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bellardacd935e2004-11-15 22:57:26 +00001@example
2@c man begin SYNOPSIS
Denis V. Lunev10985132016-06-17 17:44:13 +03003@command{qemu-img} [@var{standard} @var{options}] @var{command} [@var{command} @var{options}]
bellardacd935e2004-11-15 22:57:26 +00004@c man end
5@end example
6
Kevin Wolf48467322012-08-16 10:56:35 +02007@c man begin DESCRIPTION
8qemu-img allows you to create, convert and modify images offline. It can handle
9all image formats supported by QEMU.
10
11@b{Warning:} Never use qemu-img to modify images in use by a running virtual
12machine or any other process; this may destroy the image. Also, be aware that
13querying an image that is being modified by another process may encounter
14inconsistent state.
15@c man end
16
bellardacd935e2004-11-15 22:57:26 +000017@c man begin OPTIONS
18
Denis V. Lunev10985132016-06-17 17:44:13 +030019Standard options:
20@table @option
21@item -h, --help
22Display this help and exit
23@item -V, --version
24Display version information and exit
Denis V. Lunev06a1e0c2016-06-17 17:44:14 +030025@item -T, --trace [[enable=]@var{pattern}][,events=@var{file}][,file=@var{file}]
26@findex --trace
27@include qemu-option-trace.texi
Denis V. Lunev10985132016-06-17 17:44:13 +030028@end table
29
bellardacd935e2004-11-15 22:57:26 +000030The following commands are supported:
Stuart Brady153859b2009-06-07 00:42:17 +010031
32@include qemu-img-cmds.texi
bellardacd935e2004-11-15 22:57:26 +000033
34Command parameters:
35@table @var
Fam Zhengc150eb92018-02-09 13:29:13 +080036
bellardacd935e2004-11-15 22:57:26 +000037@item filename
Fam Zhengc150eb92018-02-09 13:29:13 +080038is a disk image filename
Daniel P. Berrangeeb769f72016-02-17 10:10:20 +000039
ths5fafdf22007-09-16 21:08:06 +000040@item fmt
Kevin Wolff932c042009-10-28 12:49:15 +010041is the disk image format. It is guessed automatically in most cases. See below
42for a description of the supported disk formats.
bellardacd935e2004-11-15 22:57:26 +000043
ths5fafdf22007-09-16 21:08:06 +000044@item size
Kevin Wolfeff44262009-06-04 15:39:39 +020045is the disk image size in bytes. Optional suffixes @code{k} or @code{K}
46(kilobyte, 1024) @code{M} (megabyte, 1024k) and @code{G} (gigabyte, 1024M)
47and T (terabyte, 1024G) are supported. @code{b} is ignored.
bellardacd935e2004-11-15 22:57:26 +000048
49@item output_filename
ths5fafdf22007-09-16 21:08:06 +000050is the destination disk image filename
bellardacd935e2004-11-15 22:57:26 +000051
52@item output_fmt
Fam Zhengc150eb92018-02-09 13:29:13 +080053is the destination format
54
Kevin Wolfeff44262009-06-04 15:39:39 +020055@item options
56is a comma separated list of format specific options in a
57name=value format. Use @code{-o ?} for an overview of the options supported
Kevin Wolf3e032362009-10-28 12:49:17 +010058by the used format or see the format descriptions below for details.
Fam Zhengc150eb92018-02-09 13:29:13 +080059
Wenchao Xiaef806542013-12-04 17:10:57 +080060@item snapshot_param
61is param used for internal snapshot, format is
62'snapshot.id=[ID],snapshot.name=[NAME]' or '[ID_OR_NAME]'
Fam Zhengc150eb92018-02-09 13:29:13 +080063
Fam Zhengc150eb92018-02-09 13:29:13 +080064@end table
65
66@table @option
67
68@item --object @var{objectdef}
69is a QEMU user creatable object definition. See the @code{qemu(1)} manual
70page for a description of the object properties. The most common object
71type is a @code{secret}, which is used to supply passwords and/or encryption
72keys.
73
74@item --image-opts
75Indicates that the source @var{filename} parameter is to be interpreted as a
76full option string, not a plain filename. This parameter is mutually
77exclusive with the @var{-f} parameter.
78
79@item --target-image-opts
80Indicates that the @var{output_filename} parameter(s) are to be interpreted as
81a full option string, not a plain filename. This parameter is mutually
82exclusive with the @var{-O} parameters. It is currently required to also use
83the @var{-n} parameter to skip image creation. This restriction may be relaxed
84in a future release.
85
Fam Zhenga7e326d2018-02-09 13:29:14 +080086@item --force-share (-U)
87If specified, @code{qemu-img} will open the image in shared mode, allowing
88other QEMU processes to open it in write mode. For example, this can be used to
89get the image information (with 'info' subcommand) when the image is used by a
90running guest. Note that this could produce inconsistent results because of
91concurrent metadata changes, etc. This option is only allowed when opening
92images in read-only mode.
93
Fam Zhengc150eb92018-02-09 13:29:13 +080094@item --backing-chain
95will enumerate information about backing files in a disk image chain. Refer
96below for further description.
