<refentry xmlns="http://docbook.org/ns/docbook"
xmlns:xlink="http://www.w3.org/1999/xlink"
xmlns:xi="http://www.w3.org/2001/XInclude"
version="5.0"
xml:id="sec-nix-store">
<refmeta>
<refentrytitle>nix-store</refentrytitle>
<manvolnum>1</manvolnum>
<refmiscinfo class="source">Nix</refmiscinfo>
<refmiscinfo class="version"><xi:include href="../version.txt" parse="text"/></refmiscinfo>
</refmeta>
<refnamediv>
<refname>nix-store</refname>
<refpurpose>manipulate or query the Nix store</refpurpose>
</refnamediv>
<refsynopsisdiv>
<cmdsynopsis>
<command>nix-store</command>
<xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="opt-common-syn.xml#xmlns(db=http://docbook.org/ns/docbook)xpointer(/db:nop/*)" />
<arg><option>--add-root</option> <replaceable>path</replaceable></arg>
<arg><option>--indirect</option></arg>
<arg choice='plain'><replaceable>operation</replaceable></arg>
<arg rep='repeat'><replaceable>options</replaceable></arg>
<arg rep='repeat'><replaceable>arguments</replaceable></arg>
</cmdsynopsis>
</refsynopsisdiv>
<refsection><title>Description</title>
<para>The command <command>nix-store</command> performs primitive
operations on the Nix store. You generally do not need to run this
command manually.</para>
<para><command>nix-store</command> takes exactly one
<emphasis>operation</emphasis> flag which indicates the subcommand to
be performed. These are documented below.</para>
</refsection>
<!--######################################################################-->
<refsection><title>Common options</title>
<para>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. <phrase condition="manual">See
also <xref linkend="sec-common-options" /> for a list of common
options.</phrase></para>
<variablelist>
<varlistentry xml:id="opt-add-root"><term><option>--add-root</option> <replaceable>path</replaceable></term>
<listitem><para>Causes the result of a realisation
(<option>--realise</option> and <option>--force-realise</option>)
to be registered as a root of the garbage collector<phrase
condition="manual"> (see <xref linkend="ssec-gc-roots"
/>)</phrase>. The root is stored in
<replaceable>path</replaceable>, which must be inside a directory
that is scanned for roots by the garbage collector (i.e.,
typically in a subdirectory of
<filename>/nix/var/nix/gcroots/</filename>)
<emphasis>unless</emphasis> the <option>--indirect</option> flag
is used.</para>
<para>If there are multiple results, then multiple symlinks will
be created by sequentially numbering symlinks beyond the first one
(e.g., <filename>foo</filename>, <filename>foo-2</filename>,
<filename>foo-3</filename>, and so on).</para></listitem>
</varlistentry>
<varlistentry><term><option>--indirect</option></term>
<listitem>
<para>In conjunction with <option>--add-root</option>, this option
allows roots to be stored <emphasis>outside</emphasis> of the GC
roots directory. This is useful for commands such as
<command>nix-build</command> 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.</para>
<para>The <option>--indirect</option> flag causes a uniquely named
symlink to <replaceable>path</replaceable> to be stored in
<filename>/nix/var/nix/gcroots/auto/</filename>. For instance,
<screen>
$ nix-store --add-root /home/eelco/bla/result --indirect -r <replaceable>...</replaceable>
$ 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</screen>
Thus, when <filename>/home/eelco/bla/result</filename> is removed,
the GC root in the <filename>auto</filename> directory becomes a
dangling symlink and will be ignored by the collector.</para>
<warning><para>Note that it is not possible to move or rename
indirect GC roots, since the symlink in the
<filename>auto</filename> directory will still point to the old
location.</para></warning>
</listitem>
</varlistentry>
</variablelist>
<variablelist condition="manpage">
<xi:include href="opt-common.xml#xmlns(db=http://docbook.org/ns/docbook)xpointer(//db:variablelist[@xml:id='opt-common']/*)" />
</variablelist>
</refsection>
<!--######################################################################-->
<refsection xml:id='rsec-nix-store-realise'><title>Operation <option>--realise</option></title>
<refsection><title>Synopsis</title>
<cmdsynopsis>
<command>nix-store</command>
<group choice='req'>
<arg choice='plain'><option>--realise</option></arg>
<arg choice='plain'><option>-r</option></arg>
</group>
<arg choice='plain' rep='repeat'><replaceable>paths</replaceable></arg>
<arg><option>--dry-run</option></arg>
</cmdsynopsis>
</refsection>
<refsection><title>Description</title>
