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Add notes about switching to SDDM
Juan Nunez-Iglesias
(Jun 28, 2026, 5:15 PM +0200)
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notes/sddm-sugar-candy.md
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notes/sddm-sugar-candy.md
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# Switching the login greeter to SDDM + Sugar Candy
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Future-me notes. Current setup (2026-06): Pop!_OS 24.04 LTS, login handled by
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**cosmic-greeter** (greetd). Both `cosmic.desktop` and `sway.desktop` live in
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`/usr/share/wayland-sessions/`, so any greeter that reads that folder offers
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both desktops automatically.
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Repo SDDM is **0.20.0 (Qt5, X11 greeter)**. That's fine: Xorg is already
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installed, and an X11 *greeter* launching a Wayland *session* (COSMIC/Sway) has
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no effect on the session you log into. The Wayland greeter needs SDDM >= 0.21,
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which is NOT in the 24.04 repos — see "Wayland greeter" at the bottom.
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## 1. Install SDDM + Sugar Candy's QML deps
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```bash
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sudo apt install sddm \
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qml-module-qtgraphicaleffects \
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qml-module-qtquick-controls2 \
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qml-module-qtquick2
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```
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Do NOT let this auto-switch the display manager yet — if apt/debconf asks which
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display manager to use, you can pick sddm, but the explicit switch is in step 5
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so it's reversible.
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## 2. Get the Sugar Candy theme
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The original (Marian Arlt) was removed from its old host; use a current mirror/
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fork. Verify the URL is alive before cloning.
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```bash
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# maintained fork that tracks current SDDM:
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sudo git clone https://github.com/Kangie/sddm-sugar-candy.git \
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/usr/share/sddm/themes/sugar-candy
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```
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(Alternatives if that 404s: search "sddm sugar candy" — there are several
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mirrors; any copy with a `Main.qml` + `theme.conf` dropped into
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`/usr/share/sddm/themes/sugar-candy/` works.)
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## 3. Select the theme
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```bash
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sudo install -d /etc/sddm.conf.d
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printf '[Theme]\nCurrent=sugar-candy\n' | sudo tee /etc/sddm.conf.d/theme.conf
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```
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## 4. Configure Sugar Candy
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Don't edit the theme's `theme.conf` directly (a theme update clobbers it).
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Sugar Candy reads `theme.conf.user` as an override:
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```bash
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sudo cp /usr/share/sddm/themes/sugar-candy/theme.conf \
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/usr/share/sddm/themes/sugar-candy/theme.conf.user
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sudo $EDITOR /usr/share/sddm/themes/sugar-candy/theme.conf.user
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```
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Good starting values (keeps it consistent with the Sway desktop wallpaper):
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```ini
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[General]
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Background="/usr/share/backgrounds/cosmic/orion_nebula_nasa_heic0601a.jpg"
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ScreenWidth="1920" # match your panel; only used for the blur preview
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ScreenHeight="1080"
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DimBackgroundImage="0.2"
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ScaleImageCropped="true"
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FullBlur="false" # true = blur whole screen; false = partial behind card
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PartialBlur="true"
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BlurRadius="40"
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HaveFormBackground="true"
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FormPosition="center" # left | center | right
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MainColor="white"
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AccentColor="#7c5cbf" # matches the swaylock ring purple
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BackgroundColor="#1e1e2e"
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Font="DejaVu Sans Mono"
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HourFormat="HH:mm"
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DateFormat="dddd, d MMMM"
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```
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## 5. Switch from cosmic-greeter to SDDM (reversible)
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Only one `display-manager.service` is active at a time.
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```bash
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sudo systemctl disable --now cosmic-greeter
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sudo systemctl enable sddm # don't --now from inside a graphical session
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```
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Then reboot (cleanest) or, from a TTY (Ctrl+Alt+F3), `sudo systemctl start sddm`.
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At the SDDM screen there's a **session selector** (dropdown, usually
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bottom-left) listing COSMIC and Sway. SDDM remembers the last choice per user.
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### Rollback
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```bash
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sudo systemctl disable --now sddm
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sudo systemctl enable --now cosmic-greeter
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```
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(Keep `cosmic-greeter` installed as the fallback.)
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## Wayland greeter (SDDM >= 0.21) — and the dist-upgrade question
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The 0.20 greeter runs on X11. To get the native **Wayland** greeter you need
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SDDM >= 0.21, which Pop!_OS 24.04 does NOT ship. Getting it would mean building
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0.21+ from source (Qt6) — i.e. self-maintaining a core login component on an
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LTS. Not worth it just so the *login screen* is Wayland; it changes nothing
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about your actual sessions.
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Do NOT dist-upgrade for this. This is **Pop!_OS**, not Ubuntu — it upgrades via
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System76's path (`pop-upgrade` / System76 repos), not by pointing apt at a newer
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Ubuntu (that would break COSMIC, drivers, and pins). 24.04 is the current
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COSMIC LTS; there's nowhere newer to go right now that hands you SDDM 0.21.
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If a future Pop!_OS release ships SDDM >= 0.21 through normal updates, revisit:
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```ini
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# /etc/sddm.conf.d/wayland.conf (0.21+ only)
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[General]
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DisplayServer=wayland
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[Wayland]
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CompositorCommand=weston --shell=fullscreen-shell.so # weston is in the repos
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```
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and use a Qt6 build of Sugar Candy. Until then, stay on the 0.20 X11 greeter.
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If you specifically want a *pure-Wayland* greeter NOW without an OS upgrade, the
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proportionate move is to stay on greetd (already installed) and use ReGreet
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(GTK, wallpaper) or tuigreet — not to chase SDDM 0.21.