NixOS OpenRC Experimental Fork

Module Architecture

nixos/
├── modules/
│   ├── services/
│   │   └── openrc/
│   │       ├── default.nix         # Main service
│   │       ├── library-setup.nix  # Library
│   │       ├── runtime.nix        # Runtime config
│   │       ├── runtime-setup.nix  # Runtime env
│   │       └── service-aggregation.nix # Service
│   └── system/
│       └── boot/
│           └── openrc-init.nix    # Core boot

Key Technical Challenges

1. Read-Only Store Compatibility

   • Problem: OpenRC expects writable /etc/init.d
   • Solution: Symlink farm in /run/openrc with Nix store backing
   • Relevant Files: service-aggregation.nix, runtime-setup.nix

2. Service Management

   • Problem: systemd-style declarative services → OpenRC scripts
   • Solution: Nix-generated init scripts with dependency resolution
   • Relevant Files: default.nix (services.openrc options)

3. Library Paths

   • Problem: OpenRC binaries expect libraries in /lib
   • Solution: Copy libraries to /lib at runtime + ldconfig in writable store
   • Relevant Files: library-setup.nix

Core Components

1. Runtime Environment (runtime-setup.nix)

# Creates writable OpenRC structure
mkdir -p /run/openrc/{init.d,conf.d,rc/sh,rc/bin}

# Critical environment variables
export RC_LIBEXECDIR=/run/openrc/rc
export PATH="${openrcPkg}/bin:${coreutils}/bin:$PATH"

# Init script patching
sed -i "1s|#!/bin/sh|#!${bash}/bin/bash|" "$target"

2. Service Aggregation (service-aggregation.nix)

# Aggregates services from Nix store
rsync -a ${openrcPkg}/etc/openrc/init.d/ $out/etc/openrc/init.d/

# User-defined services
install -Dm755 ${cfg.script} $out/etc/openrc/init.d/${name}

3. Library Initialization (library-setup.nix)

# Library copy from Nix store to /lib
cp -av ${package}/lib/lib{einfo,rc}.so* /lib/

# Writable ld.so.cache generation
TMPDIR=/run/ldconfig ldconfig -C /run/ldconfig/ld.so.cache

Known Issues & Workarounds

1. Missing rc/sh Scripts

* openrc: unable to exec `/nix/store/.../libexec/rc/sh/init.sh`: No such file or directory
* gendepends.sh: No such file or directory

Root Cause: OpenRC hardcodes paths to its libexec scripts. The Nix build puts these in the store path, but OpenRC's init process looks for them in runtime paths.

Workarounds:

1. Add explicit symlinks in service aggregation:

# service-aggregation.nix
ln -s ${openrcPkg}/libexec/rc/sh/init.sh $out/etc/openrc/init.d/
ln -s ${openrcPkg}/libexec/rc/sh/gendepends.sh $out/etc/openrc/init.d/

2. Patch OpenRC source to use runtime paths:

# openrc-nixos-init.patch
- rc_confdir = "/libexec/rc";
+ rc_confdir = "/run/openrc/rc";

3. Add to runtime-setup.nix:

# Copy critical RC scripts to runtime directory
cp -v ${openrcPkg}/libexec/rc/sh/*.sh /run/openrc/rc/sh/
chmod 755 /run/openrc/rc/sh/*

2. Library Path Resolution

ERROR: libeinfo.so.1: cannot open shared object file

Workaround: Add explicit library cache regeneration step:

# library-setup.nix
echo "Force-regenerating library cache..."
LD_LIBRARY_PATH=/lib /run/current-system/sw/bin/ldconfig

3. Partial Boot Sequence

Starting default runlevel... [hangs]

Source Patches Overview

(pkgs/openrc/)

1. Path Structure Patch (openrc-nixos-paths.patch)

diff --git a/meson.build b/meson.build
+rootprefix = get_option('prefix')
-bindir = get_option('prefix') / get_option('bindir')
+bindir = rootprefix / get_option('bindir')

Purpose: Separates build-time paths from runtime paths using rootprefix Impact: Enables Nix store path isolation while maintaining FHS compatibility

