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NAME    [Toc]    [Back]

     crontab - tables for driving cron

DESCRIPTION    [Toc]    [Back]

     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 (/etc/crontab) and each user may  have  their
own crontab
     (/var/cron/tabs/<user>).  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 in the command line.  Uucp
and News will
     usually each have their own crontab,  eliminating  the  need
for explicitly
     running su(1) as part of a cron(8) command.

     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

     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

     An active line in a crontab is either an  environment  variable setting or
     a cron(8) command.

     Environment Variable Settings

     Environment  variable  settings  create  the environment any
command in the
     crontab is run in.  An environment variable  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.

     Several environment variables are set 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.

     Note:  on  BSD  systems  the  LOGNAME  variable is sometimes
called USER.  On
     OpenBSD, cron(8) will set both USER and LOGNAME to the  same

     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 for pseudo-users that lack  an  alias  that
would otherwise
     redirect the mail to a real person.

     cron Commands

     The  format  of  a cron(8) command is very much the V7 standard, with a number
 of upward-compatible extensions.  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

     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.  Examples: ``1,2,5,9'', ``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 (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''.

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

     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
     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

     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, see Note below) match the current
time.  cron(8)
     examines crontab entries once every minute.

     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
     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 cron(8) startup.
           @yearly    Run every January 1, "0 0 1 1 *".
           @annually  (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  (same as @daily).
           @hourly    Run every hour, on the hour, "0 * * * *".

EXAMPLES    [Toc]    [Back]

     # use /bin/sh to run commands, no  matter  what  /etc/passwd
     # mail any output to `paul', no matter whose crontab this is
     # 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
     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    [Toc]    [Back]

     crontab(1), cron(8)

EXTENSIONS    [Toc]    [Back]

     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 coexist in the  same  field.
     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

     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).

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

AUTHORS    [Toc]    [Back]

     Paul Vixie <vixie@isc.org>

OpenBSD      3.6                           June      8,      1999
[ Back ]
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