    CRON(VIII)                   10/25/74                  CRON(VIII)

    NAME
         cron - clock daemon

    SYNOPSIS
         /etc/cron

    DESCRIPTION
         Cron  executes commands at specified dates and times accord-
         ing to the instructions in the file /usr/lib/crontab.  Since
         cron  never exits, it should only be executed once.  This is
         best done by running cron from  the  initialization  process
         through the file /etc/rc; see init(VIII).

         Crontab  consists  of  lines of six fields each.  The fields
         are separated by spaces or tabs.  The first five are integer
         patterns  to  specify the minute (0-59), hour (0-23), day of
         the month (1-31), month of the year (1-12), and day  of  the
         week  (1-7  with 1=monday).  Each of these patterns may con-
         tain a number in the range above; two numbers separated by a
         minus meaning a range inclusive; a list of numbers separated
         by commas meaning any of the numbers; or an asterisk meaning
         all  legal values.  The sixth field is a string that is exe-
         cuted by the Shell at the specified times.  A percent  char-
         acter  in  this field is translated to a new-line character.
         Only the first line (up to a % or end of line) of  the  com-
         mand  field  is  executed by the Shell.  The other lines are
         made available to the command as standard input.

         Crontab is examined by cron every hour.  Thus it could  take
         up  to  an  hour for entries to become effective.  If it re-
         ceives a hangup signal, however, the table is examined imme-
         diately; so `kill -1 ...' can be used.

    FILES
         /usr/lib/crontab

    SEE ALSO
         init(VIII), sh(I), kill(I)

    DIAGNOSTICS
         None - illegal lines in crontab are ignored.

    BUGS
         A  more  efficient algorithm could be used.  The overhead in
         running cron is about one percent of the machine,  exclusive
         of any commands executed.

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