CRONTAB(5)                                                                                                                          CRONTAB(5)

NAME

       crontab - tables for driving cron

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 hash-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 environment variable settings.

       An active line in a crontab will be either an environment setting or a cron command.  The crontab file is parsed from top to bottom, so
       any environment settings will affect only the cron commands below them in the file.  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. To
       define an empty variable, quotes must be used. The value string is  not  parsed  for  environmental  substitutions  or  replacement  of
       variables, thus lines like

           PATH = $HOME/bin:$PATH

       will not work as you might expect. And neither will this work

           A=1
           B=2
           C=$A $B

       There will not be any subsitution for the defined variables in the last value.

       An alternative for setting up the commands path is using the fact that many shells will treat the tilde(~) as substitution of $HOME, so
       if you use bash for your tasks you can use this:

            SHELL=/bin/bash
            PATH=~/bin:/usr/bin/:/bin

       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. PATH is set to "/usr/bin:/bin".  HOME, SHELL, and PATH may be overridden by settings
       in the crontab; LOGNAME is the user that the job is running from, and may not be changed.

       (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.  MAILTO may also be used to direct mail
       to multiple recipients by separating recipient users with a comma. If MAILTO is defined but empty (MAILTO=""), no mail  will  be  sent.
       Otherwise mail is sent to the owner of the crontab.

       On  the  Debian  GNU/Linux  system,  cron  supports  the  pam_env  module,  and loads the environment specified by /etc/environment and
       /etc/security/pam_env.conf.  It also reads locale information from /etc/default/locale.  However, the PAM settings do NOT override  the
       settings  described  above  nor  any  settings  in  the  crontab  file  itself.  Note  in particular that if you want a PATH other than
       "/usr/bin:/bin", you will need to set it in the crontab file.

       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_* environment 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 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 command, followed by a newline character ('\n').  The system crontab (/etc/crontab) uses the same format,
       except that the username for the command is specified after the time and date  fields  and  before  the  command.  The  fields  may  be
       separated by spaces or tabs.

       Commands  are  executed by cron(8) when the minute, hour, and month of year fields match the current time, and when at least one of the
       two day fields (day of month, or day of week) match the current time (see ``Note'' below).  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 ``/<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 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 executed by /bin/sh or by the shell specified in the SHELL variable of the crontab file.  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. There is no way to split a single command line onto multiple lines, like the shell's trailing "\".

       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
       (i.e., 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.  One  can,  however,
       achieve the desired result by adding a test to the command (see the last example in EXAMPLE CRON FILE below).

       Instead of the first five fields, one of eight special strings may appear:

              string         meaning
              ------         -------
              @reboot        Run once, at startup.
              @yearly        Run once a year, "0 0 1 1 *".
              @annually      (same as @yearly)
              @monthly       Run once a month, "0 0 1 * *".
              @weekly        Run once a week, "0 0 * * 0".
              @daily         Run once a day, "0 0 * * *".
              @midnight      (same as @daily)
              @hourly        Run once an hour, "0 * * * *".

       Please note that startup, as far as @reboot is concerned, is the time when the cron(8) daemon startup.  In particular, it may be before
       some system daemons, or other facilities, were startup.  This is due to the boot order sequence of the machine.

EXAMPLE CRON FILE

       The following lists an example of a user crontab file.

       # use /bin/bash to run commands, instead of the default /bin/sh
       SHELL=/bin/bash
       # mail any output to `paul', no matter whose crontab this is
       MAILTO=paul
       #
       # 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"
       # Run on every second Saturday of the month
       0 4 8-14 * *    test $(date +%u) -eq 6 && echo "2nd Saturday"

EXAMPLE SYSTEM CRON FILE

       The following lists the content of a regular system-wide crontab file. Unlinke a user's crontab, this file has the username  field,  as
       used by /etc/crontab.

       # /etc/crontab: system-wide crontab
       # Unlike any other crontab you don't have to run the `crontab'
       # command to install the new version when you edit this file
       # and files in /etc/cron.d. These files also have username fields,
       # that none of the other crontabs do.

       SHELL=/bin/sh
       PATH=/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin

       # m h dom mon dow usercommand
       17 *           * * *root    cd / && run-parts --report /etc/cron.hourly
       25 6           * * *roottest -x /usr/sbin/anacron || ( cd / && run-parts --report /etc/cron.daily )
       47 6           * * 7roottest -x /usr/sbin/anacron || ( cd / && run-parts --report /etc/cron.weekly )
       52 6           1 * *roottest -x /usr/sbin/anacron || ( cd / && run-parts --report /etc/cron.monthly )
       #

SEE ALSO

       cron(8), crontab(1)

EXTENSIONS

       When specifying day of week, both day 0 and day 7 will be considered Sunday.  BSD and AT&T 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 AT&T 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".

       Months or days of the week can be specified by name.

       Environment variables can be set in the crontab.  In BSD or AT&T, 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).

       All of the `@' commands that can appear in place of the first five fields are extensions.

LIMITATIONS

       The cron daemon runs with a defined timezone. It currently does not support per-user timezones. All the tasks: system's and user's will
       be  run based on the configured timezone. Even if a user specifies the TZ environment variable in his crontab this will affect only the
       commands executed in the crontab, not the execution of the crontab tasks themselves.

       The crontab syntax does not make it possible to define all possible periods one could image off. For example, it is not straightforward
       to  define  the  last  weekday of a month. If a task needs to be run in a specific period of time that cannot be defined in the crontab
       syntaxs the best approach would be to have the program itself check the date and time information and continue execution  only  if  the
       period matches the desired one.

       If  the  program itself cannot do the checks then a wrapper script would be required. Useful tools that could be used for date analysis
       are ncal or calendar For example, to run a program the last Saturday of every month you could use the following wrapper code:

       0 4 * * Sat   [ "$(date +%e)" = "`ncal | grep $(date +%a | sed  -e 's/.$//') | sed -e 's/^.*\s\([0-9]\+\)\s*$/\1/'`" ] && echo "Last Saturday" && program_to_run

DIAGNOSTICS

       cron requires that each entry in a crontab end in a newline character. If the last entry  in  a  crontab  is  missing  a  newline  (ie,
       terminated by EOF), cron will consider the crontab (at least partially) broken. A warning will be written to syslog.

AUTHOR

       Paul Vixie <paul@vix.com> is the author of
       cron
       and original creator of this manual page. This page has also been modified for
       Debian by Steve Greenland, Javier Fernandez-Sanguino and Christian Kastner.
 

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