|CRONTAB(5)||File Formats Manual||CRONTAB(5)|
NAME¶crontab - tables for driving bcron
DESCRIPTION¶A crontab file contains instructions to the bcron-sched(8) daemon of the general form: ``run this command at this time on this date''. Each user has their own crontab, and commands in any given crontab will be executed as the user who owns the crontab. Blank lines and leading spaces and tabs are ignored. Lines whose first non-space character is a pound-sign (#) are comments, and are ignored. Note that comments are not allowed on the same line as cron commands, since they will be taken to be part of the command. Similarly, comments are not allowed on the same line as environment variable settings. An active line in a crontab will be either an environment setting or a cron command. An environment setting is of the form,
name = value where the spaces around the equal-sign (=) are optional, and any subsequent non-leading spaces in value will be part of the value assigned to name. The value string may be placed in quotes (single or double, but matching) to preserve leading or trailing blanks. Several environment variables are set up automatically by the bcron-exec(8) program. SHELL is set to /bin/sh, and LOGNAME, USER, and HOME are set from the /etc/passwd line of the crontab's owner. In addition to LOGNAME, USER, HOME, and SHELL, bcron-exec(8) will look at MAILTO if it has any reason to send mail as a result of running commands in ``this'' crontab. If MAILTO is defined (and non-empty), mail is sent to the user so named. If MAILTO is defined but empty (MAILTO=""), no mail will be sent. Otherwise mail is sent to the owner of the crontab. This option is useful if you decide on /bin/mail instead of /usr/lib/sendmail as your mailer when you install cron -- /bin/mail doesn't do aliasing, and UUCP usually doesn't read its mail. The format of a cron command is very much the V7 standard, with a number of upward-compatible extensions. Each line has five time and date fields, followed by a user name if this is the system crontab file, followed by a command. Commands are executed by bcron-sched(8) when the minute, hour, and month of year fields match the current time, and at least one of the two day fields (day of month, or day of week) match the current time (see ``Note'' below). Jobs scheduled during non-existent times, such as "missing hours" during daylight savings conversion, will be scheduled at some point shortly after the non-existent time. Jobs scheduled during repeating times, such as "duplicate hours" during daylight savings conversion, will be scheduled only once (unless they would repeat anyways, such as jobs that run every minute or hour). The time and date fields are:
- field allowed values
EXAMPLE CRON FILE¶
# use /bin/sh to run commands, no matter what /etc/passwd says SHELL=/bin/sh # mail any output to `email@example.com', no matter whose crontab this is MAILTOfirstname.lastname@example.org # # run five minutes after midnight, every day 5 0 * * * $HOME/bin/daily.job >> $HOME/tmp/out 2>&1 # run at 2:15pm on the first of every month -- output mailed to bruce (above) 15 14 1 * * $HOME/bin/monthly 23 0-23/2 * * * echo "run 23 minutes after midn, 2am, 4am ..., everyday" 5 4 * * sun echo "run at 5 after 4 every sunday"
- System crontab file
- System crontab directory
SEE ALSO¶bcron-sched(8), bcron-spool(8), bcrontab(1)
EXTENSIONS¶When specifying day of week, both day 0 and day 7 will be considered Sunday. BSD and ATT seem to disagree about this. Lists and ranges are allowed to co-exist in the same field. "1-3,7-9" would be rejected by ATT or BSD cron -- they want to see "1-3" or "7,8,9" ONLY. Ranges can include "steps", so "1-9/2" is the same as "1,3,5,7,9". Names of months or days of the week can be specified by name. Environment variables can be set in the crontab. In BSD or ATT, the environment handed to child processes is basically the one from /etc/rc. Command output is mailed to the crontab owner (BSD can't do this), can be mailed to a person other than the crontab owner (SysV can't do this), or the feature can be turned off and no mail will be sent at all (SysV can't do this either).
Paul Vixie <email@example.com> Charles Cazabon <charlesc-cronman @ discworld.dyndns.org> Bruce Guenter <firstname.lastname@example.org>