CRON(8) cron User Manual CRON(8)
NAME
cron - daemon to execute scheduled commands (Vixie Cron)
SYNOPSIS
cron [-f] [-l] [-L loglevel] [-n fqdn] [-x debugflags]
cron [-N]
DESCRIPTION
cron is directly invoked by systemd(1) 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.
-n fqdn
Include the FQDN in the subject when sending mails. By default, cron
will abbreviate the hostname.
-N
Run cron jobs Now, immediately, and exit. This option is useful to
perform tests.
-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 loglevel is set to zero (0). A value of fifteen (15)
will select all options.
-x debugflags
Tell cron to be more verbose and output debugging information;
debugflags is the sum of those values:
1
"ext": ...
2
"sch": ...
4
"proc": ...
8
"pars": ...
16
"load": ..
32
"misc": ...
64
"test": ...
128
"bit": ...
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(1) 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.
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. The system administrator may create cron jobs in
/etc/cron.d/ with file names like "local" or "local-foo".
/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) from the owner of the crontab (or from the email address
given in the MAILFROM 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(1)
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 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/localtime 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 system-wide crontab contains four tasks: run every hour, every
day, every week and every month. Each of these tasks will execute run-
parts(8) providing each one of the directories as an argument. These
tasks are disabled if anacron(8) is installed (except for the hourly
task) to prevent conflicts between both daemons.
As described above, the files under these directories have to 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(8): 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(8). 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, .dpkg-old, 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(8).
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)
AUTHORS
Paul Vixie <paul@vix.com>
Wrote this manpage (1994).
Steve Greenland <stevegr@debian.org>
Maintained the package (1996-2005).
Javier Fernández-Sanguino Peña <jfs@debian.org>
Maintained the package (2005-2014).
Christian Kastner <ckk@debian.org>
Maintained the package (2010-2016).
Georges Khaznadar <georgesk@debian.org>
Maintained the package (2022-2024).
COPYRIGHT
Copyright © 1994 Paul Vixie
Distribute freely, except: don't remove my name from the source or
documentation (don't take credit for my work), mark your changes (don't
get me blamed for your possible bugs), don't alter or remove this
notice. May be sold if buildable source is provided to buyer. No
warranty of any kind, express or implied, is included with this
software; use at your own risk, responsibility for damages (if any) to
anyone resulting from the use of this software rests entirely with the
user.
Since year 1994, many modifications were made in this manpage, authored
by Debian Developers which maintained cron; above is a short list, more
information can be found in the file /usr/share/doc/cron/copyright.
cron 06/13/2025 CRON(8)
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