SDDM

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• Display manager
• KDE

The Simple Desktop Display Manager (SDDM) is a display manager. It is the recommended display manager for the KDE Plasma and LXQt desktop environments.

From Wikipedia:Simple Desktop Display Manager:

Simple Desktop Display Manager (SDDM) is a display manager (a graphical login program and session manager) for the X11 and Wayland windowing systems. SDDM was written from scratch in C++11 and supports theming via QML.

The KDE development team has accepted a proposal to incorporate the SDDM project into the Plasma Desktop project. SDDM will be an official part of Plasma and updates will likely be pushed alongside Plasma Desktop updates.

Note: As of SDDM version 0.20, Wayland sessions are listed and can be started from SDDM, but the SDDM greeter itself still runs in X11 mode by default, although an experimental Wayland greeter can be enabled.

Installation

Install the sddm package. Optionally install sddm-kcm for the KConfig Module.

Follow Display manager#Loading the display manager to start SDDM at boot.

Configuration

The default configuration file for SDDM can be found at /usr/lib/sddm/sddm.conf.d/default.conf. For any changes, create configuration file(s) in /etc/sddm.conf.d/. See sddm.conf(5) for all options.

The sddm-kcm package (included in the plasma group) provides a GUI to configure SDDM in Plasma's system settings. There is also a Qt-based sddm-conf-git^AUR available.

Everything should work out of the box, since Arch Linux uses systemd and SDDM defaults to using systemd-logind for session management.

Autologin

SDDM supports automatic login through its configuration file, for example:

/etc/sddm.conf.d/autologin.conf

[Autologin]
User=john
Session=plasma

This configuration causes a KDE Plasma session to be started for user john when the system is booted. Available session types can be found in /usr/share/xsessions/ for X and in /usr/share/wayland-sessions/ for Wayland.

An option to autologin into KDE Plasma while simultaneously locking the session is not available [1]

You can add a script that activates the screensaver of Plasma to the autostart as a workaround:

#!/bin/sh
/usr/bin/dbus-send --session --type=method_call --dest=org.freedesktop.ScreenSaver /ScreenSaver org.freedesktop.ScreenSaver.Lock &

Passwordless login

It is possible to configure SDDM to allow logging into some accounts without a password. This differs from automatic login in that the user still has to choose which account to log into, and it differs from simply setting the account password to the empty string in that it only allows interactive users to log in (and not, for example, remote users logged in via SSH).

To set this up you can follow the instructions for LightDM, except you will need to change /etc/pam.d/sddm instead of /etc/pam.d/lightdm.

Unlock KDE Wallet automatically on login

See KDE Wallet#Unlock KDE Wallet automatically on login.

Theme settings

Theme settings can be changed in the [Theme] section. If you use Plasma's system settings, themes may show previews.

Set to breeze for the default Plasma theme.

Some themes are available in the AUR, for example archlinux-themes-sddm^AUR.

Current theme

Set the current theme through the Current value, e.g. Current=archlinux-simplyblack.

Editing themes

The default SDDM theme directory is /usr/share/sddm/themes/. You can add your custom made themes to that directory under a separate subdirectory. Note that SDDM requires these subdirectory names to be the same as the theme names. Study the files installed to modify or create your own theme.

Customizing a theme

To override settings in the theme.conf configuration file, create a custom theme.conf.user file in the same directory. For example, to change the theme's background:

/usr/share/sddm/themes/name/theme.conf.user

[General]
background=/path/to/background.png

Testing (previewing) a theme

You can preview an SDDM theme if needed. This is especially helpful if you are not sure how the theme would look if selected or just edited a theme and want to see how it would look without logging out. You can run something like this:

$ sddm-greeter-qt6 --test-mode --theme /usr/share/sddm/themes/breeze

This should open a new window for every monitor you have connected and show a preview of the theme.

Note: This is just a preview. In this mode, some actions like shutdown, suspend or login will have no effect.

Mouse cursor

To set the mouse cursor theme, set CursorTheme to your preferred cursor theme.

Valid Plasma mouse cursor theme names are breeze_cursors, Breeze_Snow and breeze-dark.

User icon (avatar)

SDDM reads the user icon (a.k.a. "avatar") as a PNG image from either ~/.face.icon for each user, or the common location for all users specified by FacesDir in an SDDM configuration file. The configuration setting can be placed in either /etc/sddm.conf directly, or, better, a file under /etc/sddm.conf.d/ such as /etc/sddm.conf.d/avatar.conf.

