Description of problem:

The terminal multiplexer tmux is compiled without utempter. The configuration
changed in 2.4 and utempter support is no longer compiled by default
(intentionally). It is necessary to execute ./configure --enable-utempter in order
to make it working again - without it the currently logged-in user is not tracked
in tmux sessions correctly.

See also https://github.com/tmux/tmux/issues/1006

Version-Release number of selected component (if applicable):

All versions of tmux since 2.4.

How reproducible:

Steps to Reproduce:
1. Install tmux
2. Connect with SSH to the machine with tmux
3. who -m
4. tmux
5. who -m
6. sudo su -
7. who -m

Actual results:

Empty line in `who -m` after executing `tmux`.

Expected results:

All `who -m` steps (steps 3, 5 and 7) print line with the same user name.

Additional info: