unixdev.net


Switch to SpeakEasy.net DSL

The Modular Manual Browser

Home Page
Manual: (OpenBSD-5.7)
Page:
Section:
Apropos / Subsearch:
optional field

CRONTAB(5)                  BSD File Formats Manual                 CRONTAB(5)

NAME
     crontab -- tables for driving cron

DESCRIPTION
     A crontab file contains instructions to the cron(8) daemon of the general
     form: ``at these times on these dates run this command''.  There may be a
     system crontab and each user may have their own crontab.  Commands in any
     given crontab will be executed either as the user who owns the crontab
     or, in the case of the system crontab, as the user specified on the com-
     mand line.

     While a crontab is a text file, it is not intended to be directly edited.
     Creation, modification, and removal of a crontab should be done using
     crontab(1).

     Blank lines, leading spaces, and tabs are ignored.  Lines whose first
     non-space character is a pound sign ('#') are comments, and are ignored.
     Note that comments are not allowed on the same line as cron(8) 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 is either an environment variable setting or
     a cron(8) command.

     Environment variable settings create the environment any command in the
     crontab is run in.  An environment variable setting is of the form:

           name = value

     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.

     Lines in the system crontab have six fixed fields plus a command, in the
     form:

           minute hour day-of-month month day-of-week user command

     While lines in a user crontab have five fixed fields plus a command, in
     the form:

           minute hour day-of-month month day-of-week command

     Fields are separated by blanks or tabs.  The command may be one or more
     fields long.  The allowed values for the fields are:

           field           allowed values
           minute          * or 0-59
           hour            * or 0-23
           day-of-month    * or 1-31
           month           * or 1-12 or a name (see below)
           day-of-week     * or 0-7 or a name (0 or 7 is Sunday)
           user            a valid username
           command         text

     Lists are allowed.  A list is a set of numbers (or ranges) separated by
     commas.  For example, ``1,2,5,9'' or ``0-4,8-12''.

     Ranges of numbers are allowed.  Ranges are two numbers separated with a
     hyphen.  The specified range is inclusive.  For example, 8-11 for an hour
     entry specifies execution at hours 8, 9, 10 and 11.

     Step values can be used in conjunction with ranges.  Following a range
     with /number specifies skips of number through the range.  For example,
     ``0-23/2'' can be used in the hour field to specify command execution
     every other hour.  Steps are also permitted after an asterisk, so to say
     ``every two hours'', just use ``*/2''.

     An asterisk ('*') is short form for a range of all allowed values.

     Names can be used in 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 command field (the rest of the line) is 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.  Percent signs ('%') 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.

     Commands are executed by cron(8) when the minute, hour, and month 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.

     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.

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

           string       meaning
           @reboot      Run once, at startup.
           @yearly      Run every January 1 (0 0 1 1 *).
           @annually    The same as @yearly.
           @monthly     Run the first day of every month (0 0 1 * *).
           @weekly      Run every Sunday (0 0 * * 0).
           @daily       Run every midnight (0 0 * * *).
           @midnight    The same as @daily.
           @hourly      Run every hour, on the hour (0 * * * *).

ENVIRONMENT
     HOME        Set from the user's /etc/passwd entry.  May be overridden by
                 settings in the crontab.

     LOGNAME     Set from the user's /etc/passwd entry.  May not be overridden
                 by settings in the crontab.

     MAILTO      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 is useful for pseudo-users that lack an
                 alias that would otherwise redirect the mail to a real per-
                 son.

     SHELL       Set to /bin/sh.  May be overridden by settings in the
                 crontab.

     USER        Set from the user's /etc/passwd entry.  May not be overridden
                 by settings in the crontab.

FILES
     /etc/crontab              System crontab.
     /var/cron/tabs/<user>     User crontab.

EXAMPLES
     # 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
     crontab(1), cron(8)

STANDARDS
     The crontab file format is compliant with the IEEE Std 1003.1-2008
     (``POSIX.1'') specification.  The behaviours described below are all
     extensions to that standard:

     -   The day-of-week field may use 7 to represent Sunday.

     -   Ranges may include ``steps''.

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

     -   Environment variables can be set in a crontab.

     -   Command output can be mailed to a person other than the crontab
         owner, or the feature can be turned off and no mail will be sent at
         all.

     -   All of the '@' commands that can appear in place of the first five
         fields.

AUTHORS
     crontab was written by Paul Vixie <vixie@isc.org>.

BSD                             March 30, 2017                             BSD