1.\"/* Copyright 1988,1990,1993,1996 by Paul Vixie 2.\" * All rights reserved 3.\" */ 4.\" 5.\" Copyright (c) 1997,2000 by Internet Software Consortium, Inc. 6.\" 7.\" Permission to use, copy, modify, and distribute this software for any 8.\" purpose with or without fee is hereby granted, provided that the above 9.\" copyright notice and this permission notice appear in all copies. 10.\" 11.\" THE SOFTWARE IS PROVIDED "AS IS" AND INTERNET SOFTWARE CONSORTIUM DISCLAIMS 12.\" ALL WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES 13.\" OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL INTERNET SOFTWARE 14.\" CONSORTIUM BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL 15.\" DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR 16.\" PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS 17.\" ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS 18.\" SOFTWARE. 19.\" 20.\" $OpenBSD: cron.8,v 1.11 2001/08/02 18:37:34 mpech Exp $ 21.\" 22.Dd June 6, 1999 23.Dt CRON 8 24.Os 25.Sh NAME 26.Nm cron 27.Nd daemon to execute scheduled commands (Vixie Cron) 28.Sh SYNOPSIS 29.Nm cron 30.Sh DESCRIPTION 31.Nm 32should be started from 33.Pa /etc/rc 34or 35.Pa /etc/rc.local . 36It will return immediately, so you don't need to start it with 37.Ql \&& . 38.Pp 39.Nm 40searches its spool directory 41.Pf ( Pa /var/cron/tabs Ns ) 42for 43.Xr crontab 5 44files which are named after accounts in 45.Pa /etc/passwd ; 46crontabs found are loaded into memory. 47.Nm 48also searches for 49.Pa /etc/crontab 50which is in a different format (see 51.Xr crontab 5 ) . 52.Nm 53then wakes up every minute, examining all loaded crontabs, checking each 54command to see if it should be run in the current minute. 55When executing commands, any output is mailed to the user named in the 56.Ev MAILTO 57environment variable in the crontab, or to the owner of the crontab if 58.Ev MAILTO 59is not present. 60.Pp 61Additionally, 62.Nm 63checks each minute to see if its spool directory's modtime (or the modtime on 64.Pa /etc/crontab ) 65has changed, and if it has, 66.Nm 67examines the modtime on all crontabs and reloads those which have 68changed. 69Thus 70.Nm 71need not be restarted whenever a crontab file is modified. 72Note that the 73.Xr crontab 1 74command updates the modtime of the spool directory whenever it changes a 75crontab. 76.Pp 77Special considerations exist when the clock is changed by less than 3 78hours; for example, at the beginning and end of Daylight Saving 79Time. 80If the time has moved forward, those jobs which would have 81run in the time that was skipped will be run soon after the change. 82Conversely, if the time has moved backward by less than 3 hours, 83those jobs that fall into the repeated time will not be run. 84.Pp 85Only jobs that run at a particular time (not specified as @hourly, nor with 86.Ql * 87in the hour or minute specifier) 88are 89affected. 90Jobs which are specified with wildcards are run based on the 91new time immediately. 92.Pp 93Clock changes of more than 3 hours are considered to be corrections to 94the clock, and the new time is used immediately. 95.Sh SIGNALS 96On receipt of a 97.Tn SIGHUP , 98the cron daemon will close and reopen its log file. 99This is useful in scripts which rotate and age log files. 100Naturally this is not relevant if cron was built to use 101.Xr syslog 3 . 102.Sh SEE ALSO 103.Xr crontab 1 , 104.Xr crontab 5 105.Sh AUTHORS 106Paul Vixie <paul@vix.com> 107