To use the FacesDir location option, place a PNG image for each user named username.face.icon at the location specified by the FacesDir key in the configuration file. The default location for FacesDir is /usr/share/sddm/faces/. You can change the default FacesDir location to suit your needs. Here is an example:

/etc/sddm.conf.d/avatar.conf

[Theme]
FacesDir=/var/lib/AccountsService/icons/

The other option is to put a PNG image named .face.icon at the root of your home directory. In this case, no changes to any SDDM configuration file is required. However, you need to make sure that sddm user can read the PNG image file(s) for the user icon(s).

Note: In many KDE versions, the user icon image file is ~/.face and ~/.face.icon is a symlink to that file. If the user icon images are symlinks, you need to set proper file permissions to the target files.

To set proper permissions run:

$ setfacl -m u:sddm:x ~/
$ setfacl -m u:sddm:r ~/.face.icon

You can check permissions with:

$ getfacl ~/
$ getfacl ~/.face.icon

See SDDM README: No User Icon.

Numlock

If you want to enforce numlock to be enabled, set Numlock=on in the [General] section.

If SDDM is running under Wayland, the numlock setting currently does not work. You may need to change KWin settings to enable it, see this issue.

Rotate display

See Xrandr#Configuration.

DPI settings

Sometimes it is useful to set up the correct monitor's PPI settings on a "Display Manager" level.[2] To do so you need to add to ServerArguments the parameter -dpi your_dpi at the end of the string. For example:

/etc/sddm.conf.d/dpi.conf

[X11]
ServerArguments=-nolisten tcp -dpi 94

Enable HiDPI

Note: Since sddm version 0.20.0, HiDPI support is enabled by default, and the following step is not neccesary.

Create the following file:

/etc/sddm.conf.d/hidpi.conf

[Wayland]
EnableHiDPI=true

[X11]
EnableHiDPI=true

When using Wayland, the HiDPI scaling depends on the greeter used.[3] For instance, when using a Qt-based greeter such as Breeze, add the following configuration:

[General]
GreeterEnvironment=QT_SCREEN_SCALE_FACTORS=2,QT_FONT_DPI=192

Enable virtual keyboard

Install qt5-virtualkeyboard.

Create the following file:

/etc/sddm.conf.d/virtualkbd.conf

[General]
InputMethod=qtvirtualkeyboard

SDDM now displays a button in lower-left corner of login screen to open the virtual keyboard.

Using a fingerprint reader

Note: Make sure that your fingerprint is registered before making these changes. Fingerprint support is not completely working properly yet, and it seems logging in with only a password no longer works using this method.

SDDM works with a fingerprint reader when using fprint. After installing fprint and adding fingerprint signatures, add the following to the top of /etc/pam.d/sddm:

/etc/pam.d/sddm

auth 			sufficient  	pam_fprintd.so

In order to use either a password or a fingerprint, you can instead add the following to the top of the file:

/etc/pam.d/sddm

auth 			[success=1 new_authtok_reqd=1 default=ignore]  	pam_unix.so try_first_pass likeauth nullok
auth 			sufficient  	pam_fprintd.so

Note that KWallet cannot be unlocked using a fingerprint reader (see KDE Wallet#Unlock KDE Wallet automatically on login), but the first line ensures that a password login will automatically unlock KWallet.

Tip: To make this work in KDE's lock screen, you can add the following lines at the beginning of /etc/pam.d/kde:

/etc/pam.d/kde

auth 			sufficient  	pam_unix.so try_first_pass likeauth nullok
auth 			sufficient  	pam_fprintd.so

The first line looks different from the corresponding /etc/pam.d/sddm configuration because the KDE lock screen does not need to run the KWallet pam module.

If you now press enter in the empty password field, the fingerprint reader should start working.

Rootless

Traditionally, the X11 display server has been run with root privileges by default. This rootful mode allows X11 to have unrestricted access to system resources, which was necessary for its operation in environments where direct hardware access and management were common. However, with the increasing emphasis on security in modern computing environments, efforts have been made to transition to rootless modes, which is also why Wayland by default runs in rootless mode.

Starting unprivileged X11 (and Wayland) sessions has been supported since sddm 0.20.0.[4]

To enable rootless mode: create a new configuration file under /etc/sddm.conf.d/, name it something meaningful, and add the following to it, replacing x11-user with wayland if necessary.

