Prevent Ctrl+C from interrupting exec.Command in Golang

Issue

I’ve noticed that processes started with exec.Command get interrupted even when the interrupt call has been intercepted via signal.Notify. I’ve done the following example to show the issue:

package main

import (
    "log"
    "os"
    "os/exec"
    "os/signal"
    "syscall"
)

func sleep() {
    log.Println("Sleep start")
    cmd := exec.Command("sleep", "60")
    cmd.Run()
    log.Println("Sleep stop")
}

func main() {
    var doneChannel = make(chan bool)

    go sleep()

    c := make(chan os.Signal, 1)
    signal.Notify(c, os.Interrupt)
    signal.Notify(c, syscall.SIGTERM)
    go func() {
        <-c
        log.Println("Receved Ctrl + C")
    }()

    <-doneChannel
}

If Ctrl+C is pressed while this program is running, it’s going to print:

2015/10/16 10:05:50 Sleep start
^C2015/10/16 10:05:52 Receved Ctrl + C
2015/10/16 10:05:52 Sleep stop

showing that the sleep commands gets interrupted. Ctrl+C is successfully caught though and the main program doesn’t quit, it’s just the sleep commands that gets affected.

Any idea how to prevent this from happening?

Solution

The shell will signal the entire process group when you press ctrl+c. If you signal the parent process directly, the child process won’t receive the signal.

To prevent the shell from signaling the children, you need to start the command in its own process group with with the Setpgid and Pgid fields in syscall.SysProcAttr before starting the processes

cmd := exec.Command("sleep", "60")
cmd.SysProcAttr = &syscall.SysProcAttr{
    Setpgid: true,
}

Answered By – JimB

Answer Checked By – Mildred Charles (GoLangFix Admin)

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