nix-store(1)

Name
nix-store - manipulate or query the Nix store

Synopsis
nix-store operation [options…] [arguments…] [--option name value] [--add-root path]

Description
The command nix-store performs primitive operations on the Nix store. You generally do not need to run this command manually.

nix-store takes exactly one operation flag which indicates the subcommand to be performed. These are documented below.

Common options
This section lists the options that are common to all operations. These options are allowed for every subcommand, though they may not always have an effect.

•   --add-root path

    Causes the result of a realisation (--realise and --force-realise) to be registered as a root of the garbage collector. path will be created as a symlink to the resulting store path. In addition, a uniquely named symlink to path will be created in /nix/var/nix/gcroots/auto/. For instance,

    $ nix-store --add-root /home/eelco/bla/result -r ...
    $ ls -l /nix/var/nix/gcroots/auto
    lrwxrwxrwx    1 ... 2005-03-13 21:10 dn54lcypm8f8... -> /home/eelco/bla/result
    $ ls -l /home/eelco/bla/result
    lrwxrwxrwx    1 ... 2005-03-13 21:10 /home/eelco/bla/result -> /nix/store/1r11343n6qd4...-f-spot-0.0.10

    Thus, when /home/eelco/bla/result is removed, the GC root in the auto directory becomes a dangling symlink and will be ignored by the collector.

        Warning

        Note that it is not possible to move or rename GC roots, since the symlink in the auto directory will still point to the old location.

    If there are multiple results, then multiple symlinks will be created by sequentially numbering symlinks beyond the first one (e.g., foo, foo-2, foo-3, and so on).

Operation --realise

  Synopsis
nix-store {--realise | -r} paths… [--dry-run]

  Description
The operation --realise essentially “builds” the specified store paths. Realisation is a somewhat overloaded term:

•   If the store path is a derivation, realisation ensures that the output paths of the derivation are valid (i.e., the output path and its closure exist in the file system). This can be done in several ways. First, it is possible that the outputs are already valid, in which case we are done immediately. Otherwise, there may be substitutes that produce the outputs (e.g., by downloading them). Finally, the outputs can be produced by running the build task described by the derivation.

•   If the store path is not a derivation, realisation ensures that the specified path is valid (i.e., it and its closure exist in the file system). If the path is already valid, we are done immediately. Otherwise, the path and any missing paths in its closure may be produced through substitutes. If there are no (successful) substitutes, realisation fails.

The output path of each derivation is printed on standard output. (For non-derivations argument, the argument itself is printed.)

The following flags are available:

•   --dry-run
    Print on standard error a description of what packages would be built or downloaded, without actually performing the operation.

•   --ignore-unknown
    If a non-derivation path does not have a substitute, then silently ignore it.

•   --check
    This option allows you to check whether a derivation is deterministic. It rebuilds the specified derivation and checks whether the result is bitwise-identical with the existing outputs, printing an error if that’s not the case. The outputs of the specified derivation must already exist. When used with -K, if an output path is not identical to the corresponding output from the previous build, the new output path is left in /nix/store/name.check.

Special exit codes:

•   100
    Generic build failure, the builder process returned with a non-zero exit code.

•   101
    Build timeout, the build was aborted because it did not complete within the specified timeout.

•   102
    Hash mismatch, the build output was rejected because it does not match the outputHash attribute of the derivation.

•   104
    Not deterministic, the build succeeded in check mode but the resulting output is not binary reproducible.

With the --keep-going flag it’s possible for multiple failures to occur, in this case the 1xx status codes are or combined using binary or.

    1100100
       ^^^^
       |||`- timeout
       ||`-- output hash mismatch
       |`--- build failure
       `---- not deterministic

  Examples
This operation is typically used to build store derivations produced by nix-instantiate:

    $ nix-store -r $(nix-instantiate ./test.nix)
    /nix/store/31axcgrlbfsxzmfff1gyj1bf62hvkby2-aterm-2.3.1

This is essentially what nix-build does.

