$ docker exec <container> <command>

$ ssh <host> <command>

# systemd-nspawn -D <machine-root> -b 3 --link-journal host

# systemd-run --machine <machine-name> env
Running as unit run-1356.service.

# journalctl --machine <machine-name> -u run-1356 -b -q
Oct 30 07:45:09 jessie-64 systemd[1]: Started /usr/bin/env.
Oct 30 07:45:09 jessie-64 env[37]: PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin

$ nsenter
     --target=$(machinectl show --property Leader ipsec-libreswan | sed "s/^Leader=//")
     --mount --uts --ipc --net --pid