When tmux is running, GuixSD fails to reboot. No more details yet, but
confirmation from at least 3 users:

[19:24:57] <CharlieBrown> My system can't shut itself down. Once it says everything is shut down, I have to power off with the power button.
[19:25:05] <lfam> CharlieBrown: I've had that issue before
[19:25:12] <lfam> CharlieBrown: Are you using tmux or screen?
[19:25:23] <CharlieBrown> lfam: Yes.
[19:25:38] <lfam> CharlieBrown: I haven't seriously debugged yet, but I think Shepherd is failing to kill tmux, preventing shutdown
[19:25:47] <paroneayea> must be that your computer doesn't want to shut down screen
[19:25:51] <CharlieBrown> lfam: :-(
[19:25:53] <paroneayea> because it's using a screen-saver
[19:25:57] <paroneayea> sorry, bad pun
[19:25:59] <lfam> Lol
[19:26:21] <lfam> I should make a bug report
[19:26:36] <lfam> CharlieBrown: Tmux or screen?
[19:26:37] <ng0> I have this bug for 2 years now.. so it's a bug.
[19:26:46] <lfam> And ng0, tmux or screen?
[19:26:46] <ng0> here it is tmux
[19:27:07] <lfam> It's quite bad for remote machines. It breaks rebooting completely
[19:27:20] <CharlieBrown> lfam: tmux

https://gnunet.org/bot/log/guix/2017-05-14#T1386137