NixOS

NixOS documentation

Manual

The NixOS manual describes how to install and use NixOS.
The Nix manual describes how to use the Nix package manager.
Run man configuration.nix to see a list of all supported configuration options in configuration.nix.

Papers

The following research papers provide information on the rationale and design of NixOS.

Sander van der Burg and Eelco Dolstra. Automating System Tests Using Declarative Virtual Machines. In 21st IEEE International Symposium on Software Reliability Engineering (ISSRE 2010), San Jose, California, USA. November 2010. [pdf] [abstract]
Abstract: Automated regression test suites are an essential software engineering practice: they provide developers with rapid feedback on the impact of changes to a system’s source code. The inclusion of a test case in an automated test suite requires that the system’s build process can automatically provide all the environmental dependencies of the test. These are external elements necessary for a test to succeed, such as shared libraries, running programs, and so on. For some tests (e.g., a compiler’s), these requirements are simple to meet.
However, many kinds of tests, especially at the integration or system level, have complex dependencies that are hard to provide automatically, such as running database servers, administrative privileges, services on external machines or specific network topologies. As such dependencies make tests difficult to script, they are often only performed manually, if at all. This particularly affects testing of distributed systems and system-level software.
This paper shows how we can automatically instantiate the complex environments necessary for tests by creating (networks of) virtual machines on the fly from declarative specifications. Building on NixOS, a Linux distribution with a declarative configuration model, these specifications concisely model the required environmental dependencies. We also describe techniques that allow efficient instantiation of VMs. As a result, complex system tests become as easy to specify and execute as unit tests. We evaluate our approach using a number of representative problems, including automated regression testing of a Linux distribution.
Eelco Dolstra and Andres Löh and Nicolas Pierron. NixOS: A Purely Functional Linux Distribution. Cambridge University Press, 2010. [pdf] [doi] [abstract]
Abstract: Existing package and system configuration management tools suffer from an imperative model, where system administration actions such as upgrading packages or changes to system configuration files are stateful: they destructively update the state of the system. This leads to many problems, such as the inability to roll back changes easily, to deploy multiple versions of a package side-by-side, to reproduce a configuration deterministically on another machine, or to reliably upgrade a system. In this article we show that we can overcome these problems by moving to a purely functional system configuration model. This means that all static parts of a system (such as software packages, configuration files and system startup scripts) are built by pure functions and are immutable, stored in a way analogously to a heap in a purely functional language. We have implemented this model in NixOS, a non-trivial Linux distribution that uses the Nix package manager to build the entire system configuration from a modular, purely functional specification.
Eelco Dolstra and Andres Löh. NixOS: A Purely Functional Linux Distribution. In ICFP 2008: 13th ACM SIGPLAN International Conference on Functional Programming, pages 367–378, Victoria, British Columbia, Canada. September 2008. [pdf] [acm] [abstract]
Abstract: Existing package and system configuration management tools suffer from an imperative model, where system administration actions such as upgrading packages or changes to system configuration files are stateful: they destructively update the state of the system. This leads to many problems, such as the inability to roll back changes easily, to run multiple versions of a package side-by-side, to reproduce a configuration deterministically on another machine, or to reliably upgrade a system. In this paper we show that we can overcome these problems by moving to a purely functional system configuration model. This means that all static parts of a system (such as software packages, configuration files and system startup scripts) are built by pure functions and are immutable, stored in a way analogously to a heap in a purely function language. We have implemented this model in NixOS, a non-trivial Linux distribution that uses the Nix package manager to build the entire system configuration from a purely functional specification.
Eelco Dolstra and Armijn Hemel. Purely Functional System Configuration Management. In 11th Workshop on Hot Topics in Operating Systems (HotOS XI), San Diego, California, USA. USENIX, May 2007. [pdf] [abstract]
Abstract: System configuration management is difficult because systems evolve in an undisciplined way: packages are upgraded, configuration files are edited, and so on. The management of existing operating systems is strongly imperative in nature, since software packages and configuration data (e.g., /bin and /etc in Unix) can be seen as imperative data structures: they are updated in-place by system administration actions. In this paper we present an alternative approach to system configuration management: a purely functional method, analogous to languages like Haskell. In this approach, the static parts of a configuration — software packages, configuration files, control scripts — are built from pure functions, i.e., the results depend solely on the specified inputs of the function and are immutable. As a result, realising a system configuration becomes deterministic and reproducible. Upgrading to a new configuration is mostly atomic and doesn’t overwrite anything of the old configuration, thus enabling rollbacks. We have implemented the purely functional model in a small but realistic Linux-based operating system distribution called NixOS.