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ANACRONTAB(5)                Cronie Users' Manual                ANACRONTAB(5)



NAME
       crontab - tables for driving cron (ISC Cron V4.1)

DESCRIPTION
       A  crontab  file  contains  instructions to the cron(8) daemon of the general form:
       "run this command at this time on this date".  Each user has their own crontab, and
       commands  in  any  given crontab will be executed as the user who owns the crontab.
       Uucp and News will usually have  their  own  crontabs,  eliminating  the  need  for
       explicitly running su(1) as part of a cron command.

       Blank  lines  and leading spaces and tabs are ignored.  Lines whose first non-space
       character is a pound-sign (#) are comments, and are ignored.   Note  that  comments
       are  not  allowed on the same line as cron commands, since they will be taken to be
       part of the command.  Similarly, comments are not allowed on the same line as envi-
       ronment variable settings.

       An  active  line  in a crontab will be either an environment setting or a cron com-
       mand.  An environment setting is of the form,

           name = value

       where the spaces around the equal-sign (=) are optional, and  any  subsequent  non-
       leading  spaces  in  value  will  be part of the value assigned to name.  The value
       string may be placed in quotes (single or double, but matching) to preserve leading
       or trailing blanks.

       Several  environment  variables  are  set  up  automatically by the cron(8) daemon.
       SHELL is set to /bin/sh, and LOGNAME and HOME are set from the /etc/passwd line  of
       the  crontab?s owner.  HOME and SHELL may be overridden by settings in the crontab;
       LOGNAME may not.

       (Another note: the LOGNAME variable is sometimes called USER on BSD systems...   on
       these systems, USER will be set also.)

       In  addition to LOGNAME, HOME, and SHELL, cron(8) will look at MAILTO if it has any
       reason to send mail as a result of running commands in "this" crontab.   If  MAILTO
       is  defined  (and  non-empty),  mail  is  sent  to the user so named.  If MAILTO is
       defined but empty (MAILTO=""), no mail will be sent.  Otherwise mail is sent to the
       owner  of the crontab.  This option is useful if you decide on /bin/mail instead of
       /usr/lib/sendmail as your mailer when you install  cron  --  /bin/mail  doesn?t  do
       aliasing,  and UUCP usually doesn?t read its mail. If MAILFROM is defined (and non-
       empty), it will be used as the envelope sender address, otherwise, ''root'' will be
       used.

       By  default,  cron  will  send  mail  using  the  mail  'Content-Type:'  header  of
       'text/plain' with the 'charset=' parameter set to the  charmap  /  codeset  of  the
       locale  in  which crond(8) is started up - ie. either the default system locale, if
       no LC_* environment variables are set, or the locale specified by the LC_* environ-
       ment  variables  (see  locale(7)).   You  can use different character encodings for
       mailed cron job output by setting the  CONTENT_TYPE  and  CONTENT_TRANSFER_ENCODING
       variables in crontabs, to the correct values of the mail headers of those names.

       The CRON_TZ specifies the time zone specific for the cron table. User type into the
       chosen table times in the time of the specified time zone. The  time  into  log  is
       taken from local time zone, where is the daemon running.

       The  MLS_LEVEL  environment  variable provides support for multiple per-job SELinux
       security contexts in the same crontab.  By default,  cron  jobs  execute  with  the
       default  SELinux  security context of the user that created the crontab file.  When
       using multiple security levels and roles, this may not be sufficient,  because  the
       same user may be running in a different role or at a different security level.  For
       more about roles and SELinux MLS/MCS  see  selinux(8)  and  undermentioned  crontab
       example.   You  can set MLS_LEVEL to the SELinux security context string specifying
       the SELinux security context in which you want the job to run, and crond  will  set
       the  execution context of the or jobs to which the setting applies to the specified
       context.  See also the crontab(1) -s option.

       The RANDOM_DELAY variable allows delaying job startups by random amount of  minutes
       with upper limit specified by the variable. The random scaling factor is determined
       during the cron daemon startup so it remains constant for the whole run time of the
       daemon.

       If  the  CRON_CORRECT_MAIL_HEADER environment variable is present regardless of its
       value, it will make crond to send e-mails with RFC2822 compliant From  field.  (Red
       Hat Enterprise Linux 6 only)

       The format of a cron command is very much the V7 standard, with a number of upward-
       compatible extensions.  Each line has five time and date fields, followed by a user
       name  if this is the system crontab file, followed by a command.  Commands are exe-
       cuted by cron(8) when the minute, hour, and month of year fields match the  current
       time,  and  at least one of the two day fields (day of month, or day of week) match
       the current time (see "Note" below).  Note that this means that non-existent times,
       such as "missing hours" during daylight savings conversion, will never match, caus-
       ing jobs scheduled during the "missing times" not to be run.  Similarly, times that
       occur  more than once (again, during daylight savings conversion) will cause match-
       ing jobs to be run twice.

       cron(8) examines cron entries once every minute.

       The time and date fields are:

              field          allowed values
              -----          --------------
              minute         0-59
              hour           0-23
              day of month   1-31
              month          1-12 (or names, see below)
              day of week    0-7 (0 or 7 is Sun, or use names)

       A field may be an asterisk (*), which always stands for "first-last".

       Ranges of numbers are allowed.  Ranges are two numbers  separated  with  a  hyphen.
       The specified range is inclusive.  For example, 8-11 for an "hours" entry specifies
       execution at hours 8, 9, 10 and 11.

       Lists are allowed.  A list is a set of numbers (or  ranges)  separated  by  commas.
       Examples: "1,2,5,9", "0-4,8-12".

