Ubuntu 11.10
Started out troubleshooting inability to log in on my user account. This forum guided me to boot into "Grub" / recovery mode and try passwd {username} ...

My results;
passwd: Authentication token manipulation error
passwd: password unchanged

As I am at shell allegedly logged on as root,
(whoami = root ) I work the shadow file angle, per Unbuntu's support pages recommendations.

I can cd to /etc and view two shadow files;
-rw-r----- 1 root shadow 1468 2012-11-02 10:07 /etc/shadow
-rw------- 1 root root 1468 2012-11-02 10:07 /etc/shadow-

Attempts to edit shadow file to "delete password" between first and second colon bombs when I try to save;

[ Error writing shadow: Read-only file system ]

Be gentle - this is the noob (newbie) forum!

x

If the filesystem has gone read only, it would be because it is in error. Trying to update it will be pointless.
Consider yourself lucky you were prevented from hacking the shadow.

The normal first step is to fsck the filesystem - you should have an option to do that from the recovery environment on Ubuntu. Try that, reboot, and report back if you are still in strife.

Don't try your little hack (ever) again ...