[GRLUG] using flock

[Michael Glaske]

Pretty easy to implement in bash or sh..  The only problem is, if you
Crtl-C out of it, you'll have to manually remove the lock file.

if [ -f /var/run/script.lock ]; then
     print "Already running..  Exiting"
     exit 1
fi

date > /var/run/script.lock

# put your script here

# at the end
rm -f /var/run/script.lock


On Tue, Dec 24, 2013 at 9:17 AM, Eric Beversluis <
ebever at researchintegration.org> wrote:

> I've got a backup program on a server that includes a mysqldump once a
> day which overwrites the existing sysmyqldump.sql. The script also does
> rsync (of zarafa-backup, the mysqldump, and /var/lib/zarafa (the zarafa
> attachments file) to an external hard drive. Once a month is also copies
> the sysmysqldump.sql that's on the external HDD to a file with that
> day's date attached.
>
> The cron is set to run every hour. Right now, mysqldump is finishing at
> 40 min past the hour (00:40), so I think that when it also tries to make
> the copy on the 1st of the month it will run over into the next hour.
>
> As I understand it, the thing to do to prevent the script starting over
> before the old one finishes is to use 'flock.'
>
> My question is this: How does cron respond if flock prevents the script
> from starting at 01:00? Does it start it when the flock is freed or just
> skip that cycle or what?
>
> Thanks.
>
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