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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 Snow13c24ed2019-04-09 17:06:55 -0400200@item amend [--object @var{objectdef}] [--image-opts] [-p] [-q] [-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}.
Max Reitz987402c2019-05-15 09:59:16 +0200233The JSON output is an object of QAPI type @code{ImageCheck}.
Kevin Wolfe6184692011-01-17 15:35:28 +0100234
Kevin Wolf4534ff52012-05-11 16:07:02 +0200235If @code{-r} is specified, qemu-img tries to repair any inconsistencies found
236during the check. @code{-r leaks} repairs only cluster leaks, whereas
237@code{-r all} fixes all kinds of errors, with a higher risk of choosing the
Stefan Weil0546b8c2012-08-10 22:03:25 +0200238wrong fix or hiding corruption that has already occurred.
Kevin Wolf4534ff52012-05-11 16:07:02 +0200239
Kevin Wolfe6184692011-01-17 15:35:28 +0100240Only the formats @code{qcow2}, @code{qed} and @code{vdi} support
241consistency checks.
242
Max Reitzd6635c42014-06-02 22:15:21 +0200243In case the image does not have any inconsistencies, check exits with @code{0}.
244Other exit codes indicate the kind of inconsistency found or if another error
245occurred. The following table summarizes all exit codes of the check subcommand:
246
247@table @option
248
249@item 0
250Check completed, the image is (now) consistent
251@item 1
252Check not completed because of internal errors
253@item 2
254Check completed, image is corrupted
255@item 3
256Check completed, image has leaked clusters, but is not corrupted
257@item 63
258Checks are not supported by the image format
259
260@end table
261
262If @code{-r} is specified, exit codes representing the image state refer to the
263state after (the attempt at) repairing it. That is, a successful @code{-r all}
264will yield the exit code 0, independently of the image state before.
265
John Snow9775fcd2018-05-03 18:56:47 -0400266@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 +0000267
Jeff Cody37222902014-01-24 09:02:37 -0500268Commit the changes recorded in @var{filename} in its base image or backing file.
269If the backing file is smaller than the snapshot, then the backing file will be
270resized to be the same size as the snapshot. If the snapshot is smaller than
271the backing file, the backing file will not be truncated. If you want the
272backing file to match the size of the smaller snapshot, you can safely truncate
273it yourself once the commit operation successfully completes.
bellardacd935e2004-11-15 22:57:26 +0000274
Max Reitz9a86fe42014-10-24 15:57:38 +0200275The image @var{filename} is emptied after the operation has succeeded. If you do
276not need @var{filename} afterwards and intend to drop it, you may skip emptying
277@var{filename} by specifying the @code{-d} flag.
278
Max Reitz1b22bff2014-10-24 15:57:40 +0200279If the backing chain of the given image file @var{filename} has more than one
280layer, the backing file into which the changes will be committed may be
281specified as @var{base} (which has to be part of @var{filename}'s backing
282chain). If @var{base} is not specified, the immediate backing file of the top
Max Reitz67e56472017-10-26 09:59:47 +0200283image (which is @var{filename}) will be used. Note that after a commit operation
284all images between @var{base} and the top image will be invalid and may return
285garbage data when read. For this reason, @code{-b} implies @code{-d} (so that
286the top image stays valid).
Max Reitz1b22bff2014-10-24 15:57:40 +0200287
John Snow9775fcd2018-05-03 18:56:47 -0400288@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 +0100289
290Check if two images have the same content. You can compare images with
291different format or settings.
292
293The format is probed unless you specify it by @var{-f} (used for
294@var{filename1}) and/or @var{-F} (used for @var{filename2}) option.
295
296By default, images with different size are considered identical if the larger
297image contains only unallocated and/or zeroed sectors in the area after the end
298of the other image. In addition, if any sector is not allocated in one image
299and contains only zero bytes in the second one, it is evaluated as equal. You
300can use Strict mode by specifying the @var{-s} option. When compare runs in
301Strict mode, it fails in case image size differs or a sector is allocated in
302one image and is not allocated in the second one.
303
304By default, compare prints out a result message. This message displays
305information that both images are same or the position of the first different
306byte. In addition, result message can report different image size in case
307Strict mode is used.
