Re: Crontab Sanity Check

On Tue, Mar 22, 2005 at 10:58:11AM +0000, Gaby vanhegan wrote:
> Just to confirm:
> 
> # Monthly full backup run, on the first thursday of the month
> 0       17      1-7     *       4       sudo -u operator 
> /usr/local/sbin/amcheck -m ltsn_full
> 45      0       1-7     *       4       sudo -u operator 
> /usr/local/sbin/amdump ltsn_full
> 
> This crontab entry will run amanda for the ltsn_full configuration 
> *only* on the first thursday of every month?

Two things,

1) As you do, I used to believe the relationship of DOM and DOW
   (day of month/week) was an AND type relationship.  So the data
   and time would have to match 1-7 AND 4.  But it is not.  Instead
   it is an OR relationship.  Any of the first 7 days, or Thursdays.

   Here is the relevant sentence from the OpenGroup man pages for
   crontab.

        Finally, if either the month or day of month is specified
        as an element or list, and the day of week is also specified
        as an element or list, then any day matching either the month
        and day of month, or the day of week, shall be matched.

    In the above, an element is something other than an asterix ("*").

    The way to handle what you want to do is start a script from a
    crontab.  The script will determine if it is appropriate to start
    the amdump or amcheck.  The script could run every day and check
    for DOM 1-7/DOW 4, or it could run every DOW 4 and check DOM 1-7,
    or every DOM 1-7 and check for DOW 4.

2) You are running amcheck at 5 PM, 16 hours AFTER the amdump has
   already run.  It is too late to do anything about the amcheck
   then.  Remember, the 12:45 AM you probably meant is the next
   day, Friday.  In fact, 5 PM may be too late anyway.  Will you
   be there to check your mail after 5?

-- 
Jon H. LaBadie                  jon AT jgcomp DOT com
 JG Computing
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