What is a .qcow2 file?
QEMU Copy-On-Write v2 · Disk image · QEMU project · 2004
QCOW2 is the native disk image format of QEMU and KVM, the Linux virtualisation stack. It supports snapshots, compression and thin provisioning, only using disk space as data is actually written.
What is a .qcow2 file used for?
A .qcow2 file starts with the magic QFI followed by 0xFB. Copy-on-write means the image grows on demand and can layer snapshots, so you can roll a VM back to an earlier state cheaply.
It is the default for KVM-based clouds and Linux virtualisation. Manage and convert it with qemu-img.
What opens a .qcow2 file?
The .qcow2 format opens in the following apps, grouped by operating system. If one app does not work, try another from the same list.
Windows
- qemu
- qemu-img
macOS
- qemu
- qemu-img
Linux
- QEMU / KVM
- qemu-img
- virt-manager
Open a .qcow2 file step by step
- Confirm the file really is a .qcow2. Drop it into the WhatFileType identifier, which reads its signature in your browser without uploading anything.
- On Windows, open it with qemu or qemu-img.
- On Mac, use qemu or qemu-img.
- On Linux, try QEMU / KVM or qemu-img.
- Still stuck? Convert the .qcow2 to vmdk, which opens more widely.
Why can't I open my .qcow2 file?
Almost always because no installed app understands QCOW2. Install one of the apps above, or convert the file to a format your existing software already reads. If double-clicking opens the wrong program instead of nothing at all, the file association is set to the wrong app rather than the file being broken.
The other possibility is that the file is not really a .qcow2 at all. Drop it into the file identifier to check it by its bytes instead of its name. Nothing is uploaded.
How to convert a .qcow2 file
You can convert a .qcow2 file to vmdk, vhd, img using a conversion tool or the export menu of an app that opens it.
What is the .qcow2 file signature (magic bytes)?
A .qcow2 file starts with the hex bytes 51 46 49 FB, which read as QFIû in ASCII. Programs identify QCOW2 by those bytes, not by the filename, so a renamed file still gives itself away.
These are the documented signatures for QCOW2. For a full breakdown, see the QCOW2 (QEMU disk) file signature page.
| Hex signature | Offset | ASCII | Note |
|---|---|---|---|
| 51 46 49 FB | 0 | QFIû | 'QFI' + 0xFB |
See the full magic-numbers reference for every format.
Frequently asked questions
What is a .qcow2 file?
QCOW2 is the native disk image format of QEMU and KVM, the Linux virtualisation stack. It supports snapshots, compression and thin provisioning, only using disk space as data is actually written.
How do I open a qcow2 file?
Boot it with QEMU or virt-manager, or convert and inspect it with qemu-img. It is a virtual disk image for QEMU/KVM.
What are qcow2 snapshots?
Copy-on-write points in time you can return to. Because only changed blocks are stored, snapshots are cheap in space and fast to create.
How do I convert qcow2 to another format?
Use qemu-img convert, for example qemu-img convert -O vmdk disk.qcow2 disk.vmdk for VMware.
Related formats
Sources
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