.\"/* Copyright 1988,1990,1993 by Paul Vixie .\" * All rights reserved .\" * .\" * Distribute freely, except: don't remove my name from the source or .\" * documentation (don't take credit for my work), mark your changes (don't .\" * get me blamed for your possible bugs), don't alter or remove this .\" * notice. May be sold if buildable source is provided to buyer. No .\" * warrantee of any kind, express or implied, is included with this .\" * software; use at your own risk, responsibility for damages (if any) to .\" * anyone resulting from the use of this software rests entirely with the .\" * user. .\" * .\" * Send bug reports, bug fixes, enhancements, requests, flames, etc., and .\" * I'll try to keep a version up to date. I can be reached as follows: .\" * Paul Vixie <paul@vix.com> uunet!decwrl!vixie!paul .\" */ .\" .\" $FreeBSD: src/usr.sbin/cron/cron/cron.8,v 1.25 2007/06/17 17:25:53 yar Exp $ .\" .Dd June 17, 2007 .Dt CRON 8 .Os .Sh NAME .Nm cron .Nd daemon to execute scheduled commands (Vixie Cron) .Sh SYNOPSIS .Nm .Op Fl s .Op Fl o .Op Fl x Ar debugflag Ns Op , Ns Ar ... .Sh DESCRIPTION The .Nm utility is launched by .Xr launchd 8 when it sees the existence of .Pa /etc/crontab or files in .Pa /usr/lib/cron/tabs . There should be no need to start it manually. See .Pa /System/Library/LaunchDaemons/com.vix.cron.plist for details. .Pp The .Nm utility searches .Pa /usr/lib/cron/tabs for crontab files which are named after accounts in .Pa /etc/passwd ; crontabs found are loaded into memory. The .Nm utility also searches for .Pa /etc/crontab which is in a different format (see .Xr crontab 5 ) . .Pp The .Nm utility then wakes up every minute, examining all stored crontabs, checking each command to see if it should be run in the current minute. When executing commands, any output is mailed to the owner of the crontab (or to the user named in the .Ev MAILTO environment variable in the crontab, if such exists). .Pp Additionally, .Nm checks each minute to see if its spool directory's modification time (or the modification time on .Pa /etc/crontab ) has changed, and if it has, .Nm will then examine the modification time on all crontabs and reload those which have changed. Thus .Nm need not be restarted whenever a crontab file is modified. Note that the .Xr crontab 1 command updates the modification time of the spool directory whenever it changes a crontab. .Pp Available options: .Bl -tag -width indent .It Fl s Enable special handling of situations when the GMT offset of the local timezone changes, such as the switches between the standard time and daylight saving time. .Pp The jobs run during the GMT offset changes time as intuitively expected. If a job falls into a time interval that disappears (for example, during the switch from standard time) to daylight saving time or is duplicated (for example, during the reverse switch), then it is handled in one of two ways: .Pp The first case is for the jobs that run every at hour of a time interval overlapping with the disappearing or duplicated interval. In other words, if the job had run within one hour before the GMT offset change (and cron was not restarted nor the .Xr crontab 5 changed after that) or would run after the change at the next hour. They work as always, skip the skipped time or run in the added time as usual. .Pp The second case is for the jobs that run less frequently. They are executed exactly once, they are not skipped nor executed twice (unless cron is restarted or the user's .Xr crontab 5 is changed during such a time interval). If an interval disappears due to the GMT offset change, such jobs are executed at the same absolute point of time as they would be in the old time zone. For example, if exactly one hour disappears, this point would be during the next hour at the first minute that is specified for them in .Xr crontab 5 . .It Fl o Disable the special handling of situations when the GMT offset of the local timezone changes, to be compatible with the old (default) behavior. If both options .Fl o and .Fl s are specified, the option specified last wins. .It Fl x Ar debugflag Ns Op , Ns Ar ... Enable writing of debugging information to standard output. One or more of the following comma separated .Ar debugflag identifiers must be specified: .Pp .Bl -tag -width ".Cm proc" -compact .It Cm bit currently not used .It Cm ext make the other debug flags more verbose .It Cm load be verbose when loading crontab files .It Cm misc be verbose about miscellaneous one-off events .It Cm pars be verbose about parsing individual crontab lines .It Cm proc be verbose about the state of the process, including all of its offspring .It Cm sch be verbose when iterating through the scheduling algorithms .It Cm test trace through the execution, but do not perform any actions .El .El .Sh FILES .Bl -tag -width /usr/lib/cron/tabs -compact .It Pa /usr/lib/cron/tabs Directory for personal crontab files .El .Sh SEE ALSO .Xr crontab 1 , .Xr launchctl 1 , .Xr crontab 5 , .Xr launchd.plist 5 , .Xr launchd 8 .Sh AUTHORS .An Paul Vixie Aq paul@vix.com