Golang catch signals

Question

I want to implement a "process wrapper" in Go. Basically what it will do, is launch a process (lets say a node server) and monitor it (catch signals like SIGKILL, SIGTERM ...)

I think the way to do is to launch the node server in a go routine using syscall.Exec:

func launchCmd(path string, args []string) {
  err := syscall.Exec(path, args, os.Environ())
  if err != nil {
    panic(err)
  }
}

Then I'd like to catch every possible signals generated by the command executed by syscall. I'm pretty new to Go, any help would be appreciated.

Answer 1

You can use signal.Notify :

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

func main() {
    signalChannel := make(chan os.Signal, 2)
    signal.Notify(signalChannel, os.Interrupt, syscall.SIGTERM)
    go func() {
        sig := <-signalChannel
        switch sig {
        case os.Interrupt:
            //handle SIGINT
        case syscall.SIGTERM:
            //handle SIGTERM
        }
    }()
    // ...
}

Answer 2

There are three ways of executing a program in Go:

1. syscall package with syscall.Exec, syscall.ForkExec, syscall.StartProcess
2. os package with os.StartProcess
3. os/exec package with exec.Command

syscall.StartProcess is low level. It returns a uintptr as a handle.

os.StartProcess gives you a nice os.Process struct that you can call Signal on. os/exec gives you io.ReaderWriter to use on a pipe. Both use syscall internally.

Reading signals sent from a process other than your own seems a bit tricky. If it was possible, syscall would be able to do it. I don't see anything obvious in the higher level packages.

To receive a signal you can use signal.Notify like this:

sigc := make(chan os.Signal, 1)
signal.Notify(sigc,
    syscall.SIGHUP,
    syscall.SIGINT,
    syscall.SIGTERM,
    syscall.SIGQUIT)
go func() {
    s := <-sigc
    // ... do something ...
}()

You just need to change the signals you're interested in listening to. If you don't specify a signal, it'll catch all the signals that can be captured.

You would use syscall.Kill or Process.Signal to map the signal. You can get the pid from Process.Pid or as a result from syscall.StartProcess.