what is the use of nohup command in linux ?

Most of the time you login into remote server via ssh. If you start a shell script or command and you exit (abort remote connection), the process / command will get killed. Sometime job or command takes a long time. If you are not sure when the job will finish, then it is better to leave job running in background. But, if you log out of the system, the job will be stopped and terminated by your shell. What do you do to keep job running in the background when process gets SIGHUP?

 nohup command line-utility which allows to run command/process or shell script that can continue running in the background after you log out from a shell:

nohup command syntax:

The syntax is as follows

nohup command-name &

OR

nohup /path/to/command-name arg1 arg2 &

Where,

command-name : is name of shell script or command name. You can pass argument to command or a shell script.

& : nohup does not automatically put the command it runs in the background; you must do that explicitly, by ending the command line with an & symbol.

Use jobs -l command to list all jobs:

# jobs -l

nohup command examples

First, login to remote server using ssh command:

$ ssh user@remote.server.com

OR

$ ssh rajesh@linuxforfreshers.com

I am going to execute a shell script called ftp.sh:

# nohup ftp.sh &

Type exit or press CTRL + D exit from remote server:

# exit

In this example, I am going to find all programs and scripts with setuid bit set on, enter:

# nohup find / -xdev -type f -perm +u=s -print > out.txt &

Type exit or press CTRL + D exit from remote server.

# exit

Please note that nohup does not change the scheduling priority of COMMAND; use nice command for that purpose. The syntax is:

# nohup nice -n -5 ls / > out.txt &

As you can see nohup keep processes running after you exit from a shell. Read man page of nohup(1) and nice(1) for more information. Please note that nohup is almost available on Solaris/BSD/Linux/UNIX variants.