Question

Let’s say, I have 10 scripts that I want to run regularly as cron jobs. However, I don’t want all of them to run at the same time. I want only 2 of them running simultaneously.

One solution that I’m thinking of is create two script, put 5 statements on each of them, and them as separate entries in the crontab. However the solution seem very adhoc.

Is there existing unix tool to perform the task I mentioned above?

Answer 1

The jobs builtin can tell you how many child processes are running. Some simple shell scripting can accomplish this task:

MAX_JOBS=2

launch_when_not_busy()
{
    while [ $(jobs | wc -l) -ge $MAX_JOBS ]
    do
        # at least $MAX_JOBS are still running.
        sleep 1
    done
    "$@" &
}

launch_when_not_busy  bash job1.sh --args
launch_when_not_busy  bash jobTwo.sh 
launch_when_not_busy  bash job_three.sh 
...
wait