Crontab expressions
When creating tasks in crontab you have to use a specific syntax. It’s quite easy to learn, but you might like or dislike the syntax. Usually you use the crontab for the same things, either executing things on a daily basis, or on weekly/monthly basis. Personally, with the old syntax, I always forget the ordering of minutes, hours, day of week and so on. So the expressions listed below can be handy.
The commands are:
@reboot = run at boot and reboot only
@yearly = run at midnight Jan 1 each year (equiv to 0 0 1 1 *)
@annually = run at midnight Jan 1 each year (equiv to 0 0 1 1 *)
@monthly = run at midnight on the first day of each month (equiv to 0 0 1 * *)
@weekly = run at midnight each Sunday (equiv to 0 0 * * 0)
@daily = run at midnight each day (equiv to 0 0 * * *)
@midnight = run at midnight each day (equiv to 0 0 * * *)
@hourly = run on the first second of every hour (equiv to 0 * * * *)
Example of normal cron syntax:
0 0 * * * /path/to/command
This example would execute a command every night around at midnight. So instead of the above example you could use:
@daily /path/to/command
or
@midnight /path/to/command