NAME

cron − clock daemon

SYNOPSIS

/etc/cron

DESCRIPTION

Cron executes commands at specified dates and times according to the instructions in the file /usr/lib/crontab. 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).

/usr/lib/crontab consists of lines of six fields each.  The fields are separated by spaces or tabs.  The first five are integer patterns to specify the minute (0-59), hour (0-23), day of the month (1-31), month of the year (1-12), and 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; or an asterisk meaning all legal values.  The sixth field is a string that is executed by the Shell at the specified times.  A percent character in this field is translated to a new-line character.  Only the first line (up to a % or end of line) of the command field is executed by the Shell.  The other lines are made available to the command as standard input. 

Cron examines /usr/lib/crontab under the following conditions:

•At least once per hour (on the hour). 

•WHen the next command is to be run — cron looks ahead until the next command and sleeps until then. 

•When cron’s process is sent a SIGHUP.  This means that comeone who changes /usr/lib/crontab can get cron to look at it right away. 

FILES

/usr/lib/crontab

SEE ALSO

crontab(5)

Sun System Release 1.0  —  28 October 1983