i have upgraded my ubuntu 11.10 to 12.04. i could not see other login option in the login screen. it shows only Guest login and User login. The User Login ask only password and i had never entered in as User login so that i do not know about password of User login. my problem is how to login as root from the login screen? how can i get Other login option to login as root or some other user? before ask this question i have tried the following:

1. try to add the greeter-show-manual-login=true line at the bottom of /etc/lightdm/lightdm.conf file as Guest login but i get access denied error.
2. i do not know the password of User login (ask only password while login) to purpose of adding above line.
3. from the safe mode login, i could login as root but i could not add the above line the lightdm.conf file . i got read only error so that i tried to change the permission to 777 like the following > chmod 777 lightdm.conf (i am within the /etc/lightdm/). but i got the error the file marked as/is read only in the file system.
4. In 11.10 version i have created 4 users. i can see that the users exist in 12.10 . so i am sure my self users are not removed while upgrate.

In short, i need Other login option on my login screen? how to get it? please help me.

* Edited Question:*

i have add the following line the /etc/lightdm/lighdm.conf file on recovery mode

greeter-show-manual-login=true

and i saved the file using wq command.

now my /etc/lightdm/lighdm.conf file looking as the following:

[SeatDefaults]
greeter-session=unity-greeter
user-session=ubuntu
greeter-show-manual-login=true

if i commit any mistake please correct me. by this problem i have wasted the two working day and all the works are in pending... please help me.