CRON(8)                                                                                                                                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.  This  setting,  however,  does  not  affect the parsing of files under
               /etc/cron.hourly, /etc/cron.daily, /etc/cron.weekly or /etc/cron.monthly.

       -L loglevel
               Tell cron what to log about jobs (errors are logged regardless of this value) as the sum of the following values:

                   1      will log the start of all cron jobs

                   2      will log the end of all cron jobs

                   4      will log all failed jobs (exit status != 0)

                   8      will log the process number of all cron jobs

               The default is to log the start of all jobs (1). Logging will be disabled if levels is set to zero (0). A value of fifteen (15)
               will select all options.

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)).  In Debian, the content of /etc/crontab is
       predefined to run programs under /etc/cron.hourly, /etc/cron.daily,  /etc/cron.weekly  and  /etc/cron.monthly.  This  configuration  is
       specific to Debian, see the note under DEBIAN SPECIFIC below.  in order

       Additionally, in Debian, cron reads the files in the /etc/cron.d directory.  cron 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. This change is specific to Debian see the note
       under DEBIAN SPECIFIC below.

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

       /etc/crontab  and  the  files  in /etc/cron.d must be owned by root, and must not be group- or other-writable. In contrast to the spool
       area, the files under /etc/cron.d or the files under /etc/cron.hourly, /etc/cron.daily, /etc/cron.weekly and /etc/cron.monthly may also
       be symlinks, provided that both the symlink and the file it points to are owned by root.  The files under /etc/cron.d do not need to be
       executable, while the files under /etc/cron.hourly, /etc/cron.daily, /etc/cron.weekly and /etc/cron.monthly do, as they are run by run-
       parts (see run-parts(8) for more information).

       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 the /etc/crontab  file)  has  changed,
       and  if  it  has,  cron will then examine the modtime on all crontabs files 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.

       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.

DEBIAN SPECIFIC

       Debian introduces some changes to cron that were not originally available upstream. The most significant changes introduced are:

       —      Support for /etc/cron.{hourly,daily,weekly,monthly} via /etc/crontab,

       —      Support for /etc/cron.d (drop-in dir for package crontabs),

       —      PAM support,

       —      SELinux support,

       —      auditlog support,

       —      DST and other time-related changes/fixes,

       —      SGID crontab(1) instead of SUID root,

       —      Debian-specific file locations and commands,

       —      Debian-specific configuration (/etc/default/cron),

       —      numerous other smaller features and fixes.

       Support for /etc/cron.hourly, /etc/cron.daily, /etc/cron.weekly and /etc/cron.monthly is provided in Debian through the default setting
       of  the  /etc/crontab  file (see the system-wide example in crontab(5)).  The default sytem-wide crontab contains four tasks: run every
       hour, every day, every week and every month. Each of these tasks will execute run-parts providing each one of  the  directories  as  an
       argument. These tasks are disabled if anacron is installed (except for the hourly task) to prevent conflicts between both daemons.

       As  described  above,  the  files under these directories have to be pass some sanity checks including the following: be executable, be
       owned by root, not be writable by group or other and, if symlinks, point to files owned by root.  Additionally,  the  file  names  must
       conform  to  the  filename requirements of run-parts: they must be entirely made up of letters, digits and can only contain the special
       signs underscores ('_') and hyphens ('-'). Any file that does not conform to these requirements will not be executed by run-parts.  For
       example,  any  file  containing  dots will be ignored.  This is done to prevent cron from running any of the files that are left by the
       Debian package management system when handling files in /etc/cron.d/ as configuration files (i.e. files ending  in  .dpkg-dist,  .dpkg-
       orig, and .dpkg-new).

       This feature can be used by system administrators and packages to include tasks that will be run at defined intervals. Files created by
       packages in these directories should be named after the package that supplies them.

       Support for /etc/cron.d is included in the cron daemon itself, which handles this location as  the  system-wide  crontab  spool.   This
       directory  can  contain any file defining tasks following the format used in /etc/crontab, i.e. unlike the user cron spool, these files
       must provide the username to run the task as in the task definition.

       Files in this directory have to be owned by root, do not need to be executable (they are configuration files, just  like  /etc/crontab)
       and  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. This means that they cannot contain any dots.  If the -l option is specified to cron (this option can
       be  setup  through  /etc/default/cron,  see  below),  then  they  must  conform  to  the LSB namespace specification, exactly as in the
       --lsbsysinit option in run-parts.

       The  intended  purpose  of  this  feature  is  to  allow  packages  that  require  finer  control  of   their   scheduling   than   the
       /etc/cron.{hourly,daily,weekly,monthly}  directories to add a crontab file to /etc/cron.d. Such files should be named after the package
       that supplies them.

       Also, the default configuration of cron is controlled by /etc/default/cron which is read by the init.d script that  launches  the  cron
       daemon.  This file determines whether cron will read the system's environment variables and makes it possible to add additional options
       to the cron program before it is executed, either to configure its logging or to define how it will treat the files under /etc/cron.d.

SEE ALSO

       crontab(1), crontab(5), run-parts(8)

AUTHOR

       Paul Vixie <paul@vix.com> is the author of
       cron
       and original creator of this manual page. This page has also been modified for
       Debian by Steve Greenland, Javier Fernandez-Sanguino and Christian Kastner.
 

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