QEMU-IMG(1)QEMU-IMG(1)NAMEqemu-img - QEMU disk image utility
SYNOPSIS
usage: qemu-img command [command options]
OPTIONS
The following commands are supported:
check [-f fmt] [--output=ofmt] [-r [leaks | all]] filename
create [-f fmt] [-o options] filename [size]
commit [-f fmt] [-t cache] filename
convert [-c] [-p] [-f fmt] [-t cache] [-O output_fmt] [-o options] [-S
sparse_size] filename [filename2 [...]] output_filename
info [-f fmt] [--output=ofmt] filename
map [-f fmt] [--output=ofmt] filename
snapshot [-l | -a snapshot | -c snapshot | -d snapshot] filename
rebase [-f fmt] [-t cache] [-p] [-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
-p display progress bar (convert and rebase commands only)
-S size
indicates the consecutive number of bytes that must contain only
zeros for qemu-img to create a sparse image during conversion. This
value is rounded down to the nearest 512 bytes. You may use the
common size suffixes like "k" for kilobytes.
-t cache
specifies the cache mode that should be used with the (destination)
file. See the documentation of the emulator's "-drive cache=..."
option for allowed values.
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:
check [-f fmt] [--output=ofmt] [-r [leaks | all]] filename
Perform a consistency check on the disk image filename. The command
can output in the format ofmt which is either "human" or "json".
If "-r" is specified, qemu-img tries to repair any inconsistencies
found during the check. "-r leaks" repairs only cluster leaks,
whereas "-r all" fixes all kinds of errors, with a higher risk of
choosing the wrong fix or hiding corruption that has already
occured.
Only the formats "qcow2", "qed" and "vdi" support consistency
checks.
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] [-t cache] filename
Commit the changes recorded in filename in its base image.
convert [-c] [-p] [-f fmt] [-t cache] [-O output_fmt] [-o options] [-S
sparse_size] 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] [--output=ofmt] 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. The command can output in the format
ofmt which is either "human" or "json".
map [-f fmt] [--output=ofmt] filename
Dump the metadata of image filename and its backing file chain. In
particular, this commands dumps the allocation state of every
sector of filename, together with the topmost file that allocates
it in the backing file chain.
Two option formats are possible. The default format ("human") only
dumps known-nonzero areas of the file. Known-zero parts of the
file are omitted altogether, and likewise for parts that are not
allocated throughout the chain. qemu-img output will identify a
file from where the data can be read, and the offset in the file.
Each line will include four fields, the first three of which are
hexadecimal numbers. For example the first line of:
Offset Length Mapped to File
0 0x20000 0x50000 /tmp/overlay.qcow2
0x100000 0x10000 0x95380000 /tmp/backing.qcow2
means that 0x20000 (131072) bytes starting at offset 0 in the image
are available in /tmp/overlay.qcow2 (opened in "raw" format)
starting at offset 0x50000 (327680). Data that is compressed,
encrypted, or otherwise not available in raw format will cause an
error if "human" format is in use. Note that file names can
include newlines, thus it is not safe to parse this output format
in scripts.
The alternative format "json" will return an array of dictionaries
in JSON format. It will include similar information in the
"start", "length", "offset" fields; it will also include other more
specific information:
- whether the sectors contain actual data or not (boolean field
"data"; if false, the sectors are either unallocated or stored
as optimized all-zero clusters);
- whether the data is known to read as zero (boolean field
"zero");
- in order to make the output shorter, the target file is
expressed as a "depth"; for example, a depth of 2 refers to the
backing file of the backing file of filename.
In JSON format, the "offset" field is optional; it is absent in
cases where "human" format would omit the entry or exit with an
error. If "data" is false and the "offset" field is present, the
corresponding sectors in the file are not yet in use, but they are
preallocated.
For more information, consult include/block/block.h in QEMU's
source code.
snapshot [-l | -a snapshot | -c snapshot | -d snapshot ] filename
List, apply, create or delete snapshots in image filename.
rebase [-f fmt] [-t cache] [-p] [-u] -b backing_file [-F backing_fmt]
filename
Changes the backing file of an image. Only the formats "qcow2" and
"qed" support changing the backing file.
The backing file is changed to backing_file and (if the image
format of filename supports this) the backing file format is
changed to backing_fmt. If backing_file is specified as "" (the
empty string), then the image is rebased onto no backing file (i.e.
it will exist independently of any backing file).
There are two different modes in which "rebase" can operate:
Safe mode
This is the default mode and performs a real rebase operation.
The new backing file may differ from the old one and qemu-img
rebase will take care of keeping the guest-visible content of
filename unchanged.
In order to achieve this, any clusters that differ between
backing_file and the old backing file of filename are merged
into filename before 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.
Unsafe mode
qemu-img uses the unsafe mode if "-u" is specified. In this
mode, only the backing file name and format of filename is
changed without any checks on the file contents. The user must
take care of specifying the correct new backing file, or the
guest-visible content of the image will be corrupted.
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 to fix an image whose backing
file has already been moved/renamed.
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.
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, full). An
image with preallocated metadata is initially larger but can
improve performance when the image needs to grow. Full
preallocation additionally writes zeros to the whole image in
order to preallocate lower layers (e.g. the file system
containing the image file) as well. Note that full
preallocation writes to every byte of the virtual disk, so it
can take a long time for large images.
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
2013-11-21 QEMU-IMG(1)
