golang exec background process and get its pid

Question

Situation:

I want to run a command that puts itself into the background. If it makes it more possible, then I'll run the command in foreground and bring it into the background by myself.

Question:

When the process runs in background: how can I get it's pid using Go?

I tried the following:

cmd := exec.Command("ssh", "-i", keyFile, "-o", "ExitOnForwardFailure yes", "-fqnNTL", fmt.Sprintf("%d:127.0.0.1:%d", port, port), fmt.Sprintf("%s@%s", serverUser, serverIP))
cmd.Start()
pid := cmd.Process.Pid
cmd.Wait()

This returns instantly and leaves ssh running in the background. But it's pid is not the pid of the running ssh process. Moreover, it's the pid of the parent ssh process before it forked and backgrounded itself.

Answer 1

You don't need anything special, just don't tell ssh to background itself and don't Wait() for it. Example:

$ cat script.sh
#!/bin/sh
sleep 1
echo "I'm the script with pid $$"
for i in 1 2 3; do
        sleep 1
        echo "Still running $$"
done
$ cat proc.go
package main

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

func main() {
     cmd := exec.Command("./script.sh")
     cmd.Stdout = os.Stdout
     err := cmd.Start()
     if err != nil {
        log.Fatal(err)
     }
     log.Printf("Just ran subprocess %d, exiting\n", cmd.Process.Pid)
}
$ go run proc.go
2016/09/15 17:01:03 Just ran subprocess 3794, exiting
$ I'm the script with pid 3794
Still running 3794
Still running 3794
Still running 3794