97
bellardacd935e2004-11-15 22:57:26 +000098@item -c
Fam Zhengb8550432018-07-27 11:34:00 +080099indicates that target image must be compressed (qcow format only)
Fam Zhengc150eb92018-02-09 13:29:13 +0800100
blueswir1d2c639d2009-01-24 18:19:25 +0000101@item -h
102with or without a command shows help and lists the supported formats
Fam Zhengc150eb92018-02-09 13:29:13 +0800103
Jes Sorensenaaf55b42011-07-19 15:01:34 +0200104@item -p
Kevin Wolf0e3bd992014-01-20 15:12:16 +0100105display progress bar (compare, convert and rebase commands only).
106If the @var{-p} option is not used for a command that supports it, the
Max Reitz262fbae2017-02-08 00:57:57 +0100107progress is reported when the process receives a @code{SIGUSR1} or
108@code{SIGINFO} signal.
Fam Zhengc150eb92018-02-09 13:29:13 +0800109
Miroslav Rezaninaf382d432013-02-13 09:09:40 +0100110@item -q
111Quiet mode - do not print any output (except errors). There's no progress bar
112in case both @var{-q} and @var{-p} options are used.
Fam Zhengc150eb92018-02-09 13:29:13 +0800113
Kevin Wolfa22f1232011-08-26 15:27:13 +0200114@item -S @var{size}
115indicates the consecutive number of bytes that must contain only zeros
116for qemu-img to create a sparse image during conversion. This value is rounded
117down to the nearest 512 bytes. You may use the common size suffixes like
Fam Zhengb8550432018-07-27 11:34:00 +0800118@code{k} for kilobytes.
Fam Zhengc150eb92018-02-09 13:29:13 +0800119
Kevin Wolf3763f262011-12-07 13:57:13 +0100120@item -t @var{cache}
121specifies the cache mode that should be used with the (destination) file. See
122the documentation of the emulator's @code{-drive cache=...} option for allowed
123values.
Fam Zhengc150eb92018-02-09 13:29:13 +0800124
Max Reitz40055952014-07-22 22:58:42 +0200125@item -T @var{src_cache}
Stefan Hajnoczibb87fdf2014-09-02 11:01:02 +0100126specifies the cache mode that should be used with the source file(s). See
127the documentation of the emulator's @code{-drive cache=...} option for allowed
128values.
Fam Zhengc150eb92018-02-09 13:29:13 +0800129
blueswir1d2c639d2009-01-24 18:19:25 +0000130@end table
131
132Parameters to snapshot subcommand:
133
134@table @option
135
136@item snapshot
137is the name of the snapshot to create, apply or delete
138@item -a
139applies a snapshot (revert disk to saved state)
140@item -c
141creates a snapshot
142@item -d
143deletes a snapshot
144@item -l
145lists all snapshots in the given image
bellardacd935e2004-11-15 22:57:26 +0000146@end table
147
Miroslav Rezaninad14ed182013-02-13 09:09:41 +0100148Parameters to compare subcommand:
149
150@table @option
151
152@item -f
153First image format
154@item -F
155Second image format
156@item -s
Daniel P. Berrangeb6af0972015-08-26 12:17:13 +0100157Strict mode - fail on different image size or sector allocation
Miroslav Rezaninad14ed182013-02-13 09:09:41 +0100158@end table
159
Alexandre Derumierb2e10492013-09-02 19:07:24 +0100160Parameters to convert subcommand:
161
162@table @option
163
164@item -n
165Skip the creation of the target volume
Peter Lieven2d9187b2017-02-28 13:40:07 +0100166@item -m
167Number of parallel coroutines for the convert process
168@item -W
169Allow out-of-order writes to the destination. This option improves performance,
170but is only recommended for preallocated devices like host devices or other
171raw block devices.
Fam Zhenge11ce122018-07-27 11:34:01 +0800172@item -C
173Try to use copy offloading to move data from source image to target. This may
174improve performance if the data is remote, such as with NFS or iSCSI backends,
175but will not automatically sparsify zero sectors, and may result in a fully
176allocated target image depending on the host support for getting allocation
177information.
Alexandre Derumierb2e10492013-09-02 19:07:24 +0100178@end table
179
Reda Sallahi86ce1f62016-08-10 04:43:12 +0200180Parameters to dd subcommand:
181
182@table @option
183
184@item bs=@var{block_size}
185defines the block size
186@item count=@var{blocks}
187sets the number of input blocks to copy
188@item if=@var{input}
189sets the input file
190@item of=@var{output}
191sets the output file
Reda Sallahif7c15532016-08-10 16:16:09 +0200192@item skip=@var{blocks}
193sets the number of input blocks to skip
Reda Sallahi86ce1f62016-08-10 04:43:12 +0200194@end table
195
bellardacd935e2004-11-15 22:57:26 +0000196Command description:
197
198@table @option
John Snow83e6da02018-05-03 18:56:45 -0400199
John Snow9775fcd2018-05-03 18:56:47 -0400200@item amend [--object @var{objectdef}] [--image-opts] [-p] [-p] [-f @var{fmt}] [-t @var{cache}] -o @var{options} @var{filename}
John Snow83e6da02018-05-03 18:56:45 -0400201
202Amends the image format specific @var{options} for the image file
203@var{filename}. Not all file formats support this operation.
