Bash Command – How to Suspend and Resume Processes

Shell jobs live in "process groups"; look at the PGRP column in extended ps output. These are used both for job control and to determine who "owns" a terminal (real or pty).

POSIX (taken from System V) uses a negative process ID to indicate a process group, since the process group is identified by the first process in the group ("process group leader"). So you would use ps to determine the process group, then kill -s TSTP "-$pgrp". (Try ps -u"$USER" -opid,ppid,pgrp,cmd.)

In your process tree, the process group starts with the firefox script launched by bash, so the process group would be 27980 and the command would be kill -s TSTP -27980.

Naturally, to resume the process group, issue kill -s CONT -- -27980.

As Tim said, type fg to bring the last process back to foreground.

If you have more than one process running in the background, do this:

$ jobs
[1]   Stopped                 vim
[2]-  Stopped                 bash
[3]+  Stopped                 vim 23

fg %3 to bring the vim 23 process back to foreground.

To suspend the process running in the background, use:

kill -STOP %job_id

The SIGSTOP signal stops (pauses) a process in essentially the same way Ctrl+Z does.

example: kill -STOP %3.

sources: How to send signals to processes in Linux and Unix and How to manage background and foreground jobs.