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:
# 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'
@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")
There are nine possible aliases, some of which are just aliases for each other (such as
|@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))