Although flying well under the radar of the average Linux user, D-Bus has been an integral part of Linux distributions for nearly two decades and counting. Rather than using faster point-to-point interprocess communication via a Unix socket or such, an IPC bus allows for IP communication in a bus-like manner for convenience reasons. D-Bus replaced a few existing IPC buses in the Gnome and KDE desktop environments and became since that time the de-facto standard. Which isn’t to say that D-Bus is well-designed or devoid of flaws, hence attracting the ire of people like [Vaxry] who recently wrote an article on why D-Bus should die and proposes using hyprwire instead.
The broader context is provided by [Brodie Robertson], whose video adds interesting details, such as that Arch Linux wrote its own D-Bus implementation rather than use the reference one. Then there’s CVE-2018-19358 pertaining to the security risk of using an unlocked keyring on D-Bus, as any application on said bus can read the contents. The response by the Gnome developers responsible for D-Bus was very Wayland-like in that they dismissed the CVE as ‘works as designed’.
I can’t argue with that.
With the systemd example, they’ve put the bus in /run, but with different sessions and slices and environments (which could all be concurrent), they’ll spawn a new bus, so there’s no general way to tell it which bus you want.
If you have a cron job (sorry, a systemd-timer job) set up to project your mailbox to your bathroom mirror on the hour, you’d want that isolated from your regular user bus.
I love where Plasma is these days (check out the Tiles editor with Meta+T), but I do wish it was easier to pick only the desktop elements I want. It feels like it’s all-or-nothing.