<para>The operation <option>--realise</option> essentially “builds”
the specified store paths. Realisation is a somewhat overloaded term:
<itemizedlist>
<listitem><para>If the store path is a
<emphasis>derivation</emphasis>, realisation ensures that the output
paths of the derivation are <link
linkend="gloss-validity">valid</link> (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 <link
linkend="gloss-substitute">substitutes</link> that produce the
outputs (e.g., by downloading them). Finally, the outputs can be
produced by performing the build action described by the
derivation.</para></listitem>
<listitem><para>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.</para></listitem>
</itemizedlist>
</para>
<para>The output path of each derivation is printed on standard
output. (For non-derivations argument, the argument itself is
printed.)</para>
<para>The following flags are available:</para>
<variablelist>
<varlistentry><term><option>--dry-run</option></term>
<listitem><para>Print on standard error a description of what
packages would be built or downloaded, without actually performing
the operation.</para></listitem>
</varlistentry>
<varlistentry><term><option>--ignore-unknown</option></term>
<listitem><para>If a non-derivation path does not have a
substitute, then silently ignore it.</para></listitem>
</varlistentry>
</variablelist>
</refsection>
<refsection><title>Examples</title>
<para>This operation is typically used to build store derivations
produced by <link
linkend="sec-nix-instantiate"><command>nix-instantiate</command></link>:
<screen>
$ nix-store -r $(nix-instantiate ./test.nix)
/nix/store/31axcgrlbfsxzmfff1gyj1bf62hvkby2-aterm-2.3.1</screen>
This is essentially what <link
linkend="sec-nix-build"><command>nix-build</command></link> does.</para>
</refsection>
</refsection>
<!--######################################################################-->
<refsection xml:id='rsec-nix-store-gc'><title>Operation <option>--gc</option></title>
<refsection><title>Synopsis</title>
<cmdsynopsis>
<command>nix-store</command>
<arg choice='plain'><option>--gc</option></arg>
<group>
<arg choice='plain'><option>--print-roots</option></arg>
<arg choice='plain'><option>--print-live</option></arg>
<arg choice='plain'><option>--print-dead</option></arg>
<arg choice='plain'><option>--delete</option></arg>
</group>
<arg><option>--max-freed</option> <replaceable>bytes</replaceable></arg>
</cmdsynopsis>
</refsection>
<refsection><title>Description</title>
<para>Without additional flags, the operation <option>--gc</option>
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.</para>
<para>The following suboperations may be specified:</para>
<variablelist>
<varlistentry><term><option>--print-roots</option></term>
<listitem><para>This operation prints on standard output the set
of roots used by the garbage collector. What constitutes a root
is described in <xref linkend="ssec-gc-roots"
/>.</para></listitem>
</varlistentry>
<varlistentry><term><option>--print-live</option></term>
<listitem><para>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.</para></listitem>
</varlistentry>
<varlistentry><term><option>--print-dead</option></term>
<listitem><para>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.</para></listitem>
</varlistentry>
<varlistentry><term><option>--delete</option></term>
<listitem><para>This operation performs an actual garbage
collection. All dead paths are removed from the
store. This is the default.</para></listitem>
</varlistentry>
</variablelist>
<para>By default, all unreachable paths are deleted. The following
options control what gets deleted and in what order:
<variablelist>
<varlistentry><term><option>--max-freed</option> <replaceable>bytes</replaceable></term>
<listitem><para>Keep deleting paths until at least
<replaceable>bytes</replaceable> bytes have been deleted, then
stop. The argument <replaceable>bytes</replaceable> can be
followed by the multiplicative suffix <literal>K</literal>,
<literal>M</literal>, <literal>G</literal> or
<literal>T</literal>, denoting KiB, MiB, GiB or TiB
units.</para></listitem>
</varlistentry>
</variablelist>
</para>
<para>The behaviour of the collector is also influenced by the <link
linkend="conf-gc-keep-outputs"><literal>gc-keep-outputs</literal></link>
and <link
linkend="conf-gc-keep-derivations"><literal>gc-keep-derivations</literal></link>
variables in the Nix configuration file.</para>
<para>With <option>--delete</option>, the collector prints the total
number of freed bytes when it finishes (or when it is interrupted).
