Basic linux commands with syntax and examples

Basic linux commands

Basic linux commands with syntax and examples

Basic linux commands with syntax and examples tutorial includes Linux administration commands and tasks which you have to do regularly. Yes, there is GUI available, but with commands things becomes more easier. People who are working as a Linux administrator will believe my words. They very well know the fact that GUI is simply not allowed in a Linux server and it is for security reasons. If you have just started with Linux administration then you need to master some important commands of Linux. This tutorial is about making you familiar with some Linux basic commands and task for newbie Linux Administrator. For advance Linux system administrator command and task, we will be covering it in the next article. Lets see some of the basic commands for Linux administrator.

1 Downloading packages

There are some applications or packages may not be available in your system. In that case you need to download those packages in your Linux server. wget command is used for downloading any packages. To download the below package, we need to give the path of the package with wget and Enter, the required package name and path to download it to the current directory.

For example:

# wget http://mirror.lihnidos.org/CentOS/6/os/i386/Packages/NetworkManager-0.8.1-43.el6.i686.rpm

The path of the package you want to download, you will get it on internet. You have to look for the required package on the web.  

2 Installing and updating packages

Even if the application is available  on your Linux server, you cannot use it until it is installed. YUM and apt tool is a very common basic Linux commands available for updating and installing packages in Linux. Below are the examples given to use YUM and apt in Red hat and Debian respectively.

Red hat based

To update packages on Red hat based system


# yum update                                       

 Command to install any package on Red hat based system is Linux yum command. Yum is also used for managing Yum repository in Linux

# yum install <package name>          

 Debian based

To update packages on Debian based system

# apt-get update                                              

  Command to download any package on Debian based system

# apt-get install <package name>                        

 

3 Copying files and Directories

Use cp command to copy any files or directories. For example:

# cp file1 /Directory1/

The above command will copy file1 to the destination Directory1  

For more details check Copy command in Linux with examples


4 Removing files and Directories

To remove files in Linux use rm command and to remove directory use rmdir.

# rm file1

You should be very careful when using  'rm'  command, it will instantly remove the target  file from system. The bad thing about rm command is that the deleted file doesn't move to recycle bin. So, my suggestion would be using the  'i' option with rm command, It will ask for confirmation before removing any file.

# rm -i  file1

To remove directory use rmdir

# rmdir directry1

5 Renaming files and Directories

Use mv command to rename a file.

 # mv file1 file2

The above command will rename file1 to file2. Similarly you can rename any directory with the mv command.

 

6 Adding repository

What are repository? In a simple language Repositories are  central location in which data is stored and managed. When you install any application on your Linux server , it connects with these repository and look for the defined application in the repository. If the application is not available  in the repository, you installation will failed. Therefore, it is very important to add right repository  on your Linux server. So that you won't be looking here and there to install the particular package.  :-) Adding repository command is different for both Debian based and Red hat based OS. Red hat based system

# yum-config-manager --add-repo http://www.somesite.com/some.repo

Debian based system

# add-apt-repository <repository path >

 

7 Seeing the permission of files

With this command you will be able to see the list of files and directories. You can see the read, write, execute permission of the file, user and group owner of file etc.

# ls -l

8 Changing permissions of files

You sometime require to change the permission of the file. For example you may want your file to have a write permission for a specific user. Have a look at the most basic Linux commands to change permissions of file and directory.

u = user
g = group
o = others

 

r = read
w = write
x = Execute

 The above options can be used with chmod  command to change the permission of the file  for user, group and others.

Read, write and execute permission for user, group and others
# chmod ugo+rwx file1  

Assigning read and write permission to user          
# chmod u+rw file1    
                             
Assigning write and execute permission to group
# chmod g+wx file1       

Assigning only read permission to others                    
# chmod o+r file1                                    

   

9 Changing the ownership of file

Well, with chown you will be able to assigned new user or group owner to a file,.

You can add just a new user to a file.

