I have been having a pig of a problem with crontab updating
on a regular basis.  I use a perl script to update my
dynamic IP to a DNS service and it has been setup to update
hourly.  Only problem is that more often than not it does
not update... around 3 out of four times it doesn't, but
that 1 time in four it does... drives me crazy.
Here is the entry I am using in my crontab.
* 0-23 * * * (cd /usr/bin ; ./gdipc.pl )
here is the complete crontab listing:
SHELL=/bin/bash
PATH=/sbin:/bin:/usr/sbin:/usr/bin
MAILTO=root
HOME=/

# run-parts
01 * * * * root run-parts /etc/cron.hourly
02 4 * * * root run-parts /etc/cron.daily
22 4 * * 0 root run-parts /etc/cron.weekly
42 4 1 * * root run-parts /etc/cron.monthly
#0
1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23
* * * root
/usr/bin/gdipc.pl
* 0-23 * * * (cd /usr/bin ; ./gdipc.pl )
The commented out line was an earlier attempt that refused
to work at all... the perl script kept reporting an error
indicating the loss of a configuration file.  The line at
the bottom is the one that replaced it, the error went away,
but updates don't occur on a regular basis.