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Man Pages
NIX-STORE(1) Command Reference NIX-STORE(1)

nix-store - manipulate or query the Nix store

nix-store [--help] [--version] [{--verbose | -v}...] [--quiet] [--no-build-output | -Q] [{--max-jobs | -j} number] [--cores number] [--max-silent-time number] [--timeout number] [--keep-going | -k] [--keep-failed | -K] [--fallback] [--readonly-mode] [-I path] [--option name value]
[--add-root path] [--indirect] operation [options...] [arguments...]

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.

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. The root is stored in path, which must be inside a directory that is scanned for roots by the garbage collector (i.e., typically in a subdirectory of /nix/var/nix/gcroots/) unless the --indirect flag is used.

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).

--indirect

In conjunction with --add-root, this option allows roots to be stored outside of the GC roots directory. This is useful for commands such as nix-build that place a symlink to the build result in the current directory; such a build result should not be garbage-collected unless the symlink is removed.

The --indirect flag causes a uniquely named symlink to path to be stored in /nix/var/nix/gcroots/auto/. For instance,

$ nix-store --add-root /home/eelco/bla/result --indirect -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 indirect GC roots, since the symlink in the auto directory will still point to the old location.

--help

Prints out a summary of the command syntax and exits.

--version

Prints out the Nix version number on standard output and exits.

--verbose / -v

Increases the level of verbosity of diagnostic messages printed on standard error. For each Nix operation, the information printed on standard output is well-defined; any diagnostic information is printed on standard error, never on standard output.

This option may be specified repeatedly. Currently, the following verbosity levels exist:

0

“Errors only”: only print messages explaining why the Nix invocation failed.

1

“Informational”: print useful messages about what Nix is doing. This is the default.

2

“Talkative”: print more informational messages.

3

“Chatty”: print even more informational messages.

4

“Debug”: print debug information.

5

“Vomit”: print vast amounts of debug information.

--quiet

Decreases the level of verbosity of diagnostic messages printed on standard error. This is the inverse option to -v / --verbose.

This option may be specified repeatedly. See the previous verbosity levels list.

--no-build-output / -Q

By default, output written by builders to standard output and standard error is echoed to the Nix command's standard error. This option suppresses this behaviour. Note that the builder's standard output and error are always written to a log file in prefix/nix/var/log/nix.

--max-jobs / -j number

Sets the maximum number of build jobs that Nix will perform in parallel to the specified number. Specify auto to use the number of CPUs in the system. The default is specified by the max-jobs configuration setting, which itself defaults to 1. A higher value is useful on SMP systems or to exploit I/O latency.

Setting it to 0 disallows building on the local machine, which is useful when you want builds to happen only on remote builders.

--cores

Sets the value of the NIX_BUILD_CORES environment variable in the invocation of builders. Builders can use this variable at their discretion to control the maximum amount of parallelism. For instance, in Nixpkgs, if the derivation attribute enableParallelBuilding is set to true, the builder passes the -jN flag to GNU Make. It defaults to the value of the cores configuration setting, if set, or 1 otherwise. The value 0 means that the builder should use all available CPU cores in the system.

--max-silent-time

Sets the maximum number of seconds that a builder can go without producing any data on standard output or standard error. The default is specified by the max-silent-time configuration setting. 0 means no time-out.

--timeout

Sets the maximum number of seconds that a builder can run. The default is specified by the timeout configuration setting. 0 means no timeout.

--keep-going / -k

Keep going in case of failed builds, to the greatest extent possible. That is, if building an input of some derivation fails, Nix will still build the other inputs, but not the derivation itself. Without this option, Nix stops if any build fails (except for builds of substitutes), possibly killing builds in progress (in case of parallel or distributed builds).

--keep-failed / -K

Specifies that in case of a build failure, the temporary directory (usually in /tmp) in which the build takes place should not be deleted. The path of the build directory is printed as an informational message.

--fallback

Whenever Nix attempts to build a derivation for which substitutes are known for each output path, but realising the output paths through the substitutes fails, fall back on building the derivation.

