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Development shells with Nix: four quick examples
2 months ago
- Nix allows using OpenCV for GoCV development without permanently installing it, avoiding system pollution and long-term maintenance of extra packages.
- The Debian approach (apt install libopencv-dev) installs over 500 packages, while Nix provides temporary, isolated environments via nix-shell or nix develop.
- Four examples demonstrate increasing complexity: interactive nix-shell -p, shell.nix for repeatability, flake.nix with pinned dependencies, and system-independent flakes using flake-utils.
- Setup requires installing Nix, enabling flakes, and setting NIX_PATH (or using NixOS which comes pre-configured).
- Nix flakes enable hermetic, reproducible development environments with locked dependency versions in flake.lock.
- For one-off experiments, nix-shell is quick; for shared/published projects, a system-independent flake.nix is recommended despite more boilerplate.
Agda on NixOS
2 months ago
- Install Agda and its standard library using Nix by adding to `environment.systemPackages` or `home-manager` configuration with `agda.withPackages`.
- For Emacs users, install `agda2-mode` via home-manager's `programs.emacs.extraPackages`.
- Typecheck Agda files with `agda filename.agda` and compile with `agda -c filename.agda` to produce an executable.
- To use the standard library in a project, create a `.agda-lib` file in the project directory with `depend: standard-library` and `include: .` to resolve imports like `Data.Nat`.
- Without the library file, Agda will fail to find standard library modules, as shown in the example error.
Ad-Hoc Emacs Packages with Nix
2 months ago
- Nix can be used as an Emacs package manager to manage packages from MELPA or nixpkgs.
- Users can create ad-hoc packages for software not in MELPA, like inform7-mode, using trivialBuild.
- Nix handles commit pinning, security (SHA-256 hashes), and dependencies for custom packages.
- Examples of custom packaged modes include cabal-mode, xcompose-mode, eat, and lean4-mode.
- For packages needing non-ELisp files (like JSON), melpaBuild is used instead of trivialBuild.
- Nix offers a cleaner alternative to git submodules or Makefiles for vendoring Emacs packages.
Using Nix with Dockerfiles
2 months ago
- Nix provides a consistent environment across development (Linux and Mac), CI, and production, eliminating the need for separate configurations.
- Using Nix as a single source of truth prevents common issues like mismatched dependencies or environments that break after updates.
- The Dockerfile approach uses Nix to build the application and copies only the minimal closure of dependencies into a scratch image, resulting in small, reproducible images.
- A practical example with Python and Flask demonstrates how to define a Nix flake and a Dockerfile for building and running the application.
- Downsides include the learning curve of Nix and suboptimal Docker layer caching, but benefits compound when reusing the configuration for development and CI.
Linux kernel will support $ORIGIN, sort of
2 months ago
- The goal is to support relocatable binaries in Nix by allowing $ORIGIN in PT_INTERP and shebang.
- Christian Brauner suggested using eBPF for programmable interpreter selection via binfmt_misc, rather than a kernel patch.
- An eBPF program can match ELF files and dynamically determine the interpreter path, supporting $ORIGIN.
- A new binfmt_misc flag 'L' enables loader substitution, making the interpreter override transparent and preserving process identity.
- Future plans include a NixOS module that registers the BPF handler at boot, gated on a new PT_INTERP_NIX segment for opt-in.
The death and rebirth of my home server
2 months ago
- The author's home server running on a Raspberry Pi 4B with a microSD card failed after a power outage, likely due to the card reaching its write cycle limit.
- Important data was backed up on external HDDs, and the NixOS configuration was preserved, minimizing data loss.
- A new setup was configured to minimize writes to the microSD card by using zram for swap, a RAM disk for /tmp, and disabling atime.
- External HDDs were repurposed into a btrfs pool with RAID1 replication for redundancy, using an autosubvol module for declarative subvolume management per service.
- Backups were set up using restic with sops-nix integration, and permissions were managed via a media group for shared access among services.
- Monitoring plans include btrfs scrubs and potential setup of smartd, Prometheus, or Grafana for system health tracking.
- A new high-endurance microSD card was purchased, and the system was deployed using NixOS with a custom SD image build.

Development shells with Nix: four quick examples

Agda on NixOS

Ad-Hoc Emacs Packages with Nix

Using Nix with Dockerfiles

Linux kernel will support $ORIGIN, sort of

The death and rebirth of my home server