Run a script every minute without cron and allowing children

Question

I've written 2 php scripts one worker and one master.

If I run master manually it checks a rabbitmq system and spawns 1 worker for each queue it detects. Then if I run master again it checks see if the each worker process is still running if it is then it does nothing if not then it restarts it.

Fairly simple concept I'd have thought. I achieved it using nohup and & in the master for each child it spawns, now as I'm sure you can guess i want to run master every 60 seconds to check the queues are alive and respawn them if they're not.

This gives me the problem of I can't use nohub in cron jobs and just using & on its own doesn't seem to work. As far as I can tell the workers aren't even execing with the call

I've tried creating a separate shell script that then calls master.php also didn't work. I tried creating it as an upstart task then remembered that in ubuntu 17+ upstart is removed.

I'm open to any suggestions of different ways of doing this but whatever route I take it must allow my master.php to spawn the work.php files as headless background processes.

Answer 1

#!/bin/bash
#I am just like a system daemon... 
#I do not need nohup for work, and I should not be called from cron.

#My name is main_safe
#I will become a separeted process even if my father dies... 
#i will check if main is still alive, and if dies i will restart it
#nohup is not needed inside shell script. 
#IMPORTANT: to die is very different from to freeze 
main_safe(){
trap "" HUP
while sleep 120; do
   main&
   wait 
done

}

#My name is main I like to keep restarting php master.php
#everytime it go away... remove wait and I will keep starting master.php with absolutely no reason.
#If you are paranoid you can program me to restart main_safe,
#But what will happen if you try to stop me? Bad things.. so... 
#IMPORTANT: to die is very different from to freeze 
main(){
trap "" HUP
while sleep 60; do

     php master.php & 
     #do whatever you want here

     #uncomment this to prevent two instances of master.php from going up maybe it is necessary:
     wait

done
}


#nohup is not needed in shell script
main_safe& 
pstree -p | grep $! 

Is that acceptable?

Answer 2

How about using systemd. I did some searching, and as systemd replaces upstart for ubuntu's newer versions, this may be useful. The link below may be helpful.

Digital Ocean: How To Configure a Linux Service to Start Automatically After a Crash or Reboot