* Preliminary NEWS for 0.8.
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Eelco Dolstra
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NEWS
142
NEWS
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Version 0.8
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NOTE: the hashing scheme in Nix 0.8 changed (as detailed below). As a
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result, `nix-pull' manifests and channels built for Nix 0.7 and below
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will now work anymore. However, the Nix expression language has not
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changed, so you can still build from source. Also, existing user
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environments continue to work. Nix 0.8 will automatically upgrade the
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database schema of previous installations when it is first run.
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* The cryptographic hashes used in store paths are now 160 bits long,
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but encoded in base-32 so that they are still only 32 characters
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long (e.g., /nix/store/csw87wag8bqlqk7ipllbwypb14xainap-atk-1.9.0).
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(This is actually a 160 bit truncation of a SHA-256 hash.)
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* Big cleanups and simplifications of the basic store semantics. The
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notion of "closure store expressions" is gone (and so is the notion
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of "successors"); the file system references of a store path are now
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just stored in the database.
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For instance, given any store path, you can query its closure:
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$ nix-store -qR $(which firefox)
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... lots of paths ...
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Also, Nix now remembers for each store path the derivation that
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built it (the "deriver"):
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$ nix-store -qR $(which firefox)
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/nix/store/4b0jx7vq80l9aqcnkszxhymsf1ffa5jd-firefox-1.0.1.drv
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So to see the build-time dependencies, you can do
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$ nix-store -qR $(nix-store -qd $(which firefox))
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or, in a nicer format:
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$ nix-store -q --tree $(nix-store -qd $(which firefox))
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File system references are also stored in reverse. For instance,
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you can query all paths that directly or indirectly use a certain
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Glibc:
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$ nix-store -q --referers-closure \
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/nix/store/8lz9yc6zgmc0vlqmn2ipcpkjlmbi51vv-glibc-2.3.4
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* The concept of fixed-output derivations has been formalised.
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Previously, functions such as `fetchurl' in Nixpkgs used a hack
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(namely, explicitly specifying a store path hash) to prevent changes
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to, say, the URL of the file from propagating upwards through the
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dependency graph, causing rebuilds of everything. This can now be
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done cleanly by specifying the `outputHash' and `outputHashAlgo'
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attributes. Nix itself checks that the content of the output has
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the specified hash. (This is important for maintaining certain
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invariants necessary for future work on secure shared stores.)
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* One-click installation :-) It is now possible to install any
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top-level component in Nixpkgs directly, through the web - see,
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e.g., http://catamaran.labs.cs.uu.nl/dist/nixpkgs-0.8/. All you
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have to do is associate `/nix/bin/nix-install-package' with
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`application/nix-package' (or the extension `.nixpkg'), and clicking
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on a package link will cause it to be installed, with all
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appropriate dependencies. If you just want to install some specific
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application, this is easier than subscribing to a channel.
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* `nix-store -r PATHS' now builds all the derivations PATHS in
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parallel. Previously it did them sequentially (though exploiting
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possible parallelism between subderivations). This is nice for
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build farms.
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* `nix-channel' has new operations `--list' and `--remove'.
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* New ways of installing components into user environments:
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- Copy from another user environment:
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$ nix-env -i --from-profile .../other-profile firefox
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- Install a store derivation directly (bypassing the Nix expression
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language entirely):
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$ nix-env -i /nix/store/z58v41v21xd3...-aterm-2.3.1.drv
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(This is used to implement `nix-install-package', which is
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therefore immune to evolution in the Nix expression language.)
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- Install an already built store path directly:
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$ nix-env -i /nix/store/hsyj5pbn0d9i...-aterm-2.3.1
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- Install the result of a Nix expression specified as a command-line
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argument:
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$ nix-env -f .../i686-linux.nix -i -E 'x: x.firefoxWrapper'
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The difference with the normal installation mode is that `-E' does
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not use the `name' attributes of derivations. Therefore, this can
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be used to disambiguate multiple derivations with the same name.
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* A hash of the contents of a store path is now stored in the database
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after a succesful build. This allows you to check whether store
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paths have been tampered with: `nix-store --verify --check-contents'.
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* Implemented a concurrent garbage collector. It is now always safe
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to run the garbage collector, even if other Nix operations are
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happening simultaneously.
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However, there can still be GC races if you use `nix-instantiate'
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and `nix-store -r' directly to build things. To prevent races, use
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the `--add-root' flag of those commands.
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* The garbage collector now finally deletes paths in the right order
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(i.e., topologically sorted under the `references' relation), thus
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making it safe to interrupt the collector without risking a store
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that violates the closure invariant.
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* Likewise, the substitute mechanism now downloads files in the right
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order, thus preserving the closure invariant at all times.
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* The result of `nix-build' is now registered as a root of the garbage
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collector. If the `./result' link is deleted, the GC root
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disappears automatically.
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* The behaviour of the garbage collector can be changed globally by
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setting options in `/nix/etc/nix/nix.conf'.
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- `gc-keep-derivations' specifies whether deriver links should be
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followed when searching for live paths.
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- `gc-keep-outputs' specifies whether outputs of derivations should
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be followed when searching for live paths.
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- `env-keep-derivations' specifies whether user environments should
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store the paths of derivations when they are added (thus keeping
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the derivations alive).
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* New `nix-env' query flags `--drv-path' and `--out-path'.
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* `fetchurl' allows SHA-1 and SHA-256 in addition to MD5. Just use
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`sha1 = ' or `sha256 = ' instead of `md5 = '. Of course, they're
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all unsafe, really ;-)
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Version 0.7
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* Binary patching. When upgrading components using pre-built binaries
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