boot net -s
boot cdrom -s, if it ask username: root/solaris or root/password.
on x86, you need edit grub and append -s on kernel line.
after login. mount /dev/dsk/cxtxdxsx /a
if you use zfs for /, then zfs import
zfs list
zfs set mountpoint=/a rpool/ROOT/solaris
zfs mount -f rpool/ROOT/solaris
then edit /etc/shadow
remove the password section, let it looks likes.
root::15356::::::
don’t forget to reset the mountpoint back
zfs set mountpoint=/ rpool/ROOT/solaris
reboot.