Difference between revisions of "Ploop/Mount helpers"
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Despite the fact that ploop is not a file system, a trick exist | 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> | to make it look and feel like so — i.e. to use usual <code>mount</code> | ||
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This article describes how it works and can be used. | This article describes how it works and can be used. | ||
| − | == Introduction == | + | == Introduction == |
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ploop is not a filesystem per se, but a kernel [[w:loop device]] driver, providing a way | 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 | to represent a ploop image (or a set of stacked images) as a | ||
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container. | container. | ||
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Therefore a complete ploop mount consists of two steps: | Therefore a complete ploop mount consists of two steps: | ||
# "mount" ploop image(s) to create a ploop device (/dev/ploopNNNNN) | # "mount" ploop image(s) to create a ploop device (/dev/ploopNNNNN) | ||
# mount a filesystem residing on this ploop device to a mount point | # mount a filesystem residing on this ploop device to a mount point | ||
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For simplicity, these two are usually wrapped to be done together in one step (say when you use ploop mount with -m option). | 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. | In reality, step 1 is kernel assembling a device out of image(s), and step 2 is the real mount. | ||
| − | == Mounting == | + | == Mounting == |
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You can use the following syntax to mount a ploop device and the filesystem inside it: | You can use the following syntax to mount a ploop device and the filesystem inside it: | ||
| − | + | mount -t ploop [option ...] /path/to/DiskDescriptor.xml /mount/point | |
| − | mount -t ploop [option ...] /path/to/DiskDescriptor.xml /mount/point | ||
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The following options are supported: | The following options are supported: | ||
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<code>-r</code>, <code>-o ro</code> | <code>-r</code>, <code>-o ro</code> | ||
: mount read-only | : mount read-only | ||
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<code>-v</code>, <code>--verbose</code> | <code>-v</code>, <code>--verbose</code> | ||
: be more verbose | : be more verbose | ||
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<code>-f</code>, <code>--fake</code> | <code>-f</code>, <code>--fake</code> | ||
: do everything except for the actual mount | : do everything except for the actual mount | ||
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<code>-n</code>, <code>--no-mtab</code>, <code>-s</code> | <code>-n</code>, <code>--no-mtab</code>, <code>-s</code> | ||
: these options are deliberately ignored | : these options are deliberately ignored | ||
| − | == Unmounting == | + | == Unmounting == |
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To unmount, DiskDescriptor can be specified: | To unmount, DiskDescriptor can be specified: | ||
| − | + | umount /path/to/DiskDescriptor.xml | |
| − | umount /path/to/DiskDescriptor.xml | ||
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A mount point can be used as well: | A mount point can be used as well: | ||
| − | + | umount /mount/point | |
| − | umount /mount/point | ||
| − | == Limitations == | + | == Limitations == |
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Note that umount can only work if: | Note that umount can only work if: | ||
# /etc/mtab is a separate file (not a symlink to /proc/mounts); | # /etc/mtab is a separate file (not a symlink to /proc/mounts); | ||
# mounting was done using <code>mount</code> (not <code>ploop mount</code>). | # mounting was done using <code>mount</code> (not <code>ploop mount</code>). | ||
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Otherwise, umount binary will not be able to find <code>ploop</code> as the "filesystem" | 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, | 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. | file system will be unmounted, but ploop device itself will stay mounted. | ||
| − | == Alternative == | + | == Alternative == |
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<code>ploop mount</code> and <code>ploop umount</code> commands, | <code>ploop mount</code> and <code>ploop umount</code> commands, | ||
as described in {{Man|ploop|8}} man page. | as described in {{Man|ploop|8}} man page. | ||
| − | == See also == | + | == See also == |
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* [[Ploop]] | * [[Ploop]] | ||
* {{Bug|2817}} | * {{Bug|2817}} | ||
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[[Category: Storage]] | [[Category: Storage]] | ||
Latest revision as of 15:25, 10 March 2021
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 mount
and umount commands rather than the ploop(8) tool.
This article describes how it works and can be used.
Introduction[edit]
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 block device. On top of that block device provided by ploop, an ext4 file system is created and used, for example, for storing files of a specific container.
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[edit]
You can use the following syntax to mount a ploop device and the filesystem inside it:
mount -t ploop [option ...] /path/to/DiskDescriptor.xml /mount/point
The following options are supported:
-r, -o ro
- mount read-only
-v, --verbose
- be more verbose
-f, --fake
- do everything except for the actual mount
-n, --no-mtab, -s
- these options are deliberately ignored
Unmounting[edit]
To unmount, DiskDescriptor can be specified:
umount /path/to/DiskDescriptor.xml
A mount point can be used as well:
umount /mount/point
Limitations[edit]
Note that umount can only work if:
- /etc/mtab is a separate file (not a symlink to /proc/mounts);
- mounting was done using
mount(notploop mount).
Otherwise, umount binary will not be able to find ploop as the "filesystem"
field in /etc/mtab, and will not call umount.ploop helper. As a result,
file system will be unmounted, but ploop device itself will stay mounted.
Alternative[edit]
ploop mount and ploop umount commands,
as described in ploop(8) man page.
