For my home automation system I developed a purpose-built (minimal, embedded) Linux-based operating system.
This embedded Linux distribution is built using
Buildroot. To house my configuration, I
forked Buildroot on
GitHub. I added a
custom defconfig (configs/hjdskes_rpi3_defconfig) that holds my
image’s configuration, and there is a subdirectory in
board/hjdskes/rpi3/ to hold configuration files and a rootsfs
overlay.
The system is very minimal and modern: on top of the Linux kernel, it
installs systemd (only the required parts and logind), util-linux'
agetty and login, bash, Raspberry Pi firmware, wpa_supplicant,
mesa (Gallium VC4 driver, OpenGL ES and EGL), GTK+ 3, my Wayland
compositor Cage, the Cantarell font and the Adwaita
icon theme. Of course this also includes these packages' dependencies,
but with the finished filesystem using only 155 MB I think this
qualifies as a minimal system. I do still have to develop the actual
home automation application, which will add a few more dependencies to
the system.
Cage is started automatically on boot. I have written a systemd service for this, which logs in as the specified user after boot and then launches Cage. This systemd service does things the proper way, after this discussion on wayland-devel. That is, it sets up a full user session with logind and a custom PAM stack. This stack does the usual login handling through pam_unix and then launches a user session with pam_systemd.