Terminating gazebo leaves many zombie processes

[erlingrj]

Environment

• OS Version: Ubuntu 24.04
• Source or binary build: Binary build, version 8.8.0

Description

• Expected behavior: When sending a signal, e.g. SIGTERM or SIGKILL to the process launching gz sim ..., I expect all spawned processes and threads to be cleaned up.
• Actual behavior: GUI keeps running, and several threads and processes in the background keeps running.

Steps to reproduce

E.g. compiling this simple program:

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <signal.h>
#include <sys/wait.h>

int main() {
    pid_t pid = fork();
    if (pid == -1) {
        // Fork failed
        printf("Fork failed\n");
        exit(1);
    } else if (pid == 0) {
      // Child process 
      system("gz sim simple_robot.sdf -r");
      exit(0);
    } else {
      // Parent process
     sleep(3);
      kill(pid, SIGTERM);
     wait(NULL);
    }
}

Assuming a model file called simple_robot.sdf is in the current working directory, then executing it will lead to the GUI remaining open and a bunch of other threads running in the background. I have spent a lot of time trying to kill all dependent and child processes, but with no luck.

Another, simpler way to reproduce is to just launch the process from a terminal, in the background and then try to kill it:

gz sim simple_robot.sdf -r &
kill $!

[azeey]

I think this is because his piece of code in cmdsim.rb catches only SIGINT. Updating to include SIGTERM could fix it

gz-sim/src/cmd/cmdsim.rb.in

Lines 556 to 560 in 689ee9d

	Signal.trap("INT") {
	self.killProcess(guiPid, "Gazebo Sim GUI", 5.0)
	self.killProcess(serverPid, "Gazebo Sim Server", 5.0)
	return 1

Can you give it a try? If it works, do you mind opening a PR?

[erlingrj]

Thanks for your suggestion, it now works! I have submitted a PR with the fix here #2747