.TH CRON 8
.SH NAME
cron \- clock daemon
.SH SYNOPSIS
.B auth/cron
[
.B -c
]
.SH DESCRIPTION
.I Cron
executes commands at specified dates and times according
to instructions in the files
.BI /cron/ user /cron\f1.
It runs only on an authentication server.
Option
.B -c
causes
.I cron
to create
.BI /cron/ user
and
.BI /cron/ user /cron
for the current user;
it can be run from any Plan 9 machine.
.PP
Blank lines and lines beginning with
.B #
in these files are ignored.
Entries are lines with fields
.IP
.I
minute hour day month weekday host command
.PP
.I Command
is a string, which may contain spaces, that is passed to an
.IR rc (1)
running on
.I host
for execution.
The first five fields are integer patterns for
.PD0
.RS
.TP \w'month\ of\ year\ \ 'u
minute
0\-59
.TP
hour
0\-23
.TP
day of month
1\-31
.TP
month of year
1\-12
.TP
day of week
0\-6; 0=Sunday
.PD
.RE
.PP
The syntax for these patterns is
.IP
.EX
time  : '*'
      | range
range : number
      | number '-' number
      | range ',' range
.EE
.PP
Each number must be in the appropriate range.
Hyphens specify inclusive ranges of valid times;
commas specify lists of valid time ranges.
.PP
To run the job,
.I cron
calls
.I host
and authenticates remote execution, equivalent to running
.B rx
.I host
.I command
(see
.IR con (1)).
The user's profile is run with
.B $service
set to
.BR rx .
If
.I host
is
set to
.BR local ,
.I cron
will run the command as
.I user
on the local machine without using
.BR rx .
.PP
.I Cron
is not a reliable service.
It skips commands if it cannot reach
.I host
within two minutes, or if the
.I cron
daemon is
not running at the appropriate time.
.SH EXAMPLES
Here is the job that mails system news.
.IP
.EX
% cat /cron/upas/cron
# send system news
15 8-17, 21 ***	helix	/mail/lib/mailnews
%
.EE
.SH SOURCE
.B /sys/src/cmd/auth/cron.c
.SH "SEE ALSO"
.IR con (1),
.IR rc (1)