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+.\"/* Copyright 1988,1990,1993,1996 by Paul Vixie
+.\" * All rights reserved
+.\" */
+.\"
+.\" Copyright (c) 2004 by Internet Systems Consortium, Inc. ("ISC")
+.\" Copyright (c) 1997,2000 by Internet Software Consortium, Inc.
+.\"
+.\" Permission to use, copy, modify, and distribute this software for any
+.\" purpose with or without fee is hereby granted, provided that the above
+.\" copyright notice and this permission notice appear in all copies.
+.\"
+.\" THE SOFTWARE IS PROVIDED "AS IS" AND ISC DISCLAIMS ALL WARRANTIES
+.\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+.\" MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL ISC BE LIABLE FOR
+.\" ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+.\" WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+.\" ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT
+.\" OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+.\"
+.\" Modified 2010/09/12 by Colin Dean, Durham University IT Service,
+.\" to add clustering support.
+.\"
+.\" $Id: cron.8,v 1.8 2004/01/23 19:03:32 vixie Exp $
+.\"
+.TH CRON "8" "2013-09-26" "cronie" "System Administration"
+.SH NAME
+crond \- daemon to execute scheduled commands
+.SH SYNOPSIS
+.B crond
+.RB [ -c " | " -h " | " -i " | " -n " | " -p " | " -P " | " -s " | " -m \fP\fI<mail command>\fP ]
+.br
+.B crond
+.B -x
+.RB [ext,sch,proc,pars,load,misc,test,bit]
+.br
+.B crond
+.B -V
+.SH DESCRIPTION
+.I Cron
+is started from
+.I /etc/rc.d/init.d
+or
+.I /etc/init.d
+when classical sysvinit scripts are used. In case systemd is enabled, then unit file is installed into
+.I /lib/systemd/system/crond.service
+and daemon is started by
+.I systemctl start crond.service
+command. It returns immediately, thus, there is no need to need to start it with
+the '&' parameter.
+.PP
+.I Cron
+searches
+.I /var/spool/cron
+for crontab files which are named after accounts in
+.I /etc/passwd;
+The found crontabs are loaded into the memory.
+.I Cron
+also searches for
+.I /etc/anacrontab
+and any files in the
+.I /etc/cron.d
+directory, which have a different format (see
+.BR crontab (5)).
+.I Cron
+examines all stored crontabs and checks each job to see if it needs to be
+run in the current minute. When executing commands, any output is mailed
+to the owner of the crontab (or to the user specified in the
+.I MAILTO
+environment variable in the crontab, if such exists). Any job output can
+also be sent to syslog by using the
+.B "\-s"
+option.
+.PP
+There are two ways how changes in crontables are checked. The first
+method is checking the modtime of a file. The second method is using the
+inotify support. Using of inotify is logged in the
+.I /var/log/cron
+log after the daemon is started. The inotify support checks for changes
+in all crontables and accesses the hard disk only when a change is
+detected.
+.PP
+When using the modtime option,
+.I Cron
+checks its crontables' modtimes every minute to check for any changes and
+reloads the crontables which have changed. There is no need to restart
+.I Cron
+after some of the crontables were modified. The modtime option is also
+used when inotify can not be initialized.
+.PP
+.I Cron
+checks these files and directories:
+.TP
+.IR /etc/crontab
+system crontab. Nowadays the file is empty by default. Originally it
+was usually used to run daily, weekly, monthly jobs. By default these
+jobs are now run through anacron which reads
+.IR /etc/anacrontab
+configuration file. See
+.BR anacrontab (5)
+for more details.
+.TP
+.IR /etc/cron.d/
+directory that contains system cronjobs stored for different users.
+.TP
+.IR /var/spool/cron
+directory that contains user crontables created by the
+.IR crontab
+command.
+.PP
+Note that the
+.BR crontab (1)
+command updates the modtime of the spool directory whenever it changes a
+crontab.
+.PP
+.SS Daylight Saving Time and other time changes
+Local time changes of less than three hours, such as those caused by the
+Daylight Saving Time changes, are handled in a special way. This only
+applies to jobs that run at a specific time and jobs that run with a
+granularity greater than one hour. Jobs that run more frequently are
+scheduled normally.
+.PP
+If time was adjusted one hour forward, those jobs that would have run in
+the interval that has been skipped will be run immediately. Conversely,
+if time was adjusted backward, running the same job twice is avoided.
+.PP
+Time changes of more than 3 hours are considered to be corrections to the
+clock or the timezone, and the new time is used immediately.
