LightDM

Related articles

• Display manager
• GDM
• LXDM

LightDM is a cross-desktop display manager. Its key features are:

• Cross-desktop - supports different desktop technologies.
• Supports different display technologies (X, Mir, ...).
• Lightweight - low memory usage and high performance.
• Supports guest sessions.
• Supports remote login (incoming - XDMCP, VNC, outgoing - XDMCP, pluggable).
• Comprehensive test suite.
• Low code complexity.

More details about LightDM's design can be found here.

Installation

Install lightdm. Note that stable releases are even-numbered (1.8, 1.10) while development releases are odd-numbered (1.9, 1.11). These development releases are available with lightdm-devel^AUR. Also available is lightdm-bzr^AUR.

Greeter

You will probably want to install a greeter. A greeter is a GUI that prompts the user for credentials, lets the user select a session, and so on. It's possible to use LightDM without a greeter, but only if an automatic login is configured. The reference greeter is lightdm-gtk-greeter. LightDM attempts to use this greeter when started unless configured to do otherwise.

The official repositories contain the following alternative greeters.

• lightdm-kde-greeter: A greeter used with KDE4.
• lightdm-deepin-greeter (deepin-session-ui): A greeter from the Deepin project.

Other alternative greeters are available in the AUR.

• lightdm-webkit2-greeter^AUR: A greeter that uses Webkit2 for theming. It supersedes lightdm-webkit-greeter^AUR.
• lightdm-unity-greeter^AUR: The greeter used by Ubuntu's Unity.
• lightdm-pantheon-greeter^AUR: A greeter from the elementary OS project.
• lightdm-mini-greeter^AUR: A minimal, configurable, single-user greeter.

You can set the default greeter by changing the [Seat:*] section of the LightDM configuration file, like so:

/etc/lightdm/lightdm.conf

[Seat:*]
...
greeter-session=lightdm-yourgreeter-greeter

Which greeters are available? What values may be assigned to the greeter-session option? Each .desktop file in the /usr/share/xgreeters directory denotes an available greeter. In this example, the lightdm-gtk-greeter and lightdm-kde-greeter greeters are available:

$ ls -1 /usr/share/xgreeters/
lightdm-gtk-greeter.desktop
lightdm-kde-greeter.desktop

Enabling LightDM

Make sure to enable lightdm.service so LightDM will be started at boot, see also Display manager#Loading the display manager.

Command line tool

LightDM offers a command line tool, dm-tool, which can be used to lock the current seat, switch sessions, etc, which is useful with 'minimalist' window managers and for testing. To see a list of available commands, execute:

$ dm-tool --help

User switching

Warning: The use of lightDM's built-in screen lockers like dm-tool lock or dm-tool switch-to-greeter are not recommended. Use light-locker or something from List of applications/Security#Screen lockers.

LightDM's dm-tool command can be used to allow multiple users to be logged in on separate ttys. The following will send a signal requesting that the current session be locked and then will initiate a switch to LightDM's greeter, allowing a new user to log in to the system.

$ dm-tool switch-to-greeter

Testing

First, install xorg-server-xephyr from the official repositories.

Then, run LightDM as an X application:

$ lightdm --test-mode --debug

Optional configuration and tweaks

LightDM can be configured by modifying its config file, /etc/lightdm/lightdm.conf.

Some greeters have their own configuration files. For example:

lightdm-gtk-greeter: /etc/lightdm/lightdm-gtk-greeter.conf

lightdm-webkit2-greeter^AUR: /etc/lightdm/lightdm-webkit2-greeter.conf

lightdm-kde-greeter: /etc/lightdm/lightdm-kde-greeter.conf

Changing background images/colors

You can set the background to a hex color or an image. Some greeters offer more robust background options like background selection from the login screen, random backgrounds, etc.

GTK+ greeter

You can use the lightdm-gtk-greeter-settings gui.

Users wishing to customize the wallpaper on the greeter screen need to edit /etc/lightdm/lightdm-gtk-greeter.conf and define the background variable under the [greeter] section. For example:

/etc/lightdm/lightdm-gtk-greeter.conf

[greeter]
background=/usr/share/pixmaps/black_and_white_photography-wallpaper-1920x1080.jpg

Note: It is recommended to place the PNG or JPG file in /usr/share/pixmaps since the LightDM user needs read access to the wallpaper file.