With <option>--print-dead</option>, it prints the number of bytes that
would be freed.</para>
</refsection>
<refsection><title>Examples</title>
<para>To delete all unreachable paths, just do:
<screen>
$ nix-store --gc
deleting `/nix/store/kq82idx6g0nyzsp2s14gfsc38npai7lf-cairo-1.0.4.tar.gz.drv'
<replaceable>...</replaceable>
8825586 bytes freed (8.42 MiB)</screen>
</para>
<para>To delete at least 100 MiBs of unreachable paths:
<screen>
$ nix-store --gc --max-freed $((100 * 1024 * 1024))</screen>
</para>
</refsection>
</refsection>
<!--######################################################################-->
<refsection><title>Operation <option>--delete</option></title>
<refsection><title>Synopsis</title>
<cmdsynopsis>
<command>nix-store</command>
<arg choice='plain'><option>--delete</option></arg>
<arg><option>--ignore-liveness</option></arg>
<arg choice='plain' rep='repeat'><replaceable>paths</replaceable></arg>
</cmdsynopsis>
</refsection>
<refsection><title>Description</title>
<para>The operation <option>--delete</option> deletes the store paths
<replaceable>paths</replaceable> 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 <literal>nix-store --gc</literal>. Thus,
<literal>--delete</literal> is a more targeted version of
<literal>--gc</literal>.</para>
<para>With the option <option>--ignore-liveness</option>, 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).</para>
</refsection>
<refsection><title>Example</title>
<screen>
$ 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</screen>
</refsection>
</refsection>
<!--######################################################################-->
<refsection xml:id='refsec-nix-store-query'><title>Operation <option>--query</option></title>
<refsection><title>Synopsis</title>
<cmdsynopsis>
<command>nix-store</command>
<group choice='req'>
<arg choice='plain'><option>--query</option></arg>
<arg choice='plain'><option>-q</option></arg>
</group>
<group choice='req'>
<arg choice='plain'><option>--outputs</option></arg>
<arg choice='plain'><option>--requisites</option></arg>
<arg choice='plain'><option>-R</option></arg>
<arg choice='plain'><option>--references</option></arg>
<arg choice='plain'><option>--referrers</option></arg>
<arg choice='plain'><option>--referrers-closure</option></arg>
<arg choice='plain'><option>--deriver</option></arg>
<arg choice='plain'><option>--deriver</option></arg>
<arg choice='plain'><option>--graph</option></arg>
<arg choice='plain'><option>--tree</option></arg>
<arg choice='plain'><option>--binding</option> <replaceable>name</replaceable></arg>
<arg choice='plain'><option>--hash</option></arg>
<arg choice='plain'><option>--size</option></arg>
<arg choice='plain'><option>--roots</option></arg>
</group>
<arg><option>--use-output</option></arg>
<arg><option>-u</option></arg>
<arg><option>--force-realise</option></arg>
<arg><option>-f</option></arg>
<arg choice='plain' rep='repeat'><replaceable>paths</replaceable></arg>
</cmdsynopsis>
</refsection>
<refsection><title>Description</title>
<para>The operation <option>--query</option> 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
<option>--outputs</option>.</para>
<para>The paths <replaceable>paths</replaceable> 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.</para>
</refsection>
<refsection><title>Common query options</title>
<variablelist>
<varlistentry><term><option>--use-output</option></term>
<term><option>-u</option></term>
<listitem><para>For each argument to the query that is a store
