NixOS/nix

Document the installation prefix

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#7771 opened on Feb 7, 2023

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Description

Problem

Many environment variables rely on a prefix that is not further explained, and it's not clear where it is defined and what value it has. In practice we observe it to be /nix.

Grepping the source one only finds one relevant occurrence in the Makefile, which defaults to /usr/local in the makefile, but this is just the location to place the build result in, and is set to $out in the Nix-based build.

Proposal

Document what prefix defaults to, and how and where it can be set.

Checklist

Priorities

Add :+1: to issues you find important.

Contributor guide

Tech stack
cppshell
Domain
documentation
Issue type
documentation
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
2
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
under 1 hour
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
fresh
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
understanding of Makefilefamiliarity with Nix environment variables
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
80
Research direction
Examine the Makefile at mk/lib.mk to see how the prefix variable is defined and defaulted to /usr/local. Note that in practice the Nix installation uses /nix. Check the Nix manual for any existing documentation of the prefix variable. Add a new section to the manual that explains the default value, how to set it via environment variables or build options, and where it is used. See also open documentation issues for similar clarifications.