[Sunhelp] Truncating wtmp files?

[Mats Fredholm - Init System Management]

Hi,
does anyone have any experience in truncating the
wtmp/wtmpx files in a 'safe' way on a system where
users frequently login and out all the time ?
Preferrably in a way where you doesn't loose any
information, like keeping the N last entries or
something.
Maybe it's sufficient just to 'cp /dev/null /var/adm/wtmp*'
or can you loose access information ?

Thx,
Mats