derivation, apply the query to the output path of the derivation
instead.</para></listitem>
</varlistentry>
<varlistentry><term><option>--force-realise</option></term>
<term><option>-f</option></term>
<listitem><para>Realise each argument to the query first (see
<link linkend="rsec-nix-store-realise"><command>nix-store
--realise</command></link>).</para></listitem>
</varlistentry>
</variablelist>
</refsection>
<refsection xml:id='nixref-queries'><title>Queries</title>
<variablelist>
<varlistentry><term><option>--outputs</option></term>
<listitem><para>Prints out the <link
linkend="gloss-output-path">output paths</link> of the store
derivations <replaceable>paths</replaceable>. These are the paths
that will be produced when the derivation is
built.</para></listitem>
</varlistentry>
<varlistentry><term><option>--requisites</option></term>
<term><option>-R</option></term>
<listitem><para>Prints out the <link
linkend="gloss-closure">closure</link> of the store path
<replaceable>paths</replaceable>.</para>
<para>This query has one option:</para>
<variablelist>
<varlistentry><term><option>--include-outputs</option></term>
<listitem><para>Also include the output path of store
derivations, and their closures.</para></listitem>
</varlistentry>
</variablelist>
<para>This query can be used to implement various kinds of
deployment. A <emphasis>source deployment</emphasis> is obtained
by distributing the closure of a store derivation. A
<emphasis>binary deployment</emphasis> is obtained by distributing
the closure of an output path. A <emphasis>cache
deployment</emphasis> (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 <option>--include-outputs</option>.</para>
</listitem>
</varlistentry>
<varlistentry><term><option>--references</option></term>
<listitem><para>Prints the set of <link
linkend="gloss-reference">references</link> of the store paths
<replaceable>paths</replaceable>, that is, their immediate
dependencies. (For <emphasis>all</emphasis> dependencies, use
<option>--requisites</option>.)</para></listitem>
</varlistentry>
<varlistentry><term><option>--referrers</option></term>
<listitem><para>Prints the set of <emphasis>referrers</emphasis> of
the store paths <replaceable>paths</replaceable>, that is, the
store paths currently existing in the Nix store that refer to one
of <replaceable>paths</replaceable>. Note that contrary to the
references, the set of referrers is not constant; it can change as
store paths are added or removed.</para></listitem>
</varlistentry>
<varlistentry><term><option>--referrers-closure</option></term>
<listitem><para>Prints the closure of the set of store paths
<replaceable>paths</replaceable> under the referrers relation; that
is, all store paths that directly or indirectly refer to one of
<replaceable>paths</replaceable>. These are all the path currently
in the Nix store that are dependent on
<replaceable>paths</replaceable>.</para></listitem>
</varlistentry>
<varlistentry><term><option>--deriver</option></term>
<listitem><para>Prints the <link
linkend="gloss-deriver">deriver</link> of the store paths
<replaceable>paths</replaceable>. 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
<literal>unknown-deriver</literal> is printed.</para></listitem>
</varlistentry>
<varlistentry><term><option>--graph</option></term>
<listitem><para>Prints the references graph of the store paths
<replaceable>paths</replaceable> in the format of the
<command>dot</command> tool of AT&T's <link
xlink:href="http://www.graphviz.org/">Graphviz package</link>.
