Provided by: cron_3.0pl1-128ubuntu2_amd64 bug

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. The  maximum
       permitted length for the command field is 998 characters.

       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 * * *  root  test -x /usr/sbin/anacron || ( cd / && run-parts --report /etc/cron.daily )
       47 6 * * 7  root  test -x /usr/sbin/anacron || ( cd / && run-parts --report /etc/cron.weekly )
       52 6 1 * *  root  test -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.