SDDM

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The Simple Desktop Display Manager (SDDM) is the preferred display manager for KDE Plasma desktop.

From Wikipedia:

Simple Desktop Display Manager (SDDM) is a display manager (a graphical login program) for X11 and Wayland windowing systems. SDDM was written from scratch in C++11 and supports theming via QML. KDE chose SDDM to be the successor of the KDE Display Manager for KDE Plasma 5.
Note: The Wayland windowing system is not yet fully supported [1]. Wayland sessions are listed, but SDDM runs on X11.

Installation

Install the sddm package. Optionally install sddm-kcm for the KDE Config 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/sddm.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-config-editor-gitAUR available in the AUR.

Everything should work out of the box, since Arch Linux uses systemd and SDDM defaults to using systemd-logind for session management. The configuration file will therefore not be created at package installation time. SDDM offers a command for generating a sample configuration file with the default settings if you really want one:

# sddm --example-config > /etc/sddm.conf.d/sddm.conf

Autologin

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

/etc/sddm.conf.d/autologin.conf
[Autologin]
User=john
Session=plasma.desktop

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/ directory.

An option to autologin into KDE Plasma while simultaneously locking the session is not available [2]

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

#!/bin/bash
/usr/bin/qdbus-qt4 org.kde.screensaver /ScreenSaver SetActive true &
exit 0

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-sddmAUR.

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.

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 --theme /usr/share/sddm/themes/breeze

This should open a new window 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 as username.face.icon into location specified in for FacesDir in the configuration file. The default location for FacesDir is /usr/share/sddm/faces/. You can change the default FacesDir location to match your requirements. 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.

Rotate display

See Xrandr#Configuration.

DPI settings

Sometimes it is useful to set up correct monitor's PPI settings on a "Display Manager" level. To do so you need to find ServerArguments parameter in sddm.conf and add -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: HiDPI support seems to be broken since version 0.15.[3]

Create the following file:

/etc/sddm.conf.d/hidpi.conf
[General]
EnableHiDPI=true

Troubleshooting

Hangs after login

Try removing ~/.Xauthority.

SDDM starts on tty1 instead of tty7

SDDM follows the systemd convention of starting the first graphical session on tty1. If you prefer the old convention where tty1 through tty6 are reserved for text consoles, change the default value of MinimumVT variable, which comes under the [X11] section:

/etc/sddm.conf.d/tty.conf
[X11]
MinimumVT=7

One or more users do not show up on the greeter

Warning: Users set with a lower or higher UID range should generally not be exposed to a Display manager.

SDDM only displays users with a UID in the range of 1000 to 65000 by default, if the UIDs of the desired users are below this value then you will have to modify this range. For example, for a UID of 501, say:

/etc/sddm.conf.d/uid.conf
[Users]
HideShells=/sbin/nologin,/bin/false
# Hidden users, this is if any system users fall within your range, see /etc/passwd on your system.
HideUsers=git,sddm,systemd-journal-remote,systemd-journal-upload

# Maximum user id for displayed users
MaximumUid=65000

# Minimum user id for displayed users
MinimumUid=500 #My UID is 501

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.

SDDM may also incorrectly display the layout as US but will immediately change to the correct layout after you start typing your password [4]. This seems to not be a bug in SDDM but in libxcb (version 1.13-1 as of 2018) [5].

Screen resolution is too low

Issue may be caused by HiDPI usage for monitors with corrupted EDID: [6]. If you have enabled HiDPI, try to disable it.

If even the above fails, you can try setting your screen size in a Xorg conf 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 editing /etc/sddm.conf:

/etc/sddm.conf
[Theme]
EnableAvatars=false