QEMU-IMG(1)							   QEMU-IMG(1)



NAME
       qemu-img - QEMU disk image utility

SYNOPSIS
       usage: qemu-img command [command options]

DESCRIPTION
       qemu-img allows you to create, convert and modify images offline. It
       can handle all image formats supported by QEMU.

       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.

OPTIONS
       The following commands are supported:

       check [-q] [-f fmt] [--output=ofmt] [-r [leaks | all]] [-T src_cache]
       filename
       create [-q] [-f fmt] [-o options] filename [size]
       commit [-q] [-f fmt] [-t cache] [-b base] [-d] [-p] filename
       compare [-f fmt] [-F fmt] [-T src_cache] [-p] [-q] [-s] filename1
       filename2
       convert [-c] [-p] [-q] [-n] [-f fmt] [-t cache] [-T src_cache] [-O
       output_fmt] [-o options] [-s snapshot_id_or_name] [-l snapshot_param]
       [-S sparse_size] filename [filename2 [...]] output_filename
       info [-f fmt] [--output=ofmt] [--backing-chain] filename
       map [-f fmt] [--output=ofmt] filename
       snapshot [-q] [-l | -a snapshot | -c snapshot | -d snapshot] filename
       rebase [-q] [-f fmt] [-t cache] [-T src_cache] [-p] [-u] -b
       backing_file [-F backing_fmt] filename
       resize [-q] filename [+ | -]size
       amend [-p] [-q] [-f fmt] [-t cache] -o options filename

       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.

       --backing-chain
	   will enumerate information about backing files in a disk image
	   chain. Refer below for further description.

       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.

       snapshot_param
	   is param used for internal snapshot, format is
	   'snapshot.id=[ID],snapshot.name=[NAME]' or '[ID_OR_NAME]'

       snapshot_id_or_name
	   is deprecated, use snapshot_param instead

       -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 (compare, convert and rebase commands only).
	   If the -p option is not used for a command that supports it, the
	   progress is reported when the process receives a "SIGUSR1" signal.

       -q  Quiet mode - do not print any output (except errors). There's no
	   progress bar in case both -q and -p options are used.

       -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.

       -T src_cache
	   specifies the cache mode that should be used with the source
	   file(s). 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

       Parameters to compare subcommand:

       -f  First image format

       -F  Second image format

       -s  Strict mode - fail on different image size or sector allocation

       Parameters to convert subcommand:

       -n  Skip the creation of the target volume

       Command description:

       check [-f fmt] [--output=ofmt] [-r [leaks | all]] [-T src_cache]
       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
	   occurred.

	   Only the formats "qcow2", "qed" and "vdi" support consistency
	   checks.

	   In case the image does not have any inconsistencies, check exits
	   with 0.  Other exit codes indicate the kind of inconsistency found
	   or if another error occurred. The following table summarizes all
	   exit codes of the check subcommand:

	   0   Check completed, the image is (now) consistent

	   1   Check not completed because of internal errors

	   2   Check completed, image is corrupted

	   3   Check completed, image has leaked clusters, but is not
	       corrupted

	   63  Checks are not supported by the image format

	   If "-r" is specified, exit codes representing the image state refer
	   to the state after (the attempt at) repairing it. That is, a
	   successful "-r all" will yield the exit code 0, independently of
	   the image state before.

       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 [-q] [-f fmt] [-t cache] [-b base] [-d] [-p] filename
	   Commit the changes recorded in filename in its base image or
	   backing file.  If the backing file is smaller than the snapshot,
	   then the backing file will be resized to be the same size as the
	   snapshot.  If the snapshot is smaller than the backing file, the
	   backing file will not be truncated.	If you want the backing file
	   to match the size of the smaller snapshot, you can safely truncate
	   it yourself once the commit operation successfully completes.

	   The image filename is emptied after the operation has succeeded. If
	   you do not need filename afterwards and intend to drop it, you may
	   skip emptying filename by specifying the "-d" flag.

	   If the backing chain of the given image file filename has more than
	   one layer, the backing file into which the changes will be
	   committed may be specified as base (which has to be part of
	   filename's backing chain). If base is not specified, the immediate
	   backing file of the top image (which is filename) will be used. For
	   reasons of consistency, explicitly specifying base will always
	   imply "-d" (since emptying an image after committing to an indirect
	   backing file would lead to different data being read from the image
	   due to content in the intermediate backing chain overruling the
	   commit target).

       compare [-f fmt] [-F fmt] [-T src_cache] [-p] [-s] [-q] filename1
       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 -f (used for
	   filename1) and/or -F (used for filename2) option.

	   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 -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 0 in case the images are equal and with 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:

	   0   Images are identical

	   1   Images differ

	   2   Error on opening an image

	   3   Error on checking a sector allocation

	   4   Error on reading data

       convert [-c] [-p] [-n] [-f fmt] [-t cache] [-T src_cache] [-O
       output_fmt] [-o options] [-s snapshot_id_or_name] [-l snapshot_param]
       [-S sparse_size] filename [filename2 [...]] output_filename
	   Convert the disk image filename or a snapshot
	   snapshot_param(snapshot_id_or_name is deprecated) 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": the empty sectors are detected and
	   suppressed from the destination image.

	   sparse_size indicates the consecutive number of bytes (defaults to
	   4k) that must contain only zeros for qemu-img to create a sparse
	   image during conversion. If sparse_size is 0, the source will not
	   be scanned for unallocated or zero sectors, and the destination
	   image will always be fully allocated.

