@dthompson @cwebber Unprivileged namespaces are one of the three “engines”; the others are PRoot and Fakechroot:
https://guix.gnu.org/manual/devel/en/html_node/Invoking-guix-pack.html
The default with ‘-RR’ is to try namespaces and then PRoot (much slower).
You can set ‘GUIX_EXECUTION_ENGINE=performance’ to fall back to Fakechroot.