CRON(8) 						      System Manager's Manual							   CRON(8)

NAME

       cron - daemon to execute scheduled commands (Vixie Cron)

SYNOPSIS

       cron [-f] [-l] [-L loglevel]

DESCRIPTION

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

OPTIONS

       -f      Stay in foreground mode, don't daemonize.

       -l      Enable LSB compliant names for /etc/cron.d files

       -L loglevel
	       Sets  the  loglevel  for  cron.	The standard logging level (1) will log the start of all the cron jobs. A higher loglevel (2) will
	       cause cron to log also the end of all cronjobs, which can be useful to audit the behaviour of tasks run by cron.  Logging  will	be
	       disabled if the loglevel is set to zero (0).

NOTES

       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:
       it treats the files in /etc/cron.d as in the same way as the /etc/crontab file (they follow the special format  of  that  file,	i.e.  they
       include	the  user  field).  However, they are independent of /etc/crontab: they do not, for example, inherit environment variable settings
       from it. 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  to add a crontab file to /etc/cron.d. Such files should be named after the package that sup-
       plies 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.  If  the	-l option is specified, then they must conform to the LSB namespace specification,
       exactly as in the --lsbsysinit option in run-parts.

       Like /etc/crontab, the files in the /etc/cron.d directory are monitored for changes. In general, the admin should not use /etc/cron.d/, but
       use the standard system crontab /etc/crontab.

       In  contrast to the spool area, files in /etc/cron.d may be symlinks, provided that both the symlink and the file it points to are owned by
       root.

       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 have their 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.   Con-
       versely, 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.

       cron logs its action to the syslog facility 'cron', and logging may be controlled using the standard syslogd(8) facility.

ENVIRONMENT

       If configured in /etc/default/cron in Debian systems, the cron daemon localisation settings environment can be managed through the  use	of
       /etc/environment  or  through the use of /etc/default/locale with values from the latter overriding values from the former. These files are
       read and they will be used to setup the LANG, LC_ALL, and LC_CTYPE environment variables. These variables are then used to set the  charset
       of mails, which defaults to 'C'.

       This  does  NOT affect the environment of tasks running under cron. For more information on how to modify the environment of tasks, consult
       crontab(5).

       The daemon will use, if present, the definition from /etc/timezone for the timezone.

       The environment can be redefined in user's crontab definitions but cron will only handle tasks in a single timezone.

SEE ALSO

       crontab(1), crontab(5)

AUTHOR

       Paul Vixie <paul@vix.com>

4th Berkeley Distribution					   19 April 2010							   CRON(8)