Run Wayland Compostor - no Login Manager + no Getty + no File Descriptors + (optionally) no Scripts

README.md

This tutorial ensures there's no stdin/stdout/stderr (File Descriptors) as a potential performance optimization vector, furthermore no Login Manager is required nor a VT/Virtual Terminal (Getty/agetty). You can still execute a custom script (e.g. start.sh) but by default it skips login and spawns a Wayland compositor in TTYPath=/dev/tty1

Steps

1. Open your desktop environment in a different TTY (e.g. CTRL+ALT+F2).

2. Copy over all files to your editor.

3. CTRL+F and searh for following hardcoded values and replace them with what fits your system:

   Value	Description
   tty1	desired TTY number
   chvt 1	TTY number
   game	your username
   /home/user/game	PATH to your $HOME
   jay	desired command

4. Prepare the environment:

   #sudo rm /etc/systemd/system/getty@tty1.service.d/autologin.conf
   sudo nano /etc/systemd/system/ttylauncher.service                 # Paste content of the systemd unit from below
   sudo systemctl enable ttylauncher                                 # Auto start on boot
   sudo systemctl mask autovt@tty1.service                           # Prevent VT1 template unit from being triggered
   sudo systemctl disable --now getty@tty1.service                   # Disable login prompt
   sudo systemctl daemon-reload; sudo systemctl restart ttylauncher  # Run each time you make modifications

5. Verify:

   $ sudo ls -l /proc/$(pgrep -x jay)/fd/{0,1,2}
   lr-x------ 1 game game 64 Aug  3 18:00 /proc/367459/fd/0 -> /dev/null
   l-wx------ 1 game game 64 Aug  3 18:00 /proc/367459/fd/1 -> /dev/null
   l-wx------ 1 game game 64 Aug  3 18:00 /proc/367459/fd/2 -> /dev/null

References

• Script

  To run a script.sh instead of a command, tweak ttylauncher.service to use:

  ExecStart=/home/user/game/start.sh

• Troubleshooting

  To collect logs with $ journalctl -f

  StandardOutput=journal

• File Descriptors

  /usr/bin/file </dev/null 1>/dev/null 2>/dev/null is equivelent to:

  StandardInput=null
  StandardOutput=null
  StandardError=null

  /usr/bin/file <&- 1>&- 2>&- can be replicated with:

  StandardInput=closed
  StandardOutput=closed
  StandardError=closed

Documentation

Unit file (systemd)

• https://www.freedesktop.org/software/systemd/man/latest/systemd.exec.html
• https://www.freedesktop.org/software/systemd/man/latest/systemd.service.html#Command%20lines
• https://www.freedesktop.org/software/systemd/man/latest/systemd.unit.html#Specifiers

Examples

• https://github.com/systemd/systemd/blob/main/units/getty%40.service.in
• https://gitlab.archlinux.org/archlinux/packaging/packages/nodm

start.sh

#!/usr/bin/env bash
set -x

# Debug
#whoami; groups

# USER ENV
export UID="$(id -u)"
export GID="$(id -g)"

# Performance
export TZ=:/etc/localtime

# Wayland
export SDL_VIDEODRIVER='wayland,x11,windows'
export MOZ_ENABLE_WAYLAND=1
export ELECTRON_OZONE_PLATFORM_HINT='wayland'
export QT_QPA_PLATFORM='wayland;xcb'
export QT_WAYLAND_DISABLE_WINDOWDECORATION=1
export GDK_BACKEND='wayland,x11'
export CLUTTER_BACKEND='wayland'

# XDG
export XDG_RUNTIME_DIR="/run/user/${UID}"
export XDG_CONFIG_HOME="${HOME}/.config"
export XDG_CACHE_HOME="${HOME}/.cache"
export XDG_STATE_HOME="${HOME}/.local/state"
export XDG_DATA_HOME="${HOME}/.local/share"
export XDG_SESSION_TYPE='wayland'
export DBUS_STARTER_BUS_TYPE='session'

# Shell
#export SHELL=/usr/bin/bash

# Compositor
export XDG_CURRENT_DESKTOP='jay'
export XDG_SESSION_DESKTOP='jay'
export WAYLAND_DISPLAY='wayland-1'
#export JAY_LOG_LEVEL=trace

exec /usr/bin/jay run

ttylauncher.service

[Unit]
Description=ttylauncher
After=sysinit.target

[Service]
Type=simple
User=game
WorkingDirectory=~
PAMName=login
RemainAfterExit=yes
Restart=always
RestartSec=5
StandardInput=null
StandardOutput=null
StandardError=null
TTYPath=/dev/tty1
ExecStartPre=+/usr/bin/chvt 1
ExecStart=/usr/bin/jay run

[Install]
WantedBy=multi-user.target