To test whether a previously-built derivation is deterministic:

    $ nix-build '<nixpkgs>' -A hello --check -K

Use --read-log to show the stderr and stdout of a build:

    $ nix-store --read-log $(nix-instantiate ./test.nix)

Operation --serve

  Synopsis
nix-store --serve [--write]

  Description
The operation --serve provides access to the Nix store over stdin and stdout, and is intended to be used as a means of providing Nix store access to a restricted ssh user.

The following flags are available:

•   --write
    Allow the connected client to request the realization of derivations. In effect, this can be used to make the host act as a remote builder.

  Examples
To turn a host into a build server, the authorized_keys file can be used to provide build access to a given SSH public key:

    $ cat <<EOF >>/root/.ssh/authorized_keys
    command="nice -n20 nix-store --serve --write" ssh-rsa AAAAB3NzaC1yc2EAAAA...
    EOF

Operation --gc

  Synopsis
nix-store --gc [--print-roots | --print-live | --print-dead] [--max-freed bytes]

  Description
Without additional flags, the operation --gc performs a garbage collection on the Nix store. That is, all paths in the Nix store not reachable via file system references from a set of “roots”, are deleted.

The following suboperations may be specified:

•   --print-roots
    This operation prints on standard output the set of roots used by the garbage collector.

•   --print-live
    This operation prints on standard output the set of “live” store paths, which are all the store paths reachable from the roots. Live paths should never be deleted, since that would break consistency — it would become possible that applications are installed that reference things that are no longer present in the store.

•   --print-dead
    This operation prints out on standard output the set of “dead” store paths, which is just the opposite of the set of live paths: any path in the store that is not live (with respect to the roots) is dead.

By default, all unreachable paths are deleted. The following options control what gets deleted and in what order:

•   --max-freed bytes
    Keep deleting paths until at least bytes bytes have been deleted, then stop. The argument bytes can be followed by the multiplicative suffix K, M, G or T, denoting KiB, MiB, GiB or TiB units.

The behaviour of the collector is also influenced by the keep-outputs and keep-derivations settings in the Nix configuration file.

By default, the collector prints the total number of freed bytes when it finishes (or when it is interrupted). With --print-dead, it prints the number of bytes that would be freed.

  Examples
To delete all unreachable paths, just do:

    $ nix-store --gc
    deleting `/nix/store/kq82idx6g0nyzsp2s14gfsc38npai7lf-cairo-1.0.4.tar.gz.drv'
    ...
    8825586 bytes freed (8.42 MiB)

To delete at least 100 MiBs of unreachable paths:

    $ nix-store --gc --max-freed $((100 * 1024 * 1024))

Operation --delete

  Synopsis
nix-store --delete [--ignore-liveness] paths…

  Description
The operation --delete deletes the store paths paths from the Nix store, but only if it is safe to do so; that is, when the path is not reachable from a root of the garbage collector. This means that you can only delete paths that would also be deleted by nix-store --gc. Thus, --delete is a more targeted version of --gc.

With the option --ignore-liveness, reachability from the roots is ignored. However, the path still won’t be deleted if there are other paths in the store that refer to it (i.e., depend on it).

  Example

    $ nix-store --delete /nix/store/zq0h41l75vlb4z45kzgjjmsjxvcv1qk7-mesa-6.4
    0 bytes freed (0.00 MiB)
    error: cannot delete path `/nix/store/zq0h41l75vlb4z45kzgjjmsjxvcv1qk7-mesa-6.4' since it is still alive

Operation --query

  Synopsis
nix-store {--query | -q} {--outputs | --requisites | -R | --references | --referrers | --referrers-closure | --deriver | -d | --graph | --tree | --binding name | -b name | --hash | --size | --roots} [--use-output] [-u] [--force-realise] [-f] paths…

  Description
The operation --query displays various bits of information about the store paths . The queries are described below. At most one query can be specified. The default query is --outputs.

