lightdm is not starting

Question

I get a blank screen on boot :(

$ sudo tail /var/log/lightdm/lightdm.log
[+0.02s] DEBUG: Using D-Bus name org.freedesktop.DisplayManager
[+0.02s] DEBUG: Registered seat module xlocal
[+0.02s] DEBUG: Registered seat module xremote
[+0.02s] DEBUG: Registered seat module unity
[+0.02s] DEBUG: Registered seat module surfaceflinger
[+0.02s] DEBUG: Adding default seat
[+0.02s] DEBUG: Seat: Starting
[+0.02s] DEBUG: Seat: Creating greeter session
[+0.03s] DEBUG: Seat: Failed to find session configuration unity-gretter
[+0.03s] DEBUG: Seat: Failed to create greeter session

Here is the conf

$ cat /etc/lightdm/lightdm.conf
[SeatDefaults]
allow-guest=true
autologin-guest=false
autologin-user=
greeter-session=unity-gretter
user-session=ubuntu

[VNCServer]
enabled=false

[XDMCPServer]
enabled=false

here is boot log

 tail /var/log/boot.log
 * Restoring resolver state...                                                                         [ OK ]
Not starting X display manager (xdm); it is not the default display manager.
 * Stopping System V runlevel compatibility                                                            [ OK ]
 * Starting                                                                                            [ OK ]
 * Starting                                                                                            [ OK ]
 * Stopping                                                                                            [ OK ]
 * Starting Recovery options if display manager fails to start                                         [ OK ]
 * Starting Mount network filesystems                                                                  [ OK ]
 * Stopping Mount network filesystems                                                                  [ OK ]
 * Stopping Read required files in advance                                                             [ OK ]

Solution

You have a typo in your lightdm.conf file

greeter-session=unity-gretter

should be

greeter-session=unity-greeter