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cron(8) [bsd man page]

CRON(8) 						      System Manager's Manual							   CRON(8)

cron - clock daemon SYNOPSIS
/usr/sbin/cron DESCRIPTION
Cron executes commands at specified dates and times according to the instructions in the files /etc/crontab and /etc/crontab.local. None, either one, or both of these files may be present. Since cron never exits, it should only be executed once. This is best done by running cron from the initialization process through the file /etc/rc; see init(8). The crontab files consist of lines of seven fields each. The fields are separated by spaces or tabs. The first five are integer patterns to specify: o minute (0-59) o hour (0-23) o day of the month (1-31) o month of the year (1-12) o day of the week (1-7 with 1 = Monday) Each of these patterns may contain: o a number in the range above o two numbers separated by a minus meaning a range inclusive o a list of numbers separated by commas meaning any of the numbers o 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. Both crontab files are checked by cron every minute, on the minute. FILES
/etc/crontab /etc/crontab.local 7th Edition October 23, 1996 CRON(8)

Check Out this Related Man Page

CRON(8) 						      System Manager's Manual							   CRON(8)

cron - daemon to execute scheduled commands (Vixie Cron) SYNOPSIS
Cron should be started from /etc/rc or /etc/rc.local. It will return immediately, so you don't need to start it with '&'. Cron searches /var/spool/cron for crontab files which are named after accounts in /etc/passwd; crontabs found are loaded into memory. Cron also searches for /etc/crontab and the files in the /etc/cron.d/ directory, which are in a different format (see crontab(5)). Cron then wakes up every minute, examining all stored crontabs, checking each command to see if it should be run in the current minute. When execut- ing commands, any output is mailed to the owner of the crontab (or to the user named in the MAILTO environment variable in the crontab, if such exists). Additionally, cron checks each minute to see if its spool directory's modtime (or the modtime on /etc/crontab) has changed, and if it has, cron will then examine the modtime on all crontabs and reload those which have changed. Thus cron need not be restarted whenever a crontab file is modified. Note that the Crontab(1) command updates the modtime of the spool directory whenever it changes a crontab. SEE ALSO
crontab(1), crontab(5) AUTHOR
Paul Vixie <> 4th Berkeley Distribution 20 December 1993 CRON(8)
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