CRONTAB(5) FreeBSD File Formats Manual CRONTAB(5)
NAME
crontab - tables for driving cron
DESCRIPTION
A crontab file contains instructions to the cron(8) daemon of the general
form: ``run this command at this time on this date''. Each user has
their own crontab, and commands in any given crontab will be executed as
the user who owns the crontab. Uucp and News will usually have their own
crontabs, eliminating the need for explicitly running su(1) as part of a
cron command.
Blank lines and leading spaces and tabs are ignored. Lines whose first
non-space character is a pound-sign (#) are comments, and are ignored.
Note that comments are not allowed on the same line as cron commands,
since they will be taken to be part of the command. Similarly, comments
are not allowed on the same line as environment variable settings.
An active line in a crontab will be either an environment setting or a
cron command. An environment setting is of the form,
name = value
where the spaces around the equal-sign (=) are optional, and any
subsequent non-leading spaces in value will be part of the value assigned
to name. The value string may be placed in quotes (single or double, but
matching) to preserve leading or trailing blanks. The name string may
also be placed in quote (single or double, but matching) to preserve
leading, trailing or inner blanks.
Several environment variables are set up automatically by the cron(8)
daemon. SHELL is set to /bin/sh, and LOGNAME and HOME are set from the
/etc/passwd line of the crontab's owner. In addition, the environment
variables of the user's login class will be set from /etc/login.conf.db
and ~/.login_conf. (A setting of HOME in the login class will override
the value from /etc/passwd, but will not change the current directory
when the command is invoked, which can only be overridden with an
explicit setting of HOME within the crontab file itself.) If PATH is not
set by any other means, it is defaulted to
/sbin:/bin:/usr/sbin:/usr/bin:/usr/local/sbin:/usr/local/bin. HOME, PATH
and SHELL, and any variables set from the login class, may be overridden
by settings in the crontab; LOGNAME may not.
(Another note: the LOGNAME variable is sometimes called USER on BSD
systems... On these systems, USER will be set also).
If cron(8) has any reason to send mail as a result of running commands in
``this'' crontab, it will respect the following settings which may be
defined in the crontab (but which are not taken from the login class).
If MAILTO is defined (and non-empty), mail is sent to the user so named.
If MAILFROM is defined (and non-empty), its value will be used as the
from address. MAILTO may also be used to direct mail to multiple
recipients by separating recipient users with a comma. If MAILTO is
defined but empty (MAILTO=""), no mail will be sent. Otherwise mail is
sent to the owner of the crontab. This option is useful if you decide on
/bin/mail instead of /usr/lib/sendmail as your mailer when you install
cron -- /bin/mail does not do aliasing, and UUCP usually does not read
its mail.
The format of a cron command is very much the V7 standard, with a number
of upward-compatible extensions. Each line has five time and date
fields, followed by a user name (with optional ``:<group>'' and
``/<login-class>'' suffixes) if this is the system crontab file, followed
by a command. Commands are executed by cron(8) when the minute, hour,
and month of year fields match the current time, and when at least one of
the two day fields (day of month, or day of week) matches the current
time (see ``Note'' below). cron(8) examines cron entries once every
minute. The time and date fields are:
field allowed values
----- --------------
minute 0-59
hour 0-23
day of month 1-31
month 1-12 (or names, see below)
day of week 0-7 (0 or 7 is Sun, or use names)
A field may be an asterisk (*), which always stands for ``first-last''.
Ranges of numbers are allowed. Ranges are two numbers separated with a
hyphen. The specified range is inclusive. For example, 8-11 for an
``hours'' entry specifies execution at hours 8, 9, 10 and 11.
Lists are allowed. A list is a set of numbers (or ranges) separated by
commas. Examples: ``1,2,5,9'', ``0-4,8-12''.
Step values can be used in conjunction with ranges. Following a range
with ``/<number>'' specifies skips of the number's value through the
range. For example, ``0-23/2'' can be used in the hours field to specify
command execution every other hour (the alternative in the V7 standard is
``0,2,4,6,8,10,12,14,16,18,20,22''). Steps are also permitted after an
asterisk, so if you want to say ``every two hours'', just use ``*/2''.
Names can also be used for the ``month'' and ``day of week'' fields. Use
the first three letters of the particular day or month (case does not
matter). Ranges or lists of names are not allowed.
