[Linux] Packages cannot be installed into `/`

[lengau]

When using the glibc standalone Python builds for Linux containers, installing these standalone builds into / results in some weird behaviour. The root cause appears to be that sys.base_prefix is set to /install. I've created a Rockcraft file that demonstrates the issue at https://github.com/lengau/bug-reproducers/tree/python-standalone-bin

While the packages work correctly when placed into /usr, they don't work in /. If placed in /usr on a system with /usr merge, the same issues appear when calling /bin/python3 or related.

Given how different this is from the purpose of these builds I think it's reasonable to file it under quirks and move on, but I figured you ought to know :-)

[jjhelmus]

I was able to replicate this issue in a Docker container using:

FROM ubuntu:24.04

# The installer requires curl (and certificates) to download the release archive
RUN apt-get update && apt-get install -y --no-install-recommends curl ca-certificates

# Download the latest installer
ADD https://astral.sh/uv/install.sh /uv-installer.sh

# Run the installer then remove it
RUN sh /uv-installer.sh && rm /uv-installer.sh

# Ensure the installed binary is on the `PATH`
ENV PATH="/root/.local/bin/:$PATH"

RUN mkdir /blah && uv python install --no-bin --install-dir /blah 3.14

RUN apt-get install -y --no-install-recommends rsync

RUN rsync -ar /blah/cpython-*/ /

As mentioned sys.path is not set correctly:

$ docker run -it debug /bin/python -m site
Could not find platform independent libraries <prefix>
Could not find platform dependent libraries <exec_prefix>
sys.path = [
    '/',
    '/install/lib/python314.zip',
    '/lib/python3.14',
    '/install/lib/python3.14/lib-dynload',
]
USER_BASE: '/root/.local' (exists)
USER_SITE: '/root/.local/lib/python3.14/site-packages' (doesn't exist)
ENABLE_USER_SITE: True

This may be related to the getpath modifications made to support a relocatable builds done in #896.