nohup Execute Commands After You Exit From a Shell Prompt

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. However, if you logout the system, the job will be stopped. What do you do?

nohup command

Answer is simple, use nohup 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 Syntax:
nohup command-name &

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.

nohup command example

Eg.
# nohup exp system/password@dbname file=exp_dbname_date.dmp log=exp_dbname_date.log full=y &

or

# vi exp_script.sh
exp system/password@dbname file=exp_dbname_date.dmp log=exp_dbname_date.log full=y
:wq

# ls –l
Check the permissions if that has execute permissions
#chomod 755 exp_script.sh

# nohup ./exp_script.sh &

this ensures of the completion of the Job even if the session terminates... :-)

Checking the Job progress cab be done using:

tail -f nohup.out
ctrl c -- to end the checking.

Some more good options for completing jobs without or when session terminations occur:

Option 1:

You can use the below script to keep your session alive with a simple while loop to run infinite loop.

#while true
>do
>echo " Exp going on"
>sleep 200
>done

Here you will not get prompt till you press Ctl + c (^c). This process will keep your session alive till you press enter.


Option 2:

You can run exp_script.sh script to queue (one minute) later execution:

$ echo "exp_script.sh" | at now + 1 minute


Hope this helps.