Clock Service (Cron)

Cron executes commands at specified dates and times according to the instructions in the file tenon/etc/crontab. Commands may be Perl and Shell scripts, Apple scripts and applications, or any of the UNIX utilities listed in See Appendix G.

 

The crontab file consists of lines of seven fields each. The fields are separated by spaces or tabs. The first five fields are integer patterns to specify:

 

• minute (0-59)
• hour (0-23)
• day of the month (1-31)
• month of the year (1-12)
• day of the week (1-7 with 1 = Monday)

 

Each of these patterns may contain:

 

• A number in the range above.
• Two numbers separated by a minus meaning a range inclusive.
• A list of numbers separated by commas meaning any of the numbers.
• An asterisk meaning all legal values.

 

The sixth field is a user name -- the command will be run with that user's UID and permissions. The seventh field consists of all the text on a line following the sixth field, including spaces and tabs; this text is treated as a command which is executed by the Shell at the specified times. A percent character ("%") in this field is translated to a new-line character.

 

Lines beginning with a "#" are ignored by Cron.

 

The crontab file is checked by Cron every minute, on the minute.