/etc/sddm.conf.d/rootless-x11.conf

[General]
DisplayServer=x11-user

To confirm whether you are running in rootless mode check which user owns the compositor process (e.g. kwin_wayland)

Note:

• SDDM considers its Wayland support experimental.
• By default DisplayServer=wayland attempts to use the weston compositor, even if it's not installed, to use a different Wayland compositor, enter the program and relevant arguments to the CompositorCommand option as described in #KDE / KWin, see also sddm.conf(5) for more.

Wayland

KDE / KWin

Warning: By default, KWin starts up with global shortcuts enabled. This could be dangerous for a login screen, since it becomes possible to bypass the login prompt using default key bindings. Specifying --no-global-shortcuts fixes this.[5]

Adding the following lines to your configuration file sets the Wayland compositor to KWin and enables the wlr_layer_shell Wayland protocol extension. This layer shell is included in layer-shell-qt and layer-shell-qt5. The latter package is needed until SDDM drops Qt5, otherwise you will get a black screen. [6]

/etc/sddm.conf.d/10-wayland.conf

[General]
DisplayServer=wayland
GreeterEnvironment=QT_WAYLAND_SHELL_INTEGRATION=layer-shell

[Wayland]
CompositorCommand=kwin_wayland --drm --no-lockscreen --no-global-shortcuts --locale1

Virtual keyboards

To enable virtual keyboard support (e.g. using qt5-virtualkeyboard or maliit-keyboard), append the --inputmethod flag with the appropriate keyboard to the kwin_wayland command as shown below. Do not set the option InputMethod in the section General, since this will cause the virtual keyboard to no longer be shown.

/etc/sddm.conf.d/10-wayland.conf

[Wayland]
CompositorCommand=kwin_wayland --drm --no-lockscreen --no-global-shortcuts --locale1 --inputmethod maliit-keyboard

Match KDE display configuration

Changes to your display configuration made in KDE Wayland (e.g. monitor layout, resolution, etc) will not persist to SDDM. To make them persist open KDE's System Settings and navigate to Startup and Shutdown> Login Screen (SDDM) and click "Apply Plasma Settings...". You will need to have permission to perform this action.

The same can be achieved manually with the following:

To enable correct display & monitor handling in SDDM (scaling, monitor resolution, hz,...), you can copy or modify the appropriate configuration file from your home directory to the one of SDDM:

# cp ~/.config/kwinoutputconfig.json /var/lib/sddm/.config/
# chown sddm:sddm /var/lib/sddm/.config/kwinoutputconfig.json

To also enable correct input handling in SDDM (tap-to-click, touchscreen mapping,...), you can copy the appropriate configuration file from your home directory to the one of SDDM:

# cp ~/.config/kcminputrc /var/lib/sddm/.config/
# chown sddm:sddm /var/lib/sddm/.config/kcminputrc

Troubleshooting

Blank screen with cursor, but no greeter shows

Greeter crashes if there is no available disk space. Check your disk space with df -h.

If disk space is not the issue, it may be due to a bug. Switch to another TTY, and then try loginctl unlock-session session_id or to restart SDDM.

Long load time before SDDM shows the greeter

A low entropy pool can cause long SDDM load time (Bug report). See Random number generation for suggestions to increase the entropy pool.

Hangs after login

Try removing ~/.Xauthority and logging in again without rebooting. Rebooting without logging in creates the file again and the problem will persist.

SDDM starts on tty1 instead of tty7

SDDM follows the systemd convention of starting the first graphical session on tty1.

Note that the config file still has the option MinimumVT but is ignored since SDDM version 0.20: sddm.conf(5) § MinimumVT=.

One or more users do not show up on the greeter

Warning: Users set with a UID lower than 1000 or higher than 60513 should generally not be exposed to a display manager.

By default, SDDM is configured to displays only users with a UID in the range of 1000 to 60513. If the UIDs of the desired users are outside this range then you will have to modify the range.

For example, for a UID of 501, set MinimumUid and hide those with shells used by system users:

/etc/sddm.conf.d/uid.conf

[Users]
HideShells=/usr/bin/nologin,/sbin/nologin,/bin/false,/usr/bin/git-shell
MinimumUid=500

For users with a higher UIDs, set MaximumUid to the appropriate value.

