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Top Forums UNIX for Advanced & Expert Users Crontab spawning multiple at processes Post 302225959 by gstuart on Sunday 17th of August 2008 11:36:50 PM
Old 08-18-2008
Hi - Thank you for your replies ... I had intended to schedule the recordings from a script, avoiding the more tedious route via crontab itself. Regardless, since the bash scripts contain a single at command (scheduled time), I don't why cron is repeatedly spawning multiple processes (at commands, for the single, scheduled event).

That is, despite reading the file every minute, once this scheduled at command has been executed (at the appropriate time), shouldn't further calls to this bash file (with a now-expired at command start time) simply be ignored?

Or, it it the case that since the crontab-called file hasn't run it's course (completed, e.g for a scheduled recording of 1 hour), that cron thinks that the command hasn't executed, and tries to execute at the next available opportunity (here, every 1 minute)?

FYI, after I posted my original question, I had the idea (subsequently suggested, above), and directly called my record_tv_* scripts from crontab, which seems to be the solution - not quite what I had wanted, but so be it.

E.g.,

58 18 17 aug sun ~/recordings/record_tv_1
 

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CRON(8) 						      System Manager's Manual							   CRON(8)

NAME
cron - daemon to execute scheduled commands (Vixie Cron) SYNOPSIS
cron DESCRIPTION
Cron should be started from /etc/rc or /etc/rc.local. It will return immediately, so you don't need to start it with '&'. Cron searches /var/spool/cron for crontab files which are named after accounts in /etc/passwd; crontabs found are loaded into memory. Cron also searches for /etc/crontab and the files in the /etc/cron.d/ directory, which are in a different format (see crontab(5)). Cron then wakes up every minute, examining all stored crontabs, checking each command to see if it should be run in the current minute. When execut- ing commands, any output is mailed to the owner of the crontab (or to the user named in the MAILTO environment variable in the crontab, if such exists). Additionally, cron checks each minute to see if its spool directory's modtime (or the modtime on /etc/crontab) has changed, and if it has, cron will then examine the modtime on all crontabs and reload those which have changed. Thus cron need not be restarted whenever a crontab file is modified. Note that the Crontab(1) command updates the modtime of the spool directory whenever it changes a crontab. SEE ALSO
crontab(1), crontab(5) AUTHOR
Paul Vixie <paul@vix.com> 4th Berkeley Distribution 20 December 1993 CRON(8)
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