204
John Snow9775fcd2018-05-03 18:56:47 -0400205@item bench [-c @var{count}] [-d @var{depth}] [-f @var{fmt}] [--flush-interval=@var{flush_interval}] [-n] [--no-drain] [-o @var{offset}] [--pattern=@var{pattern}] [-q] [-s @var{buffer_size}] [-S @var{step_size}] [-t @var{cache}] [-w] [-U] @var{filename}
Kevin Wolfb6133b82014-08-05 14:17:13 +0200206
Kevin Wolfb6495fa2015-07-10 18:09:18 +0200207Run a simple sequential I/O benchmark on the specified image. If @code{-w} is
208specified, a write test is performed, otherwise a read test is performed.
209
210A total number of @var{count} I/O requests is performed, each @var{buffer_size}
Kevin Wolfd3199a32015-07-10 18:09:18 +0200211bytes in size, and with @var{depth} requests in parallel. The first request
Kevin Wolf83de9be2015-07-13 13:13:17 +0200212starts at the position given by @var{offset}, each following request increases
213the current position by @var{step_size}. If @var{step_size} is not given,
214@var{buffer_size} is used for its value.
Kevin Wolfb6133b82014-08-05 14:17:13 +0200215
Kevin Wolf55d539c2016-06-03 13:59:41 +0200216If @var{flush_interval} is specified for a write test, the request queue is
217drained and a flush is issued before new writes are made whenever the number of
218remaining requests is a multiple of @var{flush_interval}. If additionally
219@code{--no-drain} is specified, a flush is issued without draining the request
220queue first.
221
Kevin Wolfb6133b82014-08-05 14:17:13 +0200222If @code{-n} is specified, the native AIO backend is used if possible. On
223Linux, this option only works if @code{-t none} or @code{-t directsync} is
224specified as well.
225
Kevin Wolfb6495fa2015-07-10 18:09:18 +0200226For write tests, by default a buffer filled with zeros is written. This can be
227overridden with a pattern byte specified by @var{pattern}.
228
John Snow9775fcd2018-05-03 18:56:47 -0400229@item check [--object @var{objectdef}] [--image-opts] [-q] [-f @var{fmt}] [--output=@var{ofmt}] [-r [leaks | all]] [-T @var{src_cache}] [-U] @var{filename}
Kevin Wolfe6184692011-01-17 15:35:28 +0100230
Federico Simoncelli8599ea42013-01-28 06:59:47 -0500231Perform a consistency check on the disk image @var{filename}. The command can
232output in the format @var{ofmt} which is either @code{human} or @code{json}.
Kevin Wolfe6184692011-01-17 15:35:28 +0100233
Kevin Wolf4534ff52012-05-11 16:07:02 +0200234If @code{-r} is specified, qemu-img tries to repair any inconsistencies found
235during the check. @code{-r leaks} repairs only cluster leaks, whereas
236@code{-r all} fixes all kinds of errors, with a higher risk of choosing the
Stefan Weil0546b8c2012-08-10 22:03:25 +0200237wrong fix or hiding corruption that has already occurred.
Kevin Wolf4534ff52012-05-11 16:07:02 +0200238
Kevin Wolfe6184692011-01-17 15:35:28 +0100239Only the formats @code{qcow2}, @code{qed} and @code{vdi} support
240consistency checks.
241
Max Reitzd6635c42014-06-02 22:15:21 +0200242In case the image does not have any inconsistencies, check exits with @code{0}.
243Other exit codes indicate the kind of inconsistency found or if another error
244occurred. The following table summarizes all exit codes of the check subcommand:
245
246@table @option
247
248@item 0
249Check completed, the image is (now) consistent
250@item 1
251Check not completed because of internal errors
252@item 2
253Check completed, image is corrupted
254@item 3
255Check completed, image has leaked clusters, but is not corrupted
256@item 63
257Checks are not supported by the image format
258
259@end table
260
261If @code{-r} is specified, exit codes representing the image state refer to the
262state after (the attempt at) repairing it. That is, a successful @code{-r all}
263will yield the exit code 0, independently of the image state before.
264
John Snow9775fcd2018-05-03 18:56:47 -0400265@item commit [--object @var{objectdef}] [--image-opts] [-q] [-f @var{fmt}] [-t @var{cache}] [-b @var{base}] [-d] [-p] @var{filename}
bellardacd935e2004-11-15 22:57:26 +0000266
Jeff Cody37222902014-01-24 09:02:37 -0500267Commit the changes recorded in @var{filename} in its base image or backing file.
268If the backing file is smaller than the snapshot, then the backing file will be
269resized to be the same size as the snapshot. If the snapshot is smaller than
270the backing file, the backing file will not be truncated. If you want the
271backing file to match the size of the smaller snapshot, you can safely truncate
272it yourself once the commit operation successfully completes.
bellardacd935e2004-11-15 22:57:26 +0000273
Max Reitz9a86fe42014-10-24 15:57:38 +0200274The image @var{filename} is emptied after the operation has succeeded. If you do
275not need @var{filename} afterwards and intend to drop it, you may skip emptying
276@var{filename} by specifying the @code{-d} flag.
