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linuxbashconcurrencyscheduled-tasks

How to make sure only one instance of a Bash script is running at a time?

I want to make a sh script that will only run at most once at any point.

Say, if I exec the script then I go to exec the script again, how do I make it so that if the first exec of the script is still working the second one will fail with an error. I.e. I need to check if the script is running elsewhere before doing anything. How would I go about doing this??

The script I have runs a long running process (i.e. runs forever). I wanted to use something like cron to call the script every 15mins so in case the process fails, it will be restarted by the next cron run script.

Solution

  • You want a pid file, maybe something like this:

    pidfile=/path/to/pidfile
if [ -f "$pidfile" ] && kill -0 `cat $pidfile` 2>/dev/null; then
    echo still running
    exit 1
fi  
echo $$ > $pidfile