`

We can migrate the job from the background to the foreground by issuing the

fg command and the job ID (Listing 2-39).

$ fg %1

sleep 100

Listing 2-39

Sending a job to the foreground

At this point, the sleep command is occupying the terminal, since it’s

running in the foreground. You can press CTRL+Z to suspend the process, which

will produce the following output in the jobs table:

[1]+ Stopped sleep 100

To send this job to the background again in a running state, use the bg

command with the job ID (Listing 2-40).

$ bg %1

[1]+ sleep 100 &

Listing 2-40

Sending a job to the background

Keeping a Job Running After Logout

Whether you send a job to the background or are running a job in the

foreground, the process won’t survive if you close the terminal or log out. If you

close the terminal, the process will receive a SIGHUP signal and terminate.

What if we wanted to keep running a script in the background even after

we’ve logged out of the terminal window or closed it? To do so, we could start a

script or command with the nohup (no hangup) command prepended (Listing 2-

41).

$ nohup ./my_script.sh &

Listing 2-41

Keeping a script running after closing the terminal or logging out

The nohup command will create a file named nohup.out with standard output

stream data. So, make sure you delete this file if you don't want to leave any traces

on the disk.

There are additional ways to run background scripts, such as by plugging into

system and service managers like systemd, which provide additional features, such

as monitoring that the process is running, restarting it if it isn’t, and capturing

failures. We encourage you to read more about systemd if you have such use-cases

at https://man7.org/linux/man-pages/man1/init.1.html.

Black Hat Bash (Early Access) © 2023 by Dolev Farhi and Nick Aleks