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.</para></listitem>
</varlistentry>
<varlistentry><term><option>--tree</option></term>
<listitem><para>Prints the references graph of the store paths
<replaceable>paths</replaceable> 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.</para></listitem>
</varlistentry>
<varlistentry><term><option>--binding</option> <replaceable>name</replaceable></term>
<listitem><para>Prints the value of the attribute
<replaceable>name</replaceable> (i.e., environment variable) of
the store derivations <replaceable>paths</replaceable>. It is an
error for a derivation to not have the specified
attribute.</para></listitem>
</varlistentry>
<varlistentry><term><option>--hash</option></term>
<listitem><para>Prints the SHA-256 hash of the contents of the
store paths <replaceable>paths</replaceable> (that is, the hash of
the output of <command>nix-store --dump</command> on the given
paths). Since the hash is stored in the Nix database, this is a
fast operation.</para></listitem>
</varlistentry>
<varlistentry><term><option>--size</option></term>
<listitem><para>Prints the size in bytes of the contents of the
store paths <replaceable>paths</replaceable> — to be precise, the
size of the output of <command>nix-store --dump</command> 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.</para></listitem>
</varlistentry>
<varlistentry><term><option>--roots</option></term>
<listitem><para>Prints the garbage collector roots that point,
directly or indirectly, at the store paths
<replaceable>paths</replaceable>.</para></listitem>
</varlistentry>
</variablelist>
</refsection>
<refsection><title>Examples</title>
<para>Print the closure (runtime dependencies) of the
<command>svn</command> program in the current user environment:
<screen>
$ nix-store -qR $(which svn)
/nix/store/5mbglq5ldqld8sj57273aljwkfvj22mc-subversion-1.1.4
/nix/store/9lz9yc6zgmc0vlqmn2ipcpkjlmbi51vv-glibc-2.3.4
<replaceable>...</replaceable></screen>
</para>
<para>Print the build-time dependencies of <command>svn</command>:
<screen>
$ 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
<replaceable>... lots of other paths ...</replaceable></screen>
The difference with the previous example is that we ask the closure of
the derivation (<option>-qd</option>), not the closure of the output
path that contains <command>svn</command>.</para>
<para>Show the build-time dependencies as a tree:
<screen>
$ 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
<replaceable>...</replaceable></screen>
</para>
<para>Show all paths that depend on the same OpenSSL library as
<command>svn</command>:
<screen>
$ 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</screen>
</para>
<para>Show all paths that directly or indirectly depend on the Glibc
(C library) used by <command>svn</command>:
<screen>
$ 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
<replaceable>...</replaceable></screen>
Note that <command>ldd</command> is a command that prints out the
dynamic libraries used by an ELF executable.</para>
<para>Make a picture of the runtime dependency graph of the current
user environment:
<screen>
$ nix-store -q --graph ~/.nix-profile | dot -Tps > graph.ps
$ gv graph.ps</screen>
</para>
<para>Show every garbage collector root that points to a store path
that depends on <command>svn</command>:
<screen>
$ 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
</screen>
</para>
</refsection>
</refsection>
<!--######################################################################-->
<!--
<refsection xml:id="rsec-nix-store-reg-val"><title>Operation <option>-XXX-register-validity</option></title>
<refsection><title>Synopsis</title>
<cmdsynopsis>
<command>nix-store</command>
<arg choice='plain'><option>-XXX-register-validity</option></arg>
</cmdsynopsis>
</refsection>
<refsection><title>Description</title>
<para>TODO</para>
</refsection>
</refsection>
-->
<!--######################################################################-->
<refsection><title>Operation <option>--add</option></title>
<refsection><title>Synopsis</title>
<cmdsynopsis>
<command>nix-store</command>
<arg choice='plain'><option>--add</option></arg>
<arg choice='plain' rep='repeat'><replaceable>paths</replaceable></arg>
</cmdsynopsis>
</refsection>
<refsection><title>Description</title>
<para>The operation <option>--add</option> adds the specified paths to
the Nix store. It prints the resulting paths in the Nix store on
standard output.</para>
</refsection>
<refsection><title>Example</title>