GTK3 Dark Theme

GTK3 introduced "dark" alternate color palettes for themes, but lightdm-gtk-greeter does not yet support specifing one natively. A workaround is to override the theme with an evironment variable in /usr/share/xgreeters/lightdm-gtk-greeter.desktop For example:

/usr/share/xgreeters/lightdm-gtk-greeter.desktop

[Desktop Entry]
Name=LightDM GTK+ Greeter
Comment=This runs the GTK+ greeter, it should only be run from LightDM
Exec=env GTK_THEME=Adwaita:dark lightdm-gtk-greeter
Type=Application
X-Ubuntu-Gettext-Domain=lightdm

Webkit2 greeter

The lightdm-webkit2-greeter^AUR allows you to choose a background image directly on the login screen. It also offers an option to display a random image each time it starts. By default, images are sourced from /usr/share/backgrounds. You can change the background images directory by editing lightdm-webkit2-greeter.conf. For example:

/etc/lightdm/lightdm-webkit2-greeter.conf

[branding]
background_images = /usr/share/backgrounds

Note: The background images directory must be accessible to the LightDM user so it should not be located anywhere under /home.

Unity greeter

Users using the lightdm-unity-greeter^AUR must edit the /usr/share/glib-2.0/schemas/com.canonical.unity-greeter.gschema.xml file and then execute:

# glib-compile-schemas /usr/share/glib-2.0/schemas/

According to this page.

KDE greeter

Go to System Settings > Login Screen (LightDM) and change the background image for your theme.

Alternatively, you can edit the Background variable in lightdm-kde-greeter.conf :

/etc/lightdm/lightdm-kde-greeter.conf

[greeter]
theme-name=classic

[greeter-settings]
Background=/usr/share/archlinux/wallpaper/archlinux-underground.jpg
BackgroundKeepAspectRatio=true
GreetMessage=Welcome to %hostname%

Changing your avatar

Tip: If you are using KDE, you can change your avatar in KDE System Settings.

First, make sure the accountsservice package from the official repositories is installed, then set it up as follows, replacing username with the desired user's login name. The .png file extension should not be included in the filename.

• Edit or create the file /var/lib/AccountsService/users/username, and add the lines

[User]
Icon=/var/lib/AccountsService/icons/username

• Create the file /var/lib/AccountsService/icons/username using a 96x96 PNG image file.

Note: Make sure that both created files have 644 permissions, use chmod to correct them.

Sources of Arch-centric 64x64 icons

The archlinux-artwork^AUR package from the AUR contains some nice examples that install to /usr/share/archlinux/icons and that can be copied to /usr/share/icons/hicolor/64x64/devices as follows:

# find /usr/share/archlinux/icons -name "*64*" -exec cp {} /usr/share/icons/hicolor/64x64/devices \;

After copying, the archlinux-artwork^AUR package can be removed.

Enabling autologin

Edit the LightDM configuration file and ensure these lines are uncommented and correctly configured:

/etc/lightdm/lightdm.conf

[Seat:*]
autologin-user=username

You must be part of the autologin group to be able to login automatically without entering your password:

# groupadd -r autologin
# gpasswd -a username autologin

LightDM logs in using the session specified in the ~/.dmrc of the user getting logged in automatically. To override this file, specify autologin-session in lightdm.conf:

/etc/lightdm/lightdm.conf

[Seat:*]
autologin-user=username
autologin-session=session

Note: GNOME users, and by extension any gnome-keyring user will have to set up a blank password to their keyring for it to be unlocked automatically.

Enabling interactive passwordless login

LightDM goes through PAM so you must configure the lightdm configuration of PAM:

/etc/pam.d/lightdm

#%PAM-1.0
auth        sufficient  pam_succeed_if.so user ingroup nopasswdlogin
auth        include     system-login
...

You must then also be part of the nopasswdlogin group to be able to login interactively without entering your password:

# groupadd -r nopasswdlogin
# gpasswd -a username nopasswdlogin

Note: GNOME users, and by extension any gnome-keyring user may have to follow the instructions at the end of the previous section on enabling autologin.

To create a new user account that logs in automatically and additionally able to login again without a password the user can be created with supplementary membership of both groups, e.g.:

# useradd -mG autologin,nopasswdlogin -s /bin/bash username

Hiding system and services users

To prevent system users from showing-up in the login, install the optional dependency accountsservice, or add the user names to /etc/lightdm/users.conf under hidden-users. The first option has the advantage of not needing to update the list when more users are added or removed.

Migrating from SLiM

Move the contents of xinitrc to xprofile, removing the call to start the window manager or desktop environment.

Login using ~/.xinitrc

See Display manager#Run ~/.xinitrc as a session.

NumLock on by default

Install the numlockx package and then edit /etc/lightdm/lightdm.conf:

/etc/lightdm/lightdm.conf

[Seat:*]
greeter-setup-script=/usr/bin/numlockx on

Default session

Lightdm, like other DMs, stores the last-selected xsession in ~/.dmrc. See Display manager#Session configuration for more info.

Adjusting the login window's position

GTK+ greeter

Users need to edit /etc/lightdm/lightdm-gtk-greeter.conf and enter a value for the position variable. It accepts x and y values, either absolute (in pixels) or relative (in percent). Each value can also have an additional anchor location for the window, start, center and end separated from the value by a comma.

