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metichi
Asked: 2019-12-10 02:45:57 +0800 CST

How to prevent a cronjob from executing if another instance is already running?

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I want to record a stream whenever it is live automatically, so I thought of setting a cronjob that runs youtube-dl every 15 minutes to that url.

But once it is recording, how do I prevent the system from starting another recording 15 minutes later simultaneously?

cron

1 Answers

  1. Best Answer

    You can use flock for this. flock is a little command line tool to manage locks. It works by wrapping a lock around the execution of a command and stores the state of the lock in a lock file.

    You probably want to create a cron job based on a command like the following:

    flock -n /tmp/ytdlcron.lock <your youtube dl command>

    flock by default creates an exclusive lock (meaning only one command referencing a specific lockfile will run) and the -n flag causes subsequent jobs to fail until finished (rather the default which is to wait, would could leave you with lots of jobs backed up waiting to run)

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