mydm(5) File Formats Manual mydm(5)

mydm - session scripts format

mydm session scripts are executables stored in $MYDM_SESSION_DIR (by default in $HOME/.local/share/mydm-sessions). They can be any executables, but their most common format is shell scripts which set up the particular session environment.

Scripts can set special options, which use a special syntax. They are set inside the comments, typically near the top of the file, after the shebang, followed by the slash, followed by the option name. For example: 

#!/bin/sh
#/option

The following options are supported:

#/xsession

This script will be started through a startx executable instead of being executed directly.

It is a good practice, which applies for all kind of sessions to exec whichever program your script ultimately starts.

Users must be aware that session startup is usually quite involved and does a lot of things behind the scenes about which ordinary users are often unaware. These things must be manually replicated in session scripts. The most common ones are:

•starting a session bus, typically by dbus-launch program;
•setting up D-Bus and systemd environment;
•starting ssh-agent and gpg-agent.

When in doubt, users are adviced to check the documentation of their Operating System distributions.

#!/bin/bash
#/xsession
export XDG_CURRENT_DESKTOP=somewm
export XDG_SESSION_TYPE=x11
xrdb -merge "$HOME/.Xresources"
dbus-update-activation-environment --verbose --systemd --all
systemctl --user import-environment
exec /usr/bin/dbus-launch /usr/bin/x-window-manager


#!/bin/bash
source "${HOME}/.env"
source "${HOME}/.activate-dbus-environment
export XDG_CURRENT_DESKTOP=sway
export XDG_SESSION_TYPE=wayland
dbus-update-activation-environment --verbose --systemd --all
systemctl --user unset-environment SWAYSOCK I3SOCK WAYLAND_DISPLAY DISPLAY
systemctl --user import-environment
exec /usr/bin/dbus-launch /usr/bin/sway

A little more involved, but closer to the real world session script includes running a session bus separately: 

#!/bin/bash
#/xsession
# user-session socket has already been set up
if [ -z "$DBUS_SESSION_BUS_ADDRESS" ] && \
   [ -n "$XDG_RUNTIME_DIR" ] && \
   [ "$XDG_RUNTIME_DIR" = "/run/user/`id -u`" ] && \
   [ -S "$XDG_RUNTIME_DIR/bus" ]; then
  DBUS_SESSION_BUS_ADDRESS="unix:path=$XDG_RUNTIME_DIR/bus"
  export DBUS_SESSION_BUS_ADDRESS
fi
dbus-update-activation-environment --verbose --systemd \
  DBUS_SESSION_BUS_ADDRESS DISPLAY XAUTHORITY
# launch dbus if it isn't launched yet
if [ -z "$DBUS_SESSION_BUS_ADDRESS" ]; then
  eval $(/usr/bin/dbus-launch --exit-with-session --sh-syntax)
fi
# unset unnecessary env variables safely in a subshell and export environment
# to dbus
if [ -n "$DBUS_SESSION_BUS_ADDRESS" ]; then
  (
    unset XDG_SEAT
    unset XDG_SESSION_ID
    unset XDG_VTNR
    dbus-update-activation-environment --verbose --systemd --all
  )
fi
# dbus-update-activation-environment --systemd works only if systemd --user is
# available on dbus
systemctl --user import-environment
exec /usr/bin/x-window-manager

mydm(1) dbus-launch(1) systemctl(1)

Michał Góral <dev@goral.net.pl>

Source code: https://git.goral.net.pl/mydm.git

2024-05-10