Provided by: cron_3.0pl1-134ubuntu1_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
       or tilde(~) expansion, thus lines like

           PATH = $HOME/bin:$PATH
           PATH = ~/bin:/usr/bin:/bin

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

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

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

       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 – 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)).  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., don't start with *), 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"
       0 */4 1 * mon   echo "run every 4th hour on the 1st and on every Monday"
       0 0 */2 * sun   echo "run at midn on every Sunday that's an uneven date"
       # Run on every second Saturday of the month
       0 4 8–14 * *    test $(date +\%u) -eq 6 && echo "2nd Saturday"

       All the above examples run non-interactive programs.  If you wish to run  a  program  that
       interacts  with  the  user's desktop you have to make sure the proper environment variable
       DISPLAY is set.

       # Execute a program and run a notification every day at 10:00 am
       0 10 * * *  $HOME/bin/program | DISPLAY=:0 notify-send "Program run" "$(cat)"

EXAMPLE SYSTEM CRON FILE

       The following lists the content of a regular system-wide crontab file.   Unlike  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

       # Example of job definition:
       # .---------------- minute (0 - 59)
       # |  .------------- hour (0 - 23)
       # |  |  .---------- day of month (1 - 31)
       # |  |  |  .------- month (1 - 12) OR jan,feb,mar,apr ...
       # |  |  |  |  .---- day of week (0 - 6) (Sunday=0 or 7) OR sun,mon,tue,wed,thu,fri,sat
       # |  |  |  |  |
       # 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 )
       #

       Note  that all the system-wide tasks will run, by default, from 6 am to 7 am.  In the case
       of systems that are not powered on during that period of time, only the hourly tasks  will
       be executed unless the defaults above are changed.

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.

       POSIX specifies that the day of month and the day of week fields both need  to  match  the
       current  time  if  either of them is a *.  However, this implementation only checks if the
       first character is a *.  This is why "0 0 */2 * sun" runs every Sunday  that's  an  uneven
       date while the POSIX standard would have it run every Sunday and on every uneven date.

       The  crontab  syntax  does  not  make  it  possible to define all possible periods one can
       imagine.  For example, it is not straightforward to define the last weekday  of  a  month.
       To  have a task run in a time period that cannot be defined using crontab syntax, 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   [ "$(date +\%e)" = "$(LANG=C ncal | sed -n 's/^Sa .* \([0–9]\+\) *$/\x1/p')" ] && 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 (i.e. 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,
       Christian Kastner and Christian Pekeler.