1.16 How can I kill all descendents of a process?

There isn't a fully general approach to doing this. While you can determine the relationships between processes by parsing ps output, this is unreliable in that it represents only a snapshot of the system.

However, if you're lauching a subprocess that might spawn further subprocesses of its own, and you want to be able to kill the entire spawned job at one go, the solution is to put the subprocess into a new process group, and kill that process group if you need to.

The preferred function for creating process groups is setpgid(). Use this if possible rather than setpgrp() because the latter differs between systems (on some systems ‘setpgrp();’ is equivalent to ‘setpgid(0,0);’, on others, setpgrp() and setpgid() are identical).

See the job-control example in the examples section.

Putting a subprocess into its own process group has a number of effects. In particular, unless you explicitly place the new process group in the foreground, it will be treated as a background job with these consequences:

• it will be stopped with SIGTTIN if it attempts to read from the terminal
• if tostop is set in the terminal modes, it will be stopped with SIGTTOU if it attempts to write to the terminal (attempting to change the terminal modes should also cause this, independently of the current setting of tostop)
• The subprocess will not receive keyboard signals from the terminal (e.g. SIGINT or SIGQUIT)

In many applications input and output will be redirected anyway, so the most significant effect will be the lack of keyboard signals. The parent application should arrange to catch at least SIGINT and SIGQUIT (and preferably SIGTERM as well) and clean up any background jobs as necessary.

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