svcron.8.in

.\" vim: tw=75
.\" Copyright 1988,1990,1993,1996,2021 by Paul Vixie ("VIXIE")
.\" Copyright (c) 2004 by Internet Systems Consortium, Inc. ("ISC")
.\" Copyright (c) 1997,2000 by Internet Software Consortium, Inc.
.\"
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.\" $Id: svcron.8,v 1.8 2004/01/23 19:03:32 vixie Exp $
.\" 
.TH SCHED 8 "10 January 1996""
.UC 4
.SH NAME
svcron \- daemon to execute scheduled commands (based on Vixie Cron)
.SH SYNOPSIS
\fBsvcron\fR [ \fB\-v\fR ] [ \fB\-M\fR \fImailer\fR ]
[ \fB\-d\fR \fIcrontabs_directory\fR ]

.SH DESCRIPTION
\fBsvcron\fR searches for \fI@syscrontab@\fR file which is in a different
format (see \fIcrontab\fR(5)). It then searches \fI@crondir@/@spooldir@\fR
directory for crontab files which are named after accounts in /etc/passwd.
After this, \fBsvcron\fR checks \fI@syscrondir@\fR directory for crontab
files; all crontabs found are loaded into memory. \fBsvcron\fR 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
\fBMAILTO\fR environment variable in the crontab, if such exists).

The default mailer command is \fI@sendmail@\fR unless overridden with the
\-M command line option when \fBsvcron\fR is invoked. If exactly one %s is
present this command string, it will be replaced by the user name of the
invoking crontab.

Additionally, \fBsvcron\fR checks each minute to see if modtimes on
\fI@crondir@/@spooldir@\fR, \fI@syscrontab@\fR and \fI@syscrondir@\fR has
changed, and if it has, \fBsvcron\fR will then examine the modtime on all
crontabs and reload those which have changed. Thus \fBsvcron\fR need not be
restarted whenever a crontab file is modified. Note that the
\fBsvcrontab\fR(1) command updates the modtime of the spool directory
whenever it changes a crontab.

Unlike other versions of cron which fork into background, \fBsvcron\fR
always runs in the foreground. This allows \fBsvcron\fR(8) to be started as
a supervised service as a \fBsvscan\fR(8) / \fBsupervise\fR(8) service.

\fBsvcron\fR skips the standard cron directories when passed \fB\-d\fR
option. This allows any non-privileged user to use crontabs in their own
directories. \fBsvcron\fR skips files starting with '.' (dot) when
searching for crontabs.

.SS Daylight Saving Time and other time changes
Local time changes of less than three hours, such as those caused by the
start or end of Daylight Saving Time, are handled specially. This only
applies to jobs that run at a specific time and jobs that are run with a
granularity greater than one hour. Jobs that run more frequently are
scheduled normally.

If time has moved forward, those jobs that would have run in the interval
that has been skipped will be run immediately. Conversely, if time has
moved backward, care is taken to avoid running jobs twice.

Time changes of more than 3 hours are considered to be corrections to the
clock or timezone, and the new time is used immediately.

.SH CAVEATS
In this version of \fBsvcron\fR, @crondir@ must not be readable or writable
by any user other than root. In other words, it should be mode 0700.

.SH "SEE ALSO"
.IR svcrontab(1),
.IR svcrontab(5),
.IR svscan(8),
.IR supervise(8)

.SH AUTHOR
.nf
Paul Vixie <vixie@isc.org>