The most common scenario in which this is useful is when we have registered substitutes in order to perform binary distribution from, say, a network repository. If the repository is down, the realisation of the derivation will fail. When this option is specified, Nix will build the derivation instead. Thus, installation from binaries falls back on installation from source. This option is not the default since it is generally not desirable for a transient failure in obtaining the substitutes to lead to a full build from source (with the related consumption of resources).

--no-build-hook

Disables the build hook mechanism. This allows to ignore remote builders if they are setup on the machine.

It's useful in cases where the bandwidth between the client and the remote builder is too low. In that case it can take more time to upload the sources to the remote builder and fetch back the result than to do the computation locally.

--readonly-mode

When this option is used, no attempt is made to open the Nix database. Most Nix operations do need database access, so those operations will fail.

--arg name value

This option is accepted by nix-env, nix-instantiate and nix-build. When evaluating Nix expressions, the expression evaluator will automatically try to call functions that it encounters. It can automatically call functions for which every argument has a default value (e.g., { argName ? defaultValue }: ...). With --arg, you can also call functions that have arguments without a default value (or override a default value). That is, if the evaluator encounters a function with an argument named name, it will call it with value value.

For instance, the top-level default.nix in Nixpkgs is actually a function:

{ # The system (e.g., `i686-linux') for which to build the packages.
  system ? builtins.currentSystem
  ...
}: ...

So if you call this Nix expression (e.g., when you do nix-env -i pkgname), the function will be called automatically using the value builtins.currentSystem for the system argument. You can override this using --arg, e.g., nix-env -i pkgname --arg system \"i686-freebsd\". (Note that since the argument is a Nix string literal, you have to escape the quotes.)

--argstr name value

This option is like --arg, only the value is not a Nix expression but a string. So instead of --arg system \"i686-linux\" (the outer quotes are to keep the shell happy) you can say --argstr system i686-linux.

--attr / -A attrPath

Select an attribute from the top-level Nix expression being evaluated. (nix-env, nix-instantiate, nix-build and nix-shell only.) The attribute path attrPath is a sequence of attribute names separated by dots. For instance, given a top-level Nix expression e, the attribute path xorg.xorgserver would cause the expression e.xorg.xorgserver to be used. See nix-env --install for some concrete examples.

In addition to attribute names, you can also specify array indices. For instance, the attribute path foo.3.bar selects the bar attribute of the fourth element of the array in the foo attribute of the top-level expression.

--expr / -E

Interpret the command line arguments as a list of Nix expressions to be parsed and evaluated, rather than as a list of file names of Nix expressions. (nix-instantiate, nix-build and nix-shell only.)

-I path

Add a path to the Nix expression search path. This option may be given multiple times. See the NIX_PATH environment variable for information on the semantics of the Nix search path. Paths added through -I take precedence over NIX_PATH.

--option name value

Set the Nix configuration option name to value. This overrides settings in the Nix configuration file (see nix.conf(5)).

--repair

Fix corrupted or missing store paths by redownloading or rebuilding them. Note that this is slow because it requires computing a cryptographic hash of the contents of every path in the closure of the build. Also note the warning under nix-store --repair-path.

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

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 performing the build action 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) subsitutes, 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.

See also the build-repeat configuration option, which repeats a derivation a number of times and prevents its outputs from being registered as “valid” in the Nix store unless they are identical.

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 specified outputHash.

104

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

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

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

nix-store --serve [--write]

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.

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

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

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. What constitutes a root is described in Section 11.1, “Garbage Collector Roots”.

--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.

--delete

This operation performs an actual garbage collection. All dead paths are removed from the store. This is the default.

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 variables in the Nix configuration file.

With --delete, 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.

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))

nix-store --delete [--ignore-liveness] paths...

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).

$ 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

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...

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.

--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).

--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 output path 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[1]. 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[2] 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.

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

nix-store --add paths...

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

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

nix-store [--recursive] --add-fixed algorithm paths...

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.

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

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

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.

nix-store --verify-path paths...

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.

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

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

nix-store --repair-path paths...

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).

$ 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'...
...

nix-store --dump path

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 644 or 755 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.

nix-store --restore path

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

nix-store --export paths...

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

nix-store --import

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.

nix-store --optimise

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.

