Running Synth in jail?

[Amplificator]

I'm trying to get Synth working inside of jails. I followed the official "guidelines" on setting it up by setting the following flags on the jail:

Code:

enforce_statfs=0
allow.mount
allow.mount.nullfs
allow.mount.tmpfs
allow.mount.devfs
allow.chflags

But running 'synth status' or 'synth upgrade-system' I get the following error:

Code:

Builder mounts detected; attempting to remove them automatically ...
The attempt failed. Check for stuck or ongoing processes and kill them.
After that, try running Synth again or just manually unmount everything
still attached to /usr/obj/synth-live

Any tips on how to proceed?