There is a "Authentication Token Manipulation Error" when trying to update user's password in Ubuntu.
$ sudo passwd USERNAME # ... passwd: Authentication token manipulation error passwd: password unchanged
The reason why
passwd failed is that filesystem was mounted as read only, which prevents changing the password.
A way to fix this issue is to remount filesystem and then to check permissions of
$ mount -rw -o remount / # or $ mount -o remount,rw /
Check the write permission of
$ ls -l /etc/shadow -rw-r----- 1 root shadow 1025 Feb 11 22:11 /etc/shadow
That's OK, now
passwd will work well.
$ sudo passwd USERNAME