How to: Use qemu-img command to convert between vmdk, raw, qcow2, vdi, vhd, vhdx formats/disk images (qemu-img create, snapshot, resize etc.) First we need to have qemu installed on the system, for most of Linux systems, we can install “qemu-utils” for Windows we can download QEMU disk image utility from here.
Nov 21, 2019 These disk images are used to emulate disk storage devices. Furthermore depending on virtualization used, different disk images are utilized by different applications like QEMU/KVM, VirtualBox etc. First we would discuss how to get command-line utility qemu-img (Qemu disk image utility). # qemu-img resize filename size. To give a size relative to the current size, prefix the number of bytes with + to grow, or -to reduce the size of the disk image by that number of bytes. Adding a unit suffix allows you to set the image size in kilobytes (K).
qemu-img - QEMU disk image utility
usage: qemu-img command [command options]
The following commands are supported:
is the disk image format. It is guessed automatically in most cases. See below for a description of the supported disk formats.
indicates that target image must be compressed (qcow format only)
with or without a command shows help and lists the supported formats
display progress bar (convert and rebase commands only)
applies a snapshot (revert disk to saved state)
creates a snapshot
deletes a snapshot
lists all snapshots in the given image
Only the formats 'qcow2', 'qed' and 'vdi' support consistency checks.
If the option backing_file is specified, then the image will record only the differences from backing_file. No size needs to be specified inthis case. backing_file will never be modified unless you use the 'commit' monitor command (or qemu-img commit).
The size can also be specified using the size option with '-o', it doesn't need to be specified separately in this case.
Only the formats 'qcow' and 'qcow2' support compression. The compression is read-only. It means that if a compressed sector is rewritten,then it is rewritten as uncompressed data.
Image conversion is also useful to get smaller image when using a growable format such as 'qcow' or 'cow': the empty sectors are detectedand suppressed from the destination image.
You can use the backing_file option to force the output image to be created as a copy on write image of the specified base image; thebacking_file should have the same content as the input's base image, however the path, image format, etc may differ.
The backing file is changed to backing_file and (if the image format of filename supports this) the backing file format is changed tobacking_fmt.
There are two different modes in which 'rebase' can operate:
In order to achieve this, any clusters that differ between backing_file and the old backing file of filename are merged into filenamebefore actually changing the backing file.
Note that the safe mode is an expensive operation, comparable to converting an image. It only works if the old backing file still exists.
This mode is useful for renaming or moving the backing file to somewhere else. It can be used without an accessible old backing file, i.e. you can use it tofix an image whose backing file has already been moved/renamed.
Before using this command to shrink a disk image, you MUST use file system and partitioning tools inside the VM to reduceallocated file systems and partition sizes accordingly. Failure to do so will result in data loss!
After using this command to grow a disk image, you must use file system and partitioning tools inside the VM to actually begin using the newspace on the device.
Raw disk image format (default). This format has the advantage of being simple and easily exportable to all other emulators. If your file system supportsholes (for example in ext2 or ext3 on Linux or NTFS on Windows), then only the written sectors will reserve space. Use 'qemu-imginfo' to know the real size used by the image or 'ls -ls' on Unix/Linux.
Encryption uses the AES format which is very secure (128 bit keys). Use a long password (16 characters) to get maximum protection.
Bike racing games. User Mode Linux Copy On Write image format. Used to be the only growable image format in QEMU . It is supported only for compatibility withprevious versions. It does not work on win32.
VirtualBox 1.1 compatible image format.
VirtualPC compatible image format ( VHD ).
The HTML documentation of QEMU for more precise information and Linux user mode emulator invocation.