Today i am going to share some very easy but useful Linux commands . I have been using Cent-Os last 2 years and found these commands in my everyday life . Some of the commands may need root user permission , if you find “permission denied” exception try to switch your user to root and then run those commands . Or you can also run all the commands by adding a “sudo” before them .
Switching to a user :
$su username$
Password: Provide your password
Creating a group :
$groupadd testgroup$
Creating a user in a group :
$useradd -g groupname youruser$
Deleting a User :
$userdel youruser$
Deleting a group :
$groupdel testgroup$
Setting password to a user :
$passwd youruser$
Then provide old your password and new password to change.
To see all the available groups in your machine :
$cat /etc/group$
To change the owner of a folder along with its sub folders :
$chown -R username:groupname foldername$
For example to make youruserthe owner of all the folders of /home/youruser
$chown -R youruser:testgroup /home/youruser$
To delete a file :
rm fileName
To delete a folder :
rm -r folderName
To delete a folder without permission (It’s the supreme delete , think twice before you apply this command) :
rm -rf folderName
Change to directory :
$cd directorName$
To search for specific file/folder with a keyword in it’s name your whole OS :
$locate keyword$
If you are running this command for the very first time in your OS try running $updatedb$ and then run the command
To search for a keyword inside all the files of a folder :
$cd folderName$
$find folder_name -iname “*” | xargs grep keyword $
To see all the files along with the hidden files in a folder :
$ls -lh folder_name$
To see size of all the files in a folder :
$ls -lsh folder_name$
To see details information of all the files in a folder :
$ls -la$
To see the total size of a folder in MB :
$du -sh folder_name$
To find total free space of yous machine :
$df -h$
To ssh to a remote machine :
$ssh -l username ip$ (For example : $ssh -l testuser 192.168.164.29$)
Then provide the password of that user to login
To secure copy a folder from local computer to remote computer :
$scp -r localFolder username@ip:/path_to_copy$
And then provide the password .
For example : To copy songs folder to a machine with ip 192.168.164.29 with user testuser
$scp -r /home/testuser/songs testuser@192.168.164.29:/home/testuser/$
Similarly to copy a remote file in your local machine :
$scp -r username@ip:/file_to_copy path_to_copy$
To login to a telnet server :
$telnet hostname port $
Then provide the password
To see your internet configuration :
$/sbin/ifconfig$
To edit your internet configuration file and add a mapping to a domain with its ip:
$gedit /etc/hosts$
You will find something like
127.0.0.1 localhost.localdomain localhost
Then add your ip and domain at the end of file
10.211.112.24 myDomain.com
and save . Rememebr you have to be root to save the file .
To change the hostname of your OS :
$gedit /etc/sysconfig/network$ and change the HOSTNAME and save
To display all the network connections :
$netstat -anp$
To find which process in running in a port :
$netstat -anp | grep port_number$
To download a file :
$wget file_url$
To see all running processes in your machine:
$ps -ef$
To search for a specific process :
$ps -ef | grep process_name$ (For example to search apache : $ps -ef | grep apache$)
To kill a process:
$kill -9 processID$ (You will find the processID of the process by running the previous command )
To see the running processes along with its CPU Usage :
$top$
To start a service :
$service service_name start$
To stop a service :
$service service_name stop$
To start a service during OS boot up :
$/sbin/chkconfig service_name ON$
To stop a service to start during OS boot up :
$/sbin/chkconfig service_name OFF$
To see the run level of a service :
$/sbin/chkconfig service_name –list$
Have fun with Linux :)