path: root/usr.sbin/cron/crontab.5

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.\" $OpenBSD: crontab.5,v 1.18 2003/02/20 20:38:08 millert Exp $
.\"
.Dd June 8, 1999
.Dt CRONTAB 5
.Os
.Sh NAME
.Nm crontab
.Nd tables for driving cron
.Sh DESCRIPTION
A
.Nm
file contains instructions to the
.Xr cron 8
daemon of the general form:
.Do
at these times on these dates run this command
.Dc .
There may be a system
.Nm
.Pf ( Pa /etc/crontab )
and each user may have their own
.Nm
.Pf ( Pa /var/cron/tabs/<user> ) .
Commands in any given
.Nm
will be
executed either as the user who owns the
.Nm
or, in the case of the system
.Nm crontab ,
as the user specified in the command line.
Uucp and News will usually each have
their own
.Nm crontab ,
eliminating the need for explicitly running
.Xr su 1
as part of a
.Xr cron 8
command.
.Pp
While a
.Nm
is a text file, it is not intended to be directly edited.
Creation, modification, and removal of a
.Nm
should be done using
.Xr crontab 1 .
.Pp
Blank lines, leading spaces, and tabs are ignored.
Lines whose first non-space character is a pound sign
.Pq Ql #
are comments, and are ignored.
Note that comments are not allowed on the same line as
.Xr cron 8
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.
.Pp
An active line in a
.Nm
is either an environment variable setting or a
.Xr cron 8
command.
.Pp
.Em Environment Variable Settings
.Pp
Environment variable settings create the environment
any command in the
.Nm
is run in.
An environment variable setting is of the form:
.Pp
.Dl name \&= value
.Pp
where the spaces around the equal-sign
.Pq Ql =
are optional, and any subsequent non-leading spaces in
.Fa value
will be part of the value assigned to
.Fa name .
The
.Fa value
string may be placed in quotes
.Pq single or double , but matching
to preserve leading or trailing blanks.
.Pp
Several environment variables are set automatically by the
.Xr cron 8
daemon.
.Ev SHELL
is set to
.Pa /bin/sh ,
and
.Ev LOGNAME
and
.Ev HOME
are set from the
.Pa /etc/passwd
line of the
.Nm crontab Ns \&'s
owner.
.Ev HOME
and
.Ev SHELL
may be overridden by settings in the
.Nm crontab ;
.Ev LOGNAME
may not.
.Pp
Note: on BSD systems the
.Ev LOGNAME
variable is sometimes called
.Ev USER .
On
.Ox ,
.Xr cron 8
will set both
.Ev USER
and
.Ev LOGNAME
to the same value.
.Pp
In addition to
.Ev LOGNAME ,
.Ev HOME ,
and
.Ev SHELL ,
.Xr cron 8
will look at
.Ev MAILTO
if it has any reason to send mail as a result of running
commands in
.Dq this
.Nm crontab .
If
.Ev MAILTO
is defined (and non-empty),
mail is sent to the user so named.
If
.Ev MAILTO
is defined but empty
.Pq Ev MAILTO \&= Sq ,
no
mail will be sent.
Otherwise mail is sent to the owner of the
.Nm crontab .
This option is useful for pseudo-users that lack an alias
that would otherwise redirect the mail to a real person.
.Pp
.Em cron Commands
.Pp
The format of a
.Xr cron 8
command is very much the V7 standard, with a number of
upward-compatible extensions.
Lines in the system
.Nm
have six fixed fields plus a command in the form:
.Bd -ragged -offset indent
.Ar minute
.Ar hour
.Ar day\-of\-month
.Ar month
.Ar day\-of\-week
.Ar user
.Ar command
.Ed
.Pp
While lines in a user
.Nm
have five fixed fields plus a command in the form:
.Bd -ragged -offset indent
.Ar minute
.Ar hour
.Ar day\-of\-month
.Ar month
.Ar day\-of\-week
.Ar command
.Ed
.Pp
Fields are separated by blanks or tabs.
The command may be one or more fields long.
The allowed values for the fields are:
.Pp
.Bl -tag -width "day-of-month" -compact -offset indent
.It field
allowed values
.It -----
--------------
.It Ar minute
* or 0\-59
.It Ar hour
* or 0\-23
.It Ar day\&-of\&-month
* or 1-31
.It Ar month
* or 1-12 or a name (see below)
.It Ar day\&-of\&-week
* or 0-7 or a name (0 or 7 is Sunday)
.It Ar user
a valid username
.It Ar command
text
.El
.Pp
Lists are allowed.
