Subject: bug#73928: Bug#1080330: coreutils: who no longer works

From: Paul Eggert <[email-masked]>
Date: Sun, 16 Feb 2025 23:40:12 -0800

On 2025-02-16 23:03, Thorsten Kukuk wrote:
> The problems were already all solved with the first coreutils versions
> having systemd-logind support.  Even with all the bug reports I don't
> see a need for changes in Coreutils, only in distributions not
> enabling systemd-logind support in all packages.

Thanks for the summary. Unfortunately I'm not seeing all the problems 
solved, at least not on current Fedora (41) and Ubuntu (24.10).

If I configure current (f2e323430193956709aacca33f6b4fcab4fb9d8b) 
Coreutils with --enable-systemd on my Ubuntu 24.10 desktop, the output 
gets worse:

   $ ./who-no-systemd # Configured normally.
   eggert   seat0        2025-02-15 10:11 (login screen)
   eggert   tty2         2025-02-15 10:11 (tty2)
   $ ./who-with-systemd # Configured with --enable-systemd.
   eggert   seat0        2025-02-15 10:11
   eggert   tty2         2025-02-15 10:11

Apparently for coreutils, /var/run/utmp (the traditional interface) has 
more info than libsystemd's API. (For what it's worth, both versions of 
"who" consult /var/run/utmp on Ubuntu 24.10, but the systemd version 
also consults /run/systemd/sessions/*.)

Similarly, on a Fedora 41 desktop where I'm not currently logged in, I 
get inferior results when Coreutils is configured with --enable-systemd:

   $ ./who-no-systemd
   eggert   pts/3        2025-02-16 22:56 (47.147.225.25)
   $ ./who-with-systemd
   gdm      seat0        2025-02-13 18:04
   gdm      tty1         2025-02-13 18:04
   eggert   sshd pts/3   2025-02-16 22:56 (47.147.225.25)

Here, though I'm logged in only via ssh, the libsystemd-using 'who' 
incorrectly reports that a user named "gdm" is logged in in person.

My guess is that, once systemd was changed to continue to output via the 
traditional /var/run/utmp and /var/log/wtmp files, people stopped 
configuring coreutils with --enable-systemd and stopped worrying about 
making sure that the more-modern systemd API works, which means that the 
traditional files are still essential.

I'll add bug-gnulib to the cc list as this may be a Gnulib issue.