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2.2.1 Build Environment Setup

In a standard multi-user setup, Guix and its daemon—the guix-daemon program—are installed by the system administrator; /gnu/store is owned by root and guix-daemon runs as root. Unprivileged users may use Guix tools to build packages or otherwise access the store, and the daemon will do it on their behalf, ensuring that the store is kept in a consistent state, and allowing built packages to be shared among users.

When guix-daemon runs as root, you may not want package build processes themselves to run as root too, for obvious security reasons. To avoid that, a special pool of build users should be created for use by build processes started by the daemon. These build users need not have a shell and a home directory: they will just be used when the daemon drops root privileges in build processes. Having several such users allows the daemon to launch distinct build processes under separate UIDs, which guarantees that they do not interfere with each other—an essential feature since builds are regarded as pure functions (see Introduction).

On a GNU/Linux system, a build user pool may be created like this (using Bash syntax and the shadow commands):

# groupadd guix-builder
# for i in `seq 1 10`;
  do
    useradd -g guix-builder -G guix-builder           \
            -d /var/empty -s `which nologin`          \
            -c "Guix build user $i" --system          \
            guix-builder$i;
  done

The guix-daemon program may then be run as root with:

# guix-daemon --build-users-group=guix-builder

This way, the daemon starts build processes in a chroot, under one of the guix-builder users. On GNU/Linux, by default, the chroot environment contains nothing but:

If you are installing Guix as an unprivileged user, it is still possible to run guix-daemon. However, build processes will not be isolated from one another, and not from the rest of the system. Thus, build processes may interfere with each other, and may access programs, libraries, and other files available on the system—making it much harder to view them as pure functions.


Footnotes

(2)

“Mostly”, because while the set of files that appear in the chroot’s /dev is fixed, most of these files can only be created if the host has them.


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