A list is a set of numbers (or ranges) separated by commas.
Examples:
.Sm off
.Dq 1 , 2 , 5 , 9 ,
.Dq 0\&-4 , 8\&-12 .
.Sm on
.Pp
Ranges of numbers are allowed.
Ranges are two numbers separated with a hyphen.
The specified range is inclusive.
For example,
8\-11 for an
.Fa hour
entry specifies execution at hours 8, 9, 10 and 11.
.Pp
Step values can be used in conjunction with ranges.
Following a range with
.No \&/ Ns Ar number
specifies skips of
.Fa number
through the range.
For example,
.Dq 0-23/2
can be used in the
.Fa hour
field to specify command execution every other hour (the alternative
in the V7 standard is
.Dq 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
.Dq every two hours ,
just use
.Dq \&*\&/2 .
.Pp
An asterisk
.Pq Ql *
is short form for a range of all allowed values.
.Pp
Names can be used in the
.Fa month
and
.Fa day\&-of\&-week
fields.
Use the first three letters of the particular
day or month (case doesn't matter).
Ranges or lists of names are not allowed.
.Pp
The
.Fa command
field (the rest of the line) is the command to be
run.
The entire command portion of the line, up to a newline or %
character, will be executed by
.Pa /bin/sh
or by the shell
specified in the
.Ev SHELL
variable of the
.Nm crontab .
Percent signs
.Pq Ql %
in the command, unless escaped with a backslash
.Pq Ql \e ,
will be changed into newline characters, and all data
after the first
.Ql %
will be sent to the command as standard input.
.Pp
Commands are executed by
.Xr cron 8
when the
.Fa minute ,
.Fa hour ,
and
.Fa month
fields match the current time,
.Em and
when at least one of the two day fields
.Pf ( Fa day\&-of\&-month
or
.Fa day\&-of\&-week ,
see Note below) match the current time.
.Xr cron 8
examines
.Nm
entries once every minute.
.Pp
Note: The day of a command's execution can be specified by two
fields \(em
.Ar day\&-of\&-month
and
.Ar day\&-of\&-week .
If both fields are
restricted (i.e., aren't *), the command will be run when
.Em either
field matches the current time.
For example,
.Pp
.Dl 30 4 1\&,15 \&* 5
.Pp
would cause a command to be run at 4:30 am on the 1st and 15th of each
month, plus every Friday.
.Pp
Instead of the first five fields, one of eight special strings may appear:
.Pp
.Bl -tag -width "@annually" -offset indent -compact
.It string
meaning
.It ------
-------
.It @reboot
Run once, at
.Xr cron 8
startup.
.It @yearly
Run every January 1, "0 0 1 1 *".
.It @annually
(same as @yearly).
.It @monthly
Run the first day of every month, "0 0 1 * *".
.It @weekly
Run every Sunday, "0 0 * * 0".
.It @daily
Run every midnight, "0 0 * * *".
.It @midnight
(same as @daily).
.It @hourly
Run every hour, on the hour, "0 * * * *".
.El
.Sh EXAMPLES
.Bd -literal
# use /bin/sh to run commands, no matter what /etc/passwd says
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"
.Ed
.Sh SEE ALSO
.Xr crontab 1 ,
.Xr cron 8
.Sh EXTENSIONS
When specifying
.Fa day\&-of\&-week ,
both day 0 and day 7 will be considered Sunday.
BSD and ATT seem to disagree about this.
.Pp
Lists and ranges are allowed to coexist in the same field.
.Dq 1\&-3,7\&-9
would
be rejected by ATT or BSD
.Xr cron
\(em they want to see
.Dq 1\&-3
or
.Dq 7,8,9
.Em only .
.Pp
Ranges can include
.Dq steps ,
so
.Dq 1-9/2
is the same as
.Dq 1,3,5,7,9 .
.Pp
Months or days of the week can be specified by name.
.Pp
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.
.Pp
Command output is mailed to the crontab owner (BSD can't do this), can be
mailed to a person other than the crontab owner (SysV can't do this), or the
feature can be turned off and no mail will be sent at all (SysV can't do this
either).
.Pp
All of the
.Ql @
commands that can appear in place of the first five fields
are extensions.
.Sh AUTHORS
Paul Vixie <vixie@isc.org>