Mounting

Introduction

To mount a QEMU Copy-On-Write (QCOW) image file you can use qcowmount.

There is support for the following back-ends:

• Dokan library
• fuse
• OSXFuse

To build qcowmount see Building.

Mounting

To mount a QCOW image:

qcowmount image.qcow2 /mnt/fuse

This will expose a device file that provides the RAW storage media data contained in the QCOW image.

/mnt/fuse/qcow1

If you get the error:

No sub system to mount QCOW.

That means fuse was not detected when building the qcowtools, check if you have fuse-dev installed and if ./configure is able to detect it. The last part of the ./configure output shows you this in an overview.

If your operating system supports loop devices, such as Linux, mount can be used to mount the device file as a loop device:

mount -o loop,ro,offset=${OFFSET} /mnt/fuse/qcow1 /mnt/file_system

Make sure to define ${OFFSET} to contan the byte offset, relative to the start of the device file, of the start of the file system.

On Mac OS hdiutil can be used to mount the device file:

hdiutil attach -imagekey diskimage-class=CRawDiskImage -nomount /mnt/fuse/qcow1

Why is /mnt/fuse not accessible as root

By default fuse prevents root access to the mount point when a QCOW image is mounted. To enable this functionality first check the fuse documentation.

Make sure the fuse configuration file:

/etc/fuse.conf

Contains:

user_allow_other

Pass "allow_root" to the fuse sub system using the qcowmount -X option:

qcowmount -X allow_root image.qcow2 /mnt/fuse

Windows

To mount a QCOW image on Windows:

qcowmount image.qcow2 x:

At the moment the qcowmount keeps a hold on the console.

This will expose a device file that provides the RAW storage media data contained in the QCOW image.

X:\QCOW1

Unmounting

You can unmount /mnt/fuse using umount:

umount /mnt/fuse

Or fusermount:

fusermount -u /mnt/fuse

Windows

At the moment terminate the process running in the console.

Troubleshooting

First of all make sure to check the output of configure. If you're seeing something like the following output configure was unable to detect an usable fuse.

Building:
   ...
   FUSE support:                                    no

On Mac OS X:

• make sure that you only have OSXFuse installed and not another variant, like MacFuse, besides it.
• try adding the C pre processor flags that set the fuse API version, e.g.

CPPFLAGS=-DFUSE_USE_VERSION=26 ./configure

• if all else fails; file a support issue and attach config.log

On Ubuntu:

fusermount – failed to open /etc/fuse.conf – Permission denied

Make sure you're part of the group fuse:

sudo addgroup <username> fuse

If fusermount keeps complaining it cannot open fuse.conf:

sudo chmod o+r /etc/fuse.conf