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

<chapter 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="ch-links-nix-store">

<title><quote>Too many links</quote> Error in the Nix store</title>


<para>Symptom: when building something, you get an error message such as

<screen>
...
<literal>mkdir: cannot create directory `/nix/store/<replaceable>name</replaceable>': Too many links</literal></screen>

</para>

<para>This is usually because you have more than 32,000 subdirectories
in <filename>/nix/store</filename>, as can be seen using <command>ls
-l</command>:

<screen>
$ ls -l /nix/store
drwxrwxrwt 32000 nix nix 4620288 Sep 8 15:08 store</screen>

The <literal>ext2</literal> file system is limited to an inode link
count of 32,000 (each subdirectory increasing the count by one).
Furthermore, the <literal>st_nlink</literal> field of the
<function>stat</function> system call is a 16-bit value.</para>

<para>This only happens on very large Nix installations (such as build
machines).</para>

<para>Quick solution: run the garbage collector.  You may want to use
the <option>--max-links</option> option.</para>

<para>Real solution: put the Nix store on a file system that supports
more than 32,000 subdirectories per directory, such as ReiserFS.
(This doesn’t solve the <literal>st_nlink</literal> limit, but
ReiserFS lies to the kernel by reporting a link count of 1 if it
exceeds the limit.)</para>

</chapter>