CRONTAB(5)							   File Formats 							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 following 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
       not processed.  Note that comments are not allowed on the same line as cron commands, since they are considered	a  part  of  the  command.
       Similarly, comments are not allowed on the same line as environment variable 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 overridden 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 com-
       mands 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 MAILFROM 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 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)).   Dif-
       ferent  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 table.  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
       information 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 particular SELinux security context in which you want jobs to be
       run.  crond will then set the execution context of those jobs that meet the specifications of the particular security  context.	 For  more
       information, see 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.

       The format of a cron command is similar to the V7 standard, with a number 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.  Similarly, times that occur more than once (again,  during  the  daylight
       savings 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

       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 specify 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.

       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 following 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,  additionaly  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 main system crontab file.  /var/spool/cron/ a directory for storing crontabs defined by users.  /etc/cron.d/ a  directory  for
       storing system crontabs.

SEE ALSO

       cron(8), crontab(1)

EXTENSIONS

       These special time specification "nicknames" which replace the 5 initial 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 sym-
       linked 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>

cronie								    2012-11-22								CRONTAB(5)