cron - clock daemon
auth/cron [ -c ]
Cron executes commands at specified dates and times according to
instructions in the files /cron/user/cron. It runs only on an authen‐
tication 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
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
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 : number
| number '-' number
| range ',' range
Each number must be in the appropriate range. Hyphens specify inclu‐
sive 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. If host is set to local, cron will run
the command as user on the local machine without using 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
Here is the job that mails system news.
% cat /cron/upas/cron
# send system news
15 8-17,21 * * * helix /mail/lib/mailnews
lock file to prevent multiple crons running
SEE ALSOcon(1), rc(1)CRON(8)