$ 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

nix-store {--read-log | -l} paths...

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.

$ 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
...

nix-store --dump-db [paths...]

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.

nix-store --load-db

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.

nix-store --print-env drvpath

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. 

$ 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'

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

This command generates an Ed25519 key pair[3] 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.

IN_NIX_SHELL
Indicator that tells if the current environment was set up by nix-shell. Since Nix 2.0 the values are "pure" and "impure"

NIX_PATH

A colon-separated list of directories used to look up Nix expressions enclosed in angle brackets (i.e., <path>). For instance, the value 

/home/eelco/Dev:/etc/nixos

will cause Nix to look for paths relative to /home/eelco/Dev and /etc/nixos, in that order. It is also possible to match paths against a prefix. For example, the value

nixpkgs=/home/eelco/Dev/nixpkgs-branch:/etc/nixos

will cause Nix to search for <nixpkgs/path> in /home/eelco/Dev/nixpkgs-branch/path and /etc/nixos/nixpkgs/path.

If a path in the Nix search path starts with http:// or https://, it is interpreted as the URL of a tarball that will be downloaded and unpacked to a temporary location. The tarball must consist of a single top-level directory. For example, setting NIX_PATH to

nixpkgs=https://github.com/NixOS/nixpkgs-channels/archive/nixos-15.09.tar.gz

tells Nix to download the latest revision in the Nixpkgs/NixOS 15.09 channel.

A following shorthand can be used to refer to the official channels:

nixpkgs=channel:nixos-15.09

The search path can be extended using the -I option, which takes precedence over NIX_PATH.

NIX_IGNORE_SYMLINK_STORE

Normally, the Nix store directory (typically /nix/store) is not allowed to contain any symlink components. This is to prevent “impure” builds. Builders sometimes “canonicalise” paths by resolving all symlink components. Thus, builds on different machines (with /nix/store resolving to different locations) could yield different results. This is generally not a problem, except when builds are deployed to machines where /nix/store resolves differently. If you are sure that you’re not going to do that, you can set NIX_IGNORE_SYMLINK_STORE to 1.

Note that if you’re symlinking the Nix store so that you can put it on another file system than the root file system, on Linux you’re better off using bind mount points, e.g.,

$ mkdir /nix
$ mount -o bind /mnt/otherdisk/nix /nix

Consult the mount(8) manual page for details.

NIX_STORE_DIR

Overrides the location of the Nix store (default prefix/store).

NIX_DATA_DIR

Overrides the location of the Nix static data directory (default prefix/share).

NIX_LOG_DIR

Overrides the location of the Nix log directory (default prefix/var/log/nix).

NIX_STATE_DIR

Overrides the location of the Nix state directory (default prefix/var/nix).

NIX_CONF_DIR

Overrides the location of the Nix configuration directory (default prefix/etc/nix).

TMPDIR

Use the specified directory to store temporary files. In particular, this includes temporary build directories; these can take up substantial amounts of disk space. The default is /tmp.

NIX_REMOTE

This variable should be set to daemon if you want to use the Nix daemon to execute Nix operations. This is necessary in multi-user Nix installations. If the Nix daemon's Unix socket is at some non-standard path, this variable should be set to unix://path/to/socket. Otherwise, it should be left unset.

NIX_SHOW_STATS

If set to 1, Nix will print some evaluation statistics, such as the number of values allocated.

NIX_COUNT_CALLS

If set to 1, Nix will print how often functions were called during Nix expression evaluation. This is useful for profiling your Nix expressions.

GC_INITIAL_HEAP_SIZE

If Nix has been configured to use the Boehm garbage collector, this variable sets the initial size of the heap in bytes. It defaults to 384 MiB. Setting it to a low value reduces memory consumption, but will increase runtime due to the overhead of garbage collection.

Eelco Dolstra
Author

Copyright © 2004-2018 Eelco Dolstra

1.
Graphviz package
http://www.graphviz.org/
2.
GraphML
http://graphml.graphdrawing.org/
3.
Ed25519 key pair
http://ed25519.cr.yp.to/
05/14/2022 Nix 2.3.10
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