tmux sessions don't show up with who, users, ...

Hello and thanks for this bug report. I am able to reproduce the issue, which interestingly is not present in Groovy. I installed tmux 3.1b-1 from Groovy on a Focal system and it *does* set the utmp entries, so something must have changed between tmux 3.0a-2 and 3.1b-1. I had a look at the Ubuntu (= Debian) changelog and at the upstream commit history. Focal tmux (3.0a-2) correctly detected the utempter library [1]:

checking utempter.h usability... yes
checking utempter.h presence... yes
checking for utempter.h... yes
checking for library containing utempter_add_record... -lutempter

so that's not the issue. I'm marking this as Triaged for Focal and Fix Released for Groovy, but in order to push this forward we must identify the root cause of the issue, then we'll be able to evaluate the possibility of a SRU.

Debian doesn't not ship tmux 3.0a-2 anymore, so I don't think it's worth filing a bug in Debian even if tmux is a sync.

[1] https://launchpadlibrarian.net/458624914/buildlog_ubuntu-focal-amd64.tmux_3.0a-2_BUILDING.txt.gz

We also experience this bug on Focal. It is a real issue for us because unattended-upgrades relies on the `users` command to determine logged-in users. This means that on Focal, unattended-upgrades reboots forcefully and kills running tmux sessions even if instructed not to with `Unattended-Upgrade::Automatic-Reboot-WithUsers "false";` in the apt config.

Thanks for the feedback, Philipp.

I was able to further investigate this bug and found that the following upstream commit fixes it:

https://github.com/tmux/tmux/commit/54efe337993b5571728a09b247c7f39d493659a8

Given that this bug is affecting unattended-upgrade users, I'm raising its Importance and also tagging it as server-next.

Hello LTD, or anyone else affected,

Accepted tmux into focal-proposed. The package will build now and be available at https://launchpad.net/ubuntu/+source/tmux/3.0a-2ubuntu0.3 in a few hours, and then in the -proposed repository.

Please help us by testing this new package. See https://wiki.ubuntu.com/Testing/EnableProposed for documentation on how to enable and use -proposed. Your feedback will aid us getting this update out to other Ubuntu users.

If this package fixes the bug for you, please add a comment to this bug, mentioning the version of the package you tested, what testing has been performed on the package and change the tag from verification-needed-focal to verification-done-focal. If it does not fix the bug for you, please add a comment stating that, and change the tag to verification-failed-focal. In either case, without details of your testing we will not be able to proceed.

Further information regarding the verification process can be found at https://wiki.ubuntu.com/QATeam/PerformingSRUVerification . Thank you in advance for helping!

N.B. The updated package will be released to -updates after the bug(s) fixed by this package have been verified and the package has been in -proposed for a minimum of 7 days.

Thank you very much!

I downloaded and installed https://launchpad.net/ubuntu/+source/tmux/3.0a-2ubuntu0.3/+build/21444364/+files/tmux_3.0a-2ubuntu0.3_amd64.deb and it works fine. Tmux sessions get shown by `who` as before with `(tmux(3431814).%0)`. `users` also works.

Test results with Docker. Wrote the following files in an empty directory:

```Dockerfile
FROM ubuntu:focal
COPY proposed.list /etc/apt/sources.list.d/ubuntu-focal-proposed.list
RUN apt update && apt install -y tmux
```

```proposed.list
# Enable Ubuntu proposed archive
deb http://archive.ubuntu.com/ubuntu/ focal-proposed restricted main multiverse universe
```

Then ran:

$ docker build -t test-tmux .
$ docker run -it --rm test-tmux

Inside the container:

$ who
> No output
$ users
> no output

$ tmux
(detach with ctrl+b, then "d")
$ who
> root pts/1 Apr 23 12:14 (tmux(13).%0)
$ users
> root

Which confirms the fix.

This bug was fixed in the package tmux - 3.0a-2ubuntu0.3

---------------
tmux (3.0a-2ubuntu0.3) focal; urgency=medium

  * Fix "tmux sessions do not show up with who, users, etc" (LP: #1890406)
    - d/p/add-utempter-code.patch:
      Cherry-pick commit 54efe33 from upstream to add back utempter code to
      avoid users in tmux sessions not being accounted by the system.

 -- Athos Ribeiro <email address hidden> Thu, 22 Apr 2021 16:39:18 -0300

The verification of the Stable Release Update for tmux has completed successfully and the package is now being released to -updates. Subsequently, the Ubuntu Stable Release Updates Team is being unsubscribed and will not receive messages about this bug report. In the event that you encounter a regression using the package from -updates please report a new bug using ubuntu-bug and tag the bug report regression-update so we can easily find any regressions.