# chown  <user-owner>  file1

You can add just a group owner to a file

# chown  :<group-owner>  file1

You can add user and group-owner to a file at the same time

# chown <user-owner>:<group-owner> file1    
             
 Note the colon : between user-owner and group-owner

 

10 Disk space check

As a system administrator you are required to check disk space every now and then, use  'df'  to check disk space of your server. Regular disk space check will help you avoid crashing of your hard disk.

# df -h            
                    
use -h option with df  to see disk space in GB format

Just using df command without -h option will show you space in KB format, which is very tough to analyze.  

11 Starting and stopping services

When any services is newly configured or installed in your Linux server, you need to manually start the service to allow the service to be in action.

In Red hat based system:-

To know the status of the service
# service <service name> status  

To start the service                          
# service <service name> start                                          
To stop the service
# service <service name> stop                              

In Debian based system:-

To know the status of the service
# /etc/init.d/<service name>  status  

To start the service                                      
# /etc/init.d/<service name>  start                                                     
To stop the service
# /etc/init.d/<service name>   stop                                                      

   

12 Adding user and Group

To add new user use the command 'useradd'.

# useradd  <user name>

For example create an user 'john'

# useradd john

Check your 'passwd' file to see your created users.

# cat /etc/passwd
basic linux commands
Basic Linux commands - user add

To add new group use the command 'groupadd'.

# groupadd  <group name>  

For example create a group 'accountant'       

# groupadd accountant   

Check 'group' file to see the created groups.

# cat /etc/group
Basic Linux commands
Basic Linux commands - group add

13 Assigning users and groups  password expiry date

If you are assigning users with a password expiration date, then you are making a very wise choice. Weather it's a server root password or a normal user password, password must be changed with a regular interval.

# chage -l <user name>

Use the above command to know the password expiration date and other information about the particular user. To see the password expiration date of user 'john' do the following.

# chage -l john
Basic Linux commands
Basic Linux commands - Chage

 You can see in the above screen shot that the password of 'john' expires never. Hence, lets set the password expiration date of 'john'.

# chage  -M 30  john    
Basic Linux commands
Basic Linux commands - chage -m

This command will set the password expiration date of the user to 30 days.

 

14 Changing user and group password

To change the password of any user use or group, use the command 'passwd'

# passwd <user name>
# passwd <group name>

   

15 Monitoring last login

The data of any successful as well as unsuccessful login into your system is generated in a log file of your system. It is very important  to look this log files everyday to monitor your system. Any login from a suspicious IP address into your system can be a real havoc. After studying these logs you can block these IP addresses so that it won't be able to enter into your system the next time. Use 'last '  command to see the last logins in your server.

# last

 

16 Monitoring load on the server

You can monitor the average load on the server with command w

# w

The  'w'  command also shows you the number of users currently  logged in onto your Linux server.

 

17 Changing directory

To move from current directory to another directory use cd command.

# cd /                                        To move to the root directory

Similarly you can move to any directory with cd command, you have to provide the correct path of the directory.

# cd ..                                      To move one directory back ward

 

18 Know what process are running

To know the number of processes are running use ' ps'  command

# ps

There are various options available that can be used with ps.

 

19 Know the current directory

To know the current directory use pwd

# pwd             
                                    

pwd stands for Present Working Directory

 

20.cat command

Cat commands are used to view files, to append something more in your file, and to just write something in your file.

To see what is written inside the file.

# cat file1                  
                            
# cat > file1

The above command that is 'cat > file1'  will open a blank space for you to write something in it. Write what you need then press   CTRL+D  to save the file.  

To add something  some more text to your file that is appending in your file.

# cat >> file1        
            

 

21. Nmap command

Nmap command is used to scan all ports and identify open and closed ports in a computer. It is helpful to detect all active machines in a network.  To scan an IP in a given network, see the Nmap scan all ports command given below.

# nmap 192.168.0.21

 


That's it with the article Basic linux commands with syntax and examples tutorial.
Also see tutorials on Sed command examples.

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