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<h3 class="section">30.3 Controlling and Querying Mounts</h3>

<p>All files are in filesystems, and before you can access any file, its
filesystem must be mounted.  Because of Unix's concept of
<em>Everything is a file</em>, mounting of filesystems is central to doing
almost anything.  This section explains how to find out what filesystems
are currently mounted and what filesystems are available for mounting,
and how to change what is mounted.

   <p>The classic filesystem is the contents of a disk drive.  The concept is
considerably more abstract, though, and lots of things other than disk
drives can be mounted.

   <p>Some block devices don't correspond to traditional devices like disk
drives.  For example, a loop device is a block device whose driver uses
a regular file in another filesystem as its medium.  So if that regular
file contains appropriate data for a filesystem, you can by mounting the
loop device essentially mount a regular file.

   <p>Some filesystems aren't based on a device of any kind.  The &ldquo;proc&rdquo;
filesystem, for example, contains files whose data is made up by the
filesystem driver on the fly whenever you ask for it.  And when you
write to it, the data you write causes changes in the system.  No data
gets stored.

<!-- It would be good to mention NFS mounts here. -->
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<li><a accesskey="1" href="Mount-Information.html#Mount-Information">Mount Information</a>:            What is or could be mounted? 
<li><a accesskey="2" href="Mount_002dUnmount_002dRemount.html#Mount_002dUnmount_002dRemount">Mount-Unmount-Remount</a>:        Controlling what is mounted and how
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