NAME

cron − clock daemon

USAGE

/etc/cron

DESCRIPTION

The cron utility executes commands at the dates and times specified in the file /usr/lib/crontab. Since cron does not exit, it should be executed only once.  This is best done by running cron from the initialization process. 

The crontab file consists of lines with six fields each; fields are separated by spaces or tabs.  The first five fields contain integer patterns that specify time and date in the following format:

 
minute (0-59)
hour (0-23)
day of the month (1-31)
month of the year (1-12)
day of the week (1-7, 1 is Monday)

Each field may contain a number or numbers.  Two numbers separated by a minus sign indicate an inclusive range.  A list of numbers separated by commas means that cron will execute when any of those values is true.  For example, if the month field contains:

1 3 5

cron will execute at all times in January, March, and May when the other fields’ values are true.  An asterisk means that cron will execute at all legal values for that field. 

The sixth field is a string that is executed by the Shell at the time(s) and date(s) specified.  A percent character (%) anywhere in the sixth field is translated to a newline character.  The Shell executes only the first line (up to a % or end of line) of the command field.  Cron interprets any characters after a % as standard input to the command. 

Cron checks /usr/lib/crontab once a minute. 

FILES

/usr/lib/crontab