308
309Compare exits with @code{0} in case the images are equal and with @code{1}
310in case the images differ. Other exit codes mean an error occurred during
311execution and standard error output should contain an error message.
312The following table sumarizes all exit codes of the compare subcommand:
313
314@table @option
315
316@item 0
317Images are identical
318@item 1
319Images differ
320@item 2
321Error on opening an image
322@item 3
323Error on checking a sector allocation
324@item 4
325Error on reading data
326
327@end table
328
Fam Zhenge11ce122018-07-27 11:34:01 +0800329@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 +0000330
Thomas Huth46e8d272018-06-06 14:35:51 +0200331Convert the disk image @var{filename} or a snapshot @var{snapshot_param}
Wenchao Xiaef806542013-12-04 17:10:57 +0800332to disk image @var{output_filename} using format @var{output_fmt}. It can be optionally compressed (@code{-c}
Kevin Wolfeff44262009-06-04 15:39:39 +0200333option) or use any format specific options like encryption (@code{-o} option).
bellardacd935e2004-11-15 22:57:26 +0000334
Kevin Wolf8063d0f2009-10-28 12:49:16 +0100335Only the formats @code{qcow} and @code{qcow2} support compression. The
bellardacd935e2004-11-15 22:57:26 +0000336compression is read-only. It means that if a compressed sector is
337rewritten, then it is rewritten as uncompressed data.
338
bellardacd935e2004-11-15 22:57:26 +0000339Image conversion is also useful to get smaller image when using a
Stefan Hajnoczi550830f2014-09-16 15:24:24 +0100340growable format such as @code{qcow}: the empty sectors are detected and
341suppressed from the destination image.
bellardacd935e2004-11-15 22:57:26 +0000342
Peter Lieven11b66992013-10-24 12:07:05 +0200343@var{sparse_size} indicates the consecutive number of bytes (defaults to 4k)
344that must contain only zeros for qemu-img to create a sparse image during
345conversion. If @var{sparse_size} is 0, the source will not be scanned for
346unallocated or zero sectors, and the destination image will always be
347fully allocated.
348
Kevin Wolf8063d0f2009-10-28 12:49:16 +0100349You can use the @var{backing_file} option to force the output image to be
350created as a copy on write image of the specified base image; the
351@var{backing_file} should have the same content as the input's base image,
352however the path, image format, etc may differ.
353
Fam Zhenga16efd52017-08-04 22:36:58 +0800354If a relative path name is given, the backing file is looked up relative to
355the directory containing @var{output_filename}.
356
Alexandre Derumierb2e10492013-09-02 19:07:24 +0100357If the @code{-n} option is specified, the target volume creation will be
358skipped. This is useful for formats such as @code{rbd} if the target
359volume has already been created with site specific options that cannot
360be supplied through qemu-img.
361
Peter Lieven2d9187b2017-02-28 13:40:07 +0100362Out of order writes can be enabled with @code{-W} to improve performance.
363This is only recommended for preallocated devices like host devices or other
364raw block devices. Out of order write does not work in combination with
365creating compressed images.
366
367@var{num_coroutines} specifies how many coroutines work in parallel during
368the convert process (defaults to 8).
369
John Snow9775fcd2018-05-03 18:56:47 -0400370@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 -0400371
372Create the new disk image @var{filename} of size @var{size} and format
373@var{fmt}. Depending on the file format, you can add one or more @var{options}
374that enable additional features of this format.
375
376If the option @var{backing_file} is specified, then the image will record
377only the differences from @var{backing_file}. No size needs to be specified in
378this case. @var{backing_file} will never be modified unless you use the
379@code{commit} monitor command (or qemu-img commit).
380
381If a relative path name is given, the backing file is looked up relative to
382the directory containing @var{filename}.
383
384Note that a given backing file will be opened to check that it is valid. Use
385the @code{-u} option to enable unsafe backing file mode, which means that the
386image will be created even if the associated backing file cannot be opened. A
387matching backing file must be created or additional options be used to make the
388backing file specification valid when you want to use an image created this
389way.
