Cron – Can a Crontab Job Run Concurrently with Itself?

cron

If I have a crontab job that runs, for instance, every hour, but that job may take more than an hour to complete, will the next job fail to run?

Best Answer

No, cron scripts run parallelly, if you do not implement some locking mechanism.

See Quick-and-dirty way to ensure only one instance of a shell script is running at a time and Correct locking in shell scripts? for possible solutions.

A simpler way is to use lockfile, like in this answer or the run-one package (see this answer) - thanks to gertvdijk for suggesting it.

Related Solutions

Cron – Troubleshooting Why a Crontab Job Isn’t Running

Specifying a username like mylogin is for the /etc/crontab file. With your command sudo crontab -e you are actually editing /var/spool/cron/crontabs/root and you should not specify a username in such a file, only in /etc/crontab.

If you have to run the command as user mylogin you have to put the line in /etc/crontab (and edit this with root privileges), or just put it in the mylogin user's crontab.

From man 5 crontab:

EXAMPLE SYSTEM CRON FILE
    The following lists the content of a regular system-wide crontab  file.
    Unlinke  a user's crontab, this file has the username field, as used by
    /etc/crontab.

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Cron – Troubleshooting Why a Crontab Job Isn’t Running

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