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1990-11-16
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NAME:
cron - Executes commands at specified times.
AUTHOR:
Eric Williams WD6CMU, 71336,1424
SYSTEM CONFIGURATION:
OS9/68K, MW C v2.0
SYNTAX:
cron
DESCRIPTION:
The cron clock daemon executes commands at specified dates and times
according to the instructions in the file /dd/misc/crontab. cron should
be run detached from the terminal (shell "&" option) usually with a low
process priority.
The file /dd/misc/crontab consists of (up to 24) lines of six fields
each. The fields are separated by spaces or tabs. The first five are
integer patterns that specify the minute (0-59), hour (0-23), day of the
month (1-31), month of the year (1-12), and day of the week (0-6, with
0=Sunday). Each of the patterns may contain:
o A number in the (respective) range indicated above
o Two numbers separated by a hyphen
o Any number of the above formats separated by commas
o An asterisk (*)
The two numbers separated by a hyphen indicates a range of valid
event times. If the second value is larger than the first, the range is
inclusive between the two values. If the first value is larger than the
second, the range is inclusive outside of the two values. For example,
the weekend can be specified by weekday 6-0. An asterisk matches any
legal value.
The sixth field (up to the end of the line) is a string that is
executed by the shell at the specified time(s). Standard I/O is inherited
from cron by default, so any redirection of I/O must be explicitly defined
in this field.
The crontab file is only read at the time cron is executed. Any
change to the file will require the cron task to be killed and restarted.
BUGS:
Argument checking is not extensive and incorrect values in crontab
could cause unpredictable results.