390
391The size can also be specified using the @var{size} option with @code{-o},
392it doesn't need to be specified separately in this case.
393
John Snow9775fcd2018-05-03 18:56:47 -0400394@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 +0200395
396Dd copies from @var{input} file to @var{output} file converting it from
397@var{fmt} format to @var{output_fmt} format.
398
399The data is by default read and written using blocks of 512 bytes but can be
400modified by specifying @var{block_size}. If count=@var{blocks} is specified
401dd will stop reading input after reading @var{blocks} input blocks.
402
403The size syntax is similar to dd(1)'s size syntax.
404
John Snow9775fcd2018-05-03 18:56:47 -0400405@item info [--object @var{objectdef}] [--image-opts] [-f @var{fmt}] [--output=@var{ofmt}] [--backing-chain] [-U] @var{filename}
bellardacd935e2004-11-15 22:57:26 +0000406
407Give information about the disk image @var{filename}. Use it in
408particular to know the size reserved on disk which can be different
bellard19d36792006-08-07 21:34:34 +0000409from the displayed size. If VM snapshots are stored in the disk image,
Max Reitz987402c2019-05-15 09:59:16 +0200410they are displayed too.
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
Max Reitz987402c2019-05-15 09:59:16 +0200427The command can output in the format @var{ofmt} which is either @code{human} or
428@code{json}. The JSON output is an object of QAPI type @code{ImageInfo}; with
429@code{--backing-chain}, it is an array of @code{ImageInfo} objects.
430
Max Reitz4db43902019-05-15 09:59:17 +0200431@code{--output=human} reports the following information (for every image in the
432chain):
433@table @var
434@item image
435The image file name
436
437@item file format
438The image format
439
440@item virtual size
441The size of the guest disk
442
443@item disk size
444How much space the image file occupies on the host file system (may be shown as
4450 if this information is unavailable, e.g. because there is no file system)
446
447@item cluster_size
448Cluster size of the image format, if applicable
449
450@item encrypted
451Whether the image is encrypted (only present if so)
452
453@item cleanly shut down
454This is shown as @code{no} if the image is dirty and will have to be
455auto-repaired the next time it is opened in qemu.
456
457@item backing file
458The backing file name, if present
459
460@item backing file format
461The format of the backing file, if the image enforces it
462
463@item Snapshot list
464A list of all internal snapshots
465
466@item Format specific information
467Further information whose structure depends on the image format. This section
468is a textual representation of the respective @code{ImageInfoSpecific*} QAPI
469object (e.g. @code{ImageInfoSpecificQCow2} for qcow2 images).
470@end table
471
John Snow13c24ed2019-04-09 17:06:55 -0400472@item map [--object @var{objectdef}] [--image-opts] [-f @var{fmt}] [--output=@var{ofmt}] [-U] @var{filename}
Paolo Bonzinifacd6e22013-09-04 19:00:34 +0200473
474Dump the metadata of image @var{filename} and its backing file chain.
475In particular, this commands dumps the allocation state of every sector
476of @var{filename}, together with the topmost file that allocates it in
477the backing file chain.
478
479Two option formats are possible. The default format (@code{human})
480only dumps known-nonzero areas of the file. Known-zero parts of the
481file are omitted altogether, and likewise for parts that are not allocated
482throughout the chain. @command{qemu-img} output will identify a file
483from where the data can be read, and the offset in the file. Each line
484will include four fields, the first three of which are hexadecimal
485numbers. For example the first line of:
486@example
487Offset Length Mapped to File
4880 0x20000 0x50000 /tmp/overlay.qcow2
4890x100000 0x10000 0x95380000 /tmp/backing.qcow2
490@end example
491@noindent
492means that 0x20000 (131072) bytes starting at offset 0 in the image are
493available in /tmp/overlay.qcow2 (opened in @code{raw} format) starting
494at offset 0x50000 (327680). Data that is compressed, encrypted, or
495otherwise not available in raw format will cause an error if @code{human}
496format is in use. Note that file names can include newlines, thus it is
497not safe to parse this output format in scripts.