Example:

position=200,start 50%,center

VNC Server

Lightdm can also be used to connect to via VNC. Make sure to install tigervnc on the server side and optionally as your VNC client on the client PC.

Setup an authentication password on the server as root:

# vncpasswd /etc/vncpasswd

Edit the LightDM configuration file as shown below. Note that listen-address configures the VNC to only listen to connections from localhost. This is used to only allow connections via SSH and port forwarding. On the SSH client, make sure that you use localhost:5900 for the tunnel destination; using 127.0.0.1:5900 or ::1:5900 is not reliable on dual stack network connections. If you want to allow insecure connections you can disable this setting.

/etc/lightdm/lightdm.conf

[VNCServer]
enabled=true
command=Xvnc -rfbauth /etc/vncpasswd
port=5900
listen-address=localhost
width=1024
height=768
depth=24

Now open an SSH tunnel and connect to localhost as described in TigerVNC#On the client.

Note: If you get a blank screen upon opening the VNC connection, try a different LightDM greeter.

Lock the screen using light-locker

light-locker is a simple screen locker using LightDM to authenticate the user. Once it is installed and running you can lock your session using

$ light-locker-command -l

This requires light-locker to be started at the beginning of your session - see Autostarting.

Troubleshooting

If you encounter consistent screen flashing and ultimately no LightDM on boot, ensure that you have defined the greeter correctly in LightDM's config file. And if you have correctly defined the GTK greeter, make sure the xsessions-directory (default: /usr/share/xsessions) exists and contains at least one .desktop file.

The same error can happen on lightdm startup if the last used session is not available anymore (eg. you last used gnome and then removed the gnome-session package): the easiest workaround is to temporarily restore the removed package. Another solution might be:

# dbus-send --system --type=method_call --print-reply --dest=org.freedesktop.Accounts /org/freedesktop/Accounts/User1000 org.freedesktop.Accounts.User.SetXSession string:xfce

This example sets the session "xfce" as default for the user 1000.

Wrong locale displayed

In case of your locale not being displayed correctly in Lightdm add your locale to /etc/environment

 LANG=pt_PT.utf8

Alternatively if you want LightDM and its greeters to be in a language other than your set system locale, you can use the Environment= option in Systemd#Drop-in files.

Missing icons with GTK greeter

If you are using lightdm-gtk-greeter as a greeter and it shows placeholder images as icons, make sure valid icon themes and themes are installed and configured. Check the following file:

/etc/lightdm/lightdm-gtk-greeter.conf

[greeter]
theme-name=mate      # this should be the name of a directory under /usr/share/themes/
icon-theme-name=mate # this should be the name of a fully featured icons set directory under /usr/share/icons/

LightDM freezes on login attempt

You may find that after entering the correct username and password and attempting to log in, LightDM freezes and you are unable to continue to the desktop. To fix the issue, reinstall the gdk-pixbuf2 package. See this forum thread.

LightDM displaying in wrong monitor

If you are using multiple monitors, LightDM may display in the wrong one (e.g. if your primary monitor is on the right). To force the LightDM login screen to display on a specific monitor, edit /etc/lightdm/lightdm.conf and change the display-setup-script parameter like this:

/etc/lightdm/lightdm.conf

display-setup-script=xrandr --output HDMI1 --primary

Replace HDMI1 with your real monitor ID, which you can find from xrandr command output.

Alternatively, if you are using the GTK+ greeter, you can edit /etc/lightdm/lightdm-gtk-greeter.conf and add the active-monitor parameter like this:

/etc/lightdm/lightdm-gtk-greeter.conf

[greeter]
active-monitor=0

Replace 0 with the desired display number.

LightDM does not appear

It may happen that your system boots so fast that LightDM service is started before your graphics drivers are properly loaded. If this is your case, you will want to add the following config to your lightdm.conf file:

   [LightDM]
   logind-check-graphical=true

This setting will tell LightDM to wait until graphics devices are ready before spawning greeters/autostarting sessions on them.

Pulseaudio not starting automatically

See PulseAudio#Running.

Long pause before LightDM shows up when home is encrypted

Some LightDM themes try to access the user avatar located in HOME. If your HOME is encrypted, LightDM cannot access it and hangs. To prevent this from happening, you can either:

• Set your avatar as explained in #Changing your avatar
• for lightdm-gtk-greeter only: hide-user-image = true in /etc/lightdm/lightdm-gtk-greeter.conf

Missing power buttons in GTK greeter

The GTK greeter used to have a button to power off / restart the computer in the top right corner. This has been removed from the default configuration in newer versions of the upstream package (bug report). To get it back, adapt the following line in /etc/lightdm/lightdm-gtk-greeter.conf:

/etc/lightdm/lightdm-gtk-greeter.conf

indicators = ~host;~spacer;~clock;~spacer;~language;~session;~a11y;~power

See also

• Ubuntu Wiki article
• Gentoo Wiki article
• Launchpad Page
• LightDM blog