More additional information:
Terminating a container that booted up properly with machinectl results in the same error. Killing the systemd-nspawn process directly with kill -9 works, the container can be started again.

Looks like duplicate of 988877

Hi. I run into this too with systemd-208-26.fc20.x86_64.

[root@zaphod centos-6]# systemd-nspawn --bind=/home -b
Spawning namespace container on /home/containers/centos-6 (console is /dev/pts/2).
Init process in the container running as PID 11409.
Failed to register machine: Input/output error
Container failed with error code 251.

It's happened after I had killed the machine with 'machinectl terminate centos-6'. I still can see these files/directories on my machine even though the container is not running:

/sys/fs/cgroup/systemd/machine.slice/machine-centos\x2d6.scope/
/run/systemd/system/machine-centos\x2d6.scope
/run/systemd/system/machine-centos\x2d6.scope.d/

It seems like the cgroup and scope units were not properly cleaned up.

Additional information from the journal:

systemd[1]: machine-rawhide.scope stopping timed out. Killing.
systemd[1]: machine-rawhide.scope still around after SIGKILL. Ignoring.

Not fixed by upstream commit 21b2ce39d4038cd6176394836fdcfb7fba63f424 (service: use the right timeout for stop processes we fork).

As a work around one can specify a new name with -M.

One more observation:

Deleting the leftover files does *not* solve the problem.

After debugging this, it appears to be the same problem as described in http://lists.freedesktop.org/archives/systemd-devel/2014-November/025700.html (follow-up in http://lists.freedesktop.org/archives/systemd-devel/2014-December/025778.html).

The problem is "fixed" by backporting http://cgit.freedesktop.org/systemd/systemd/commit/?id=1baccdda2e954214e0c5463d6ed8f06009b33c41. However, after the fix, the terminal that was used to spawn the container (using -b) gets stalled and the systemd-nspawn process has to be killed by a SIGKILL. I think that the "fix" is the lesser of two evils, so I'll probably backport it.

Zbyszek, any objections?

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