277
Max Reitz1b22bff2014-10-24 15:57:40 +0200278If the backing chain of the given image file @var{filename} has more than one
279layer, the backing file into which the changes will be committed may be
280specified as @var{base} (which has to be part of @var{filename}'s backing
281chain). If @var{base} is not specified, the immediate backing file of the top
Max Reitz67e56472017-10-26 09:59:47 +0200282image (which is @var{filename}) will be used. Note that after a commit operation
283all images between @var{base} and the top image will be invalid and may return
284garbage data when read. For this reason, @code{-b} implies @code{-d} (so that
285the top image stays valid).
Max Reitz1b22bff2014-10-24 15:57:40 +0200286
John Snow9775fcd2018-05-03 18:56:47 -0400287@item compare [--object @var{objectdef}] [--image-opts] [-f @var{fmt}] [-F @var{fmt}] [-T @var{src_cache}] [-p] [-q] [-s] [-U] @var{filename1} @var{filename2}
Miroslav Rezaninad14ed182013-02-13 09:09:41 +0100288
289Check if two images have the same content. You can compare images with
290different format or settings.
291
292The format is probed unless you specify it by @var{-f} (used for
293@var{filename1}) and/or @var{-F} (used for @var{filename2}) option.
294
295By default, images with different size are considered identical if the larger
296image contains only unallocated and/or zeroed sectors in the area after the end
297of the other image. In addition, if any sector is not allocated in one image
298and contains only zero bytes in the second one, it is evaluated as equal. You
299can use Strict mode by specifying the @var{-s} option. When compare runs in
300Strict mode, it fails in case image size differs or a sector is allocated in
301one image and is not allocated in the second one.
302
303By default, compare prints out a result message. This message displays
304information that both images are same or the position of the first different
305byte. In addition, result message can report different image size in case
306Strict mode is used.
307
308Compare exits with @code{0} in case the images are equal and with @code{1}
309in case the images differ. Other exit codes mean an error occurred during
310execution and standard error output should contain an error message.
311The following table sumarizes all exit codes of the compare subcommand:
312
313@table @option
314
315@item 0
316Images are identical
317@item 1
318Images differ
319@item 2
320Error on opening an image
321@item 3
322Error on checking a sector allocation
323@item 4
324Error on reading data
325
326@end table
327
Fam Zhenge11ce122018-07-27 11:34:01 +0800328@item convert [--object @var{objectdef}] [--image-opts] [--target-image-opts] [-U] [-C] [-c] [-p] [-q] [-n] [-f @var{fmt}] [-t @var{cache}] [-T @var{src_cache}] [-O @var{output_fmt}] [-B @var{backing_file}] [-o @var{options}] [-l @var{snapshot_param}] [-S @var{sparse_size}] [-m @var{num_coroutines}] [-W] @var{filename} [@var{filename2} [...]] @var{output_filename}
bellardacd935e2004-11-15 22:57:26 +0000329
Thomas Huth46e8d272018-06-06 14:35:51 +0200330Convert the disk image @var{filename} or a snapshot @var{snapshot_param}
Wenchao Xiaef806542013-12-04 17:10:57 +0800331to disk image @var{output_filename} using format @var{output_fmt}. It can be optionally compressed (@code{-c}
Kevin Wolfeff44262009-06-04 15:39:39 +0200332option) or use any format specific options like encryption (@code{-o} option).
bellardacd935e2004-11-15 22:57:26 +0000333
Kevin Wolf8063d0f2009-10-28 12:49:16 +0100334Only the formats @code{qcow} and @code{qcow2} support compression. The
bellardacd935e2004-11-15 22:57:26 +0000335compression is read-only. It means that if a compressed sector is
336rewritten, then it is rewritten as uncompressed data.
337
bellardacd935e2004-11-15 22:57:26 +0000338Image conversion is also useful to get smaller image when using a
Stefan Hajnoczi550830f2014-09-16 15:24:24 +0100339growable format such as @code{qcow}: the empty sectors are detected and
340suppressed from the destination image.
bellardacd935e2004-11-15 22:57:26 +0000341
Peter Lieven11b66992013-10-24 12:07:05 +0200342@var{sparse_size} indicates the consecutive number of bytes (defaults to 4k)
343that must contain only zeros for qemu-img to create a sparse image during
344conversion. If @var{sparse_size} is 0, the source will not be scanned for
345unallocated or zero sectors, and the destination image will always be
346fully allocated.
347
Kevin Wolf8063d0f2009-10-28 12:49:16 +0100348You can use the @var{backing_file} option to force the output image to be
349created as a copy on write image of the specified base image; the
350@var{backing_file} should have the same content as the input's base image,
351however the path, image format, etc may differ.
352
Fam Zhenga16efd52017-08-04 22:36:58 +0800353If a relative path name is given, the backing file is looked up relative to
354the directory containing @var{output_filename}.
355
Alexandre Derumierb2e10492013-09-02 19:07:24 +0100356If the @code{-n} option is specified, the target volume creation will be
357skipped. This is useful for formats such as @code{rbd} if the target
358volume has already been created with site specific options that cannot
359be supplied through qemu-img.
360
Peter Lieven2d9187b2017-02-28 13:40:07 +0100361Out of order writes can be enabled with @code{-W} to improve performance.
362This is only recommended for preallocated devices like host devices or other
363raw block devices. Out of order write does not work in combination with
364creating compressed images.
365
366@var{num_coroutines} specifies how many coroutines work in parallel during
367the convert process (defaults to 8).
