It is not possible to unset a variable in the dbus-daemon's activation environment, or with `dbus-update-activation-environment`: that's an API limitation in the org.freedesktop.DBus interface. I've thought about adding an UnsetAndSetActivationEnvironment() that could do this. It *is* possible to unset a variable in the `systemd --user` activation environment, with `systemctl --user unset-environment` or the UnsetEnvironment() and UnsetAndSetEnvironment() D-Bus methods on the systemd manager. If your distribution is using dbus-broker rather than dbus-daemon, and if Mantas was correct to say that dbus-broker does not have its own separate activation environment, then that should be enough to affect all D-Bus session services. It will also affect all other systemd user services.
Thank you. I now recommend dbus-broker in my session manager's readme (https://github.com/Vladimir-csp/uwsm), and management of dbus activation environment is now conditional on dbus unit true name not being dbus-broker.service.
BTW, the whole reason I even decided to interact with dbus is rather aggressive session termination by systemd. It seems to send signals not only to existing processes in the session, but even to new ones which were spawned in response to those signals. This makes it impossible to fork a systemctl process to stop related user units.
I solved this by interacting with dbus without spawning new processes, but, just for info, is there a proper way to fork something that survives for a bit in a session that is being terminated? With simple tools like `trap 'something' TERM HUP` in a shell? Or maybe there is some other more native way to bind a user level unit to a particular session scope?
