Provided by: nix-bin_2.6.0+dfsg-3_amd64 
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 (../glossary.md) (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 (../glossary.md) 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) 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.
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 outputHash attribute of the
derivation (../expressions/advanced-attributes.md).
• 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-
instantiate.md):
$ nix-store -r $(nix-instantiate ./test.nix)
/nix/store/31axcgrlbfsxzmfff1gyj1bf62hvkby2-aterm-2.3.1
This is essentially what nix-build (nix-build.md) does.
To test whether a previously-built derivation is deterministic:
$ nix-build '<nixpkgs>' -A hello --check -K
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 (#operation---realise)).
Queries
• --outputs
Prints out the output paths (../glossary.md) of the store derivations paths. These are the paths that
will be produced when the derivation is built.
• --requisites; -R
Prints out the closure (../glossary.md) 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 (../glossary.md) 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 (../glossary.md) 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 (http://www.graphviz.org/). 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 (http://graphml.graphdrawing.org/)
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 (http://ed25519.cr.yp.to/) 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.
nix-store(1)