368
John Snow9775fcd2018-05-03 18:56:47 -0400369@item create [--object @var{objectdef}] [-q] [-f @var{fmt}] [-b @var{backing_file}] [-F @var{backing_fmt}] [-u] [-o @var{options}] @var{filename} [@var{size}]
John Snow83e6da02018-05-03 18:56:45 -0400370
371Create the new disk image @var{filename} of size @var{size} and format
372@var{fmt}. Depending on the file format, you can add one or more @var{options}
373that enable additional features of this format.
374
375If the option @var{backing_file} is specified, then the image will record
376only the differences from @var{backing_file}. No size needs to be specified in
377this case. @var{backing_file} will never be modified unless you use the
378@code{commit} monitor command (or qemu-img commit).
379
380If a relative path name is given, the backing file is looked up relative to
381the directory containing @var{filename}.
382
383Note that a given backing file will be opened to check that it is valid. Use
384the @code{-u} option to enable unsafe backing file mode, which means that the
385image will be created even if the associated backing file cannot be opened. A
386matching backing file must be created or additional options be used to make the
387backing file specification valid when you want to use an image created this
388way.
389
390The size can also be specified using the @var{size} option with @code{-o},
391it doesn't need to be specified separately in this case.
392
John Snow9775fcd2018-05-03 18:56:47 -0400393@item dd [--image-opts] [-U] [-f @var{fmt}] [-O @var{output_fmt}] [bs=@var{block_size}] [count=@var{blocks}] [skip=@var{blocks}] if=@var{input} of=@var{output}
Reda Sallahi86ce1f62016-08-10 04:43:12 +0200394
395Dd copies from @var{input} file to @var{output} file converting it from
396@var{fmt} format to @var{output_fmt} format.
397
398The data is by default read and written using blocks of 512 bytes but can be
399modified by specifying @var{block_size}. If count=@var{blocks} is specified
400dd will stop reading input after reading @var{blocks} input blocks.
401
402The size syntax is similar to dd(1)'s size syntax.
403
John Snow9775fcd2018-05-03 18:56:47 -0400404@item info [--object @var{objectdef}] [--image-opts] [-f @var{fmt}] [--output=@var{ofmt}] [--backing-chain] [-U] @var{filename}
bellardacd935e2004-11-15 22:57:26 +0000405
406Give information about the disk image @var{filename}. Use it in
407particular to know the size reserved on disk which can be different
bellard19d36792006-08-07 21:34:34 +0000408from the displayed size. If VM snapshots are stored in the disk image,
Benoît Canetc054b3f2012-09-05 13:09:02 +0200409they are displayed too. The command can output in the format @var{ofmt}
410which is either @code{human} or @code{json}.
blueswir1d2c639d2009-01-24 18:19:25 +0000411
Kashyap Chamarthye5357562012-10-18 11:25:34 +0530412If a disk image has a backing file chain, information about each disk image in
413the chain can be recursively enumerated by using the option @code{--backing-chain}.
414
415For instance, if you have an image chain like:
416
417@example
418base.qcow2 <- snap1.qcow2 <- snap2.qcow2
419@end example
420
421To enumerate information about each disk image in the above chain, starting from top to base, do:
422
423@example
424qemu-img info --backing-chain snap2.qcow2
425@end example
426
Paolo Bonzinifacd6e22013-09-04 19:00:34 +0200427@item map [-f @var{fmt}] [--output=@var{ofmt}] @var{filename}
428
429Dump the metadata of image @var{filename} and its backing file chain.
430In particular, this commands dumps the allocation state of every sector
431of @var{filename}, together with the topmost file that allocates it in
432the backing file chain.
433
434Two option formats are possible. The default format (@code{human})
435only dumps known-nonzero areas of the file. Known-zero parts of the
436file are omitted altogether, and likewise for parts that are not allocated
437throughout the chain. @command{qemu-img} output will identify a file
438from where the data can be read, and the offset in the file. Each line
439will include four fields, the first three of which are hexadecimal
440numbers. For example the first line of:
441@example
442Offset Length Mapped to File
4430 0x20000 0x50000 /tmp/overlay.qcow2
4440x100000 0x10000 0x95380000 /tmp/backing.qcow2
445@end example
446@noindent
447means that 0x20000 (131072) bytes starting at offset 0 in the image are
448available in /tmp/overlay.qcow2 (opened in @code{raw} format) starting
449at offset 0x50000 (327680). Data that is compressed, encrypted, or
450otherwise not available in raw format will cause an error if @code{human}
451format is in use. Note that file names can include newlines, thus it is
452not safe to parse this output format in scripts.
453
454The alternative format @code{json} will return an array of dictionaries
455in JSON format. It will include similar information in
456the @code{start}, @code{length}, @code{offset} fields;
457it will also include other more specific information:
458@itemize @minus
459@item
460whether the sectors contain actual data or not (boolean field @code{data};
461if false, the sectors are either unallocated or stored as optimized
462all-zero clusters);
463
464@item
465whether the data is known to read as zero (boolean field @code{zero});
466
467@item
468in order to make the output shorter, the target file is expressed as
469a @code{depth}; for example, a depth of 2 refers to the backing file
470of the backing file of @var{filename}.
