Bug#1125486: gdm3: /tmp/.X11-unix/ owned by gdm-greeter, causes user session to fail to start

[Simon McVittie]

Control: tags -1 + moreinfo

On Wed, 14 Jan 2026 at 09:52:10 -0800, Ian McKellar wrote:
>When I looked, indeed /tmp/.X11-unix is owned by the gdm greeter user

That directory should have been created early in the boot with correct 
ownership and permissions by /usr/lib/tmpfiles.d/x11.conf, which is part 
of the systemd package. Is that not happening on your system?

What is the output of "systemd-tmpfiles --boot --dry-run --create" and 
"systemd-tmpfiles --tldr"?

Are there any errors logged in the systemd Journal before gdm starts? 
Specifically, the relevant part of the log is what's between

     Starting systemd-tmpfiles-setup.service - Create System Files and Directories...

and

     Finished systemd-tmpfiles-setup.service - Create System Files and Directories.

As a result of #1120032, you should see at least one message "Duplicate line 
for path "/run/lock", ignoring", and possibly more.

>When I looked, indeed /tmp/.X11-unix is owned by the gdm greeter user

If the overall system is working as intended, by the time gdm starts, 
those directories should already exist, therefore the gdm greeter should 
not be able to create them owned by itself, even if it wanted to.

     smcv