498
499The alternative format @code{json} will return an array of dictionaries
500in JSON format. It will include similar information in
501the @code{start}, @code{length}, @code{offset} fields;
502it will also include other more specific information:
503@itemize @minus
504@item
505whether the sectors contain actual data or not (boolean field @code{data};
506if false, the sectors are either unallocated or stored as optimized
507all-zero clusters);
508
509@item
510whether the data is known to read as zero (boolean field @code{zero});
511
512@item
513in order to make the output shorter, the target file is expressed as
514a @code{depth}; for example, a depth of 2 refers to the backing file
515of the backing file of @var{filename}.
516@end itemize
517
518In JSON format, the @code{offset} field is optional; it is absent in
519cases where @code{human} format would omit the entry or exit with an error.
520If @code{data} is false and the @code{offset} field is present, the
521corresponding sectors in the file are not yet in use, but they are
522preallocated.
523
524For more information, consult @file{include/block/block.h} in QEMU's
525source code.
526
Stefan Hajnoczifd03c2b2017-07-05 13:57:36 +0100527@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}]
528
529Calculate the file size required for a new image. This information can be used
530to size logical volumes or SAN LUNs appropriately for the image that will be
531placed in them. The values reported are guaranteed to be large enough to fit
532the image. The command can output in the format @var{ofmt} which is either
Max Reitz987402c2019-05-15 09:59:16 +0200533@code{human} or @code{json}. The JSON output is an object of QAPI type
534@code{BlockMeasureInfo}.
Stefan Hajnoczifd03c2b2017-07-05 13:57:36 +0100535
536If the size @var{N} is given then act as if creating a new empty image file
537using @command{qemu-img create}. If @var{filename} is given then act as if
538converting an existing image file using @command{qemu-img convert}. The format
539of the new file is given by @var{output_fmt} while the format of an existing
540file is given by @var{fmt}.
541
542A snapshot in an existing image can be specified using @var{snapshot_param}.
543
544The following fields are reported:
545@example
546required size: 524288
547fully allocated size: 1074069504
548@end example
549
550The @code{required size} is the file size of the new image. It may be smaller
551than the virtual disk size if the image format supports compact representation.
552
553The @code{fully allocated size} is the file size of the new image once data has
554been written to all sectors. This is the maximum size that the image file can
555occupy with the exception of internal snapshots, dirty bitmaps, vmstate data,
556and other advanced image format features.
557
John Snow9775fcd2018-05-03 18:56:47 -0400558@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 +0000559
560List, apply, create or delete snapshots in image @var{filename}.
Stefan Hajnocziae6b0ed2010-04-24 09:12:12 +0100561
John Snow9775fcd2018-05-03 18:56:47 -0400562@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 +0100563
564Changes the backing file of an image. Only the formats @code{qcow2} and
565@code{qed} support changing the backing file.
566
567The backing file is changed to @var{backing_file} and (if the image format of
568@var{filename} supports this) the backing file format is changed to
Alex Bligha6166732012-10-16 13:46:18 +0100569@var{backing_fmt}. If @var{backing_file} is specified as ``'' (the empty
570string), then the image is rebased onto no backing file (i.e. it will exist
571independently of any backing file).
Kevin Wolfe6184692011-01-17 15:35:28 +0100572
Fam Zhenga16efd52017-08-04 22:36:58 +0800573If a relative path name is given, the backing file is looked up relative to
574the directory containing @var{filename}.
575
Max Reitz40055952014-07-22 22:58:42 +0200576@var{cache} specifies the cache mode to be used for @var{filename}, whereas
Stefan Hajnoczi3ba67962014-09-02 11:01:03 +0100577@var{src_cache} specifies the cache mode for reading backing files.
Max Reitz40055952014-07-22 22:58:42 +0200578
Kevin Wolfe6184692011-01-17 15:35:28 +0100579There are two different modes in which @code{rebase} can operate:
580@table @option
581@item Safe mode
582This is the default mode and performs a real rebase operation. The new backing
583file may differ from the old one and qemu-img rebase will take care of keeping
584the guest-visible content of @var{filename} unchanged.
585
586In order to achieve this, any clusters that differ between @var{backing_file}
587and the old backing file of @var{filename} are merged into @var{filename}
588before actually changing the backing file.
