Re: Multiple sessions for the same user?

[Brian Nitz <Brian Nitz Sun COM>]

One problem I hear about from time to time is when someone is using the 
same home directory for several sessions on different machines which may 
be running different versions of GNOME.

e.g. Logged into my NFS home directory on a laptop running Gnome 2.10 in 
ubuntu.
Simultaneously logged into the same home directory on Sun Ray running 
GNOME 2.20 on Solaris Nevada.  (and/or Gnome 2.6 on Solaris 10!)

I know we can't fix past problems (easily), but if we consider the 
possibility of this sort of use, we might make things better down the road.



Havoc Pennington wrote:
> Hi,
>
> Stef Walter wrote:
>   
> > This may be a dumb question, but I'm wondering if we support (or it is a
> > goal to support) multiple sessions for the same user in GNOME.
> >
> > As far as I can tell a lot of GNOME software doesn't currently take that
> > into account. I'm working on gnome-keyring-daemon, and I'm wondering if
> > I need to keep multiple sessions in mind or just take the much simpler
> > approach of one session per user.
> >
> >     
>
> Everything needs to hang off either the session dbus daemon or the X 
> server, then it should Just Work for multiple sessions. By "hang off" I 
> mean some arrangement such that the user gets 1 daemon for each X server 
> or dbus bus, and such that the 1 daemon exits when either the X server 
> or the dbus bus exits. The lifetime of the  X server and the dbus bus 
> should be the same (they should exit together) in a properly-configured 
> GNOME setup, so it does not matter which one you use.
>
> The only other, possibly-sane alternative is per-machine or 
> per-(user,machine) or per-(session,machine) scoping (i.e. have a socket 
> in /tmp, or hang off the system dbus daemon, possibly including username 
> or dbus session uuid in the socket or bus name). However, this is wrong 
> for most purposes, so be careful. And you have to be sure there's some 
> way to exit the daemon when there are no active sessions.
>
> Historical GNOME problems in this area have come from gconfd and Bonobo 
> components getting the scoping wrong; they should have been per-session, 
> but were not.
>
> The temptation is to think that per-user scoping is possible, but it 
> isn't. One reason is that there's no way to coordinate copies of the 
> daemon on multiple machines. You can't reliably have a network 
> connection between machines, and fcntl() locking in the home directory 
> does not reliably work in the real world due to NFS and AFS. (If you 
> need to do locking to support multiple daemons operating on one homedir, 
> I suggest the approach used by the dbus cookie file code.)
>
> Havoc
>
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