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CRONTAB(5)		     Cronie Users' Manual		    CRONTAB(5)

NAME
       crontab - files used to schedule the execution of programs

DESCRIPTION
       A crontab file contains instructions for the cron(8) daemon in the fol‐
       lowing simplified manner: "run this command at this time on this date".
       Each  user  can define their own crontab. Commands defined in any given
       crontab are executed under the user who owns that  particular  crontab.
       Uucp and News usually have their own crontabs, eliminating the need for
       explicitly running su(1) as part of a cron command.

       Blank lines, leading spaces, and tabs are ignored.  Lines  whose	 first
       non-white  space	 character  is	a pound-sign (#) are comments, and are
       note processed.	Note that comments are not allowed on the same line as
       cron  commands, since they are considered a part of the command.	 Simi‐
       larly, comments are not allowed on the same line as  environment	 vari‐
       able settings.

       An  active line in a crontab is either an environment setting or a cron
       command.	 An environment setting is of the form:

	  name = value

       where the white spaces around the equal-sign (=) are optional, and  any
       subsequent  non-leading	white  spaces  in value is a 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 white spaces.

       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 can be over‐
       ridden by settings in the crontab; LOGNAME can not.

       (Note: the LOGNAME variable is sometimes called USER on BSD systems and
       is also automatically set).

       In  addition  to	 LOGNAME, HOME, and SHELL, cron(8) looks at the MAILTO
       variable if a mail needs to be send as a result of running any commands
       in that particular crontab.  If MAILTO is defined (and non-empty), mail
       is sent to the specified address.   If  MAILTO  is  defined  but	 empty
       (MAILTO=""),  no mail is sent.  Otherwise, mail is sent to the owner of
       the crontab.  This option is useful if  you  decide  to	use  /bin/mail
       instead	of  /usr/lib/sendmail as your mailer. Note that /bin/mail does
       not provide aliasing and UUCP usually does not read its mail. If	 MAIL‐
       FROM  is	 defined  (and	non-empty),  it is used as the envelope sender
       address, otherwise, ``root'' is used.

       By default, cron sends a	 mail  using  the  '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 - i.e. either the default
       system  locale, if no LC_* environment variables are set, or the locale
       specified by the LC_* environment variables (see locale(7)).  Different
       character encodings can be used for mailing cron job outputs by setting
       the CONTENT_TYPE and CONTENT_TRANSFER_ENCODING variables in  a  crontab
       to the correct values of the mail headers of those names.

       The  CRON_TZ variable specifies the time zone specific for the cron ta‐
       ble.  The user should enter a time according to the specified time zone
       into  the  table.   The	time used for writing into a log file is taken
       from the local time zone, where the daemon is 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  different roles or in different security levels.  For more informa‐
       tion about roles and SELinux MLS/MCS, see selinux(8)  and  the  crontab
       example	mentioned  later  on  in this text.  You can set the MLS_LEVEL
       variable to the SELinux security context string specifying the particu‐
       lar  SELinux  security context in which you want jobs to be run.	 crond
       will then set the execution context of those jobs that meet the	speci‐
       fications  of  the  particular security context.	 For more information,
       see crontab(1) -s option.

       The format of a cron command is similar to the V7 standard, with a num‐
       ber  of upward-compatible extensions.  Each line has five time-and-date
       fields followed by a username (if this is the system crontab file), and
       followed	 by  a	command.  Commands  are	 executed  by cron(8) when the
       'minute', 'hour', and 'month of the  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	 the  "missing
       hours"  during  the daylight savings time conversion, will never match,
       causing jobs scheduled during the "missing times" not to be run.	 Simi‐
       larly, times that occur more than once (again, during the daylight sav‐
       ings time conversion) will cause matching jobs to be run twice.

       cron(8) examines cron entries 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 Sunday, or use names)

       A  field	 may  contain  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  "/<number>"  specifies  skips  of	the number's value through the
       range.  For example, "0-23/2" can be used in the 'hours' field to spec‐
       ify  command  execution for every other hour (the alternative in the V7
       standard is "0,2,4,6,8,10,12,14,16,18,20,22").  Step  values  are  also
       permitted after an asterisk, so if specifying a job to be run every two
       hours, you can 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 does not
       matter).	 Ranges or lists of names are not allowed.

       If the uid of the owner is 0 (root), he can put a "-" as first  charac‐
       ter  of	a crontab entry.  This will prevent cron from writing a syslog
       message about this command getting executed.

       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 a "%"
       character, will be executed by /bin/sh or by the shell specified in the
       SHELL variable of the cronfile.	A "%" character in the command, unless
       escaped with a 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 in the  follow‐
       ing two fields — 'day of month', and 'day of week'.  If both fields are
       restricted (i.e., do not contain the "*" character), 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 and /etc/crontab are system  jobs,  which  are  used
       usually for more than one user, thus, the username is needed. MAILTO on
       the first line is optional.

EXAMPLE OF A 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 a crontab, it is important to specify a 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. When using crontab
       in the MLS mode, it is especially important to:
       - check/change the 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

FILES
       /etc/crontab  system  crontab  file  for	 jobs like cron.daily, weekly,
       monthly.	 /var/spool/cron/ a directory for storing crontabs defined  by
       users.  /etc/cron.d/ a directory for storing system crontables.

SEE ALSO
       cron(8), crontab(1)

EXTENSIONS
       These  special  time specification "nicknames" which replace the 5 ini‐
       tial time and date fields, and are prefixed with the '@' character, are
       supported:
       @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
       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 -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.

AUTHOR
       Paul Vixie <vixie@isc.org>

Marcela Mašláňová		   July 2010			    CRONTAB(5)
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