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Linux System Administration
book

Linux System Administration

by Tom Adelstein, Bill Lubanovic
March 2007
Intermediate to advanced content levelIntermediate to advanced
304 pages
11h 12m
English
O'Reilly Media, Inc.
Content preview from Linux System Administration
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Chapter 10: Scripting
month is a number between 1 and 12 or a name such as February.
day_of_week is a number between 0 and 7 (0 or 7 is Sunday, 6 is Saturday) or a
name such as
Tuesday.
day_of_month and day_of_week are ORed together, which may cause surprises.
For instance, if each field contains a
1, cron will execute the command in Janu-
ary as well as on Mondays. Usually, the crontab line puts a specific value in only
one of these fields.
In any field, a value means an exact match; for instance, a
1 in the month field
means only January.
An asterisk (
*) means any value.
Two values separated by a hyphen indicate a range. Thus,
11-12 in the month
field means November through December.
To specify more than one value, separate the values with commas. A
month list of
2,3,5-6 means February, March, and May through June.
•Astep modifier may follow values and a slash (
/), and it indicates how many
units to increment between values. A
month value of */3 means every third
month. A
month value of 4-9/2 means months 4, 6, and 8.
The shell executes the command, so it can use the features mentioned in this chap-
ter. Some examples using direct commands rather than scripts are:
5 * * * * rm /tmp/*.gif # remove all GIF files every 5 minutes
5 * * * * rm -v /tmp/*.gif >> /tmp/gif.log # the same, logged
When cron runs the command, it emails its standard output and standard error to
the owner of the crontab ...
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Publisher Resources

ISBN: 9780596009526Supplemental ContentCatalog PageErrata