AIX reduce wtmp size

To edit the /var/adm/wtmp file, first copy the file temporarily with the following
command:
# /usr/sbin/acct/fwtmp < /var/adm/wtmp >/tmp/out
#
Edit the /tmp/out file to remove unwanted entries, then replace the original file
with the following command:
# tail -1000 /tmp/out > /tmp/in
# /usr/sbin/acct/fwtmp -ic < /tmp/in > /var/adm/wtmp

or

#cp /dev/null /var/adm/wtmp