       Step  values can be used in conjunction with ranges.  Following a range with "<num-
       ber>" specifies skips of the  number's  value  through  the  range.   For  example,
       "0-23/2"  can  be  used in the hours field to specify command execution every other
       hour (the alternative in  the  V7  standard  is  "0,2,4,6,8,10,12,14,16,18,20,22").
       Steps  are  also  permitted  after  an  asterisk,  so if you want to say "every two
       hours", just use "*/2".

       Names can also be used for the "month" and "day of week"  fields.   Use  the  first
       three  letters  of  the  particular  day or month (case doesn't matter).  Ranges or
       lists of names are not allowed.

       The "sixth" field (the rest of the line) specifies the  command  to  be  run.   The
       entire  command  portion  of the line, up to a newline or % character, will be exe-
       cuted by /bin/sh or by the shell specified in the SHELL variable of  the  cronfile.
       Percent-signs  (%)  in  the  command,  unless  escaped  with backslash (\), will be
       changed into newline characters, and all data after the first % will be sent to the
       command as standard input.

       Note:  The  day  of  a  command's execution can be specified by two fields -- day of
       month, and day of week.  If both fields are restricted (ie, aren't *), the  command
       will be run when either field matches the current time.  For example,
       "30  4  1,15 * 5" would cause a command to be run at 4:30 am on the 1st and 15th of
       each month, plus every Friday.

EXAMPLE CRON FILE
       # use /bin/sh to run commands, no matter what /etc/passwd says
       SHELL=/bin/sh
       # mail any output to 'paul', no matter whose crontab this is
       MAILTO=paul
       #
       CRON_TZ=Japan
       # run five minutes after midnight, every day
       5 0 * * *       $HOME/bin/daily.job >> $HOME/tmp/out 2>&1
       # run at 2:15pm on the first of every month -- output mailed to paul
       15 14 1 * *     $HOME/bin/monthly
       # run at 10 pm on weekdays, annoy Joe
       0 22 * * 1-5    mail -s "It's 10pm" joe%Joe,%%Where are your kids?%
       23 0-23/2 * * * echo "run 23 minutes after midn, 2am, 4am ..., everyday"
       5 4 * * sun     echo "run at 5 after 4 every sunday"

Jobs in /etc/cron.d/
       The jobs in cron.d are system jobs, which are used usually for more than one  user.
       That's  the  reason  why  is  name  of the user needed. MAILTO on the first line is
       optional.

EXAMPLE FOR JOB IN /etc/cron.d/job
       #login as root
       #create job with preferred editor (e.g. vim)
       MAILTO=root
       * * * * * root touch /tmp/file

SELinux with multi level security (MLS)
       In crontab is important specified security level by crontab -s  or  specifying  the
       required  level  on  the  first  line  of  the  crontab. Each level is specified in
       /etc/selinux/targeted/seusers. For using crontab in MLS mode is really important:
       - check/change actual role,
       - set correct role for directory, which is used for input/output.

EXAMPLE FOR SELINUX MLS
       # login as root
       newrole -r sysadm_r
       mkdir /tmp/SystemHigh
       chcon -l SystemHigh /tmp/SystemHigh
       crontab -e
       # write in crontab file
       MLS_LEVEL=SystemHigh
       0-59 * * * * id -Z > /tmp/SystemHigh/crontest
       When I log in as a normal user, it can't work, because /tmp/SystemHigh is
       higher than my level.

FILES
       /etc/anacrontab system crontab file for  jobs  like  cron.daily,  weekly,  monthly.
       /var/spool/cron/ usual place for storing users crontab.  /etc/cron.d/ stored system
       crontables.

SEE ALSO
       cron(8), crontab(1)

EXTENSIONS
       When specifying day of week, both day 0 and day 7 will be considered  Sunday.   BSD
       and ATT seem to disagree about this.

       Lists  and  ranges  are  allowed to co-exist in the same field.  "1-3,7-9" would be
       rejected by ATT or BSD cron -- they want to see "1-3" or "7,8,9" ONLY.

       Ranges can include "steps", so "1-9/2" is the same as "1,3,5,7,9".

       Names of months or days of the week can be specified by name.

       Environment variables can be set in the crontab.  In BSD or  ATT,  the  environment
       handed to child processes is basically the one from /etc/rc.

       Command output is mailed to the crontab owner (BSD can't do this), can be mailed to
       a person other than the crontab owner (SysV can't do this), or the feature  can  be
       turned off and no mail will be sent at all (SysV can't do this either).

       These  special  time  specification  "nicknames" are supported, which replace the 5
       initial time and date fields, and are prefixed by the '@' character:
       @reboot    :    Run once after reboot.
       @yearly    :    Run once a year, ie.  "0 0 1 1 *".
       @annually  :    Run once a year, ie.  "0 0 1 1 *".
       @monthly   :    Run once a month, ie. "0 0 1 * *".
       @weekly    :    Run once a week, ie.  "0 0 * * 0".
       @daily     :    Run once a day, ie.   "0 0 * * *".
       @hourly    :    Run once an hour, ie. "0 * * * *".

CAVEATS
       The crontab files have to be regular files or symlinks to regular files, they  must
       not  be executable or writable by anyone else than the owner.  This requirement can
       be overridden by using the -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 to reload the crontabs.  This is
       a limitation of inotify API.


AUTHOR
       Paul Vixie <vixie AT isc.org>



Marcela Maslanova                20 July 2009                    ANACRONTAB(5)

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