kdm does not restart X server (that crashed on logout)

KDM, as an X application, goes down along with the X server. So if KDM is not running I think it's a bit much to expect it to restart X ;-)

Hi Jonathan,
that a common prejudice: kdm runs fine without X and even without a gfx card, e.g. on a mulituser server, kdm only announces the login service via XDMCP ;)

Back to topic: Current behaviour is broken: in the good-old-days, before alt-ctrl-del was disbled, kdm restarted the Xserver when it was killed (or crashed). In case of a broken Xserver kdm tried 3 times to start the Xsever, then gave up [today AFAIK a VESA Xserver will now be started instead?].

As further 'prove' of broken behaviour: /etc/init.d/kdm reload starts an Xserver then shows the login screen. Bugfree behaviour would be to restart X without a kick into the kdms a** via the reload command ;)

Achim

Since xserver-xorg-video-intel (2:2.8.1-1ubuntu2) upload the intel gfx driver does not crash
anymore but nevertheless, kdm does not start a new greeter.

After the crash I had a completely black screen, now I see black screen, for a short time
the busy mouse cursor (2 rotating white dots) then the standard mouse cursor appear
but screen stays black. No login greeter.

Now I have to 'service kdm restart' instead of reload, to get the login greeter back.

Achim

If I could edit bugs right now, I'd refocus the text of this bug to be primarily about what's in comment #3. The Intel crash is fixed, so fixing the kdm behavior when X doesn't crash is the priority.

A work around for this right now is to uncomment 'TerminateServer=true' in /etc/kde4/kdm/kdmrc.

Here is the work I have done thus far and tested without any resolve. I built a completely, patch-free, version of kdebase-workspace and tested it. I was still unable to logout. Further research will be done on this and hopefully we will have a valid fix instead of incorporating the work around. If anyone is able to come up with a valid fix, please state so in this report or in #kubuntu-devel on IRC ASAP. Thanks!

I tested the workaround for user switching. It does not wipe out the
original user's session as I had feared it might. User switching works.
Although not ideal, I think this is a valid work around if we can't get the
root cause solved before release.

I take it back. I lose compositing with that option set (and get it back if I unset it).

OK. Maybe it was something else. I'll test some more.

If this is any help:

The screen stays black, but the login still seems to work. You can see the cursor changing over the (non visible) username and password entry fields. If you manage to type your password in the right field, kdm will happily login.

If KDM logins in, do you see your screen at all or is it still black? I just did it, heard the startup sound, but everything was black.

Hmm, you're right. The screen stays black on login. (No idea, if it's really logging in, though.) But i remember having the behaviour described in comment #9 yesterday. Don't know what i changed :( Happens with and without compositing.

I've tried 4 computers: 3 with intel gfx card and one with radeon. The radeon show login after logout again. The three onboard intel gfx did not: Black screen with 'standard' mouse cursor visible.

While merging my jaunty config changes to karmic I've found this (forgotten) hack/workaround that 'fixes' this problem for all 3 intel gfx hardware: After logout as root. e.g.,

   DISPLAY=:0 XAUTHORITY=/var/run/xauth/A:0-w764YP xrandr --output VGA1 --off
   DISPLAY=:0 XAUTHORITY=/var/run/xauth/A:0-w764YP xrandr --output VGA1 --auto

This results in one flicker, but works. Simple Patch for /etc/kde4/kdm/Xsetup appended.
(does not dynamicly check with xrandr output(s) to use.

Achim

I've checked which config needed the hack in jaunty. The Intel driver was (all hardware running jaunty here has intel gfx GM45):

xserver-xorg-video-intel 2:2.6.3-0ubuntu9.3

In jaunty the login screen was black after a cold boot, not after logout. Now in karmic with

xserver-xorg-video-intel 2:2.8.1-1ubuntu2

it's the other way round: cold boot is fine, but screen black after logout.

Achim

When I installed jaunty kde 4.3.0 was in ppa. So I've only seem the problem with kdm of 4.3.0 and 4.3.1 never
tried 4.2.* yet. So it looks like at least kdm 4.3* and inter gfx driver 2.6 or 2.8 don't like each other.

I just did a fresh Kubuntu Karmic Beta install on my Macbook Pro(3,1) which has nVidia graphics. I was able to logout and back in again with no issues.

Based on some of the other comments, I was starting to feel like this was
another Intel issue. I think your test confirms it.

Testing shows this problem only occurs with KMS active.

Debugging with gdb shows we get a new frontbuffer when we logout and the xserver is reset. However, the new frontbuffer is not connected to the crtc .
in drmmode_set_mode_major we have:
        if (drmmode->fb_id == 0) {
                ret = drmModeAddFB(drmmode->fd,
and because fb_id is not null when the xserver is reset, drmModeAddFB is not called.

Attached patch solves this problem for me. I consider this a proof of concept patch; upstream may want to fix the issue in a different way (I don't like I had to add a new public function in drmmode_display.c).

Can someone confirm this patch solves the issue for them as well? If so, I will forward the bug and patch upstream tomorrow.

That pretty much confirms it's a driver issue then. Thanks for investigating this.

Retested after today's X updates and the problem is still present.

If I logout of the only user session, I get the problem described (cursor only and the KDM screen is present, so I can put a password in, but not see anything other than the mouse pointer). If I activate a second user session (from the option from a locked screen) I can start the new user session, switch back and forth, and log out of the second one with no problems.

This bug was fixed in the package xserver-xorg-video-intel - 2:2.9.0-1ubuntu2

---------------
xserver-xorg-video-intel (2:2.9.0-1ubuntu2) karmic; urgency=low

  * Add 100_drop_fb_from_crtc.patch. Fixes lockup with black screen on
    logout of KDE with KMS enabled. Patch zeroes out the framebuffer id
    to clean up on screen closure. Cherrypick from upstream.
    (LP: #432521)

 -- Bryce Harrington <email address hidden> Tue, 13 Oct 2009 11:31:29 -0700

Great! Thx a lot!!! I've installed 2:2.9.0-1ubuntu2 and now I get the login greeter again after logout.

Hi,

After installing this update, the login screen (kdm in my case) doesn't show up any more. I only get a black screen with sometimes video garbage.
Changing to another VT doesn't work, there is also only a black screen with a lonley "_" somewhere on the screen (not in the native video resolution by the way).
Restarting in recovery mode or with the nomodeset kernel parameter does work sometimes, sometimes this only leads to a black screen as well. Sometimes, after starting in recovery mode or with nomodeset, the normal startup works again once, but after another restart the black screen problem occurs again.

I would like to test if my problem really relates to the latest update, but I couldn't find the older package any more. Where can I find it, and would there be a problem if I simply reinstall the older package?

Regards,
Thomas