The paths paths may also be symlinks from outside of the Nix store, to the Nix store. In that case, the query is applied to the target of the symlink.

  Common query options

•   --use-output; -u
    For each argument to the query that is a store derivation, apply the query to the output path of the derivation instead.

•   --force-realise; -f
    Realise each argument to the query first (see nix-store --realise).

  Queries

•   --outputs
    Prints out the output paths of the store derivations paths. These are the paths that will be produced when the derivation is built.

•   --requisites; -R
    Prints out the closure of the store path paths.

    This query has one option:

    •   --include-outputs Also include the existing output paths of store derivations, and their closures.

    This query can be used to implement various kinds of deployment. A source deployment is obtained by distributing the closure of a store derivation. A binary deployment is obtained by distributing the closure of an output path. A cache deployment (combined source/binary deployment, including binaries of build-time-only dependencies) is obtained by distributing the closure of a store derivation and specifying the option --include-outputs.

•   --references
    Prints the set of references of the store paths paths, that is, their immediate dependencies. (For all dependencies, use --requisites.)

•   --referrers
    Prints the set of referrers of the store paths paths, that is, the store paths currently existing in the Nix store that refer to one of paths. Note that contrary to the references, the set of referrers is not constant; it can change as store paths are added or removed.

•   --referrers-closure
    Prints the closure of the set of store paths paths under the referrers relation; that is, all store paths that directly or indirectly refer to one of paths. These are all the path currently in the Nix store that are dependent on paths.

•   --deriver; -d
    Prints the deriver of the store paths paths. If the path has no deriver (e.g., if it is a source file), or if the deriver is not known (e.g., in the case of a binary-only deployment), the string unknown-deriver is printed.

•   --graph
    Prints the references graph of the store paths paths in the format of the dot tool of AT&T’s Graphviz package. This can be used to visualise dependency graphs. To obtain a build-time dependency graph, apply this to a store derivation. To obtain a runtime dependency graph, apply it to an output path.

•   --tree
    Prints the references graph of the store paths paths as a nested ASCII tree. References are ordered by descending closure size; this tends to flatten the tree, making it more readable. The query only recurses into a store path when it is first encountered; this prevents a blowup of the tree representation of the graph.

•   --graphml
    Prints the references graph of the store paths paths in the GraphML file format. This can be used to visualise dependency graphs. To obtain a build-time dependency graph, apply this to a store derivation. To obtain a runtime dependency graph, apply it to an output path.

•   --binding name; -b name
    Prints the value of the attribute name (i.e., environment variable) of the store derivations paths. It is an error for a derivation to not have the specified attribute.

•   --hash
    Prints the SHA-256 hash of the contents of the store paths paths (that is, the hash of the output of nix-store --dump on the given paths). Since the hash is stored in the Nix database, this is a fast operation.

•   --size
    Prints the size in bytes of the contents of the store paths paths — to be precise, the size of the output of nix-store --dump on the given paths. Note that the actual disk space required by the store paths may be higher, especially on filesystems with large cluster sizes.

•   --roots
    Prints the garbage collector roots that point, directly or indirectly, at the store paths paths.

  Examples
Print the closure (runtime dependencies) of the svn program in the current user environment:

    $ nix-store -qR $(which svn)
    /nix/store/5mbglq5ldqld8sj57273aljwkfvj22mc-subversion-1.1.4
    /nix/store/9lz9yc6zgmc0vlqmn2ipcpkjlmbi51vv-glibc-2.3.4
    ...

Print the build-time dependencies of svn:

    $ nix-store -qR $(nix-store -qd $(which svn))
    /nix/store/02iizgn86m42q905rddvg4ja975bk2i4-grep-2.5.1.tar.bz2.drv
    /nix/store/07a2bzxmzwz5hp58nf03pahrv2ygwgs3-gcc-wrapper.sh
    /nix/store/0ma7c9wsbaxahwwl04gbw3fcd806ski4-glibc-2.3.4.drv
    ... lots of other paths ...