471@end itemize
472
473In JSON format, the @code{offset} field is optional; it is absent in
474cases where @code{human} format would omit the entry or exit with an error.
475If @code{data} is false and the @code{offset} field is present, the
476corresponding sectors in the file are not yet in use, but they are
477preallocated.
478
479For more information, consult @file{include/block/block.h} in QEMU's
480source code.
481
Stefan Hajnoczifd03c2b2017-07-05 13:57:36 +0100482@item measure [--output=@var{ofmt}] [-O @var{output_fmt}] [-o @var{options}] [--size @var{N} | [--object @var{objectdef}] [--image-opts] [-f @var{fmt}] [-l @var{snapshot_param}] @var{filename}]
483
484Calculate the file size required for a new image. This information can be used
485to size logical volumes or SAN LUNs appropriately for the image that will be
486placed in them. The values reported are guaranteed to be large enough to fit
487the image. The command can output in the format @var{ofmt} which is either
488@code{human} or @code{json}.
489
490If the size @var{N} is given then act as if creating a new empty image file
491using @command{qemu-img create}. If @var{filename} is given then act as if
492converting an existing image file using @command{qemu-img convert}. The format
493of the new file is given by @var{output_fmt} while the format of an existing
494file is given by @var{fmt}.
495
496A snapshot in an existing image can be specified using @var{snapshot_param}.
497
498The following fields are reported:
499@example
500required size: 524288
501fully allocated size: 1074069504
502@end example
503
504The @code{required size} is the file size of the new image. It may be smaller
505than the virtual disk size if the image format supports compact representation.
506
507The @code{fully allocated size} is the file size of the new image once data has
508been written to all sectors. This is the maximum size that the image file can
509occupy with the exception of internal snapshots, dirty bitmaps, vmstate data,
510and other advanced image format features.
511
John Snow9775fcd2018-05-03 18:56:47 -0400512@item snapshot [--object @var{objectdef}] [--image-opts] [-U] [-q] [-l | -a @var{snapshot} | -c @var{snapshot} | -d @var{snapshot}] @var{filename}
blueswir1d2c639d2009-01-24 18:19:25 +0000513
514List, apply, create or delete snapshots in image @var{filename}.
Stefan Hajnocziae6b0ed2010-04-24 09:12:12 +0100515
John Snow9775fcd2018-05-03 18:56:47 -0400516@item rebase [--object @var{objectdef}] [--image-opts] [-U] [-q] [-f @var{fmt}] [-t @var{cache}] [-T @var{src_cache}] [-p] [-u] -b @var{backing_file} [-F @var{backing_fmt}] @var{filename}
Kevin Wolfe6184692011-01-17 15:35:28 +0100517
518Changes the backing file of an image. Only the formats @code{qcow2} and
519@code{qed} support changing the backing file.
520
521The backing file is changed to @var{backing_file} and (if the image format of
522@var{filename} supports this) the backing file format is changed to
Alex Bligha6166732012-10-16 13:46:18 +0100523@var{backing_fmt}. If @var{backing_file} is specified as ``'' (the empty
524string), then the image is rebased onto no backing file (i.e. it will exist
525independently of any backing file).
Kevin Wolfe6184692011-01-17 15:35:28 +0100526
Fam Zhenga16efd52017-08-04 22:36:58 +0800527If a relative path name is given, the backing file is looked up relative to
528the directory containing @var{filename}.
529
Max Reitz40055952014-07-22 22:58:42 +0200530@var{cache} specifies the cache mode to be used for @var{filename}, whereas
Stefan Hajnoczi3ba67962014-09-02 11:01:03 +0100531@var{src_cache} specifies the cache mode for reading backing files.
Max Reitz40055952014-07-22 22:58:42 +0200532
Kevin Wolfe6184692011-01-17 15:35:28 +0100533There are two different modes in which @code{rebase} can operate:
534@table @option
535@item Safe mode
536This is the default mode and performs a real rebase operation. The new backing
537file may differ from the old one and qemu-img rebase will take care of keeping
538the guest-visible content of @var{filename} unchanged.
539
540In order to achieve this, any clusters that differ between @var{backing_file}
541and the old backing file of @var{filename} are merged into @var{filename}
542before actually changing the backing file.
543
544Note that the safe mode is an expensive operation, comparable to converting
545an image. It only works if the old backing file still exists.
546
547@item Unsafe mode
548qemu-img uses the unsafe mode if @code{-u} is specified. In this mode, only the
549backing file name and format of @var{filename} is changed without any checks
550on the file contents. The user must take care of specifying the correct new
551backing file, or the guest-visible content of the image will be corrupted.
552
553This mode is useful for renaming or moving the backing file to somewhere else.
554It can be used without an accessible old backing file, i.e. you can use it to
555fix an image whose backing file has already been moved/renamed.
556@end table
557
Richard W.M. Jones9fda6ab2012-05-21 14:58:05 +0100558You can use @code{rebase} to perform a ``diff'' operation on two
559disk images. This can be useful when you have copied or cloned
560a guest, and you want to get back to a thin image on top of a
561template or base image.
