /dev/sdb1 /dev/usb

Now you can navigate to /dev/usb from terminal or X-windows system and acess file from the mounted directory.

Time for Code Developer to know how rich Linux environment is

38. Command: gcc

gcc is the in-built compiler for ‘c‘ language in Linux Environment. A simple c program, save it on ur desktop as Hello.c (remember ‘.c‘ extension is must).

#include <stdio.h>
int main()
  printf("Hello world\n");
  return 0;
Compile it
root@tecmint:~# gcc Hello.c
Run it
root@tecmint:~# ./a.out 

Hello world

Note: On compiling a c program the output is automatically generated to a new file “a.out” and everytime you compile a c program same file “a.out” gets modified. Hence it is a good advice to define a output file during compile and thus there is no risk of overwrite to output file.

Compile it this way
root@tecmint:~# gcc -o Hello Hello.c

Here ‘-o‘ sends the output to ‘Hello‘ file and not ‘a.out‘. Run it again.

root@tecmint:~# ./Hello 

Hello world

39. Command: g++

g++ is the in-built compiler for ‘C++‘ , the first object oriented programming language. A simple c++ program, save it on ur desktop as Add.cpp (remember ‘.cpp‘ extension is must).

#include <iostream>

using namespace std;

int main() 
          int a;
          int b;
          cout<<"Enter first number:\n";
          cin >> a;
          cout <<"Enter the second number:\n";
          cin>> b;
          int result = a + b;
          cout<<"Result is"<<"  "<<result<<endl;
          return 0;
Compile it
root@tecmint:~# g++ Add.cpp
Run it
root@tecmint:~# ./a.out

Enter first number: 

Note: On compiling a c++ program the output is automatically generated to a new file “a.out” and everytime you compile a c++ program same file “a.out” gets modified. Hence it is a good advice to define a output file during compile and thus there is no risk of overwrite to output file.

Compile it this way
root@tecmint:~# g++ -o Add Add.cpp
Run it
root@tecmint:~# ./Add 

Enter first number: 

40. Command: java

Java is one of the world’s highly used programming language and is considered fast, secure, and reliable. Most of the the web based service of today runs on java.

Create a simple java program by pasting the below test to a file, named tecmint.java (remember ‘.java‘ extension is must).

class tecmint {
  public static void main(String[] arguments) {
    System.out.println("Tecmint ");
compile it using javac
root@tecmint:~# javac tecmint.java
Run it
root@tecmint:~# java tecmint

Note: Almost every distribution comes packed with gcc compiler, major number of distros have inbuilt g++ and java compiler, while some may not have. You can apt or yum the required package.

Don’t forget to mention your valueable comment and the type of article you want to see here. I will soon be back with an interesting topic about the lesser known facts about Linux.

A Passionate GNU/Linux Enthusiast and Software Developer with over a decade in the field of Linux and Open Source technologies.

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56 thoughts on “20 Advanced Commands for Middle Level Linux Users”

  1. thank you very much for ur wonderful lecture and I want to know more abt Linux and ethical hacking could you refer the best books and ideas

    • Dear arunprasad,
      We work to bring to you Linux How-TO, Linux/Package/Tool Installation, Shell Scripting, and every other Genre of Linux but we at this point of time and in recent future have no plan to deal in Ethical Hacking.

  2. Hi Avi,

    thanks so much for all ur last Q&A interview series and bash learning series.would u please extend ur series with new how configure DNS & DHCP servers in deep level, i believe we will get so many questions and answers and as of like me new sysadmins have so much issues , trouble to configure this servers :) !!

    • Dear sushant,
      keep connected we will be coming up with your recommendation very soon and don’t forget to remind us, if we forget.

  3. Good deal and good stuff (although I’d agree that a lot of this is more beginner than advanced but all good). Regarding file name extensions as in your example of the .sh, that requirement is a Windows/DOS construct and not a *nix one. There is no requirement that a shell script have a .sh at the end. It is a convention that some/many distros recognize and a good practice but it is not required. A script is executable by setting the execute bit and not by its extension. So myscript.sh and myscript both are valid as is myscript.bob or myscript.great-it doesn’t matter what the extension is or even if it has one.

    Also, in order for it to work, the first line *must* have the so-called she-bang and path to the shell/binary you want to handle the script as in #!/bin/bash or #!/bin/ksh etc. or other binary if using perl, #!/usr/bin/perl or python and so on. Without this it will not work.

    Now, maybe distros are getting smarter and assuming a .sh means use the default shell or X is assuming that but it is a bad practice to use assumptions like that.

    Also, using chmod 777 is a dangerous thing unless you are sure that you want *everyone* and *everything* on the system to be able to read/write/execute the file/script. A better way is to use chmod 755 or 775 or 764 — really it depends on what you want you and others on the system to be able to do. Or simply make it executable via the alpha way–chmod +x and leave other permissions as they are. Make sure that you do a ls -l and review what the permissions are.

    • @ Mark Dean, Your concern is very important, and we welcome your views. we did above 777, just to ensure that a newbie dont get trapped into any kind of permission issue.

  4. Not a perfect list, some of these I’d actually consider beginner-level stuff, but I wanna go over a few things.

    “sudo” is not guaranteed to be on a Linux system. It’s one of my personal essentials but most Linux distributions outside of those centered almost exclusively on desktops actually don’t install it by default. They figure any administrator knows how to become root without sudo. In my opinion its still a good idea to have sudo since it can protect you from yourself. (Heck, you could just do a su root -c ” for roughly the same effect as sudo.)

    gcc and g++ are not built in commands. In fact, a lot of distributions don’t install them by default and many others use alternatives like egcc or even llvm (Somehow.). Like sudo, they are on my essentials list.

    A shame your daemon commands here are Ubuntu-centric. Upstart is considered almost universally in the *nix sphere to be an abysmal init replacement compared to systemd or openrc. Largely because it has a completely backwards unit dependency system (It makes no sense to launch EVERY unit possible that depends on a unit you launch, instead it makes more sense to NOT launch a particular unit unless explicitly asked for or if required by another unit.), but either way,for a general “Linux” command listing it’s bad form to suggest anything more than perhaps “/etc/init.d/ ” with no command to invoke the service.

  5. Useful commands for beginners, you have written “service /etc/init.d/apache2 start”. while it should be “/etc/init.d/apache2 start” you can’t use service while using /etc/init.d/


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