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Cron executes commands at specified dates and times according
to instructions in the files /cron/user/cron. It runs only on
an authentication 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
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minute hour day month weekday host command
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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
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minute 0–59
hour 0–23
day of month1–31
month of year1–12
day of week 0–6; 0=Sunday
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The syntax for these patterns is
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time : '*'
range : number
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| number '–' number
| range ',' range
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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. 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 appropriate time.
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