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NAME    [Toc]    [Back]

       cron - daemon to execute scheduled commands (Vixie Cron)

SYNOPSIS    [Toc]    [Back]


DESCRIPTION    [Toc]    [Back]

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

       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  different	format
       (see  crontab(5)).   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 output 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 modified.  Note that the crontab(1) command updates the modtime
       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 immediately.

DEBIAN SPECIFIC    [Toc]    [Back]

       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 purpose 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(8): 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    [Toc]    [Back]

       crontab(1), crontab(5)

AUTHOR    [Toc]    [Back]

       Paul Vixie <paul@vix.com>

4th Berkeley Distribution      20 December 1993 		       CRON(8)
[ Back ]
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