252 lines
6.8 KiB
Groff
252 lines
6.8 KiB
Groff
.\"/* Copyright 1988,1990,1993 by Paul Vixie
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.\" * All rights reserved
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.\" */
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.\"
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.\" Copyright (c) 2004 by Internet Systems Consortium, Inc. ("ISC")
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.\" Copyright (c) 1997,2000 by Internet Software Consortium, Inc.
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.\"
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.\" Permission to use, copy, modify, and distribute this software for any
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.\" purpose with or without fee is hereby granted, provided that the above
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.\" copyright notice and this permission notice appear in all copies.
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.\"
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.\" THE SOFTWARE IS PROVIDED "AS IS" AND ISC DISCLAIMS ALL WARRANTIES
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.\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
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.\" MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL ISC BE LIABLE FOR
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.\" ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
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.\" WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
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.\" ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT
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.\" OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
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.\"
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.\" Modified 2010/09/12 by Colin Dean, Durham University IT Service,
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.\" to add clustering support.
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.\"
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.\" $Id: crontab.1,v 1.7 2004/01/23 19:03:32 vixie Exp $
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.\"
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.TH CRONTAB 1 "2019-10-29" "cronie" "User Commands"
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.SH NAME
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crontab \- maintains crontab files for individual users
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.SH SYNOPSIS
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.B crontab
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.RB [ -u
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.IR user ]
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.RI < "file"
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.RB | \ - >
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.br
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.B crontab
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.RB [ -T ]
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.RI < "file"
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.RB | \ - >
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.br
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.B crontab
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.RB [ -u
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.IR user ]
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.RB < -l " | " -r " | " -e >\ [ -i ]
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.RB [ -s ]
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.br
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.B crontab
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.BR -n \ [
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.IR "hostname " ]
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.br
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.B crontab
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.BR -c
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.br
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.B crontab
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.BR -V
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.SH DESCRIPTION
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.I Crontab
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is the program used to install a crontab table
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.IR file ,
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remove or list the existing tables used to serve the
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.BR cron (8)
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daemon. Each user can have their own crontab, and though these are files
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in
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.IR /var/spool/ ,
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they are not intended to be edited directly. For SELinux in MLS mode,
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you can define more crontabs for each range. For more information, see
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.BR selinux (8).
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.PP
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In this version of
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.IR Cron
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it is possible to use a network-mounted shared
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.I /var/spool/cron
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across a cluster of hosts and specify that only one of the hosts should
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run the crontab jobs in the particular directory at any one time. You
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may also use
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.BR crontab
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from any of these hosts to edit the same shared set of crontab files, and
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to set and query which host should run the crontab jobs.
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.PP
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Scheduling cron jobs with
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.BR crontab
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can be allowed or disallowed for different users. For this purpose, use the
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.I cron.allow
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and
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.I cron.deny
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files. If the
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.I cron.allow
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file exists, a user must be listed in it to be allowed to use
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.BR crontab .
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If the
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.I cron.allow
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file does not exist but the
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.I cron.deny
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file does exist, then a user must
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.I not
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be listed in the
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.I cron.deny
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file in order to use
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.BR crontab.
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If neither of these files exist, then only the super user is allowed to use
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.BR crontab .
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.PP
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Another way to restrict the scheduling of cron jobs beyond
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.BR crontab
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is to use PAM authentication in
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.I /etc/security/access.conf
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to set up users, which are allowed or disallowed to use
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.BR crontab
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or modify system cron jobs in the
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.IR /etc/cron.d/
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directory.
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.PP
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The temporary directory can be set in an environment variable. If it is
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not set by the user, the
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.I /tmp
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directory is used.
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.PP
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When listing a crontab on a terminal the output will be colorized unless
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an environment variable
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.I NO_COLOR
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is set.
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.PP
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.SH "OPTIONS"
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.TP
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.B "\-u"
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Specifies the name of the user whose crontab is to be modified. If this
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option is not used,
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.BR crontab
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examines "your" crontab, i.e., the crontab of the person executing the
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command. If no crontab exists for a particular user, it is created for
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them the first time the
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.B crontab -u
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command is used under their username.
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.TP
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.B "\-T"
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Test the crontab file syntax without installing it.
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Once an issue is found, the validation is interrupted, so this will not return all the existing issues at the same execution.
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.TP
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.B "\-l"
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Displays the current crontab on standard output.
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.TP
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.B "\-r"
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Removes the current crontab.
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.TP
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.B "\-e"
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Edits the current crontab using the editor specified by the
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.I VISUAL
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or
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.I EDITOR
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environment variables. After you exit from the editor, the modified
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crontab will be installed automatically.
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.TP
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.B "\-i"
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This option modifies the
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.B "\-r"
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option to prompt the user for a 'y/Y' response before actually removing
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the crontab.
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.TP
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.B "\-s"
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Appends the current SELinux security context string as an MLS_LEVEL
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setting to the crontab file before editing / replacement occurs - see the
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documentation of MLS_LEVEL in
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.BR crontab (5).
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.TP
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.B "\-n"
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This option is relevant only if
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.BR cron (8)
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was started with the
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.B \-c
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option, to enable clustering support. It is used to set the host in the
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cluster which should run the jobs specified in the crontab files in the
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.I /var/spool/cron
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directory. If a hostname is supplied, the host whose hostname returned
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by
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.BR gethostname (2)
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matches the supplied hostname, will be selected to run the selected cron jobs subsequently. If there
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is no host in the cluster matching the supplied hostname, or you explicitly specify
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an empty hostname, then the selected jobs will not be run at all. If the hostname
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is omitted, the name of the local host returned by
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.BR gethostname (2)
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is used. Using this option has no effect on the
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.I /etc/crontab
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file and the files in the
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.I /etc/cron.d
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directory, which are always run, and considered host-specific. For more
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information on clustering support, see
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.BR cron (8).
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.TP
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.B "\-c"
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This option is only relevant if
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.BR cron (8)
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was started with the
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.B \-c
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option, to enable clustering support. It is used to query which host in
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the cluster is currently set to run the jobs specified in the crontab
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files in the directory
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.I /var/spool/cron
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, as set using the
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.B \-n
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option.
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.TP
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.B "\-V"
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Print version and exit.
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.SH CAVEATS
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The files
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.I cron.allow
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and
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.I cron.deny
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cannot be used to restrict the execution of cron jobs; they only restrict the
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use of
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.BR crontab .
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In particular, restricting access to
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.BR crontab
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has no effect on an existing
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.I crontab
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of a user. Its jobs will continue to be executed until the crontab is removed.
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.PP
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The files
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.I cron.allow
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and
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.I cron.deny
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must be readable by the user invoking
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.BR crontab .
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If this is not the case, then they are treated as non-existent.
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.SH "SEE ALSO"
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.BR crontab (5),
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.BR cron (8)
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.SH FILES
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.nf
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/etc/cron.allow
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/etc/cron.deny
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.fi
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.SH STANDARDS
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The
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.I crontab
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command conforms to IEEE Std1003.2-1992 (``POSIX'') with one exception:
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For replacing the current crontab with data from standard input the
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.B \-
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has to be specified on the command line if the standard input is a TTY.
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This new command syntax differs from previous versions of Vixie Cron,
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as well as from the classic SVR3 syntax.
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.SH DIAGNOSTICS
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An informative usage message appears if you run a crontab with a faulty
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command defined in it.
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.SH AUTHOR
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.MT vixie@isc.org
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Paul Vixie
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.ME
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.br
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.MT colin@colin-dean.org
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Colin Dean
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.ME
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