<screen>
$ nix-store --add ./foo.c
/nix/store/m7lrha58ph6rcnv109yzx1nk1cj7k7zf-foo.c</screen>
</refsection>
</refsection>
<!--######################################################################-->
<refsection xml:id='refsec-nix-store-verify'><title>Operation <option>--verify</option></title>
<refsection>
<title>Synopsis</title>
<cmdsynopsis>
<command>nix-store</command>
<arg choice='plain'><option>--verify</option></arg>
<arg><option>--check-contents</option></arg>
<arg><option>--repair</option></arg>
</cmdsynopsis>
</refsection>
<refsection><title>Description</title>
<para>The operation <option>--verify</option> 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.</para>
<para>This operation has the following options:
<variablelist>
<varlistentry><term><option>--check-contents</option></term>
<listitem><para>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, <option>--check-contents</option> is obviously quite
slow.</para></listitem>
</varlistentry>
<varlistentry><term><option>--repair</option></term>
<listitem><para>If any valid path is missing from the store, or
(if <option>--check-contents</option> is given) the contents of a
valid path has been modified, then try to repair the path by
redownloading it. See <command>nix-store --repair-path</command>
for details.</para></listitem>
</varlistentry>
</variablelist>
</para>
</refsection>
</refsection>
<!--######################################################################-->
<refsection><title>Operation <option>--verify-path</option></title>
<refsection>
<title>Synopsis</title>
<cmdsynopsis>
<command>nix-store</command>
<arg choice='plain'><option>--verify-path</option></arg>
<arg choice='plain' rep='repeat'><replaceable>paths</replaceable></arg>
</cmdsynopsis>
</refsection>
<refsection><title>Description</title>
<para>The operation <option>--verify-path</option> 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.</para>
</refsection>
<refsection><title>Example</title>
<para>To verify the integrity of the <command>svn</command> command and all its dependencies:
<screen>
$ nix-store --verify-path $(nix-store -qR $(which svn))
</screen>
</para>
</refsection>
</refsection>
<!--######################################################################-->
<refsection><title>Operation <option>--repair-path</option></title>
<refsection>
<title>Synopsis</title>
<cmdsynopsis>
<command>nix-store</command>
<arg choice='plain'><option>--repair-path</option></arg>
<arg choice='plain' rep='repeat'><replaceable>paths</replaceable></arg>
</cmdsynopsis>
</refsection>
<refsection><title>Description</title>
<para>The operation <option>--repair-path</option> attempts to
“repair” the specified paths by redownloading them using the available
substituters. If no substitutes are available, then repair is not
possible.</para>
<warning><para>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).</para></warning>
</refsection>
<refsection><title>Example</title>
<screen>
$ 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'...
…
</screen>
</refsection>
</refsection>
<!--######################################################################-->
<refsection xml:id='refsec-nix-store-dump'><title>Operation <option>--dump</option></title>
<refsection>
<title>Synopsis</title>
<cmdsynopsis>
<command>nix-store</command>
<arg choice='plain'><option>--dump</option></arg>
<arg choice='plain'><replaceable>path</replaceable></arg>
</cmdsynopsis>
</refsection>
<refsection><title>Description</title>
<para>The operation <option>--dump</option> produces a NAR (Nix
ARchive) file containing the contents of the file system tree rooted
at <replaceable>path</replaceable>. The archive is written to
standard output.</para>
<para>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.</para>
<para>Also, a NAR archive is <emphasis>canonical</emphasis>, 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 <link linkend="refsec-nix-store-query"><literal>nix-store -q
--hash</literal></link>) are SHA-256 hashes of the NAR dump of each
store path.</para>
<para>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).</para>
<para>A Nix archive can be unpacked using <literal>nix-store
--restore</literal>.</para>
</refsection>
</refsection>
<!--######################################################################-->
<refsection><title>Operation <option>--restore</option></title>
<refsection>
<title>Synopsis</title>
<cmdsynopsis>
<command>nix-store</command>
<arg choice='plain'><option>--restore</option></arg>
