@c man end
@end example
+@c man begin DESCRIPTION
+qemu-img allows you to create, convert and modify images offline. It can handle
+all image formats supported by QEMU.
+
+@b{Warning:} Never use qemu-img to modify images in use by a running virtual
+machine or any other process; this may destroy the image. Also, be aware that
+querying an image that is being modified by another process may encounter
+inconsistent state.
+@c man end
+
@c man begin OPTIONS
The following commands are supported:
@table @var
@item filename
is a disk image filename
-@item base_image
-is the read-only disk image which is used as base for a copy on
- write image; the copy on write image only stores the modified data
-@item output_base_image
-forces the output image to be created as a copy on write
-image of the specified base image; @code{output_base_image} should have the same
-content as the input's base image, however the path, image format, etc may
-differ
-@item base_fmt
-is the disk image format of @var{base_image}. for more information look at @var{fmt}
@item fmt
is the disk image format. It is guessed automatically in most cases. See below
for a description of the supported disk formats.
+@item --backing-chain
+will enumerate information about backing files in a disk image chain. Refer
+below for further description.
+
@item size
is the disk image size in bytes. Optional suffixes @code{k} or @code{K}
(kilobyte, 1024) @code{M} (megabyte, 1024k) and @code{G} (gigabyte, 1024M)
@item options
is a comma separated list of format specific options in a
name=value format. Use @code{-o ?} for an overview of the options supported
-by the used format
+by the used format or see the format descriptions below for details.
@item -c
indicates that target image must be compressed (qcow format only)
@item -h
with or without a command shows help and lists the supported formats
+@item -p
+display progress bar (convert and rebase commands only)
+@item -q
+Quiet mode - do not print any output (except errors). There's no progress bar
+in case both @var{-q} and @var{-p} options are used.
+@item -S @var{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
+@code{k} for kilobytes.
+@item -t @var{cache}
+specifies the cache mode that should be used with the (destination) file. See
+the documentation of the emulator's @code{-drive cache=...} option for allowed
+values.
@end table
Parameters to snapshot subcommand:
lists all snapshots in the given image
@end table
+Parameters to compare subcommand:
+
+@table @option
+
+@item -f
+First image format
+@item -F
+Second image format
+@item -s
+Strict mode - fail on on different image size or sector allocation
+@end table
+
Command description:
@table @option
-@item create [-F @var{base_fmt}] [-b @var{base_image}] [-f @var{fmt}] [-o @var{options}] @var{filename} [@var{size}]
+@item check [-f @var{fmt}] [--output=@var{ofmt}] [-r [leaks | all]] @var{filename}
+
+Perform a consistency check on the disk image @var{filename}. The command can
+output in the format @var{ofmt} which is either @code{human} or @code{json}.
+
+If @code{-r} is specified, qemu-img tries to repair any inconsistencies found
+during the check. @code{-r leaks} repairs only cluster leaks, whereas
+@code{-r all} fixes all kinds of errors, with a higher risk of choosing the
+wrong fix or hiding corruption that has already occurred.
+
+Only the formats @code{qcow2}, @code{qed} and @code{vdi} support
+consistency checks.
+
+@item create [-f @var{fmt}] [-o @var{options}] @var{filename} [@var{size}]
Create the new disk image @var{filename} of size @var{size} and format
-@var{fmt}.
+@var{fmt}. Depending on the file format, you can add one or more @var{options}
+that enable additional features of this format.
-If @var{base_image} is specified, then the image will record only the
-differences from @var{base_image}. No size needs to be specified in
-this case. @var{base_image} will never be modified unless you use the
-@code{commit} monitor command.
+If the option @var{backing_file} is specified, then the image will record
+only the differences from @var{backing_file}. No size needs to be specified in
+this case. @var{backing_file} will never be modified unless you use the
+@code{commit} monitor command (or qemu-img commit).
The size can also be specified using the @var{size} option with @code{-o},
it doesn't need to be specified separately in this case.
