CRON(8) System Manager's Manual CRON(8)
NAME
cron - clock daemon
SYNOPSIS
auth/cron [-c]
DESCRIPTION
Cron executes commands at specified dates and times according to instructions in the files /cron/user/cron. It runs only on an authentica-
tion server. Option -c causes cron to create /cron/user and /cron/user/cron for the current user; it can be run from any Plan 9 machine.
Blank lines and lines beginning with # in these files are ignored. Entries are lines with fields
minute hour day month weekday host command
Command is a string, which may contain spaces, that is passed to an rc(1) running on host for execution. The first five fields are integer
patterns for
minute 0-59
hour 0-23
day of month 1-31
month of year 1-12
day of week 0-6; 0=Sunday
The syntax for these patterns is
time : '*'
| range
range : number
| number '-' number
| range ',' range
Each number must be in the appropriate range. Hyphens specify inclusive ranges of valid times; commas specify lists of valid time ranges.
To run the job, cron calls host and authenticates remote execution, equivalent to running rx host command (see con(1)). The user's profile
is run with $service set to rx.
Cron is not a reliable service. It skips commands if it cannot reach host within two minutes, or if the cron daemon is not running at the
appropriate time.
EXAMPLES
Here is the job that mails system news.
% cat /cron/upas/cron
# send system news
15 8-17, 21 *** helix /mail/lib/mailnews
%
SOURCE
/sys/src/cmd/auth/cron.c
SEE ALSO
con(1), rc(1)
CRON(8)