Can't get flatpak running

[Bastien Nocera]

Hey,

I'd like to try running Flatpak on an ARM system, now that we have ARM
runtimes. It's running Debian with a slightly older kernel, but not
ancient by any means.

I though the problem was user namespaces:

# /sbin/sysctl kernel.unprivileged_userns_clone=1
sysctl: cannot stat /proc/sys/kernel/unprivileged_userns_clone: No such
file or directory

# grep USER_NS /boot/config-4.3.0 
CONFIG_USER_NS=y

As a normal user:
$ flatpak run org.gnome.clocks
Can't mount devpts on /newroot/dev/pts: Operation not permitted
Can't read from privileged_op_socket

As root:
# flatpak run org.gnome.clocks
error: No systemd user session available, sandboxing not available

Which is expected as I'm running this on the console.
What am I missing here?

It's flatpak 0.6.5-1.

Cheers