CRON(N)                                                   CRON(N)



NAME
       cron - daemon to execute scheduled commands (Vixie Cron)

SYNOPSIS
       cron

DESCRIPTION
       cron is started automatically from /etc/init.d on entering
       multi-user runlevels.

       cron searches its  spool  area  (/var/spool/cron/crontabs)
       for  crontab  files  (which  are  named  after accounts in
       /etc/passwd); crontabs found are loaded into memory.  Note
       that  crontabs  in  this  directory should not be accessed
       directly - the crontab command should be  used  to  access
       and update them.

       cron  also reads /etc/crontab, which is in a slightly dif-
       ferent format (see crontab(b)).  Additionally, cron  reads
       the  files in /etc/cron.d; see the DEBIAN SPECIFIC section
       below for more details.

       cron then wakes up  every  minute,  examining  all  stored
       crontabs, checking each command to see if it should be run
       in the current minute.  When executing commands, any  out-
       put  is mailed to the owner of the crontab (or to the user
       named in the MAILTO environment variable in  the  crontab,
       if  such  exists).   The  children  copies of cron running
       these processes has its name coerced to uppercase, as will
       be seen in the syslog and ps output.

       Additionally,  cron checks each minute to see if its spool
       directory's modtime (or the modtime on  /etc/crontab)  has
       changed, and if it has, cron will then examine the modtime
       on all crontabs and reload those which have changed.  Thus
       cron need not be restarted whenever a crontab file is mod-
       ified.  Note that the crontab(b) command updates the  mod-
       time of the spool directory whenever it changes a crontab.

       Special considerations exist when the clock is changed  by
       less than 3 hours, for example at the beginning and end of
       daylight savings time. If the  time  has  moved  forwards,
       those  jobs  which  would  have  run  in the time that was
       skipped will be run soon after the change.  Conversely, if
       the  time  has moved backwards by less than 3 hours, those
       jobs that fall into the repeated time will not be  re-run.

       Only  jobs that run at a particular time (not specified as
       @hourly, nor with '*' in the hour or minute specifier) are
       affected.  Jobs which are specified with wildcards are run
       based on the new time immediately.

       Clock changes of more than 3 hours are  considered  to  be
       corrections to the clock, and the new time is used immedi-
       ately.

DEBIAN SPECIFIC
       cron treats the files in /etc/cron.d as extensions to  the
       /etc/crontab  file (they follow the special format of that
       file, i.e. they include the user field). The intended pur-
       pose  of  this  feature  is to allow packages that require
       finer   control   of    their    scheduling    than    the
       /etc/cron.{daily,weekly,monthly}  directories allow to add
       a crontab file to /etc/cron.d. Such files should be  named
       after  the  package that supplies them. Files must conform
       to the same naming convention  as  used  by  run-parts(s):
       they must consist solely of upper- and lower-case letters,
       digits, underscores, and hyphens. Like  /etc/crontab,  the
       files  in  the  /etc/cron.d  directory  are  monitored for
       changes.

SEE ALSO
       crontab(b), crontab(b)

AUTHOR
       Paul Vixie <paul@vix.com>



                         20 December 1993                 CRON(N)