The difference with the previous example is that we ask the closure of the derivation (-qd), not the closure of the output path that contains svn.

Show the build-time dependencies as a tree:

    $ nix-store -q --tree $(nix-store -qd $(which svn))
    /nix/store/7i5082kfb6yjbqdbiwdhhza0am2xvh6c-subversion-1.1.4.drv
    +---/nix/store/d8afh10z72n8l1cr5w42366abiblgn54-builder.sh
    +---/nix/store/fmzxmpjx2lh849ph0l36snfj9zdibw67-bash-3.0.drv
    |   +---/nix/store/570hmhmx3v57605cqg9yfvvyh0nnb8k8-bash
    |   +---/nix/store/p3srsbd8dx44v2pg6nbnszab5mcwx03v-builder.sh
    ...

Show all paths that depend on the same OpenSSL library as svn:

    $ nix-store -q --referrers $(nix-store -q --binding openssl $(nix-store -qd $(which svn)))
    /nix/store/23ny9l9wixx21632y2wi4p585qhva1q8-sylpheed-1.0.0
    /nix/store/5mbglq5ldqld8sj57273aljwkfvj22mc-subversion-1.1.4
    /nix/store/dpmvp969yhdqs7lm2r1a3gng7pyq6vy4-subversion-1.1.3
    /nix/store/l51240xqsgg8a7yrbqdx1rfzyv6l26fx-lynx-2.8.5

Show all paths that directly or indirectly depend on the Glibc (C library) used by svn:

    $ nix-store -q --referrers-closure $(ldd $(which svn) | grep /libc.so | awk '{print $3}')
    /nix/store/034a6h4vpz9kds5r6kzb9lhh81mscw43-libgnomeprintui-2.8.2
    /nix/store/15l3yi0d45prm7a82pcrknxdh6nzmxza-gawk-3.1.4
    ...

Note that ldd is a command that prints out the dynamic libraries used by an ELF executable.

Make a picture of the runtime dependency graph of the current user environment:

    $ nix-store -q --graph ~/.nix-profile | dot -Tps > graph.ps
    $ gv graph.ps

Show every garbage collector root that points to a store path that depends on svn:

    $ nix-store -q --roots $(which svn)
    /nix/var/nix/profiles/default-81-link
    /nix/var/nix/profiles/default-82-link
    /nix/var/nix/profiles/per-user/eelco/profile-97-link

Operation --add

  Synopsis
nix-store --add paths…

  Description
The operation --add adds the specified paths to the Nix store. It prints the resulting paths in the Nix store on standard output.

  Example

    $ nix-store --add ./foo.c
    /nix/store/m7lrha58ph6rcnv109yzx1nk1cj7k7zf-foo.c

Operation --add-fixed

  Synopsis
nix-store --add-fixed [--recursive] algorithm paths…

  Description
The operation --add-fixed adds the specified paths to the Nix store. Unlike --add paths are registered using the specified hashing algorithm, resulting in the same output path as a fixed-output derivation. This can be used for sources that are not available from a public url or broke since the download expression was written.

This operation has the following options:

•   --recursive
    Use recursive instead of flat hashing mode, used when adding directories to the store.

  Example

    $ nix-store --add-fixed sha256 ./hello-2.10.tar.gz
    /nix/store/3x7dwzq014bblazs7kq20p9hyzz0qh8g-hello-2.10.tar.gz

Operation --verify

  Synopsis
nix-store --verify [--check-contents] [--repair]

  Description
The operation --verify verifies the internal consistency of the Nix database, and the consistency between the Nix database and the Nix store. Any inconsistencies encountered are automatically repaired. Inconsistencies are generally the result of the Nix store or database being modified by non-Nix tools, or of bugs in Nix itself.

This operation has the following options:

•   --check-contents
    Checks that the contents of every valid store path has not been altered by computing a SHA-256 hash of the contents and comparing it with the hash stored in the Nix database at build time. Paths that have been modified are printed out. For large stores, --check-contents is obviously quite slow.

