It seems that on a fresh trixie install, nothing creates /run/utmp
anymore. Is that a bug or is utmp deprecated? who and who -b still seem
to work, so not sure how who finds its information, and if this means
utmp is not required anymore.
According to Googel Gemini (sorry...):
Yes, it is by design that /run/utmp is no longer provided in Debian
Trixie.
This change is primarily due to:
Year 2038 Problem (Y2K38): The traditional utmp file format uses 32-bit
timestamps, which are susceptible to the Year 2038 problem. After
January 19, 2038, these timestamps will overflow, leading to incorrect
date and time readings. Upstream developers for the utmp format have
been unwilling to change it.

Modern systemd Session Management: systemd (which Debian uses as its
init system) has its own, more robust, and modern session management
capabilities. Information about active sessions, login times, and other
user accounting data is now primarily managed by systemd itself, often
exposed via logind and its API.
So maybe sshd should ignore any error connected to utmp, instead of
throwing an error.
Thanks,
Paul
