version 1, including all changes.
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perry |
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CRON |
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!!!CRON |
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NAME |
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SYNOPSIS |
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DESCRIPTION |
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DEBIAN SPECIFIC |
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SEE ALSO |
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AUTHOR |
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---- |
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!!NAME |
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cron - daemon to execute scheduled commands (Vixie Cron) |
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!!SYNOPSIS |
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cron |
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!!DESCRIPTION |
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''cron'' is started automatically from /etc/init.d on |
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entering multi-user runlevels. |
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''cron'' searches its spool area |
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(/var/spool/cron/crontabs) for crontab files (which are |
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named after accounts in /etc/passwd); crontabs found are |
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loaded into memory. Note that crontabs in this directory |
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should not be accessed directly - the ''crontab'' command |
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should be used to access and update them. |
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''cron'' also reads /etc/crontab, which is in a slightly |
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different format (see ''crontab(5)).'' Additionally, cron |
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reads the files in /etc/cron.d; see the __DEBIAN |
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SPECIFIC__ section below for more details. |
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''cron'' then wakes up every minute, examining all stored |
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crontabs, checking each command to see if it should be run |
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in the current minute. When executing commands, any output |
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is mailed to the owner of the crontab (or to the user named |
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in the MAILTO environment variable in the crontab, if such |
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exists). The children copies of cron running these processes |
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has its name coerced to uppercase, as will be seen in the |
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syslog and ps output. |
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Additionally, ''cron'' checks each minute to see if its |
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spool directory's modtime (or the modtime on |
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''/etc/crontab)'' has changed, and if it has, ''cron'' |
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will then examine the modtime on all crontabs and reload |
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those which have changed. Thus ''cron'' need not be |
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restarted whenever a crontab file is modified. Note that the |
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crontab(1) command updates the modtime of the spool |
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directory whenever it changes a crontab. |
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Special considerations exist when the clock is changed by |
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less than 3 hours, for example at the beginning and end of |
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daylight savings time. If the time has moved forwards, those |
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jobs which would have run in the time that was skipped will |
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be run soon after the change. Conversely, if the time has |
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moved backwards by less than 3 hours, those jobs that fall |
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into the repeated time will not be re-run. |
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Only jobs that run at a particular time (not specified as |
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@hourly, nor with '*' in the hour or minute specifier) are |
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affected. Jobs which are specified with wildcards are run |
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based on the new time immediately. |
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Clock changes of more than 3 hours are considered to be |
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corrections to the clock, and the new time is used |
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immediately. |
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!!DEBIAN SPECIFIC |
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''cron'' treats the files in /etc/cron.d as extensions to |
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the /etc/crontab file (they follow the special format of |
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that file, i.e. they include the ''user'' field). The |
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intended purpose of this feature is to allow packages that |
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require finer control of their scheduling than the |
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/etc/cron.{daily,weekly,monthly} directories allow to add a |
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crontab file to /etc/cron.d. Such files should be named |
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after the package that supplies them. Files must conform to |
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the same naming convention as used by run-parts(8): they |
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must consist solely of upper- and lower-case letters, |
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digits, underscores, and hyphens. Like /etc/crontab, the |
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files in the /etc/cron.d directory are monitored for |
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changes. |
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!!SEE ALSO |
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crontab(1), crontab(5) |
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!!AUTHOR |
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Paul Vixie |
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---- |