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Ploop/Mount helpers

316 bytes removed, 15:25, 10 March 2021
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Despite the fact that ploop is not a file system, a trick exist
to make it look and feel like so — i.e. to use usual <code>mount</code>
This article describes how it works and can be used.
== Introduction == <!--T:2-->
ploop is not a filesystem per se, but a kernel [[w:loop device]] driver, providing a way
to represent a ploop image (or a set of stacked images) as a
Therefore a complete ploop mount consists of two steps:
# "mount" ploop image(s) to create a ploop device (/dev/ploopNNNNN)
# mount a filesystem residing on this ploop device to a mount point
For simplicity, these two are usually wrapped to be done together in one step (say when you use ploop mount with -m option).
In reality, step 1 is kernel assembling a device out of image(s), and step 2 is the real mount.
== Mounting == <!--T:6-->
You can use the following syntax to mount a ploop device and the filesystem inside it:
<!--T:8-->mount -t ploop [option ...] /path/to/DiskDescriptor.xml /mount/point
The following options are supported:
<code>-r</code>, <code>-o ro</code>
: mount read-only
<code>-v</code>, <code>--verbose</code>
: be more verbose
<code>-f</code>, <code>--fake</code>
: do everything except for the actual mount
<code>-n</code>, <code>--no-mtab</code>, <code>-s</code>
: these options are deliberately ignored
== Unmounting == <!--T:14-->
To unmount, DiskDescriptor can be specified:
<!--T:16-->umount /path/to/DiskDescriptor.xml
A mount point can be used as well:
<!--T:18-->umount /mount/point
== Limitations == <!--T:19-->
Note that umount can only work if:
# /etc/mtab is a separate file (not a symlink to /proc/mounts);
# mounting was done using <code>mount</code> (not <code>ploop mount</code>).
Otherwise, umount binary will not be able to find <code>ploop</code> as the "filesystem"
field in /etc/mtab, and will not call <code>umount.ploop</code> helper. As a result,
file system will be unmounted, but ploop device itself will stay mounted.
== Alternative == <!--T:22-->
<code>ploop mount</code> and <code>ploop umount</code> commands,
as described in {{Man|ploop|8}} man page.
== See also == <!--T:24-->
* [[Ploop]]
* {{Bug|2817}}
[[Category: Storage]]

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