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" />.</para>

<variablelist>

  <varlistentry><term><option>--add-root</option> <replaceable>path</replaceable></term>

    <listitem><para>Causes the result of a build action
    (<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></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>--install</option> realises in the file
system the store expressions stored in
<replaceable>paths</replaceable>.  If these expressions are derivation
expressions, they are first <emphasis>normalised</emphasis> into a
closure expression.  This may happen in two ways.  First, the
corresponding closure expression (the <emphasis>successor</emphasis>)
may already known (either because the build has already been
performed, or because a successor was explicitly registered through
the <option>--successor</option> operation).  Otherwise, the build
action described by the derivation is performed, and a closure
expression is computed by scanning the result of the build for
references to other paths in the store.</para>

<para>The paths of the closure expression corresponding to each
expression in <replaceable>paths</replaceable> is printed on standard
output.</para>

</refsection>
            
</refsection>

  

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

  <refsection>
    <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-live</option></arg>
          <arg choice='plain'><option>--print-dead</option></arg>
          <arg choice='plain'><option>--delete</option></arg>
        </group>
        <arg><option>--min-age</option> <replaceable>age</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 <quote>roots</quote>, are deleted.
      </para>

      <para>
	The following flags 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
              <quote>live</quote> 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
              <quote>dead</quote> 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.
            </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>


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

  <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 expressions or 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>--normalise</option> / <option>-n</option></term>
          <listitem>
            <para>
              For those queries that take a Nix store expression, this
              option causes those expressions to be normalised first.
            </para>
          </listitem>
        </varlistentry>

        <varlistentry>
          <term><option>--force-realise</option> / <option>-f</option></term>
          <listitem>
            <para>
              For those queries that take a Nix store expression, this
              option causes those expressions to be realised first.
              This is just a short-cut for the common idiom
            </para>
            <screen>
nix-store --realise /nix/store/bla.store
x=`nix-store --query --normalise /nix/store/bla.store`
<emphasis>(do something with the path $x</emphasis></screen>
            <para>
              which using this flag can be written as
            </para>
            <screen>
x=`nix-store --query --normalise --force-realise /nix/store/bla.store`
<emphasis>(do something with the path $x</emphasis></screen>
          </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 a number of options:
            </para> 

            <variablelist>

              <varlistentry>
                <term><option>--exclude-exprs</option></term>
                <listitem>
                  <para>
                    Excludes the paths of store expressions.  This
                    causes the closure property to be lost, that is,
                    the resulting set of paths is not enough to ensure
                    realisibility.
                  </para>
                </listitem>
              </varlistentry>

              <varlistentry>
                <term><option>--include-successors</option></term>
                <listitem>
                  <para>
                    Also include the requisites of successors (normal forms).
                    Only the requisites of <emphasis>known</emphasis>
                    successors are included, i.e., the normal forms of
                    derivation expressions that have never been normalised will
                    not be included.
                  </para>

                  <para>
                    Note that not just the successor of a derivation expression
                    will be included, but also the successors of all input
                    expressions of that derivation expression.  I.e., all
                    normal forms of subterms involved in the normalisation of
                    the top-level term are included.
                  </para>
                </listitem>
              </varlistentry>

            </variablelist>

          </listitem>
        </varlistentry>

        <varlistentry>
          <term><option>--predecessors</option></term>
          <listitem>
            <para>
              For each store expression stored at paths
              <replaceable>args</replaceable>, prints its
              <emphasis>predecessors</emphasis>.  A derivation
              expression <varname>p</varname> is a predecessor of a
              store expression <varname>q</varname> iff
              <varname>q</varname> is a successor of
              <varname>p</varname>.
            </para>
          </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>
    <title>Operation <option>--successor</option></title>

    <refsection>
      <title>Synopsis</title>
      <cmdsynopsis>
        <command>nix-store</command>
        <arg choice='req'><option>--successor</option></arg>
        <arg choice='plain'
        rep='repeat'><replaceable>srcpath</replaceable> <replaceable>sucpath</replaceable></arg>
      </cmdsynopsis>
    </refsection>

    <refsection>
      <title>Description</title>
            
      <para>
        The operation <option>--successor</option> registers that the
        closure expression in <replaceable>sucpath</replaceable> is a
        successor of the derivation expression in
        <replaceable>srcpath</replaceable>.  This is used to implement
        binary deployment.
      </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>


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