-@item commit [-f @var{fmt}] @var{filename}
+@item commit [-f @var{fmt}] [-t @var{cache}] @var{filename}
Commit the changes recorded in @var{filename} in its base image.
-@item convert [-c] [-f @var{fmt}] [-O @var{output_fmt}] [-o @var{options}] [-B @var{output_base_image}] @var{filename} [@var{filename2} [...]] @var{output_filename}
+@item compare [-f @var{fmt}] [-F @var{fmt}] [-p] [-s] [-q] @var{filename1} @var{filename2}
+
+Check if two images have the same content. You can compare images with
+different format or settings.
+
+The format is probed unless you specify it by @var{-f} (used for
+@var{filename1}) and/or @var{-F} (used for @var{filename2}) option.
-Convert the disk image @var{filename} to disk image @var{output_filename}
+By default, images with different size are considered identical if the larger
+image contains only unallocated and/or zeroed sectors in the area after the end
+of the other image. In addition, if any sector is not allocated in one image
+and contains only zero bytes in the second one, it is evaluated as equal. You
+can use Strict mode by specifying the @var{-s} option. When compare runs in
+Strict mode, it fails in case image size differs or a sector is allocated in
+one image and is not allocated in the second one.
+
+By default, compare prints out a result message. This message displays
+information that both images are same or the position of the first different
+byte. In addition, result message can report different image size in case
+Strict mode is used.
+
+Compare exits with @code{0} in case the images are equal and with @code{1}
+in case the images differ. Other exit codes mean an error occurred during
+execution and standard error output should contain an error message.
+The following table sumarizes all exit codes of the compare subcommand:
+
+@table @option
+
+@item 0
+Images are identical
+@item 1
+Images differ
+@item 2
+Error on opening an image
+@item 3
+Error on checking a sector allocation
+@item 4
+Error on reading data
+
+@end table
+
+@item convert [-c] [-p] [-f @var{fmt}] [-t @var{cache}] [-O @var{output_fmt}] [-o @var{options}] [-s @var{snapshot_name}] [-S @var{sparse_size}] @var{filename} [@var{filename2} [...]] @var{output_filename}
+
+Convert the disk image @var{filename} or a snapshot @var{snapshot_name} to disk image @var{output_filename}
using format @var{output_fmt}. It can be optionally compressed (@code{-c}
option) or use any format specific options like encryption (@code{-o} option).
-Only the formats @code{qcow} and @code{qcow2} support encryption or compression. The
+Only the formats @code{qcow} and @code{qcow2} support compression. The
compression is read-only. It means that if a compressed sector is
rewritten, then it is rewritten as uncompressed data.
-Encryption uses the AES format which is very secure (128 bit keys). Use
-a long password (16 characters) to get maximum protection.
-
Image conversion is also useful to get smaller image when using a
growable format such as @code{qcow} or @code{cow}: the empty sectors
are detected and suppressed from the destination image.
-@item info [-f @var{fmt}] @var{filename}
+You can use the @var{backing_file} option to force the output image to be
+created as a copy on write image of the specified base image; the
+@var{backing_file} should have the same content as the input's base image,
+however the path, image format, etc may differ.
+
+@item info [-f @var{fmt}] [--output=@var{ofmt}] [--backing-chain] @var{filename}
Give information about the disk image @var{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.
+they are displayed too. The command can output in the format @var{ofmt}
+which is either @code{human} or @code{json}.
+
+If a disk image has a backing file chain, information about each disk image in
+the chain can be recursively enumerated by using the option @code{--backing-chain}.
+
+For instance, if you have an image chain like:
+
+@example
+base.qcow2 <- snap1.qcow2 <- snap2.qcow2
+@end example
+
+To enumerate information about each disk image in the above chain, starting from top to base, do:
+
+@example
+qemu-img info --backing-chain snap2.qcow2
+@end example
@item snapshot [-l | -a @var{snapshot} | -c @var{snapshot} | -d @var{snapshot} ] @var{filename}
List, apply, create or delete snapshots in image @var{filename}.
