[systemd-devel] systemd session mode

[Lennart Poettering]

On Sun, 01.12.13 21:25, Hristo Venev (hristo at venev.name) wrote:

> I've implemented session mode for systemd. I am currently using it and it works
> pretty okay. I just had to generate D-Bus user services for D-Bus activation to
> work.
> 
> A new variable, XDG_SESSION_DIR, has been added. It defaults to
> /run/session/$XDG_SESSION_ID and is to be used for session-specific files as it
> is `rm -rf`-ed on logout. There, in ./systemd/private, the systemd socket is
> stored. Also, my implementation of session units stores the D-Bus socket in
> ./dbus/session_bus_socket.
> 
> Sorry if I am sending this for the third time but I can't see it in the mailing
> list.

Hmm, so, as Kay already mentioned, it was actually an explicit decision
not to support a session mode in systemd, or a per-session runtime
dir. Having system + user + session instances of systemd certainly
sounds like overkill, and we should actually encourage sharing of data
between sessions of the same user, so that he for example gets access to
an existing session's keyring when also logging in via ssh.

Moreover more apps than not actually do not support running multiple
times by same same user in multiple sessions. A few (like firefox)
explicitly block against that with a lock file, but in most cases this
is just something that isn't tested and hence a game of luck.

So, in order to keep things simply we are trying to push things towards
a per-user bus, a per-user systemd instance and a per-user runtime
dir. Then, for things where it's worth it programs can include the
session identifier in whatever resource they need on their own. For
example, if an application really wants to be compatible with running
multiple times from different sessions by the same user, then it can
include XDG_SESSION_ID in the bus name it grabs, in the files it creates
in XDG_RUNTIME_DIR and so on. 

The net result of that is probably that while users can easily have
multiple text logins at the same time, there's going to be only one
graphical session.

I hope this makes some sense,

Lennart

-- 
Lennart Poettering, Red Hat