+.PP
+It is possible to use different time zones for crontables. See
+.BR crontab (5)
+for more information.
+.SS PAM Access Control
+.IR Cron
+supports access control with PAM if the system has PAM installed. For
+more information, see
+.BR pam (8).
+A PAM configuration file for
+.IR crond
+is installed in
+.IR /etc/pam.d/crond .
+The daemon loads the PAM environment from the pam_env module. This can
+be overridden by defining specific settings in the appropriate crontab
+file.
+.SH "OPTIONS"
+.TP
+.B "\-h"
+Prints a help message and exits.
+.TP
+.B "\-i"
+Disables inotify support.
+.TP
+.B "\-m"
+This option allows you to specify a shell command to use for sending
+.I Cron
+mail output instead of using
+.BR sendmail (8)
+This command must accept a fully formatted mail message (with headers) on
+standard input and send it as a mail message to the recipients specified
+in the mail headers. Specifying the string
+.I "off"
+(i.e., crond -m off)
+will disable the sending of mail.
+.TP
+.B "\-n"
+Tells the daemon to run in the foreground. This can be useful when
+starting it out of init. With this option is needed to change pam setting.
+.I /etc/pam.d/crond
+must not enable
+.I pam_loginuid.so
+module.
+.TP
+.B "\-f"
+the same as -n, consistent with other crond implementations.
+.TP
+.B "\-p"
+Allows
+.I Cron
+to accept any user set crontables.
+.TP
+.B "\-P"
+Don't set PATH. PATH is instead inherited from the environment.
+.TP
+.B "\-c"
+This option enables clustering support, as described below.
+.TP
+.B "\-s"
+This option will direct
+.I Cron
+to send the job output to the system log using
+.BR syslog (3).
+This is useful if your system does not have
+.BR sendmail (8)
+installed or if mail is disabled.
+.TP
+.B "\-x"
+This option allows you to set debug flags.
+.TP
+.B "\-V"
+Print version and exit.
+.SH SIGNALS
+When the
+.I SIGHUP
+is received, the
+.I Cron
+daemon will close and reopen its log file. This proves to be useful in
+scripts which rotate and age log files. Naturally, this is not relevant
+if
+.I Cron
+was built to use
+.IR syslog (3).
+.SH CLUSTERING SUPPORT
+In this version of
+.IR Cron
+it is possible to use a network-mounted shared
+.I /var/spool/cron
+across a cluster of hosts and specify that only one of the hosts should
+run the crontab jobs in this directory at any one time. This is done by
+starting
+.I Cron
+with the
+.B \-c
+option, and have the
+.I /var/spool/cron/.cron.hostname
+file contain just one line, which represents the hostname of whichever
+host in the cluster should run the jobs. If this file does not exist, or
+the hostname in it does not match that returned by
+.BR gethostname (2),
+then all crontab files in this directory are ignored. This has no effect
+on cron jobs specified in the
+.I /etc/crontab
+file or on files in the
+.I /etc/cron.d
+directory. These files are always run and considered host-specific.
+.PP
+Rather than editing
+.I /var/spool/cron/.cron.hostname
+directly, use the
+.B \-n
+option of
+.BR crontab (1)
+to specify the host.
+.PP
+You should ensure that all hosts in a cluster, and the file server from
+which they mount the shared crontab directory, have closely synchronised
+clocks, e.g., using
+.BR ntpd (8),
+otherwise the results will be very unpredictable.
+.PP
+Using cluster sharing automatically disables inotify support, because
+inotify cannot be relied on with network-mounted shared file systems.
+.SH CAVEATS
+All
+.BR crontab
+files have to be regular files or symlinks to regular files, they must
+not be executable or writable for anyone else but the owner. This
+requirement can be overridden by using the
+.B \-p
+option on the crond command line. If inotify support is in use, changes
+in the symlinked crontabs are not automatically noticed by the cron
+daemon. The cron daemon must receive a SIGHUP signal to reload the
+crontabs. This is a limitation of the inotify API.
+.PP
+The syslog output will be used instead of mail, when sendmail is not
+installed.
+.SH "SEE ALSO"
+.BR crontab (1),
+.BR crontab (5),
+.BR inotify (7),
+.BR pam (8)
+.SH AUTHOR
+.MT vixie@isc.org
+Paul Vixie
+.ME
+.br
+.MT mmaslano@redhat.com
+Marcela Mašláňová
+.ME
+.br
+.MT colin@colin-dean.org
+Colin Dean
+.ME
+.br
+.MT tmraz@fedoraproject.org
+Tomáš Mráz
+.ME