<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-file-systems">

<title>File Systems</title>

<para>You can define file systems using the
<option>fileSystems</option> configuration option.  For instance, the
following definition causes NixOS to mount the Ext4 file system on
device <filename>/dev/disk/by-label/data</filename> onto the mount
point <filename>/data</filename>:

<programlisting>
fileSystems."/data" =
  { device = "/dev/disk/by-label/data";
    fsType = "ext4";
  };
</programlisting>

Mount points are created automatically if they don’t already exist.
For <option>device</option>, it’s best to use the topology-independent
device aliases in <filename>/dev/disk/by-label</filename> and
<filename>/dev/disk/by-uuid</filename>, as these don’t change if the
topology changes (e.g. if a disk is moved to another IDE
controller).</para>

<para>You can usually omit the file system type
(<option>fsType</option>), since <command>mount</command> can usually
detect the type and load the necessary kernel module automatically.
However, if the file system is needed at early boot (in the initial
ramdisk) and is not <literal>ext2</literal>, <literal>ext3</literal>
or <literal>ext4</literal>, then it’s best to specify
<option>fsType</option> to ensure that the kernel module is
available.</para>

<note><para>System startup will fail if any of the filesystems fails to mount,
dropping you to the emergency shell.
You can make a mount asynchronous and non-critical by adding
<literal>options = [ "nofail" ];</literal>.
</para></note>

<xi:include href="luks-file-systems.xml" />

</chapter>