+
+@item rebase [-f @var{fmt}] [-t @var{cache}] [-p] [-u] -b @var{backing_file} [-F @var{backing_fmt}] @var{filename}
+
+Changes the backing file of an image. Only the formats @code{qcow2} and
+@code{qed} support changing the backing file.
+
+The backing file is changed to @var{backing_file} and (if the image format of
+@var{filename} supports this) the backing file format is changed to
+@var{backing_fmt}. If @var{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 @code{rebase} can operate:
+@table @option
+@item 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 @var{filename} unchanged.
+
+In order to achieve this, any clusters that differ between @var{backing_file}
+and the old backing file of @var{filename} are merged into @var{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.
+
+@item Unsafe mode
+qemu-img uses the unsafe mode if @code{-u} is specified. In this mode, only the
+backing file name and format of @var{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.
+@end table
+
+You can use @code{rebase} to perform a ``diff'' operation on two
+disk images. This can be useful when you have copied or cloned
+a guest, and you want to get back to a thin image on top of a
+template or base image.
+
+Say that @code{base.img} has been cloned as @code{modified.img} by
+copying it, and that the @code{modified.img} guest has run so there
+are now some changes compared to @code{base.img}. To construct a thin
+image called @code{diff.qcow2} that contains just the differences, do:
+
+@example
+qemu-img create -f qcow2 -b modified.img diff.qcow2
+qemu-img rebase -b base.img diff.qcow2
+@end example
+
+At this point, @code{modified.img} can be discarded, since
+@code{base.img + diff.qcow2} contains the same information.
+
+@item resize @var{filename} [+ | -]@var{size}
+
+Change the disk image as if it had been created with @var{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.
@end table
+@c man end
+@ignore
+@c man begin NOTES
Supported image file formats:
@table @option
space. Use @code{qemu-img info} to know the real size used by the
image or @code{ls -ls} on Unix/Linux.
-@item 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.
-
@item 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.
-@item qcow
-Old QEMU image format. Left for compatibility.
-@item 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.
-@item vdi
-VirtualBox 1.1 compatible image format.
-@item vmdk
-VMware 3 and 4 compatible image format.
-@item cloop
-Linux Compressed Loop image, useful only to reuse directly compressed
-CD-ROM images present for example in the Knoppix CD-ROMs.
+
+Supported options:
+@table @code
+@item compat
+Determines the qcow2 version to use. @code{compat=0.10} uses the traditional
+image format that can be read by any QEMU since 0.10 (this is the default).
+@code{compat=1.1} enables image format extensions that only QEMU 1.1 and
+newer understand. Amongst others, this includes zero clusters, which allow
+efficient copy-on-read for sparse images.
+
+@item backing_file
+File name of a base image (see @option{create} subcommand)
+@item backing_fmt
+Image format of the base image
+@item encryption
+If this option is set to @code{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.
+
+@item 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.
+
+@item 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.
+
+@item lazy_refcounts
+If this option is set to @code{on}, reference count updates are postponed with
+the goal of avoiding metadata I/O and improving performance. This is
+particularly interesting with @option{cache=writethrough} which doesn't batch
+metadata updates. The tradeoff is that after a host crash, the reference count
+tables must be rebuilt, i.e. on the next open an (automatic) @code{qemu-img
+check -r all} is required, which may take some time.
+
+This option can only be enabled if @code{compat=1.1} is specified.
+
@end table
+@item Other
+QEMU also supports various other image file formats for compatibility with
+older QEMU versions or other hypervisors, including VMDK, VDI, VHD (vpc), qcow1
+and QED. For a full list of supported formats see @code{qemu-img --help}.
+For a more detailed description of these formats, see the QEMU Emulation User
+Documentation.
-@c man end
+The main purpose of the block drivers for these formats is image conversion.
+For running VMs, it is recommended to convert the disk images to either raw or
+qcow2 in order to achieve good performance.
+@end table
-@ignore
+
+@c man end
@setfilename qemu-img
@settitle QEMU disk image utility
projects / qemu.git / blobdiff