Killing a command tree

help
1

Hi there!

I currently have a problem with a program of mine where I spawn a sh -c "<...>" command.

Basically I want to be able to run this command asynchronously and kill it in specific conditions. So I create a Command that I .spawn() and store the Child handle somewhere in the application's state.

But when I call .kill() on it, nothing happens. If I get the child's ID and kill it with my shell's kill command then it stops.

This is the first problem, but I have another: even when manually killing the shell process, the underlying command isn't killed. So for instance, if I spawn a Command with sh -c "sleep 100" and I kill the sh process, the sleep command keeps running. How can I avoid that and kill both at the same time?

Thanks in advance for your help!

2

Kill the "process group". In Unix you have process groups. Typically, when you have a sh -c <command>, then the <command> and the sh should be in the same process group. You kill a process group by sending the negative of the PGID. Thus if the PGID is 100, then you should do kill -s SIGTERM -100.

This happens because the way shells work. When a shell spawns a child (in this case the <command> the sh is spawning), it makes the child the foreground process. Thus sending SIGTERM signals to the parent process (which is the shell, and now is a background process) will not help. You need to send the signal to the child process.

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3

Interesting!

So there's no "native Rust" way of doing that? I need to deal with the system's signals myself?

Also, is it guaranteed that (on unix systems at least) the child's .id() will return me the PID to kill?

4

There is. If you directly spawn the <command> without going through the sh, then this problem won't arise and kill behaves the way you expect it to.

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5

I ran some tests and the problem is that the command itself can spawn other children, which would need to be killed to.

So I finally found out that running pkill -P <child ID> solved the problem. It termines all the processes properly and is correctly reported as a failed Command in Rust.

Thanks for your help!

6

A quick search for "process group" on lib.rs found command-group — Rust OS-specific library // Lib.rs which seems to do what you want.

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7

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