2.11BSD#431 - /usr/man/cat5/crontab.0

CRONTAB(5)          UNIX Programmer's Manual           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 cron-
     tabs, 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 pound-sign (#) are com-
     ments, 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.  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 lead-
     ing or trailing blanks.

     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 may be overridden by settings in the
     crontab; LOGNAME may not.

     (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.  If
     MAILTO is defined but empty (MAILTO=""), no mail will be
     sent.  Otherwise mail is sent to the owner of the crontab.
     This option is useful if you decide on /bin/mail instead of
     /usr/lib/sendmail as your mailer when you install cron --
     /bin/mail doesn't do aliasing, and UUCP usually doesn't read
     its mail.


Printed 11/26/99         24 January 1994                        1


CRONTAB(5)          UNIX Programmer's Manual           CRONTAB(5)


     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 user name if
     this is the system crontab file, followed by a command.
     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   0-31
          month          0-12 (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.  Follow-
     ing 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 permit-
     ted 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 cron-
     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.


Printed 11/26/99         24 January 1994                        2


CRONTAB(5)          UNIX Programmer's Manual           CRONTAB(5)


     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 (ie, 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.

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
     #
     # 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"

SEE ALSO
     cron(8), crontab(1)

EXTENSIONS
     When specifying day of week, both day 0 and day 7 will be
     considered Sunday.  BSD and ATT 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 ATT 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".

     Names of months or days of the week can be specified by
     name.

     Environment variables can be set in the crontab.  In BSD or
     ATT, 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).

AUTHOR
     Paul Vixie <paul@vix.com>


Printed 11/26/99         24 January 1994                        3