A possibility is to get a livecd and log into root mode. Use mkdir to make a root dir called /listserver . Then edit the fstab to have /listerver /mnt/your_actual_listerver_root_partition.
Then effectively chroot into the root partition from the root cd and change password, this is what I did when I locked myself out of arch
[root@localhost flebber]# chroot /archroot su
[root@localhost flebber]# passwd
Changing password for user root.
New UNIX password:
Retype new UNIX password:
passwd: all authentication tokens updated successfully.
Gentoo docs are a good reference to this as well and I would recommend you read it before going ahead, my info is basically right but as its early morning and I am tired you should do some backup reading.
Hope it helps.