George Hubka

From the internet, and slightly adjusted for a linux system… [http://www.kalab.com/freeware/cron/cron.htm]

The Crontab file

Each line of CRONTAB has the following structure:

Position:     Values:
Minute     0-59
Hour     0-23
Day     1-31
Month     1-12
Day of week     0-6 (0=Sunday, 1=Monday, …, 6=Saturday)

Instead of minute, hour, day, month or day of week it’s also possible to specify a *. A * represents all possible values for that position (e.g. a * on 2nd position is the same as specifying all the possible values for hour)

It’s also possible to specify several values separated by commas: e.g. if you want a command to be executed every 10th minute so you can specify 0,10,20,30,40,50 for minute. A range of values can be specified with a -: e.g. value 0-12 for hour -> every hour a.m.

Comments

Every line not starting with a number is treated as a comment.

Examples

execute a command every minute

* * * * * /somecommand

execute the program every hour

0 * * * * /somecommand

every day at 0.30 p.m.

30 12 * * * /somecommand

every tuesday at midnight

0 0 * * 3 /somecommand

1st of every month at 2.45 p.m.

45 14 1 * * /somecommand

every half hour

0,30 * * * * /somecommand

every hour (a.m.) only on weekdays

0 0-12 * * 1-5 /somecommand