path: root/doc/manual/nix-store.xml

<refentry>

<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#xpointer(/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.  See also <xref
linkend="sec-common-options" /> for a list of common options.</para>

<variablelist>

  <varlistentry 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 (see <xref
    linkend="ssec-gc-roots" />).  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>

</refsection>

  

<!--######################################################################-->

<refsection 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>
</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
  (succesful) 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>

</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 ./foo.nix)</screen>

This is essentially what <link
linkend="sec-nix-build"><command>nix-build</command></link> does.</para>

</refsection>


</refsection>

  

<!--######################################################################-->

<refsection 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 choice='req'>
    <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>
</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.</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>

</refsection>


<refsection><title>Roots</title>

<para>The roots of the garbage collector are all store paths to which
there are symlinks in the directory
<filename><replaceable>prefix</replaceable>/nix/var/nix/gcroots</filename>.
For instance, the following command makes the path
<filename>/nix/store/d718ef...-foo</filename> a root of the collector:

<screen>
$ ln -s /nix/store/d718ef...-foo /nix/var/nix/gcroots/bar</screen>
	
That is, after this command, the garbage collector will not remove
<filename>/nix/store/d718ef...-foo</filename> or any of its
dependencies.</para>

<para>Subdirectories of
<filename><replaceable>prefix</replaceable>/nix/var/nix/gcroots</filename>
are also searched for symlinks.  Symlinks to non-store paths are
followed and searched for roots, but TODO.</para>

</refsection>


<refsection><title>Configuration file</title>

<para>TODO</para>

</refsection>


<refsection><title>Examples</title>

<para>To delete all unreachable paths, just do:
    
<screen>
$ nix-store --gc</screen>

</para>

</refsection>


</refsection>


  
<!--######################################################################-->

<refsection><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>--list</option></arg>
    <arg choice='plain'><option>-l</option></arg>
    <arg choice='plain'><option>--requisites</option></arg>
    <arg choice='plain'><option>-R</option></arg>
    <arg choice='plain'><option>--predecessors</option></arg>
    <arg choice='plain'><option>--graph</option></arg>
  </group>
  <arg><option>--normalise</option></arg>
  <arg><option>-n</option></arg>
  <arg><option>--force-realise</option></arg>
  <arg><option>-f</option></arg>
  <arg choice='plain' rep='repeat'><replaceable>args</replaceable></arg>
</cmdsynopsis>

</refsection>


<refsection><title>Description</title>
            
<para>The operation <option>--query</option> displays various bits of
information about store paths.  The queries are described below.  At
most one query can be specified.  The default query is
<option>--list</option>.</para>

</refsection>


<refsection><title>Common query options</title>

<variablelist>

  <varlistentry><term><option>--use-output</option> / <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> / <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 id='nixref-queries'><title>Queries</title>
            
<variablelist>

  <varlistentry><term><option>--list</option> / <option>-l</option></term>

    <listitem><para>Prints out the <emphasis>output paths</emphasis>
    of the store expressions indicated by the identifiers
    <replaceable>args</replaceable>.  In the case of a derivation
    expression, these are the paths that will be produced when the
    derivation is realised.  In the case of a closure expression,
    these are the paths that were produced the derivation expression
    of which the closure expression is a successor.</para></listitem>
    
  </varlistentry>

  <varlistentry><term><option>--requisites</option> / <option>-R</option></term>

    <listitem><para>Prints out the requisite paths of the store
    expressions indicated by the identifiers
    <replaceable>args</replaceable>.  The requisite paths of a Nix
    expression are the paths that need to be present in the system to
    be able to realise the expression.  That is, they form the
    <emphasis>closure</emphasis> of the expression in the file system
    (i.e., no path in the set of requisite paths points to anything
    outside the set of requisite paths).</para>

    <para>The notion of requisite paths is very useful when one wants
    to distribute store expressions.  Since they form a closure, they
    are the only paths one needs to distribute to another system to be
    able to realise the expression on the other system.</para>

    <para>This query is generally used to implement various kinds of
    deployment.  A <emphasis>source deployment</emphasis> is obtained
    by distributing the requisite paths of a derivation expression.  A
    <emphasis>binary deployment</emphasis> is obtained by distributing
    the requisite paths of a closure expression.  A <emphasis>cache
    deployment</emphasis> is obtained by distributing the requisite
    paths of a derivation expression and specifying the option
    <option>--include-successors</option>.  This will include not just
    the paths of a source and binary deployment, but also all
    expressions and paths of subterms of the source.  This is useful
    if one wants to realise on the target system a Nix expression that
    is similar but not quite the same as the one being distributed,
    since any common subterms will be reused.</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>

    </listitem>

  </varlistentry>


  <varlistentry><term><option>--graph</option></term>
  
    <listitem><para>Prints a graph of the closure of the store
    expressions identified by <replaceable>args</replaceable> in the
    format of the <command>dot</command> tool of AT&amp;T's GraphViz
    package.</para></listitem>

  </varlistentry>

</variablelist>

</refsection>


</refsection>

  

<!--######################################################################-->

<refsection id="rsec-nix-store-reg-val"><title>Operation <option>--register-validity</option></title>

<refsection><title>Synopsis</title>

<cmdsynopsis>
  <command>nix-store</command>
  <arg choice='req'><option>--register-validity</option></arg>
</cmdsynopsis>
</refsection>

<refsection><title>Description</title>
            
<para>TODO</para>

</refsection>
            
</refsection>



<!--######################################################################-->

<refsection><title>Operation <option>--substitute</option></title>

<refsection><title>Synopsis</title>

<cmdsynopsis>
  <command>nix-store</command>
  <arg choice='req'><option>--substitute</option></arg>
  <arg choice='plain'
       rep='repeat'><replaceable>srcpath</replaceable> <replaceable>subpath</replaceable></arg>
</cmdsynopsis>
</refsection>

<refsection><title>Description</title>
            
<para>The operation <option>--substitute</option> registers that the
store path <replaceable>srcpath</replaceable> can be built by
realising the derivation expression in
<replaceable>subpath</replaceable>.  This is used to implement binary
deployment.</para>

</refsection>
            
</refsection>



<!--######################################################################-->

<refsection><title>Operation <option>--verify</option></title>

<refsection>
  <title>Synopsis</title>
  <cmdsynopsis>
    <command>nix-store</command>
    <arg choice='req'><option>--verify</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>

</refsection>
            
</refsection>



</refentry>