Re: GDM failsafe session query

[Telsa Gwynne <hobbit aloss ukuu org uk>]

On Mon, May 03, 2004 at 03:31:12PM +0100 or thereabouts, Roger Burroughes wrote:
> On Sat, 1 May 2004, Telsa Gwynne wrote:
> > On Thu, Apr 29, 2004 at 10:16:01AM +0100 or thereabouts, 
> > Roger Burroughes wrote: 
> > 
> > > 	I have a question about failsafe sessions when a user's home
> > > directory isn't available (for whatever reason)...
> > > 
> > > 	When a user starts logging-in via GDM using the standard
> > > greeter (and assuming there is no home directory available for this
> > > user - everything works OK when it IS available), a warning message is
> > > displayed:
> > > 
> > >    "Your home directory is listed as:
> > >     '/home/infteach'
> > >     but it does not appear to exist.
> > >     Do you want to log in with the root
> > >     directory as your home directory?
> > > 
> > >     It is unlikely anything else will work unless
> > >     you use a failsafe session"
> > > 
> > > 	(This message is displayed even when a failsafe session is
> > > explicitly selected from the "Session" menu.) 
> > 
> > This suggestion came from someone else. Pardon me if it is not too 
> > coherent :) 
> > 
> > If there is no home directory, it can't write to the home 
> > directory. (Well, yes...) If it can't write to the home directory, 
> > it can't write the .Xauthority file. Is that .Xauthority file 
> > needed for applications to run?
> > 
> > The person who mentioned this thinks it might be. 
> > It might explain this, at least: 
> > 
> > > it's not even trying to run /etc/X11/gdm/Xsession (no
> > > /tmp/xses-infteach is created).
> 
> 	Many thanks for the feedback (and the only response so far!).

Well, I thought someone should give it a go! I confess, I was
rather hoping that someone would see mine and think "no, that's
not right" and correct it all :) 

> 	Given that it IS possible to log in via other methods (ssh,
> for example - which complains "/usr/bin/X11/xauth: error in locking
> authority file /home/infteach/.Xauthority", but does succeed), and
> then run something like /usr/X11R6/bin/xterm without error, I'm
> guessing that the lack of a .Xauthority file isn't a showstopper (but
> I'm willing to be proved wrong :-).

Oh. Hmm. All this stuff is rather beyond me, to be honest. I
used to have a rough idea about what happens as X starts and
clients connect, but after much reading I understood about
half of it for about half an hour and then forgot it all :( 
> 
> 	It would also appear that /etc/X11/gdm/Xsession assumes that
> the home directory MIGHT not be available, since it redirects errors
> to /tmp/xses-$USER if ~/.xsession-errors isn't available (although I
> suppose this could just be for non-writability or some other error,
> rather than complete a absence of home directory) - but in this case
> it isn't even getting the chance to check...
> 
> 	BTW, if anyone knows of any documentation that explains
> the components/programs invoked as part of the GDM login process,
> pointers would be appreciated...

There is documentation for GDM but I have lost it. I went to a
talk about it, but the talk turned out to be a one-hour talk
and the time for it was 30 minutes, so it went by rather fast
and a lot was missed. The best I can do is these notes from
it and I am not sure whether these are what you want:

    There are lots of system-specific things in X session 
    initialisation, so hard-coding things in is bad. Instead, GDM 
    puts things into three or (more recently) four directories in 
    /etc/X11/gdm/. The contents of those are shell scripts.

    The first directory is Init/. The script found here controls 
    the set-up of the login screen and is looked at before the 
    greeter process starts.

    Next comes PostLogin/ which is run just after authentication 
    has successfully ocrrued but before GDM has even decided which 
    session to use or the correct home directory for the user has been found.

    Next comes PreSession/. This is run after the login setup is 
    completely but before the X session starts. For example, utmp 
    and wtmp have not been written to yet.

    After this, the user is in Gnome (or KDE, or X, or..)

Are these the components you're talking about? 

The gdm.conf file is heavily-commented, but I don't think it
contains the stuff you're really looking for. 

Telsa