Re: Cron sometimes starts two jobs from the same crontab entry

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Hi

On Tue, 07 Apr 2020 07:07:36 +0100 Terry Barnaby wrote:

> # Min Hour Day Month WeekDay

> # Perform incremental backup to every work day
> 01 23 * * 1 root /src/bbackup/bbackup-beam
> 01 23 * * 2 root /src/bbackup/bbackup-beam
> 01 23 * * 3 root /src/bbackup/bbackup-beam
> 01 23 * * 4 root /src/bbackup/bbackup-beam
> 01 23 * * 5 root /src/bbackup/bbackup-beam

> This system has been in use for 10 years or more on various Fedora 
> versions. However about 18 months ago I have seen a problem where cron 
> will start two backups with identical start times occasionally.

I have seen that also a few time, but years ago.

> I have had to add a file lock system in the bbackup-beam to cope with this.

I did the same, also for frequent cron jobs that may be stuck for a
too long time, for example if a network outage occurs.

Then (years later) an alternative to cron appeared: systemd.timer.

Pros:
   - Gratuitous execution locking
     "systemctl start X" is a noop if X runs.

   - Ease log management
     By default in the system log.
     No more need to redirect stdout and stderr to /dev/null as seen
     in so many crontabs

   - Ease tracking processes
     With "systemctl status" "systemctl stop" ...

Cons:
   - It's systemd-ish :-)

I can show you how to convert your crontab to systemd.{service,timer}
if you want.

-- 
francis
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