Starting detached child process

[Hein Meling]

Hi

I've been spending my day looking for a way to start child processes from a Go program (the parent) such that, if the parent process dies, the children doesn't. I tried using 'nohup' as a go-between, but can't seem to start the child processes in the background. Are there any recommended (or reasonable) work-arounds for this?

Thanks,

:) Hein

[Shawn Milochik]

It looks like exec.Start() does what you want.

http://golang.org/pkg/os/exec/#Cmd.Start

[Hein Meling]

No, because if the go program (the parent) is killed, the children also gets killed.

Hein :)

Sent from my iPad

On 17 Jul 2014, at 18:15, Shawn Milochik <shawn...@gmail.com> wrote:

It looks like exec.Start() does what you want.

http://golang.org/pkg/os/exec/#Cmd.Start

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[Shawn Milochik]

On Thu, Jul 17, 2014 at 9:56 PM, Hein Meling <hein....@gmail.com> wrote:

No, because if the go program (the parent) is killed, the children also gets killed.

Hein :)

That doesn't seem to be the case.

package main

import (

    "os/exec"

)

func main() {

    cmd := exec.Command("/tmp/monkey.sh")

    cmd.Start()

}

When I run that, with monkey.sh  being a program  that just appends text to a file, it keeps running after the Go program exits. I can even run the Go program multiple times and multiple instances of monkey.sh are running.

 

[Hein Meling]

Your solution seems to work when then parent process exits cleanly. But if you do:

func main() {

cmd := exec.Command("sleep", "15")

cmd.Start()

time.Sleep(20 * time.Second)

}

And CTRL-C the parent process before it exits cleanly, then also the sleep process goes away. Does the same happen to your monkey.sh process?

Moreover, my use case is actually somewhat more involved. That is, I would like to do cmd.Wait() (from different goroutines), in order to monitor the child processes, but I don't want the child processes to fail if the parent fails. 

:) Hein

[Bryan Whitehead]

You need to use os/signal to intercept SIGKILL or SIGTERM and exit cleanly so your children continue to live.

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[Ian Lance Taylor]

On Thu, Jul 17, 2014 at 8:12 PM, Hein Meling <hein....@gmail.com> wrote:
>
> Your solution seems to work when then parent process exits cleanly. But if
> you do:
>
> func main() {
> cmd := exec.Command("sleep", "15")
> cmd.Start()
> time.Sleep(20 * time.Second)
> }
>
> And CTRL-C the parent process before it exits cleanly, then also the sleep
> process goes away. Does the same happen to your monkey.sh process?
>
> Moreover, my use case is actually somewhat more involved. That is, I would
> like to do cmd.Wait() (from different goroutines), in order to monitor the
> child processes, but I don't want the child processes to fail if the parent
> fails.

^C kills all the processes because on Unix typing ^C on the terminal
sends a signal to every process in the process group. So you want to
have a child process that is in a different process group. You do
that by setting Setpgid to true in the Cmd.SysProcAttr field.

Ian

[Hein Meling]

Thanks Ian, that worked as expected!!

:) Hein

[calin...@gmail.com]

Setting Setpgid to true in Cmd.SysProcAttr works out great on platforms like OS X and Ubuntu (the only ones I tested on), but for some reason it doesn't appear to work on CentOS 7.1.1503 kernel version 3.10.0-229.4.2.el7.x86_64. Anyone else having this problem?

[m...@tejas.io]

For some reason, this does not seem to work for `ssh` (at least on OS X) unless you have `ControlPath` in ssh config. Are there any side-effects of SysProcAttr that I could be missing?