Hello all,
The original question was:
 I have very large wtmp & wtmpx files is /var/adm.
 I wander if i can delette those files without rebooting the machine ?
I got a lot of replies to my query and i thank you all !!!
Most of the answers were the same,  they were something like :
As root:
cat /dev/null > /var/adm/wtmp
cat /dev/null > /var/adm/wtmpx
most of you gave me the same advise that it is recomended to 
zero those files from time to time .
So thanks again to :
Padraig Houlahan
Alex.De-La-Salle
Jonathan.Loh
Tom Erickson
Bill Hebert
Renny Koshy
Larry Chin
Ray Delaney
Peter Polasek
boenning 
Ginny Bolyard
Patrick Hooper
Benedict Roque
Oleg Olovyannikov
Hamelin Francois-Rene
Gustavo A.
Michael Salehi
Claude Charest
Todd M.
Rick Fincher
Colin_Melville
Enrique Vadillo
Mary Verge
John D.
foster@bial1.ucsd.edu 
Carlo Musante
Mark_Conroy@em.fcnbd.c 
Chad Price
Tim Carlson
dharringt@deq.state.va 
Walter Gebelein
Michael J.
Tom Vayda
Fernandes, Eustace
Coffindaffer, Virginia
Ilhan Narli
Thiyagarajan V.
Thiyagarajan V.
Sapiro, Vadim
Israel Bravo
John Black
Olivier.GIRAUD@cedelgr 
Kwok.Che.Tang@chase.co 
Simon.Millard@barclays 
Nick Hindley
nesrin_ozus@karmaint.c 
sandesh
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