SLiMM

Stateless Lightweight Modern Manager — an ultra-lightweight graphical login bootstrapper for Wayland-era Linux.

Boot → SLiMM → PAM auth → exec compositor (in place) → logout → systemd respawns SLiMM

No SLiMM process after login. The greeter authenticates then exec()s the compositor in place — the main PID becomes the compositor, so nothing lingers. systemd is the supervisor: slimm.service is Restart=always, so when the compositor exits (logout) a fresh greeter starts.

Session lifecycle

Login → greeter exec()s compositor (no slimm process left)
      → logout (compositor exits) → systemd Restart=always → login screen

• Greeter exec()s the compositor in place — the main PID becomes the compositor, so 0 MB slimm RSS during the session (the point of a stateless greeter)
• exec closes slimm's DRM/render/input fds (an explicit exec_close_inherited_fds() guards it regardless of O_CLOEXEC), so no leftover DRM client stalls the compositor's first modeset — this is what fixed the NVIDIA post-login freeze
• setsid() + ignore SIGHUP so VT hangups don't disturb the compositor
• systemd is the supervisor: slimm.service Restart=always starts a fresh greeter when the compositor exits
• StartLimitBurst=5 / 30s crash-loop guard — falls back to a usable tty instead of flickering forever
• RestartPreventExitStatus=42 — Escape exits the greeter (status 42) to a console and systemd does not respawn it

Features

• Direct DRM/KMS rendering (primary backend)
• STE2 precompiled themes — mmap at runtime, zero TOML/font/image parsing in production
• PAM authentication
• Session discovery from /usr/share/wayland-sessions/
• OS logo auto-detected at build time from /etc/os-release
• One-shot execution (~52 KB stripped MINIMAL binary)
• GLES3 UI with cached panel/field FBOs

Requirements

Runtime (production slimm):

• DRM/KMS, EGL/GLES (Mesa), libinput, libxkbcommon, PAM, systemd-libs

Build (slimc theme compiler + makepkg):

• base-devel, FreeType, fontconfig, JetBrains Mono Nerd Font (Arch: ttf-jetbrains-mono-nerd)

Build

make                         # MINIMAL=1: slimm + slimc + theme.slimt
make dev                     # dev binary: TOML + Wayland overlay
make V=1                     # verbose compile
makepkg -si                  # Arch package (from this directory)

Make variable	Default	Meaning
MINIMAL=1	yes	Production: STE2-only, no FreeType/fontconfig at runtime
VERSION=x.y.z	0.2.5	Footer string SLiMM x.y.z
V=0	yes	Quiet build (PKGBUILD uses this)

Build auto-detects host OS logo → baked into theme.slimt. Override with logo_path in theme.toml.

Install

sudo make install
sudo systemctl enable --now slimm.service

Disable another DM first (e.g. sudo systemctl disable --now slim2).

Configuration

File	Role
/etc/slimm/theme.slimt	Production — precompiled STE2 blob (required)
/etc/slimm/theme.toml	Source for slimc; edit then recompile
/etc/pam.d/slimm	PAM authentication stack

After editing theme.toml:

sudo slimc /etc/slimm/theme.toml -o /etc/slimm/theme.slimt
sudo systemctl restart slimm

theme.toml notes

• No inline comments on value lines — put # comments on their own line (parser strips inline # but keep values clean)
• autologin_user = "name" — pre-fill username; greeter starts on password field
• autologin_delay = 0 — wait for password + Enter (non-zero = auto-login without password)

Login flow

Step	Action
1	Type username (or skip if autologin_user set)
2	Enter
3	Type password (* in field)
4	Enter

Low-RAM theme tips

• Solid background_color only (default) — no wallpaper GPU texture
• bg_max_width / bg_max_height cap wallpaper at compile time (default 1280×720)

Usage

slimm --help
slimm --ste2 /path/to/theme.slimt

Dev build only:

slimm --config ./theme.toml    # TOML fallback
# theme.toml: mode = "wayland"  # overlay inside Hyprland/Sway

Logout

The slimm.service main PID is the compositor (SLiMM exec'd it from the .desktop file — usually start-hyprland, not Hyprland alone). When that exits, the unit's Restart=always starts a fresh greeter.

Hyprland bind	Effect
hl.dsp.exit() (Super+M)	Exits Hyprland; start-hyprland exits on clean shutdown → unit restarts → greeter returns
loginctl terminate-user $USER	Ends full user session → compositor exits → unit restarts → greeter returns

If logout shows a black screen or getty instead of SLiMM, check the journal:

journalctl -t slimm -b -e          # greeter (syslog)
journalctl -u slimm -b -e          # systemd unit (start/restart)
journalctl -b | rg 'session:'      # either source

Expect session: pid … exec '…' as <user> right after login; on logout, systemd restarts the unit and a fresh greeter comes up (RestartSec=1).

Debugging

journalctl -t slimm -b -e -f

After login, confirm no slimm process lingers (the PID became the compositor):

pgrep -a slimm                     # expect: no output during an active session
pstree -ps "$(pgrep -x Hyprland | head -1)"
# expect: systemd → start-hyprland → Hyprland  (no slimm in the chain)

Look for login ok for '…', launching '/usr/bin/…' after auth.

Development overlay

make dev + mode = "wayland" in theme.toml — test UI inside a running compositor without taking over tty1.

Related

• SLiM2 — persistent DRM/KMS greeter (same author)
• Classic SLiM — historical X11 login manager

License

MIT — see LICENSE.