•   --repair
    If any valid path is missing from the store, or (if --check-contents is given) the contents of a valid path has been modified, then try to repair the path by redownloading it. See nix-store --repair-path for details.

Operation --verify-path

  Synopsis
nix-store --verify-path paths…

  Description
The operation --verify-path compares the contents of the given store paths to their cryptographic hashes stored in Nix’s database. For every changed path, it prints a warning message. The exit status is 0 if no path has changed, and 1 otherwise.

  Example
To verify the integrity of the svn command and all its dependencies:

    $ nix-store --verify-path $(nix-store -qR $(which svn))

Operation --repair-path

  Synopsis
nix-store --repair-path paths…

  Description
The operation --repair-path attempts to “repair” the specified paths by redownloading them using the available substituters. If no substitutes are available, then repair is not possible.

    Warning

    During repair, there is a very small time window during which the old path (if it exists) is moved out of the way and replaced with the new path. If repair is interrupted in between, then the system may be left in a broken state (e.g., if the path contains a critical system component like the GNU C Library).

  Example

    $ nix-store --verify-path /nix/store/dj7a81wsm1ijwwpkks3725661h3263p5-glibc-2.13
    path `/nix/store/dj7a81wsm1ijwwpkks3725661h3263p5-glibc-2.13' was modified!
      expected hash `2db57715ae90b7e31ff1f2ecb8c12ec1cc43da920efcbe3b22763f36a1861588',
      got `481c5aa5483ebc97c20457bb8bca24deea56550d3985cda0027f67fe54b808e4'
    $ nix-store --repair-path /nix/store/dj7a81wsm1ijwwpkks3725661h3263p5-glibc-2.13
    fetching path `/nix/store/d7a81wsm1ijwwpkks3725661h3263p5-glibc-2.13'...
    …

Operation --dump

  Synopsis
nix-store --dump path

  Description
The operation --dump produces a NAR (Nix ARchive) file containing the contents of the file system tree rooted at path. The archive is written to standard output.

A NAR archive is like a TAR or Zip archive, but it contains only the information that Nix considers important. For instance, timestamps are elided because all files in the Nix store have their timestamp set to 0 anyway. Likewise, all permissions are left out except for the execute bit, because all files in the Nix store have 444 or 555 permission.

Also, a NAR archive is canonical, meaning that “equal” paths always produce the same NAR archive. For instance, directory entries are always sorted so that the actual on-disk order doesn’t influence the result. This means that the cryptographic hash of a NAR dump of a path is usable as a fingerprint of the contents of the path. Indeed, the hashes of store paths stored in Nix’s database (see nix-store -q --hash) are SHA-256 hashes of the NAR dump of each store path.

NAR archives support filenames of unlimited length and 64-bit file sizes. They can contain regular files, directories, and symbolic links, but not other types of files (such as device nodes).

A Nix archive can be unpacked using nix-store --restore.

Operation --restore

  Synopsis
nix-store --restore path

  Description
The operation --restore unpacks a NAR archive to path, which must not already exist. The archive is read from standard input.

Operation --export

  Synopsis
nix-store --export paths…

  Description
The operation --export writes a serialisation of the specified store paths to standard output in a format that can be imported into another Nix store with nix-store --import. This is like nix-store --dump, except that the NAR archive produced by that command doesn’t contain the necessary meta-information to allow it to be imported into another Nix store (namely, the set of references of the path).

This command does not produce a closure of the specified paths, so if a store path references other store paths that are missing in the target Nix store, the import will fail. To copy a whole closure, do something like:

    $ nix-store --export $(nix-store -qR paths) > out

To import the whole closure again, run:

    $ nix-store --import < out

Operation --import

  Synopsis
nix-store --import

  Description
The operation --import reads a serialisation of a set of store paths produced by nix-store --export from standard input and adds those store paths to the Nix store. Paths that already exist in the Nix store are ignored. If a path refers to another path that doesn’t exist in the Nix store, the import fails.