	   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.

	   If the "-n" option is specified, the target volume creation will be
	   skipped. This is useful for formats such as "rbd" if the target
	   volume has already been created with site specific options that
	   cannot be supplied through qemu-img.

       info [-f fmt] [--output=ofmt] [--backing-chain] 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".

	   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 "--backing-chain".

	   For instance, if you have an image chain like:

		   base.qcow2 <- snap1.qcow2 <- snap2.qcow2

	   To enumerate information about each disk image in the above chain,
	   starting from top to base, do:

		   qemu-img info --backing-chain snap2.qcow2

       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] [-T src_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).

	   cache specifies the cache mode to be used for filename, whereas
	   src_cache specifies the cache mode for reading backing files.

	   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.

	   You can use "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 "base.img" has been cloned as "modified.img" by copying
	   it, and that the "modified.img" guest has run so there are now some
	   changes compared to "base.img".  To construct a thin image called
	   "diff.qcow2" that contains just the differences, do:

		   qemu-img create -f qcow2 -b modified.img diff.qcow2
		   qemu-img rebase -b base.img diff.qcow2

	   At this point, "modified.img" can be discarded, since "base.img +
	   diff.qcow2" contains the same information.

       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.

       amend [-p] [-f fmt] [-t cache] -o options filename
	   Amends the image format specific options for the image file
	   filename. Not all file formats support this operation.

NOTES
       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.

	   Supported options:

	   "preallocation"
	       Preallocation mode (allowed values: "off", "falloc", "full").
	       "falloc" mode preallocates space for image by calling
	       posix_fallocate().  "full" mode preallocates space for image by
	       writing zeros to underlying storage.

       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:

	   "compat"
	       Determines the qcow2 version to use. "compat=0.10" uses the
	       traditional image format that can be read by any QEMU since
	       0.10.  "compat=1.1" enables image format extensions that only
	       QEMU 1.1 and newer understand (this is the default). Amongst
	       others, this includes zero clusters, which allow efficient
	       copy-on-read for sparse images.

	   "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 with
	       128-bit AES-CBC.

	       The use of encryption in qcow and qcow2 images is considered to
	       be flawed by modern cryptography standards, suffering from a
	       number of design problems:

	       -<The AES-CBC cipher is used with predictable initialization
	       vectors based>
		   on the sector number. This makes it vulnerable to chosen
		   plaintext attacks which can reveal the existence of
		   encrypted data.

	       -<The user passphrase is directly used as the encryption key. A
	       poorly>
		   chosen or short passphrase will compromise the security of
		   the encryption.

	       -<In the event of the passphrase being compromised there is no
	       way to>
		   change the passphrase to protect data in any qcow images.
		   The files must be cloned, using a different encryption
		   passphrase in the new file. The original file must then be
		   securely erased using a program like shred, though even
		   this is ineffective with many modern storage technologies.

	       Use of qcow / qcow2 encryption is thus strongly discouraged.
	       Users are recommended to use an alternative encryption
	       technology such as the Linux dm-crypt / LUKS system.

	   "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",
	       "falloc", "full"). An image with preallocated metadata is
	       initially larger but can improve performance when the image
	       needs to grow. "falloc" and "full" preallocations are like the
	       same options of "raw" format, but sets up metadata also.

	   "lazy_refcounts"
	       If this option is set to "on", reference count updates are
	       postponed with the goal of avoiding metadata I/O and improving
	       performance. This is particularly interesting with
	       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) "qemu-img
	       check -r all" is required, which may take some time.

	       This option can only be enabled if "compat=1.1" is specified.

	   "nocow"
	       If this option is set to "on", it will turn off COW of the
	       file. It's only valid on btrfs, no effect on other file
	       systems.

	       Btrfs has low performance when hosting a VM image file, even
	       more when the guest on the VM also using btrfs as file system.
	       Turning off COW is a way to mitigate this bad performance.
	       Generally there are two ways to turn off COW on btrfs: a)
	       Disable it by mounting with nodatacow, then all newly created
	       files will be NOCOW. b) For an empty file, add the NOCOW file
	       attribute. That's what this option does.

	       Note: this option is only valid to new or empty files. If there
	       is an existing file which is COW and has data blocks already,
	       it couldn't be changed to NOCOW by setting "nocow=on". One can
	       issue "lsattr filename" to check if the NOCOW flag is set or
	       not (Capital 'C' is NOCOW flag).

       Other
	   QEMU also supports various other image file formats for
	   compatibility with older QEMU versions or other hypervisors,
	   including VMDK, VDI, VHD (vpc), VHDX, qcow1 and QED. For a full
	   list of supported formats see "qemu-img --help".  For a more
	   detailed description of these formats, see the QEMU Emulation User
	   Documentation.

	   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.

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

AUTHOR
       Fabrice Bellard



				  2017-09-20			   QEMU-IMG(1)