[linux] passwd: Authentication token manipulation error

root@test1:~# passwd root
New password:
Retype new password:
Sorry, passwords do not match.
passwd: Authentication token manipulation error
passwd: password unchanged

root@test:~# passwd root
New password:
Retype new password:
Sorry, passwords do not match.
passwd: Module is unknown
passwd: password unchanged

solution

chmod 0640 /etc/shadow

mount -o remount,rw /