Operation --optimise

  Synopsis
nix-store --optimise

  Description
The operation --optimise reduces Nix store disk space usage by finding identical files in the store and hard-linking them to each other. It typically reduces the size of the store by something like 25-35%. Only regular files and symlinks are hard-linked in this manner. Files are considered identical when they have the same NAR archive serialisation: that is, regular files must have the same contents and permission (executable or non-executable), and symlinks must have the same contents.

After completion, or when the command is interrupted, a report on the achieved savings is printed on standard error.

Use -vv or -vvv to get some progress indication.

  Example

    $ nix-store --optimise
    hashing files in `/nix/store/qhqx7l2f1kmwihc9bnxs7rc159hsxnf3-gcc-4.1.1'
    ...
    541838819 bytes (516.74 MiB) freed by hard-linking 54143 files;
    there are 114486 files with equal contents out of 215894 files in total

Operation --read-log

  Synopsis
nix-store {--read-log | -l} paths…

  Description
The operation --read-log prints the build log of the specified store paths on standard output. The build log is whatever the builder of a derivation wrote to standard output and standard error. If a store path is not a derivation, the deriver of the store path is used.

Build logs are kept in /nix/var/log/nix/drvs. However, there is no guarantee that a build log is available for any particular store path. For instance, if the path was downloaded as a pre-built binary through a substitute, then the log is unavailable.

  Example

    $ nix-store -l $(which ktorrent)
    building /nix/store/dhc73pvzpnzxhdgpimsd9sw39di66ph1-ktorrent-2.2.1
    unpacking sources
    unpacking source archive /nix/store/p8n1jpqs27mgkjw07pb5269717nzf5f8-ktorrent-2.2.1.tar.gz
    ktorrent-2.2.1/
    ktorrent-2.2.1/NEWS
    ...

Operation --dump-db

  Synopsis
nix-store --dump-db [paths…]

  Description
The operation --dump-db writes a dump of the Nix database to standard output. It can be loaded into an empty Nix store using --load-db. This is useful for making backups and when migrating to different database schemas.

By default, --dump-db will dump the entire Nix database. When one or more store paths is passed, only the subset of the Nix database for those store paths is dumped. As with --export, the user is responsible for passing all the store paths for a closure. See --export for an example.

Operation --load-db

  Synopsis
nix-store --load-db

  Description
The operation --load-db reads a dump of the Nix database created by --dump-db from standard input and loads it into the Nix database.

Operation --print-env

  Synopsis
nix-store --print-env drvpath

  Description
The operation --print-env prints out the environment of a derivation in a format that can be evaluated by a shell. The command line arguments of the builder are placed in the variable _args.

  Example

    $ nix-store --print-env $(nix-instantiate '<nixpkgs>' -A firefox)
    …
    export src; src='/nix/store/plpj7qrwcz94z2psh6fchsi7s8yihc7k-firefox-12.0.source.tar.bz2'
    export stdenv; stdenv='/nix/store/7c8asx3yfrg5dg1gzhzyq2236zfgibnn-stdenv'
    export system; system='x86_64-linux'
    export _args; _args='-e /nix/store/9krlzvny65gdc8s7kpb6lkx8cd02c25c-default-builder.sh'

Operation --generate-binary-cache-key

  Synopsis
nix-store --generate-binary-cache-key key-name secret-key-file public-key-file

  Description
This command generates an Ed25519 key pair that can be used to create a signed binary cache. It takes three mandatory parameters:

1.  A key name, such as cache.example.org-1, that is used to look up keys on the client when it verifies signatures. It can be anything, but it’s suggested to use the host name of your cache (e.g. cache.example.org) with a suffix denoting the number of the key (to be incremented every time you need to revoke a key).

2.  The file name where the secret key is to be stored.

3.  The file name where the public key is to be stored.