CRON(VIII) 10/25/74 CRON(VIII) 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 (VIII). 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. Crontab is examined by cron every hour. Thus it could take up to an hour for entries to become effective. If it receives a hangup signal, however, the table is examined immediately; so `kill -1 ...' can be used. FILES /usr/lib/crontab SEE ALSO init(VIII), sh(I), kill (I) DIAGNOSTICS None - illegal lines in crontab are ignored. BUGS A more efficient algorithm could be used. The overhead in running cron is about one percent of the machine, exclusive of any commands executed.