cron & backup

At office we have a Win2k LAN to which my freebsd postgresql server box
is connected via Samba. On this box I have a script, called 'crono', which
is dealt by /usr/bin/cron every working day's night at 1 am. As you can
see below this crono script vacuums all the DBs and dumps mydb to a samba
share.

##crono file
vacuumdb -a -U victor
pg_dump --create --format=c -O -Uvictor --file=/root/my_dump/mydb.sql.gz
mydb
##

Now if I execute the script by hand as root it all works smoothly but cron
fails frequently to start or complete the execution of the script even though
in the cron log I see that it starts it regularly as root at 1 am.

The fact is that I don't have any other clue on what is going wrong because
of the poor log.

What logs shoiuld I enable in the postgresql.conf configuration file to
trace what's going on with the vacuumdb and pg_dump commands?

Ciao
Vittorio