With systemd version 230+ detachind and logout from remote machine will kill tmux session.

Systemd config

First solution is to disable killing user processes systemwide. Edit /etc/systemd/logind.conf and set

KillUserProcesses=no

Then restart systemd-logind.service:

# systemctl restart systemd-logind

Tmux as a service

Second solution is running tmux as a service. Just add RemainAfterExit=yes option to /etc/systemd/system/tmux@.service:

[Unit]
Description=tmux default session (detached)
Documentation=man:tmux(1)

[Service]
Type=oneshot
RemainAfterExit=yes
ExecStart=/usr/bin/tmux new-session -d -s %I
ExecStop=/usr/bin/tmux kill-server
KillMode=none

[Install]
WantedBy=multiplexer.target

And then use it like this:

# systemctl start tmux@instanceone.service
# systemctl start tmux@instancetwo.service
# tmux list-sessions

instanceone: 1 windows (created Sun Jul 24 00:52:15 2016) [193x49]
instancetwo: 1 windows (created Sun Jul 24 00:52:19 2016) [193x49]

# tmux attach-session -t instanceone

(instanceone)#

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