Bug#1019502: xfce4-session: sometimes fails to start from gdm3: /usr/bin/startxfce4: X server already running on display :0

[Simon McVittie]

Package: xfce4-session
Version: 4.16.0-1
Severity: normal

While testing installation media for #debian-cd, I tried the test-case
that involved installing all the available desktop environments (GNOME,
XFCE, etc.). I chose gdm3 as the display manager when prompted (it was the
default), finished the installation, and rebooted to the installed system.

Most of the desktop environments that I tried worked fine, but XFCE failed
to log in (bounced back to the gdm3 prompt after a brief blank screen).
This log message in the systemd journal might be relevant:

Sep 10 17:41:04 espresso /usr/libexec/gdm-x-session[10361]: /usr/bin/startxfce4: X server already running on display :0

I'm surprised if startxfce4 is starting its own X11 server, since the
traditional situation for X11 display managers is that the display manager
is responsible for starting Xorg.

It worked OK when I used dpkg-reconfigure to swap from gdm3 to lightdm
(which is a better choice anyway on systems where you'd want to use XFCE).

This doesn't seem to be 100% reproducible: after a couple of cycles of
switching the display manager and rebooting, XFCE started up fine even
from gdm3. I'm not sure what was going on there.

As a hint for any XFCE maintainers who might look into this while not
being familiar with gdm3, the interface for choosing a desktop environment
in gdm3 is:

- choose your user
- don't enter your password immediately
- click on the gear wheel icon in the lower right corner
- choose the desired desktop environment
- *now* enter your password

smcv

-- System Information:
Debian Release: 11.5
APT prefers stable-updates
APT policy: (500, 'stable-updates'), (500, 'stable-security'), (500, 'stable')
Architecture: amd64 (x86_64)

Kernel: Linux 5.10.0-18-amd64 (SMP w/4 CPU threads)
Locale: LANG=en_GB.UTF-8, LC_CTYPE=en_GB.UTF-8 (charmap=UTF-8), LANGUAGE=en_GB:en
Shell: /bin/sh linked to /usr/bin/dash
Init: systemd (via /run/systemd/system)
LSM: AppArmor: enabled

Versions of packages xfce4-session depends on:
ii libatk1.0-0 2.36.0-2
ii libc6 2.31-13+deb11u4
ii libcairo2 1.16.0-5
ii libgdk-pixbuf-2.0-0 2.42.2+dfsg-1
ii libglib2.0-0 2.66.8-1
ii libgtk-3-0 3.24.24-4+deb11u2
ii libice6 2:1.0.10-1
ii libpango-1.0-0 1.46.2-3
ii libpolkit-gobject-1-0 0.105-31+deb11u1
ii libsm6 2:1.2.3-1
ii libwnck-3-0 3.36.0-1
ii libx11-6 2:1.7.2-1
ii libxfce4ui-2-0 4.16.0-1
ii libxfce4util7 4.16.0-1
ii libxfconf-0-3 4.16.0-2
ii x11-xserver-utils 7.7+8
ii xfce4-settings 4.16.0-1
ii xfconf 4.16.0-2

Versions of packages xfce4-session recommends:
ii dbus-user-session [default-dbus-session-bus] 1.12.20-2
ii dbus-x11 [dbus-session-bus] 1.12.20-2
ii libpam-systemd [logind] 247.3-7+deb11u1
ii light-locker 1.8.0-3
ii systemd-sysv 247.3-7+deb11u1
ii upower 0.99.11-2
ii xfdesktop4 4.16.0-1
ii xfwm4 4.16.1-1

Versions of packages xfce4-session suggests:
pn fortunes-mod <none>
ii sudo 1.9.5p2-3

-- no debconf information

[Nicolas Patrois]

Package: xfce4-session
Version: 4.18.3-1
Followup-For: Bug #1019502

Dear Maintainer,

After a reboot, XFCE refuses to run using wdm, here is what I read in
~/.xession-errors:

/usr/bin/startxfce4: X server already running on display :0

If you want more logs, just ask!

Yours,
n.


-- System Information:
Debian Release: trixie/sid
APT prefers unstable
APT policy: (500, 'unstable'), (500, 'stable')
Architecture: i386 (i686)

Kernel: Linux 5.16.0-6-686-pae (SMP w/3 CPU threads; PREEMPT)
Kernel taint flags: TAINT_PROPRIETARY_MODULE, TAINT_OOT_MODULE, TAINT_UNSIGNED_MODULE
Locale: LANG=fr_FR.UTF-8, LC_CTYPE=fr_FR.UTF-8 (charmap=UTF-8), LANGUAGE=fr_FR:fr:en_GB:en

Shell: /bin/sh linked to /usr/bin/dash
Init: systemd (via /run/systemd/system)
LSM: AppArmor: enabled

Versions of packages xfce4-session depends on:

ii libatk1.0-0 2.49.90-2
ii libc6 2.37-7
ii libcairo-gobject2 1.16.0-7
ii libcairo2 1.16.0-7
ii libgdk-pixbuf-2.0-0 2.42.10+dfsg-1+b1
ii libglib2.0-0 2.77.1-2
ii libgtk-3-0 3.24.38-4
ii libice6 2:1.0.10-1
ii libpango-1.0-0 1.50.14+ds-1
ii libpolkit-gobject-1-0 123-1
ii libsm6 2:1.2.3-1
ii libwnck-3-0 43.0-3
ii libx11-6 2:1.8.6-1
ii libxfce4ui-2-0 4.18.4-1
ii libxfce4util7 4.18.1-2
ii libxfconf-0-3 4.18.1-1
ii x11-xserver-utils 7.7+9+b1
ii xfce4-settings 4.18.3-1
ii xfconf 4.18.1-1

Versions of packages xfce4-session recommends:

ii dbus-user-session [default-dbus-session-bus] 1.14.8-2
ii dbus-x11 [dbus-session-bus] 1.14.8-2
ii gnome-screensaver 3.6.1-13+b2
ii libpam-systemd [logind] 254.1-2
ii systemd-sysv 254.1-2
ii upower 1.90.2-4
ii xfdesktop4 4.18.1-1
ii xfwm4 4.18.0-1

Versions of packages xfce4-session suggests:

ii fortune-mod 1:1.99.1-7.3
ii sudo 1.9.14p2-1

-- no debconf information