562
563Say that @code{base.img} has been cloned as @code{modified.img} by
564copying it, and that the @code{modified.img} guest has run so there
565are now some changes compared to @code{base.img}. To construct a thin
566image called @code{diff.qcow2} that contains just the differences, do:
567
568@example
569qemu-img create -f qcow2 -b modified.img diff.qcow2
570qemu-img rebase -b base.img diff.qcow2
571@end example
572
573At this point, @code{modified.img} can be discarded, since
574@code{base.img + diff.qcow2} contains the same information.
575
John Snow9775fcd2018-05-03 18:56:47 -0400576@item resize [--object @var{objectdef}] [--image-opts] [-f @var{fmt}] [--preallocation=@var{prealloc}] [-q] [--shrink] @var{filename} [+ | -]@var{size}
Stefan Hajnocziae6b0ed2010-04-24 09:12:12 +0100577
578Change the disk image as if it had been created with @var{size}.
579
580Before using this command to shrink a disk image, you MUST use file system and
581partitioning tools inside the VM to reduce allocated file systems and partition
582sizes accordingly. Failure to do so will result in data loss!
583
Pavel Butsykin4ffca892017-09-18 15:42:27 +0300584When shrinking images, the @code{--shrink} option must be given. This informs
585qemu-img that the user acknowledges all loss of data beyond the truncated
586image's end.
587
Stefan Hajnocziae6b0ed2010-04-24 09:12:12 +0100588After using this command to grow a disk image, you must use file system and
589partitioning tools inside the VM to actually begin using the new space on the
590device.
Max Reitz6f176b42013-09-03 10:09:50 +0200591
Max Reitzdc5f6902017-06-13 22:20:55 +0200592When growing an image, the @code{--preallocation} option may be used to specify
593how the additional image area should be allocated on the host. See the format
594description in the @code{NOTES} section which values are allowed. Using this
595option may result in slightly more data being allocated than necessary.
596
bellardacd935e2004-11-15 22:57:26 +0000597@end table
Kevin Wolfd3067b02012-11-21 14:21:47 +0100598@c man end
bellardacd935e2004-11-15 22:57:26 +0000599
Kevin Wolfd3067b02012-11-21 14:21:47 +0100600@ignore
601@c man begin NOTES
Kevin Wolff932c042009-10-28 12:49:15 +0100602Supported image file formats:
603
604@table @option
605@item raw
606
607Raw disk image format (default). This format has the advantage of
608being simple and easily exportable to all other emulators. If your
609file system supports @emph{holes} (for example in ext2 or ext3 on
610Linux or NTFS on Windows), then only the written sectors will reserve
611space. Use @code{qemu-img info} to know the real size used by the
612image or @code{ls -ls} on Unix/Linux.
613
Hu Tao06247422014-09-10 17:05:48 +0800614Supported options:
615@table @code
616@item preallocation
617Preallocation mode (allowed values: @code{off}, @code{falloc}, @code{full}).
618@code{falloc} mode preallocates space for image by calling posix_fallocate().
619@code{full} mode preallocates space for image by writing zeros to underlying
620storage.
621@end table
622
Kevin Wolff932c042009-10-28 12:49:15 +0100623@item qcow2
624QEMU image format, the most versatile format. Use it to have smaller
625images (useful if your filesystem does not supports holes, for example
626on Windows), optional AES encryption, zlib based compression and
627support of multiple VM snapshots.
Kevin Wolf8063d0f2009-10-28 12:49:16 +0100628
Kevin Wolf3e032362009-10-28 12:49:17 +0100629Supported options:
630@table @code
Kevin Wolfd3067b02012-11-21 14:21:47 +0100631@item compat
Stefan Hajnoczi7fa9e1f2014-01-06 12:39:01 +0800632Determines the qcow2 version to use. @code{compat=0.10} uses the
633traditional image format that can be read by any QEMU since 0.10.
Kevin Wolfd3067b02012-11-21 14:21:47 +0100634@code{compat=1.1} enables image format extensions that only QEMU 1.1 and
Stefan Hajnoczi7fa9e1f2014-01-06 12:39:01 +0800635newer understand (this is the default). Amongst others, this includes zero
636clusters, which allow efficient copy-on-read for sparse images.
Kevin Wolfd3067b02012-11-21 14:21:47 +0100637
Kevin Wolf3e032362009-10-28 12:49:17 +0100638@item backing_file
639File name of a base image (see @option{create} subcommand)
640@item backing_fmt
641Image format of the base image
642@item encryption
Daniel P. Berrange136cd192014-01-22 15:47:10 +0000643If this option is set to @code{on}, the image is encrypted with 128-bit AES-CBC.
Kevin Wolf3e032362009-10-28 12:49:17 +0100644
Daniel P. Berrange136cd192014-01-22 15:47:10 +0000645The use of encryption in qcow and qcow2 images is considered to be flawed by
646modern cryptography standards, suffering from a number of design problems:
647
648@itemize @minus
Daniel P. Berrange0b4ee902017-06-23 17:24:02 +0100649@item
650The AES-CBC cipher is used with predictable initialization vectors based
Daniel P. Berrange136cd192014-01-22 15:47:10 +0000651on the sector number. This makes it vulnerable to chosen plaintext attacks
652which can reveal the existence of encrypted data.
Daniel P. Berrange0b4ee902017-06-23 17:24:02 +0100653@item
654The user passphrase is directly used as the encryption key. A poorly
Daniel P. Berrange136cd192014-01-22 15:47:10 +0000655chosen or short passphrase will compromise the security of the encryption.
