理解lightdm.conf

Before you do anything to your lightdm.conf file, you should make a backup, simply run:

sudo cp /etc/lightdm/lightdm.conf /etc/lightdm/lightdm.conf.old  

Once you’ve made a backup, the simplest and safest way to modify lightdm.conf is to use lightdm-set-defaults. lightdm-set-defaults was written so that lightdm.conf could be modified via script, but you can also use it to easily make changes. I’ve made several changes to this tool to add new features that I needed, and best of all, I even wrote a manpage for it, which should show up in raring at some point. If you’re not using raring, then just run /usr/lib/lightdm/lightdm-set-defaults with no arguments and you’ll get a clear picture on what it can do.

Usage:
lightdm-set-defaults [OPTION...] - set lightdm default values

Help Options:
-h, --help Show help options

Application Options:
-d, --debug Enable debugging
-k, --keep-old Only update if no default already set
-r, --remove Remove default value if it's the current one
-s, --session Set default session
-g, --greeter Set default greeter
-a, --autologin Set autologin user
-i, --hide-users Set greeter-hide-users to true or false
-m, --show-manual-login Set show-manual-login to true or false
-R, --show-remote-login Set show-remote-login to true or false
-l, --allow-guest Set allow-guest to true or false  

You can also edit the file manually, but in either case, manual edit or set-defaults, you’ll need to use sudo. And now that you know how to modify the file, let’s cover what the most frequently asked about items are.

Disabling Guest Login

Some people really get annoyed by guest login, so if you want to disable it, simply use:

sudo /usr/lib/lightdm/lightdm-set-defaults --allow-guest false  

Or, you can manually add the following line in the [SeatDefaults] section:

allow-guest=false  

The default for this option is true, so if unset, the guest account will be enabled.  Note: See how great the command option for lightdm-set-defaults was named? Whoever added that was a genius.

Hiding the User List

If you don’t want a user list to be displayed by the greeter, you can enable this option. This should also be used with the enabling manual login (below) or logging in may be a challenge (actually I’ve never tried one without the other, I’m not sure what will happen).

sudo /usr/lib/lightdm/lightdm-set-defaults --hide-users true  

Or, you can manually add the following line in the [SeatDefaults] section:

greeter-hide-users=true  

The default for this option is false, so if unset, you will get a user list in the greeter.

Show Manual Login Box

If you previously hid your user list and would like a box where you can manually type in a user name then this option is for you.

sudo /usr/lib/lightdm/lightdm-set-defaults --show-manual-login true  

Or, you can manually add the following line in the [SeatDefaults] section:

greeter-show-manual-login=true  

The default for this option is false, so if unset, you won’t get a manual login box.

Autologin

You can enable autologin by specifying the autologin user.

sudo /usr/lib/lightdm/lightdm-set-defaults --autologin username  

Or, you can manually add the following line in the [SeatDefaults] section:

autologin-user=username  

There are other autologin related options which you may want to set, but none of these can be set using lightdm-set-defaults:

To change how long the greeter will delay before starting autologin.  If not set, the delay is 0, so if you want this to be 0, you don’t need to change it.  Note: the default for all unset integers in the [SeatDefaults] section is 0.

autologin-user-timeout=delay  

To enable autologin of the guest account:

autologin-guest=true  

Run a Command When X Starts, When The Greeter Starts, When the User Session Starts

When lightdm starts X you can run a command or script, like xset perhaps.

display-setup-script=[script|command]  

You can do something similar when the greeter starts:

greeter-setup-script=[script|command]  

or when the user session starts:

session-setup-script=[script|command]  

Change the Default Session

If you want a different session for the default, you can modify this option. I think that the greeter will default to give you the last session you chose, so this option will only change the default session.Note: The session switcher will only show up if you have more than one VALID session; a valid session is one that points to a valid executable. By default in 12.10 you will have a session file for gnome-shell, but gnome-shell won’t be installed, so the session is invalid, leaving you with a single valid session (Ubuntu), and hence no session selector!

/usr/lib/lightdm/lightdm-set-defaults --session [session name]  

Or, you can manually add the following line in the [SeatDefaults] section:

user-session=true  

The list of user sessions is in /usr/share/xsessions, although even that location is configurable (see Advanced Options).

You can change the default greeter in the same manner, using –greeter for lightdm-set-defaults or greeter-session for the config file. The list of installed greeters is in /usr/share/xgreeters.

Advanced Options and All Other Options

There is no manpage for lighdm.conf, but there is an example that lists all the options and a bit about what they do, just look in /usr/share/doc/lightdm/lightdm.conf.gz.  If you use vim, you can just edit the file and it will be automagically ungzipped for you, users of other editors are on their own.

原文：http://www.mattfischer.com/blog/?p=343