Ubuntu – Lubuntu 16.10: How to make login through greeter without typing password work

How to allow an account to login at the greeter without typing the password in Lubuntu 16.10?

I think I remember that worked in Ubuntu but I have not found a way to make that work in Lubuntu

GUI Try 1

I tried the gui way: "user & groups" -> change password -> [check] "don't ask password on login". And then reboot computer.

That doesn't work. The lightdm gtk greeter surely doesn't ask for a password for the user (let's say it is called user2), but then after I click ok, then the hard disk run for a while and then I go back to the login in screen again.

Original Config

/etc/lightdm/lightdm.conf:

[SeatDefaults]
# Check https://bugs.launchpad.net/lightdm/+bug/854261 before setting a timeout
user-session=Lubuntu
greeter-session=lightdm-gtk-greeter
allow-guest=false

Config File Try 1

I undo the gui try.
Added the following lines to /etc/lightdm/lightdm.conf.d/20-lubuntu.conf, which was empty before I added these lines.

[SeatDefaults]
user-session=Lubuntu
autologin-user=user2
autologin-user-timeout=delay

I reboot the computer, and find that I still need to password to login at lightgreeter.

Config File Try 2

I undo other changes to the configuration files. Undo the gui try.
I followed How to make Lubuntu login automatically?

Add the following lines to /etc/lightdm/lightdm.conf

[Seat:*]
pam-service=lightdm
pam-autologin-service=lightdm-autologin
autologin-user=user2
autologin-user-timeout=0

After that I reboot the computer.
Still need password to login.

Config File Try 3

I undo other changes to the configuration files. Undo the gui try.
I followed How to make Lubuntu login automatically?

add the following lines under the existing section [SeatDefaults]
to /etc/lightdm/lightdm.conf,

autologin-user=user2
autologin-user-timeout=0
user-session=Lubuntu
greeter-session=lightdm-gtk-greeter

After that , I reboot the computer.
Still need password for login.

Config File Try 4

I undo config file try 3, and didn't use the gui try.
I back up /etc/lightdm/lightdm.conf to /etc/lightdm/lightdm.conf.orig and then replace /etc/lightdm/lightdm.conf with Organic Marble's config file:

[Seat:*]
autologin-guest = false
autologin-user = user2
autologin-user-timeout = 0

[SeatDefaults]
allow-guest = false

After that, I reboot the computer. Still need password to log in as user2 at the greeter.

New Account (Workaround 1)

I create a new account called user3. When I create it I choose not to encrypt homefolder, I also choose to login automatically before I actually log into the account. After that, automatic login on the account seems to work, so far.

I can try to replicate everything I did for user2 at the user3 account. But ideally, I should just click the checkbox for user2, and make autologin work for the existing account…

Summary

I don't know why only the gui way changes the behavior of the greeter (it makes the greeter doesn't ask for a password, but it also doesn't let me login. I certain hear some hard-disk noise for a few seconds though.).