User avatars do not show up on the greeter

User avatars are not shown on the greeter if the number of users exceeds DisableAvatarsThreshold parameter or if avatars are not enabled at all as controlled by EnableAvatars parameter. To circumvent this add the following lines to your sddm configuration:

/etc/sddm.conf.d/avatars.conf

[Theme]
EnableAvatars=true # enable avatars
DisableAvatarsThreshold=7 # set the threshold for the number of users. Avatars are not shown if this threshold is exceeded.

SDDM loads only US keyboard layout

SDDM loads the keyboard layout specified in /etc/X11/xorg.conf.d/00-keyboard.conf. You can generate this configuration file by localectl set-x11-keymap command. See Keyboard configuration in Xorg for more information.

An alternative way of setting the keyboard layout that will only set it in SDDM and not subsequent sessions is to invoke a setxkbmap command in the startup script of SDDM, located at /usr/share/sddm/scripts/Xsetup. See Xorg/Keyboard configuration#Using setxkbmap for examples.

SDDM may also incorrectly display the layout as US but will immediately change to the correct layout after you start typing your password [7]. This seems to not be a bug in SDDM but in X server.[8]

Screen resolution is too low

Issue may be caused by HiDPI usage for monitors with corrupted EDID [9]. If you have enabled HiDPI, try to disable it.

If even the above fails, you can try setting your screen size in a Xorg configuration file:

/etc/X11/xorg.conf.d/90-monitor.conf

Section "Monitor"
        Identifier      "<default monitor>"
        DisplaySize     345 194 # in millimeters
EndSection

Long load time on autofs home directory

SDDM by default tries to display avatars of users by accessing ~/.face.icon file. If your home directory is an autofs, for example if you use dm-crypt, this will make it wait for 60 seconds, until autofs reports that the directory cannot be mounted.

You can disable avatars by creating the following configuration file:

/etc/sddm.conf.d/avatar.conf

[Theme]
EnableAvatars=false

X authority (aka MIT-MAGIC-COOKIE) file

SDDM uses a random fresh UUID for the auth file as described in details at [10]. So in order to find that file one may use a script:

# find /var/run/sddm/ -type f

This may be needed if one needs to start x11vnc when there is no user logged in. For example:

# x11vnc -display :0 -auth "$( find /var/run/sddm/ -type f )"

Overlapping greeters on multiscreen setup

It happens that the X monitor layout is not setup correctly on multiscreen setup leading to overlapping greeters. To solve this add the following lines to order your sddm greeter layout from left to right:

/usr/share/sddm/scripts/Xsetup

for next in $(xrandr --listmonitors | grep -E " *[0-9]+:.*" | cut -d" " -f6); do
  [ -z "$current" ] && current=$next && continue
  xrandr --output $current --auto --output $next --auto --right-of $current
  current=$next
done

Login session appears on an unexpected display

It can happen that the SDDM login session appears on a different display than your primary display if multiple displays are connected. This problem can be annoying if the secondary display is rotated and the primary display is not. A simple fix to this problem is to use xrandr to configure the displays before the login session using Xsetup script. E.g. here xrandr reports that there are two connected displays where the secondary display (DP-2) is left of the primary display (DP-4).

# xrandr | grep -w connected
DP-2 connected 2160x3840+0+0 left (normal left inverted right x axis y axis) 597mm x 336mm
DP-4 connected primary 3840x2160+2160+0 (normal left inverted right x axis y axis) 697mm x 392mm

The following Xsetup recreates the above setup for the login window:

/usr/share/sddm/scripts/Xsetup

#!/bin/sh
# Xsetup - run as root before the login dialog appears

xrandr --output DP-4 --auto --primary
xrandr --output DP-2 --left-of DP-4 --rotate left --noprimary

Black screen after logout with NVIDIA graphics card

One may encounter a complete black screen or with only cursor/display device logo on it after the logout of any user. This happens because sddm.service starts faster than the NVIDIA drivers. Consider using early KMS.

Failing first password attempt results in text clearing itself after a few keystrolkes on subsequent attempts

Use a different theme than the default.

Screen out of sync on hybrid graphics with Wayland

If you set up SDDM with kwin_wayland compositor, one may encounter a screen out of sync when booting. If returning back to X11 works well, and you're using mesa-amber drivers, chances are Wayland will work well by just replacing your current mesa-amber drivers with mesa. You can find more details about this issue at KDE Bug 483804.