<arg choice='plain'><replaceable>path</replaceable></arg>
</cmdsynopsis>
</refsection>
<refsection><title>Description</title>
<para>The operation <option>--restore</option> unpacks a NAR archive
to <replaceable>path</replaceable>, which must not already exist. The
archive is read from standard input.</para>
</refsection>
</refsection>
<!--######################################################################-->
<refsection xml:id='refsec-nix-store-export'><title>Operation <option>--export</option></title>
<refsection>
<title>Synopsis</title>
<cmdsynopsis>
<command>nix-store</command>
<arg choice='plain'><option>--export</option></arg>
<arg choice='plain' rep='repeat'><replaceable>paths</replaceable></arg>
</cmdsynopsis>
</refsection>
<refsection><title>Description</title>
<para>The operation <option>--export</option> writes a serialisation
of the specified store paths to standard output in a format that can
be imported into another Nix store with <command
linkend="refsec-nix-store-import">nix-store --import</command>. This
is like <command linkend="refsec-nix-store-dump">nix-store
--dump</command>, 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).</para>
<para>This command does not produce a <emphasis>closure</emphasis> 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
<screen>
$ nix-store --export $(nix-store -qR <replaceable>paths</replaceable>) > out</screen>
</para>
<para>For an example of how <option>--export</option> and
<option>--import</option> can be used, see the source of the <command
linkend="sec-nix-copy-closure">nix-copy-closure</command>
command.</para>
</refsection>
</refsection>
<!--######################################################################-->
<refsection xml:id='refsec-nix-store-import'><title>Operation <option>--import</option></title>
<refsection>
<title>Synopsis</title>
<cmdsynopsis>
<command>nix-store</command>
<arg choice='plain'><option>--import</option></arg>
</cmdsynopsis>
</refsection>
<refsection><title>Description</title>
<para>The operation <option>--import</option> reads a serialisation of
a set of store paths produced by <command
linkend="refsec-nix-store-export">nix-store --export</command> 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.</para>
</refsection>
</refsection>
<!--######################################################################-->
<refsection><title>Operation <option>--optimise</option></title>
<refsection>
<title>Synopsis</title>
<cmdsynopsis>
<command>nix-store</command>
<arg choice='plain'><option>--optimise</option></arg>
</cmdsynopsis>
</refsection>
<refsection><title>Description</title>
<para>The operation <option>--optimise</option> 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.</para>
<para>After completion, or when the command is interrupted, a report
on the achieved savings is printed on standard error.</para>
<para>Use <option>-vv</option> or <option>-vvv</option> to get some
progress indication.</para>
</refsection>
<refsection><title>Example</title>
<screen>
$ nix-store --optimise
hashing files in `/nix/store/qhqx7l2f1kmwihc9bnxs7rc159hsxnf3-gcc-4.1.1'
<replaceable>...</replaceable>
541838819 bytes (516.74 MiB) freed by hard-linking 54143 files;
there are 114486 files with equal contents out of 215894 files in total
</screen>
</refsection>
</refsection>
<!--######################################################################-->
<refsection><title>Operation <option>--read-log</option></title>
<refsection>
<title>Synopsis</title>
<cmdsynopsis>
<command>nix-store</command>
<group choice='req'>
<arg choice='plain'><option>--read-log</option></arg>
<arg choice='plain'><option>-l</option></arg>
</group>
<arg choice='plain' rep='repeat'><replaceable>paths</replaceable></arg>
</cmdsynopsis>
</refsection>
<refsection><title>Description</title>
<para>The operation <option>--read-log</option> 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.</para>
<para>Build logs are kept in
<filename>/nix/var/log/nix/drvs</filename>. 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. If the log is not available
locally, then <command>nix-store</command> will try to download the
log from the servers specified in the Nix option
<option>log-servers</option>. For example, if it’s set to
<literal>http://hydra.nixos.org/log</literal>, then Nix will check
<literal>http://hydra.nixos.org/log/<replaceable>base-name</replaceable></literal>.</para>
</refsection>
<refsection><title>Example</title>
<screen>
$ 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
