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))
Michael is a polyglot software engineer, committed to reducing complexity in systems and making them more predictable. Working with a variety of languages and tools, he shares his technical expertise to audiences all around the world at user groups and conferences. You can follow @mheap on Twitter