Special cron entries

05 May 2015 in Tech

There are some special entries that can be used when creating a crontab entry (crontab -e), most of which are just shortcuts for the standard crontab entries that we all know and love.

You can use them in your crontab just like you would a normal entry:

bash
# m h dom mon dow  command
# Say hello each time the machine boots up
@reboot echo 'Hello world. I just booted up'
# Say Happy new year, using both forms of entry
@yearly echo 'Happy new year'
0 0 1 1 * echo 'Happy new year from me too'

The @reboot entry could be useful for keeping track of when a machine is rebooted. Just add the crontab and each time the machine restarts you'll get an email with any output from the crontab (in this case, "Hello world. I just booted up")

Possible entries

There are nine possible aliases, some of which are just aliases for each other (such as @yearly and @annually)

Entry	Description	Equivalent Entry
@reboot	Run once, at startup	None
@yearly	Run once a year	0 0 1 1 _
@annually	Same as @yearly	0 0 1 1 _
@monthly	Run once a month	0 0 1 * _
@weekly	Run once a week	0 0 _ _ 0
@daily	Run once a day	0 0 _ * _
@midnight	Same as @daily	0 0 _ * _
@hourly	Run once an hour	0 _ * * *

I'm not sure I'd recommend using any of these (except maybe @reboot) as the standard syntax is well known by anyone that should be editing a crontab, but it's interesting to know that there are aliases in there for common time periods.

(via mkaz (now offline))