11-27-2006
The first line works because it's running every minute of every day and the program being called accepts passed parameters that control what actually happens when. When I write programs that have the capability of checking date/time for acting on whatever, I usually have it do something very different from the schedule cron runs, ie:
If a program runs every Monday morning, but only if there's data to collect and act on, then Cron runs every Monday morning and the program checks for the data being present. Actually that example is a no-brainer.... It's Monday and I don't drink coffee. But, I hope that gives some semblance of understanding.
The above example, poor as it is, should also apply to your second line.
Oh, I just noticed the '&' at the end of the lines. If the called programs run once and then die, cron needs to be set to run often. If they run forever, then cron doesn't need to be run so often. In that case, the called programs should have a PID file in /var/run to check against. If the file is there and the PID is active, then the program isn't run, else it is run.
HTH,
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LEARN ABOUT POSIX
queuedefs
queuedefs(4) File Formats queuedefs(4)
NAME
queuedefs - queue description file for at, batch, and cron
SYNOPSIS
/etc/cron.d/queuedefs
DESCRIPTION
The queuedefs file describes the characteristics of the queues managed by cron(1M). Each non-comment line in this file describes one queue.
The format of the lines are as follows:
q.[njobj][nicen][nwaitw]
The fields in this line are:
q The name of the queue. a is the default queue for jobs started by at(1); b is the default queue for jobs started by batch (see
at(1)); c is the default queue for jobs run from a crontab(1) file.
njob The maximum number of jobs that can be run simultaneously in that queue; if more than njob jobs are ready to run, only the first
njob jobs will be run, and the others will be run as jobs that are currently running terminate. The default value is 100.
nice The nice(1) value to give to all jobs in that queue that are not run with a user ID of super-user. The default value is 2.
nwait The number of seconds to wait before rescheduling a job that was deferred because more than njob jobs were running in that job's
queue, or because the system-wide limit of jobs executing has been reached. The default value is 60.
Lines beginning with # are comments, and are ignored.
EXAMPLES
Example 1: A sample file.
#
#
a.4j1n
b.2j2n90w
This file specifies that the a queue, for at jobs, can have up to 4 jobs running simultaneously; those jobs will be run with a nice value
of 1. As no nwait value was given, if a job cannot be run because too many other jobs are running cron will wait 60 seconds before trying
again to run it.
The b queue, for batch(1) jobs, can have up to 2 jobs running simultaneously; those jobs will be run with a nice(1) value of 2. If a job
cannot be run because too many other jobs are running, cron(1M) will wait 90 seconds before trying again to run it. All other queues can
have up to 100 jobs running simultaneously; they will be run with a nice value of 2, and if a job cannot be run because too many other jobs
are running cron will wait 60 seconds before trying again to run it.
FILES
/etc/cron.d/queuedefs queue description file for at, batch, and cron.
SEE ALSO
at(1), crontab(1), nice(1), cron(1M)
SunOS 5.10 1 Mar 1994 queuedefs(4)