crontab(5)

NAME
     crontab - table of jobs to be performed by cron

SYNOPSIS
     /usr/lib/crontab
     /usr/local/lib/crontab
     /var/lib/crontab
     /var/opt/name/lib/crontab  (Minix-vmd only)
     /usr/spool/crontabs/user

DESCRIPTION
     The cron(8) daemon runs jobs at regular intervals.  These jobs are listed
     in  crontab  files.   The  format  of  entries in a crontab file are five
     fields of numbers specifying the minute (0-59), hour (0-23), day  of  the
     month  (1-31),  month  (1-12),  and day of the week (0-6 with 0 = Sunday)
     that a task must be executed.  The task to be executed follows as a shell
     command.

     The time numbers can be  given  as  a  comma  separated  list  of  simple
     numbers,  ranges  ("2-5"  is  the  same as "2,3,4,5"), and repeats ("2:5"
     means "2,7,12,17,22" in the hour field).  A repeat is cyclic affair, i.e.
     2:5  and 12:5 are the same thing.  A single "*" can be used in a field to
     indicate all valid numbers in that field, so it translates  to  "always".
     In  the  minute  field  you  can  use "?" for the current minute that the
     crontab file is loaded.  It can be used in  a  repeat,  i.e.  "?:10"  for
     every  10  minutes.   This  keeps  machines  with identical crontabs from
     executing tasks at exactly the same time, causing a burst of  traffic  if
     anything is done over a network.

     If a given time is valid in all five fields then a command  is  executed.
     Here are a few examples that illustrate the possibilities:

     # min hour mday mon wday command
        ?   3    *    *   *   /usr/etc/daily  # Daily system cleanup
        0   *    *    *   *   date            # Print date on the hour
       30   4    *    *  2-6  /var/etc/backup # After workdays on 4:30
        0   9   25   12   *   -u ast sing     # Andy sings on Xmas morning
        0   0   13    *   5   echo Beware!    # For the superstitious

     The command may optionally be prefixed by -u user to specify under  which
     user  the  command  should  be  run.  Commands from crontabs in the spool
     directory are always run under the id of the crontab's owner, the -u flag
     is ignored.

     A command can be placed on the same line as the time fields,  or  on  the
     next  line  indented  by  one  TAB character.  (A TAB, not eight spaces.)
     More TAB indented lines can be added for a multiline command.   The  tabs
     are  removed  from the command when passed to the shell.  If a command is
     put on the same line as the  time  fields  then  percent  characters  are
     changed  into newlines, this is not done for a TAB indented command.  The
     following three entries give the same output:

          0 12  *  *  *   echo 'Hello'; echo '  World!'
          #1
          0 12  *  *  *   echo 'Hello%  World!'  #2
          0 12  *  *  *        #3
                  cat <<EOF    #4
                  Hello
                    World!
                  EOF

     Comments start with a "#" character  and  continue  until  end  of  line.
     They, excess whitespace, and empty lines are ignored.  Of the comments in
     the example above #1 and #3 are ignored by cron, but #2 and  #4  are  not
     recognized  as comments, but are seen as part of a command and are passed
     to the shell who then happens to ignore them.  There is no interpretation
     of  command  characters  other  than the percent in a oneliner.  The time
     fields must all be on the same line.

FILES

     /usr/lib/crontab         Main Minix crontab file.

     /usr/local/lib/crontab   Local jobs for all systems in an organization.

     /var/lib/crontab         System specific jobs.

     /var/opt/name/lib/crontab
                              Per package jobs for Minix-vmd.

     /usr/lib/packages        List of installed packages.

     /usr/spool/crontabs/user Per user jobs.

SEE ALSO
     crontab(1), cron(8).

NOTES
     The "?" in the minute field, the repeat field (e.g. "2:5"), TAB  indented
     multiline   commands   and   the  -u  option  are  unique  to  this  cron
     implementation.  This doesn't mean you shouldn't use these features,  but
     just that you should be aware of the differences with other systems.  You
     are even advised to use these features and avoid  the  percent  hack  for
     multiline commands.

     Other crons allow one to specify input to a job in  some  way,  something
     this  cron  can't.   Simply  use  the << shell feature to do that.  Other
     crons often choke on empty lines.


     It is a common bug to use 0 for Sunday instead of  7.   This  cron,  like
     most other crons out there accepts this without comment.

     A job is not reissued until a previous instance of it  has  exited.   The
     next  time  to execute is computed from the previous time it ran.  If job
     issuing lags behind on the system time then the next time to  run  it  is
     computed from the current system time.

AUTHOR
     Kees J. Bot (kjb@cs.vu.nl)