you specifiy it to run on minute fifty of every hour of day 25 of every month
specify it to run on only one of the hours, not every one of them. 
e.g. 
50 4 blah blah

isildur

On Sun, 25 Feb 2001, Bruce Lane wrote:

> Fellow VAX'ers,
> 
> 	I have a job in my crontab that I want to run once only on the 25th day of
> every month. The entry (NetBSD 1.5) looks like this.
> 
> -=-=-=-=-=-=-=-=- <break> 
> 
> # 50     *       25      *       *       /usr/local/apache/conf/rc.monthly
> 
> -=-=-=-=-=-=-=-=- <break>
> 
> 	The reason it's commented out right now is because I discovered it was
> running at 50 minutes past every hour on this day (which is indeed the 25th).
> 
> 	I only want the job to run ONCE on the 25th, every month. Is this even
> possible with cron? Perhaps I need to use at or batch?
> 
> 	The man pages and my dead-tree archives haven't helped much.
> 
> 	Thanks much.
> 
> 
> -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
> Bruce Lane, Owner and head honcho, Blue Feather Technologies
> http://www.bluefeathertech.com  // E-mail: kyrrin@bluefeathertech.com
> Amateur Radio: WD6EOS since Dec. '77 (Extra class as of June-2K)
> "I'll get a life when someone demonstrates to me that it would be
> superior to what I have now..." (Gym Z. Quirk, aka Taki Kogoma).
>