Daniel P. Berrange0b4ee902017-06-23 17:24:02 +0100656@item
657In the event of the passphrase being compromised there is no way to
Daniel P. Berrange136cd192014-01-22 15:47:10 +0000658change the passphrase to protect data in any qcow images. The files must
659be cloned, using a different encryption passphrase in the new file. The
660original file must then be securely erased using a program like shred,
661though even this is ineffective with many modern storage technologies.
Daniel P. Berrange0b4ee902017-06-23 17:24:02 +0100662@item
663Initialization vectors used to encrypt sectors are based on the
664guest virtual sector number, instead of the host physical sector. When
665a disk image has multiple internal snapshots this means that data in
666multiple physical sectors is encrypted with the same initialization
667vector. With the CBC mode, this opens the possibility of watermarking
668attacks if the attack can collect multiple sectors encrypted with the
669same IV and some predictable data. Having multiple qcow2 images with
670the same passphrase also exposes this weakness since the passphrase
671is directly used as the key.
Daniel P. Berrange136cd192014-01-22 15:47:10 +0000672@end itemize
673
674Use of qcow / qcow2 encryption is thus strongly discouraged. Users are
675recommended to use an alternative encryption technology such as the
676Linux dm-crypt / LUKS system.
Kevin Wolf3e032362009-10-28 12:49:17 +0100677
678@item cluster_size
679Changes the qcow2 cluster size (must be between 512 and 2M). Smaller cluster
680sizes can improve the image file size whereas larger cluster sizes generally
681provide better performance.
682
683@item preallocation
Hu Tao0e4271b2014-09-10 17:05:49 +0800684Preallocation mode (allowed values: @code{off}, @code{metadata}, @code{falloc},
685@code{full}). An image with preallocated metadata is initially larger but can
686improve performance when the image needs to grow. @code{falloc} and @code{full}
687preallocations are like the same options of @code{raw} format, but sets up
688metadata also.
Kevin Wolf3e032362009-10-28 12:49:17 +0100689
Kevin Wolfd3067b02012-11-21 14:21:47 +0100690@item lazy_refcounts
691If this option is set to @code{on}, reference count updates are postponed with
692the goal of avoiding metadata I/O and improving performance. This is
693particularly interesting with @option{cache=writethrough} which doesn't batch
694metadata updates. The tradeoff is that after a host crash, the reference count
695tables must be rebuilt, i.e. on the next open an (automatic) @code{qemu-img
696check -r all} is required, which may take some time.
697
698This option can only be enabled if @code{compat=1.1} is specified.
699
Chunyan Liu4ab15592014-06-30 14:29:58 +0800700@item nocow
Chunyan Liubc3a7f92014-07-02 12:27:29 +0800701If this option is set to @code{on}, it will turn off COW of the file. It's only
Chunyan Liu4ab15592014-06-30 14:29:58 +0800702valid on btrfs, no effect on other file systems.
703
704Btrfs has low performance when hosting a VM image file, even more when the guest
705on the VM also using btrfs as file system. Turning off COW is a way to mitigate
706this bad performance. Generally there are two ways to turn off COW on btrfs:
707a) Disable it by mounting with nodatacow, then all newly created files will be
708NOCOW. b) For an empty file, add the NOCOW file attribute. That's what this option
709does.
710
711Note: this option is only valid to new or empty files. If there is an existing
712file which is COW and has data blocks already, it couldn't be changed to NOCOW
713by setting @code{nocow=on}. One can issue @code{lsattr filename} to check if
Chunyan Liubc3a7f92014-07-02 12:27:29 +0800714the NOCOW flag is set or not (Capital 'C' is NOCOW flag).
Chunyan Liu4ab15592014-06-30 14:29:58 +0800715
Kevin Wolf3e032362009-10-28 12:49:17 +0100716@end table
717
Kevin Wolfd3067b02012-11-21 14:21:47 +0100718@item Other
719QEMU also supports various other image file formats for compatibility with
Jeff Cody8282db12013-12-17 13:56:06 -0500720older QEMU versions or other hypervisors, including VMDK, VDI, VHD (vpc), VHDX,
721qcow1 and QED. For a full list of supported formats see @code{qemu-img --help}.
Kevin Wolfd3067b02012-11-21 14:21:47 +0100722For a more detailed description of these formats, see the QEMU Emulation User
723Documentation.
Stefan Hajnoczif0858002012-06-13 14:29:15 +0100724
Kevin Wolfd3067b02012-11-21 14:21:47 +0100725The main purpose of the block drivers for these formats is image conversion.
726For running VMs, it is recommended to convert the disk images to either raw or
727qcow2 in order to achieve good performance.
Kevin Wolff932c042009-10-28 12:49:15 +0100728@end table
729
730
bellardacd935e2004-11-15 22:57:26 +0000731@c man end
732
bellardacd935e2004-11-15 22:57:26 +0000733@setfilename qemu-img
734@settitle QEMU disk image utility
735
736@c man begin SEEALSO
737The HTML documentation of QEMU for more precise information and Linux
738user mode emulator invocation.
739@c man end
740
741@c man begin AUTHOR
742Fabrice Bellard
743@c man end
744
745@end ignore