Question

I want to run a cron job every minute that will launch a script. Simple enough there. However, I need to make sure that not more than X number (defined in the script) of instances are ever running. These are queue workers, so if at any minute interval 6 workers are still active, then I would not launch another instance. The script simply launches a PHP script which exits if no job available. Right now I have a shell script that perpetually launches itself every 10 seconds after exit… but there are long periods of time where there are no jobs, and a minute delay is fine. Eventually I would like to have two cron jobs for peak and off-peak, with different intervals.

Answer 1

1. Make sure you have unique script name.

2. Then check if 6 instances are already running

   if [ $(pgrep '^UNIQUE_SCIPT_NAME$' -c) -lt 6 ]
   then 
       # start my script
   else
       # do not start my script
   fi