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