A coredump is a snapshot of a process’s memory that is usually created by the kernel when a crash happens. These can be fairly helpful to find out which part of the code broke by looking at the backtrace or finding any kind of corruption by introspecting the memory itself. Unfortunately it can be a bit tedious to work with these. This article aims to give an overview over helpful tools & tricks to leverage the full power of coredumps on Nix-based systems.
One of the most important features for system administrators who operate NixOS systems are atomic upgrades which means that a deployment won’t reach an inconsistent state: if building a new system’s configuration succeeds, it will be activated in a single step by replacing the /run/current-system-symlink. If a build fails, e.g. due to broken packages, the configuration won’t be activated. This also means that downgrades are fairly simple since a previous configuration can be reactivated in a so-called rollback by changing the symlink to /run/current-system back to the previous store-path.
This is part 2 of a series of blog posts explaining how we took an existing Windows installation on hardware and moved it into a VM running on top of NixOS. Previously, we discussed how we performed the actual storage migration. In this post, we’ll cover the various performance optimisations we tried, what worked, and what didn’t work. GPU passthrough Since the machine is, amongst other things, used for gaming, graphics performance is critical.
In Nix 2 a new parameter to the derivation primitive was added. It changes how information is passed to the derivation builder. Current State In order to show how it changes the handling of parameters to derivation, the first example will show the current state with __structuredAttrs set to false and the stdenv.mkDerivation wrapper around derivation. All parameters are passed to the builder as environment variables, canonicalised by Nix in imitation of shell script conventions:
This is part 1 of a series of blog posts explaining how we took an existing Windows installation on hardware and moved it into a VM running on top of NixOS. Background We have a decently-equipped desktop PC sitting in our office, which is designated for data experiments using TensorFlow and such. During off-hours, it’s also used for games, and for that purpose it has Windows installed on it. We decided to try moving Windows into a VM within NixOS so that we could run both operating systems in parallel.
History The NixOS RFC process was established in March 2017, initiated by zimbatm, teh and Moretea in order to standardise a process to find an agreement on larger changes to Nix/NixOS/Nixpkgs and the ecosystem in general. Over the following one and a half years a few uncontroversial RFCs were merged but for most of the RFCs that needed further discussion nobody felt responsible to make a decision. That is the reason RFC 36 was written in collaboration with most core Nix/Nixpkgs members at the last NixCon and merged in December 2018 in order to streamline the process and define clearer responsibilities.
NixOS contains infrastructure for building integration tests based on QEMU/KVM virtual machines running NixOS. Tests built on this infrastructure are continuously run on new nixpkgs versions to ensure that NixOS continues to install and boot and that various services continue to operate correctly. This post illustrates how one may test a simple web service using NixOS tests. To have a simple enough example at hand, we wrote a small service in PHP—a classical guestbook in which visitors can leave a message that will then be written to a database and subsequently shown to later visitors of the same site.
Avoiding code repetition in a nixops deployment As with most configuration management tools, there are some options in nixops that need to be defined for virtually any machine in a deployment. These global options tend to be abstracted in a common base profile that is simply included at the top of a node configuration. This base profile can be used for including default packages, services or machine configuration usually needed on all machines—like networking debug tools and admin users with access to the whole network.
The resources.machines attribute set NixOps provides the evaluated node configurations of a deployment network in the resources.machines attribute set. Using this information, one can easily implement machine configurations that are generated from options in an existing network. For example, a reverse proxy that automatically proxies to all other webservers in the network—one which could handle TLS termination for all of them—can be generated without having to manually define individual virtual hosts.
To set up a NixOS system, you usually boot into a live NixOS system and install it onto a local disk as outlined in the manual. You can then modify the system configuration to tailor it to your needs. The build system Hydra builds live images like ISO images, container tarballs or AMIs based on their definition in nixpkgs. These images are made available for download on the official website.