2. Runlevel Symlink Patch (openrc-nixos-runlevels.patch)

diff --git a/tools/meson_runlevels.sh b/tools/meson_runlevels.sh
-ln -snf "${init_d_dir}/$x" "${DESTDIR}${sysinitdir}/$x"
+ln -snf "${DESTDIR}${init_d_dir}/$x" "${DESTDIR}${sysinitdir}/$x"

Purpose: Fixes symlink creation with DESTDIR during installation Why Needed: Prevents broken symlinks in final Nix package

3. Init Process Patch (openrc-nixos-init.patch)

diff --git a/src/openrc-init/openrc-init.c b/src/openrc-init/openrc-init.c
-execlp("openrc", "openrc", runlevel, NULL);
+execlp("@OPENRC@/bin/openrc", "openrc", runlevel, NULL);

Purpose: Hardcodes Nix store path for init process Critical For: Stage 2 initialization reliability

4. Script Compatibility Patch (openrc-nixos-scripts.patch)

diff --git a/init.d/bootmisc.in b/init.d/bootmisc.in
-need localmount
+use localmount
-migrate_to_run /var/lock /run/lock
+migrate_to_run /var/lock /run/openrc/lock

Purpose: Adapts service scripts for NixOS directory structure Key Change: Lock file relocation prevents conflicts

Package Build Configuration

(pkgs/openrc/default.nix)

Core Build Parameters

mesonFlags = [
  "-Drootprefix=${placeholder "out"}"
  "--localstatedir=/run/openrc"
  "-Dselinux=disabled"
  "-Dnewnet=false"
];

Critical Build Steps

1. Path Substitution:

substituteInPlace src/openrc-init/openrc-init.c \
  --replace "@PATH@" "${lib.makeBinPath [ coreutils bash ]}" \
  --replace "@OPENRC@" "$out"

2. Library Installation:

# Install OpenRC libraries with versioned symlinks
install -Dm755 "$libfile" "$out/lib/$(basename $libfile)"
ln -sf "$(basename $libfile)" "$out/lib/$base_libname.so"

3. Runtime Directory Setup:

postInstall = ''
  mkdir -p $out/{bin,sbin,lib,libexec/rc/{bin,sh}}
  install -Dm644 sh/functions.sh $out/libexec/rc/sh/functions.sh
'';

Debugging Patch Effects

Verify Applied Patches

nix-store --query --references $(which openrc) | grep openrc
nix-shell -p patchelf --run "patchelf --print-rpath ${pkgs.openrc}/lib/lib*"

Test Symlink Resolution

# In NixOS VM:
ls -l /run/openrc/init.d/functions.sh
readlink /etc/init.d/functions.sh

Patch Development Workflow

1. Modify patch files in pkgs/openrc/
2. Rebuild with debug symbols:

nix-build -E 'with import <nixpkgs> {}; openrc.overrideAttrs (o: {
  NIX_CFLAGS_COMPILE = "-O0 -g";
  patches = [ ./patches/new-patch.patch ];
})'

Critical Path Analysis

Patch Dependency Chain

1. openrc-nixos-paths.patch → Meson configuration
2. openrc-nixos-runlevels.patch → Runlevel setup
3. openrc-nixos-init.patch → Init process execution
4. openrc-nixos-scripts.patch → Service compatibility

Build Artifact Validation

# Verify library presence
ls -l ${pkgs.openrc}/lib/lib{einfo,rc}.so*

# Check init script paths
grep -r '/run/openrc' ${pkgs.openrc}/share/openrc/init.d/

Integration Points

NixOS Overrides

# In system configuration
boot.initrd.systemd.enable = false;
boot.initrd.openrc.enable = true;
services.openrc.enable = true;

Activation Hooks

# default.nix
system.activationScripts.openrc = ''
  ${openrcPkg}/bin/rc-update -u
'';

Contributor Access Points

1. Service Dependency Resolution

   • File: service-aggregation.nix
   • Key Function: Service ordering in runlevels

2. Init Script Compatibility

   • File: runtime-setup.nix
   • Key Function: Script patching logic

3. Boot Process Integration

   • File: system/boot/openrc-init.nix
   • Key Function: Stage 2 initialization