しばらく再起動していなかったのだが，諸事情により再起動すると，Xが起動しないという Debian GNU/Linux sid (unstable) に良くあるいつものパタン．
以下のような環境で，まず Xorg が起動しない．
- xinit 1.3.4-3
- xserver-xorg-core 2:1.18.4-1
- nvidia-kernel-dkms 361.45.18-2
/var/log/messages によると以下のループ．
Sep 5 10:16:23 hoge gdm-launch-environment]: AccountsService: Could not get current seat: No data available Sep 5 10:16:23 hoge /usr/lib/gdm3/gdm-wayland-session[5493]: Unable to register display with display manager Sep 5 10:16:23 hoge gdm3: Child process -5493 was already dead. Sep 5 10:16:23 hoge gdm3: Child process 5489 was already dead. Sep 5 10:16:23 hoge gdm3: Unable to kill session worker process
/var/lib/gdm3/.local/share/xorg/Xorg.0.log によると nvidia の driver が見つからなくて EE で落ちている．最近 CRON-APT で横着して upgrade していたのだが何かの拍子に xserver-xorg-video-nvidia が抜けてしまったらしい．ということで入れる．
次は Xorg も /usr/lib/gdm3/gdm-x-session も起動しているが gnome-shell が起動しない(ログイン画面が出ず真っ黒のまま)．/var/log/messages によると以下のようにまた nvidia まわりでコケている．
Sep 5 10:16:52 hoge gnome-session[9184]: modprobe: ERROR: could not insert 'nvidia_current_modeset': Operation not permitted Sep 5 10:16:52 hoge gnome-session[9184]: modprobe: ERROR: ../libkmod/libkmod-module.c:977 command_do() Error running install command for nvidia_modeset Sep 5 10:16:52 hoge gnome-session[9184]: modprobe: ERROR: could not insert 'nvidia_modeset': Operation not permitted Sep 5 10:16:52 hoge gnome-session[9184]: gnome-session-binary[9184]: WARNING: Could not parse desktop file orca-autostart.desktop or it references a not found TryExec binary Sep 5 10:16:52 hoge org.gnome.Shell.desktop[9210]: modprobe: ERROR: could not insert 'nvidia_current_modeset': Operation not permitted Sep 5 10:16:52 hoge org.gnome.Shell.desktop[9210]: modprobe: ERROR: ../libkmod/libkmod-module.c:977 command_do() Error running install command for nvidia_modeset Sep 5 10:16:52 hoge org.gnome.Shell.desktop[9210]: modprobe: ERROR: could not insert 'nvidia_modeset': Operation not permitted Sep 5 10:16:52 hoge kernel: [ 1059.936725] gnome-shell[9210]: segfault at 14 ip 00007faf5bd4a817 sp 00007fff6e0c7a80 error 4 in libmutter.so.0.0.0[7faf5bcfb000+127000] Sep 5 10:16:52 hoge gnome-session[9184]: gnome-session-binary[9184]: WARNING: Application 'org.gnome.Shell.desktop' killed by signal 11 Sep 5 10:16:52 hoge org.gnome.Shell.desktop[9221]: modprobe: ERROR: could not insert 'nvidia_current_modeset': Operation not permitted Sep 5 10:16:52 hoge org.gnome.Shell.desktop[9221]: modprobe: ERROR: ../libkmod/libkmod-module.c:977 command_do() Error running install command for nvidia_modeset Sep 5 10:16:52 hoge org.gnome.Shell.desktop[9221]: modprobe: ERROR: could not insert 'nvidia_modeset': Operation not permitted Sep 5 10:16:52 hoge kernel: [ 1060.010282] gnome-shell[9221]: segfault at 14 ip 00007f08d9038817 sp 00007ffd8e2648a0 error 4 in libmutter.so.0.0.0[7f08d8fe9000+127000] Sep 5 10:16:52 hoge gnome-session[9184]: gnome-session-binary[9184]: WARNING: Application 'org.gnome.Shell.desktop' killed by signal 11 Sep 5 10:16:52 hoge gnome-session[9184]: gnome-session-binary[9184]: WARNING: App 'org.gnome.Shell.desktop' respawning too quickly Sep 5 10:16:52 hoge gnome-session[9184]: Unable to init server: Could not connect: Connection refused Sep 5 10:16:52 hoge gnome-session-f[9231]: Cannot open display: Sep 5 10:16:52 hoge gnome-session-binary[9184]: Entering running state Sep 5 10:16:53 hoge gdm3: GdmDisplay: display lasted 2.595077 seconds
どうやら modprobe nvidia_modeset の権限がなくてコケている様子．ということで，/etc/modules に nvidia-current-modeset およびついでに nvidia-current-uvm を追加して解決．