Script to launch (and restart when stopped servers)

server_launcher.rb

require "etc"

# Script used to launch servers, and track their status

groups = {}
pid = nil
uid = nil

ARGV.each do |argument|

  case argument
  when /(\w+):(.*)/
    group, command = [$1, $2]
    groups[group] ||= []
    groups[group] << command

  when /pid=(.*)/
    pid = $1

  when /uid=(\d+)$/
    uid = $1.to_i

  when /uid=(.*)/
    uid = Etc.getpwnam($1).uid

  end

end

def log(message)
  print "[#{Time.now.strftime("%F %X")}] [Launcher] #{message}\n"
end

if pid
  log("Write PID to #{pid}")
  File.open(pid, "w") {|f| f.write $$ }
end

if uid
  log("Set UID to #{uid}")
  Process.uid = uid
  Process.euid = uid
end

PIDs = {}

def run(command)
  pid = fork { exec("/bin/sh", "-c", command) }
  log("[PID #{pid}] #{command.inspect}")
  PIDs[pid] = command
end

Signal.trap("CLD") do
  pid = Process.wait()
  command = PIDs[pid]

  log "<#{command}> terminated. Restarting"
  PIDs.delete(pid)
  run(command)
end

groups.each_value do |group|
  group.each do |command|
    run(command)
  end
end

sleep 1000 while true