<replaceable>...</replaceable>
</screen>
</refsection>
</refsection>
<!--######################################################################-->
<refsection><title>Operation <option>--dump-db</option></title>
<refsection>
<title>Synopsis</title>
<cmdsynopsis>
<command>nix-store</command>
<arg choice='plain'><option>--dump-db</option></arg>
</cmdsynopsis>
</refsection>
<refsection><title>Description</title>
<para>The operation <option>--dump-db</option> writes a dump of the
Nix database to standard output. It can be loaded into an empty Nix
store using <option>--load-db</option>. This is useful for making
backups and when migrating to different database schemas.</para>
</refsection>
</refsection>
<!--######################################################################-->
<refsection><title>Operation <option>--load-db</option></title>
<refsection>
<title>Synopsis</title>
<cmdsynopsis>
<command>nix-store</command>
<arg choice='plain'><option>--load-db</option></arg>
</cmdsynopsis>
</refsection>
<refsection><title>Description</title>
<para>The operation <option>--load-db</option> reads a dump of the Nix
database created by <option>--dump-db</option> from standard input and
loads it into the Nix database.</para>
</refsection>
</refsection>
<!--######################################################################-->
<refsection><title>Operation <option>--print-env</option></title>
<refsection>
<title>Synopsis</title>
<cmdsynopsis>
<command>nix-store</command>
<arg choice='plain'><option>--print-env</option></arg>
<arg choice='plain'><replaceable>drvpath</replaceable></arg>
</cmdsynopsis>
</refsection>
<refsection><title>Description</title>
<para>The operation <option>--print-env</option> 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 <envar>_args</envar>.</para>
</refsection>
<refsection><title>Example</title>
<screen>
$ nix-store --print-env $(nix-instantiate '<nixpkgs>' -A firefox)
<replaceable>…</replaceable>
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'
</screen>
</refsection>
</refsection>
<!--######################################################################-->
<refsection><title>Operation <option>--query-failed-paths</option></title>
<refsection>
<title>Synopsis</title>
<cmdsynopsis>
<command>nix-store</command>
<arg choice='plain'><option>--query-failed-paths</option></arg>
</cmdsynopsis>
</refsection>
<refsection><title>Description</title>
<para>If build failure caching is enabled through the
<literal>build-cache-failure</literal> configuration option, the
operation <option>--query-failed-paths</option> will print out all
store paths that have failed to build.</para>
</refsection>
<refsection><title>Example</title>
<screen>
$ nix-store --query-failed-paths
/nix/store/000zi5dcla86l92jn1g997jb06sidm7x-perl-PerlMagick-6.59
/nix/store/0011iy7sfwbc1qj5a1f6ifjnbcdail8a-haskell-gitit-ghc7.0.4-0.8.1
/nix/store/001c0yn1hkh86gprvrb46cxnz3pki7q3-gamin-0.1.10
<replaceable>…</replaceable>
</screen>
</refsection>
</refsection>
<!--######################################################################-->
<refsection><title>Operation <option>--clear-failed-paths</option></title>
<refsection>
<title>Synopsis</title>
<cmdsynopsis>
<command>nix-store</command>
<arg choice='plain'><option>--clear-failed-paths</option></arg>
<arg choice='plain' rep='repeat'><replaceable>paths</replaceable></arg>
</cmdsynopsis>
</refsection>
<refsection><title>Description</title>
<para>If build failure caching is enabled through the
<literal>build-cache-failure</literal> configuration option, the
operation <option>--clear-failed-paths</option> clears the “failed”
state of the given store paths, allowing them to be built again. This
is useful if the failure was actually transient (e.g. because the disk
was full).</para>
<para>If a path denotes a derivation, its output paths are cleared.
You can provide the argument <literal>*</literal> to clear all store
paths.</para>
</refsection>
<refsection><title>Example</title>
<screen>
$ nix-store --clear-failed-paths /nix/store/000zi5dcla86l92jn1g997jb06sidm7x-perl-PerlMagick-6.59
$ nix-store --clear-failed-paths *
</screen>
</refsection>
</refsection>
<!--######################################################################-->
<refsection condition="manpage"><title>Environment variables</title>
<variablelist>
<xi:include href="env-common.xml#xmlns(db=http://docbook.org/ns/docbook)xpointer(//db:variablelist[@xml:id='env-common']/*)" />
</variablelist>
</refsection>
</refentry>
