Recovery

boot> boot -s

Enter pathname of shell or RETURN for sh: [ENTER]

fsck -p /
fsck -p /usr

mount -uw /
mount /usr

passwd

and finally: reboot

fsck /dev/sd1a
fsck -y /dev/sd1a

boot -s
mount /usr
mount /
export TERM=vt100
/usr/bin/vi /etc/fstab
fix it !