The ``sixth'' field (the rest of the line) specifies the command to be
run. One or more command options may precede the command to modify
processing behavior. The entire command portion of the line, up to a
newline or % character, will be executed by /bin/sh or by the shell
specified in the SHELL variable of the cronfile. Percent-signs (%) in
the command, unless escaped with backslash (\), will be changed into
newline characters, and all data after the first % will be sent to the
command as standard input.
The following command options can be supplied:
-n No mail is sent after a successful run. The execution output
will only be mailed if the command exits with a non-zero exit
code. The -n option is an attempt to cure potentially copious
volumes of mail coming from cron(8).
-q Execution will not be logged.
Duplicate options are not allowed.
Note: The day of a command's execution can be specified by two fields --
day of month, and day of week. If both fields are restricted (ie, are
not *), the command will be run when either field matches the current
time. For example, ``30 4 1,15 * 5'' would cause a command to be run at
4:30 am on the 1st and 15th of each month, plus every Friday.
Instead of the first five fields, a line may start with `@' symbol
followed either by one of eight special strings or by a numeric value.
The recognized special strings are:
string meaning
------ -------
@reboot Run once, at startup of cron.
@yearly Run once a year, "0 0 1 1 *".
@annually (same as @yearly)
@monthly Run once a month, "0 0 1 * *".
@weekly Run once a week, "0 0 * * 0".
@daily Run once a day, "0 0 * * *".
@midnight (same as @daily)
@hourly Run once an hour, "0 * * * *".
@every_minute Run once a minute, "*/1 * * * *".
@every_second Run once a second.
The `@' symbol followed by a numeric value has a special notion of
running a job that many seconds after completion of the previous
invocation of the job. Unlike regular syntax, it guarantees not to
overlap two or more invocations of the same job during normal cron
execution. Note, however, that overlap may occur if the job is running
when the file containing the job is modified and subsequently reloaded.
The first run is scheduled for the specified number of seconds after cron
is started or the crontab entry is reloaded.
EXAMPLE CRON FILE
# use /bin/sh to run commands, overriding the default set by cron
SHELL=/bin/sh
# mail any output to `paul', no matter whose crontab this is
MAILTO=paul
#
# run five minutes after midnight, every day
5 0 * * * $HOME/bin/daily.job >> $HOME/tmp/out 2>&1
# run at 2:15pm on the first of every month -- output mailed to paul
15 14 1 * * $HOME/bin/monthly
# run at 10 pm on weekdays, annoy Joe
0 22 * * 1-5 mail -s "It's 10pm" joe%Joe,%%Where are your kids?%
23 0-23/2 * * * echo "run 23 minutes after midn, 2am, 4am ..., everyday"
5 4 * * sun echo "run at 5 after 4 every sunday"
# run at 5 minutes intervals, no matter how long it takes
@300 svnlite up /usr/src
# run every minute, suppress logging
* * * * * -q date
# run every minute, only send mail if ping fails
* * * * * -n ping -c 1 freebsd.org
SEE ALSO
crontab(1), cron(8)
EXTENSIONS
When specifying day of week, both day 0 and day 7 will be considered
Sunday. BSD and ATT seem to disagree about this.
Lists and ranges are allowed to co-exist in the same field. "1-3,7-9"
would be rejected by ATT or BSD cron -- they want to see "1-3" or "7,8,9"
ONLY.
Ranges can include "steps", so "1-9/2" is the same as "1,3,5,7,9".
Names of months or days of the week can be specified by name.
Environment variables can be set in the crontab. In BSD or ATT, the
environment handed to child processes is basically the one from /etc/rc.
Command output is mailed to the crontab owner (BSD cannot do this), can
be mailed to a person other than the crontab owner (SysV cannot do this),
or the feature can be turned off and no mail will be sent at all (SysV
cannot do this either).
All of the `@' directives that can appear in place of the first five
fields are extensions.
Command processing can be modified using command options. The `-q'
option suppresses logging. The `-n' option does not mail on successful
run.
AUTHORS
Paul Vixie <paul@vix.com>
BUGS
If you are in one of the 70-odd countries that observe Daylight Savings
Time, jobs scheduled during the rollback or advance may be affected if
cron(8) is not started with the -s flag. In general, it is not a good
idea to schedule jobs during this period if cron(8) is not started with
the -s flag, which is enabled by default. See cron(8) for more details.
For US timezones (except parts of AZ and HI) the time shift occurs at 2AM
local time. For others, the output of the zdump(8) program's verbose
(-v) option can be used to determine the moment of time shift.
FreeBSD 13.1-RELEASE-p6 March 29, 2020 FreeBSD 13.1-RELEASE-p6
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