GoSpawn

GoSpawn is a cross between dumb-init, a simplified supervisord and syslog2stdout, implemented in Go.

Because it's implemented in Go, you don't need the prerequisites for supervisord which you would have to install otherwise. One statically compiled binary is enough.

Usage

Syntax:

gospawn [SYSLOGD_PORTS_AND_PATHS...] -- [COMMANDS...]

To spawn a syslog daemon on UDP port 514 and in /dev/log, and to spawn cron and uwsgi, you use this:

gospawn 514 /dev/log -- /usr/sbin/cron -f -L 15 -- /usr/bin/uwsgi /uwsgi.ini

Quick download:

$ if ! curl -so gospawn https://junk.devs.nu/go/gospawn.upx ||
     ! printf '%s%s  gospawn\n' \
       939760978b2e56dd2c60d7c85d27770612aa862007f9f6b81d756a23761ed09f \
       c074f1f1badf3b00fd68b66a8ab7f0498a5424db68a59d86264a90ef34815b48 |
       sha512sum -c; then
    rm -f gospawn; false
  fi

When processes succeed (return with code 0), they are not respawned. If they fail, they are respawned:

$ gospawn -- sleep 1 -- false
GoSpawn 46ce713 starting...
Spawned process 29087 [sleep 1], running
Spawned process 29089 [false], running
Reaped process 29089 [false], status 1
Reaped process 29087 [sleep 1], status 0

(after 10 seconds)

Spawned process 29095 [false], running
Reaped process 29095 [false], status 1

If there is at least one process and all processes have completed successfully, gospawn ends as well. If no commands are supplied, but syslog ports are, it will run forever as a syslog daemon.

Other examples:

• The environment is preserved, and so are stdin/stdout.

  $ docker run -e VALUE=val -it IMG /gospawn -- sh -c 'echo $VALUE'
  
  Spawned process 13: [sh -c echo $VALUE]
  val
  Reaped process 13: [sh -c echo $VALUE], status 0

• Zombies are reaped immediately; observe how the sleep 5 background job is reaped in a timely fashion (see the process list) and that syslog messages are captured.

  $ docker run -it IMG /gospawn /dev/log -- python -c '\
  import subprocess,time,syslog;
  p=subprocess.Popen("setsid sleep 5 &", shell=True);p.wait();
  syslog.syslog("subprocess done");time.sleep(10);
  syslog.syslog("sleep done")' | wtimestamp
  
  14:15:11: GoSpawn 46ce713 starting...
  14:15:11: Spawned syslogd at UNIX(/dev/log)
  14:15:11: Spawned process 12 [python3 -c ...], running
  14:15:11: user.info: -c: subprocess done
  14:15:16: Reaped process 15, status 0
  14:15:21: user.info: -c: sleep done
  14:15:21: Reaped process 12 [python3 -c ...], status 0
  14:15:21: DBG: UNIX(/dev/log): read unixgram /dev/log: use of closed netw..

TODO

• Check what we do with stale sockets in syslog2stdout and do the same here.
• Also parse RFC5424? See: ./gospawn 8514 -- logger -n 127.0.0.1 -P 8514 -p user.info Test and https://github.com/ossobv/syslog2stdout/blob/master/syslog2stdout.c#L224
• Future: add cron-daemon?
• Should we have called this "minitgo" or "initgo" (mini, init in go?).
• See also: http://git.suckless.org/sinit/tree/sinit.c
• See also: https://github.com/Yelp/dumb-init/blob/master/dumb-init.c