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  any-
     thing 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 com-
     ments, 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 3 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 pre-
     vious 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)