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qemu-img

NAME

qemu-img - QEMU disk image utility

SYNOPSIS

usage: qemu-img command [command options]

OPTIONS

The following commands are supported:

check [-f fmt] filename

create [-f fmt] [-o options] filename [size]

commit [-f fmt] filename

convert [-c] [-f fmt] [-O output_fmt] [-o options] filename [filename2 [...]] output_filename

info [-f fmt] filename

snapshot [-l | -a snapshot | -c snapshot | -d snapshot] filename

rebase [-f fmt] [-u] -b backing_file [-F backing_fmt] filename

resize filename [+ | -]size

Command parameters:

filename

  is a disk image filename
 
 

fmt

is the disk image format. It is guessed automatically in most cases. See below for a description of the supported disk formats.

size

is the disk image size in bytes. Optional suffixes "k" or "K" (kilobyte, 1024) "M" (megabyte, 1024k) and "G" (gigabyte, 1024M) and T (terabyte, 1024G) are supported. "b" is ignored.

output_filename

is the destination disk image filename

output_fmt

  is the destination format
 
 

options

is a comma separated list of format specific options in a name=value format. Use "-o ?" for an overview of the options supported by the used format or see the format descriptions below for details.

-c

indicates that target image must be compressed (qcow format only)

-h

with or without a command shows help and lists the supported formats

Parameters to snapshot subcommand:

snapshot

is the name of the snapshot to create, apply or delete

-a

applies a snapshot (revert disk to saved state)

-c

creates a snapshot

-d

deletes a snapshot

-l

lists all snapshots in the given image

Command description:

create [-f fmt] [-o options] filename [size]

Create the new disk image filename of size size and format fmt. Depending on the file format, you can add one or more options that enable additional features of this format.

If the option backing_file is specified, then the image will record only the differences from backing_file. No size needs to be specified in this 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.

commit [-f fmt] filename

Commit the changes recorded in filename in its base image.

convert [-c] [-f fmt] [-O output_fmt] [-o options] filename [filename2 [...]] output_filename

Convert the disk image filename to disk image output_filename using format output_fmt. It can be optionally compressed ("-c" option) or use any format specific options like encryption ("-o" option).

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 detected and 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; the backing_file should have the same content as the input's base image, however the path, image format, etc may differ.

info [-f fmt] filename

Give information about the disk image filename. Use it in particular to know the size reserved on disk which can be different from the displayed size. If VM snapshots are stored in the disk image, they are displayed too.

snapshot [-l | -a snapshot | -c snapshot | -d snapshot ] filename

List, apply, create or delete snapshots in image filename.

resize filename [+ | -]size

Change the disk image as if it had been created with size.

Before using this command to shrink a disk image, you MUST use file system and partitioning tools inside the VM to reduce allocated 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 new space on the device.

Supported image file formats:

raw

Raw disk image format (default). This format has the advantage of being simple and easily exportable to all other emulators. If your file system supports holes (for example in ext2 or ext3 on Linux or NTFS on Windows), then only the written sectors will reserve space. Use "qemu-img info" to know the real size used by the image or "ls -ls" on Unix/Linux.

host_device

Host device format. This format should be used instead of raw when converting to block devices or other devices where ``holes'' are not supported.

qcow2

QEMU image format, the most versatile format. Use it to have smaller images (useful if your filesystem does not supports holes, for example on Windows), optional AES encryption, zlib based compression and support of multiple VM snapshots.

Supported options:

backing_file

File name of a base image (see create subcommand)

backing_fmt

Image format of the base image

encryption

If this option is set to "on", the image is encrypted.

Encryption uses the AES format which is very secure (128 bit keys). Use a long password (16 characters) to get maximum protection.

cluster_size

Changes the qcow2 cluster size (must be between 512 and 2M). Smaller cluster sizes can improve the image file size whereas larger cluster sizes generally provide better performance.

preallocation

Preallocation mode (allowed values: off, metadata). An image with preallocated metadata is initially larger but can improve performance when the image needs to grow.

qcow

Old QEMU image format. Left for compatibility.

Supported options:

backing_file

File name of a base image (see create subcommand)

encryption

If this option is set to "on", the image is encrypted.

cow

User Mode Linux Copy On Write image format. Used to be the only growable image format in QEMU. It is supported only for compatibility with previous versions. It does not work on win32.

vdi

VirtualBox 1.1 compatible image format.

vmdk

VMware 3 and 4 compatible image format.

Supported options:

backing_fmt

Image format of the base image

compat6

Create a VMDK version 6 image (instead of version 4)

vpc

VirtualPC compatible image format (VHD).

cloop

Linux Compressed Loop image, useful only to reuse directly compressed CD-ROM images present for example in the Knoppix CD-ROMs.

SEE ALSO

The HTML documentation of QEMU for more precise information and Linux user mode emulator invocation.

AUTHOR

Fabrice Bellard