Useful crontab short cuts


While reading through crontab(5) this morning I came across this useful nugget of information:

“These special time specification “nicknames” are supported, which replace the 5 initial time and date fields, and are prefixed by the @ character”

This translates into the following known time periods:

@reboot : Run once, at startup.
@yearly : Run once a year
@annually : Run once a year
@monthly : Run once a month
@weekly : Run once a week
@daily : Run once a day
@hourly : Run once an hour

So instead of writing:

0 * * * * command

You can specify hourly to accomplish the same thing:

@hourly command_to_run

Or if you want to run something when a machine is rebooted you can add this:

@reboot echo “” | mail -s “/bin/hostname was recently rebooted” root

Several of these short cuts are rather handy and it makes things easier to read IMHO. Gotta love short cuts!

This article was posted by Matty on 2011-09-30 10:36:00 -0400 EDT