589
590Note that the safe mode is an expensive operation, comparable to converting
591an image. It only works if the old backing file still exists.
592
593@item Unsafe mode
594qemu-img uses the unsafe mode if @code{-u} is specified. In this mode, only the
595backing file name and format of @var{filename} is changed without any checks
596on the file contents. The user must take care of specifying the correct new
597backing file, or the guest-visible content of the image will be corrupted.
598
599This mode is useful for renaming or moving the backing file to somewhere else.
600It can be used without an accessible old backing file, i.e. you can use it to
601fix an image whose backing file has already been moved/renamed.
602@end table
603
Richard W.M. Jones9fda6ab2012-05-21 14:58:05 +0100604You can use @code{rebase} to perform a ``diff'' operation on two
605disk images. This can be useful when you have copied or cloned
606a guest, and you want to get back to a thin image on top of a
607template or base image.
608
609Say that @code{base.img} has been cloned as @code{modified.img} by
610copying it, and that the @code{modified.img} guest has run so there
611are now some changes compared to @code{base.img}. To construct a thin
612image called @code{diff.qcow2} that contains just the differences, do:
613
614@example
615qemu-img create -f qcow2 -b modified.img diff.qcow2
616qemu-img rebase -b base.img diff.qcow2
617@end example
618
619At this point, @code{modified.img} can be discarded, since
620@code{base.img + diff.qcow2} contains the same information.
621
John Snow9775fcd2018-05-03 18:56:47 -0400622@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 +0100623
624Change the disk image as if it had been created with @var{size}.
625
626Before using this command to shrink a disk image, you MUST use file system and
627partitioning tools inside the VM to reduce allocated file systems and partition
628sizes accordingly. Failure to do so will result in data loss!
629
Pavel Butsykin4ffca892017-09-18 15:42:27 +0300630When shrinking images, the @code{--shrink} option must be given. This informs
631qemu-img that the user acknowledges all loss of data beyond the truncated
632image's end.
633
Stefan Hajnocziae6b0ed2010-04-24 09:12:12 +0100634After using this command to grow a disk image, you must use file system and
635partitioning tools inside the VM to actually begin using the new space on the
636device.
Max Reitz6f176b42013-09-03 10:09:50 +0200637
Max Reitzdc5f6902017-06-13 22:20:55 +0200638When growing an image, the @code{--preallocation} option may be used to specify
639how the additional image area should be allocated on the host. See the format
640description in the @code{NOTES} section which values are allowed. Using this
641option may result in slightly more data being allocated than necessary.
642
bellardacd935e2004-11-15 22:57:26 +0000643@end table
Kevin Wolfd3067b02012-11-21 14:21:47 +0100644@c man end
bellardacd935e2004-11-15 22:57:26 +0000645
Kevin Wolfd3067b02012-11-21 14:21:47 +0100646@ignore
647@c man begin NOTES
Kevin Wolff932c042009-10-28 12:49:15 +0100648Supported image file formats:
649
650@table @option
651@item raw
652
653Raw disk image format (default). This format has the advantage of
654being simple and easily exportable to all other emulators. If your
655file system supports @emph{holes} (for example in ext2 or ext3 on
656Linux or NTFS on Windows), then only the written sectors will reserve
657space. Use @code{qemu-img info} to know the real size used by the
658image or @code{ls -ls} on Unix/Linux.
659
Hu Tao06247422014-09-10 17:05:48 +0800660Supported options:
661@table @code
662@item preallocation
663Preallocation mode (allowed values: @code{off}, @code{falloc}, @code{full}).
664@code{falloc} mode preallocates space for image by calling posix_fallocate().
665@code{full} mode preallocates space for image by writing zeros to underlying
666storage.
667@end table
668
Kevin Wolff932c042009-10-28 12:49:15 +0100669@item qcow2
670QEMU image format, the most versatile format. Use it to have smaller
671images (useful if your filesystem does not supports holes, for example
672on Windows), optional AES encryption, zlib based compression and
673support of multiple VM snapshots.
Kevin Wolf8063d0f2009-10-28 12:49:16 +0100674
Kevin Wolf3e032362009-10-28 12:49:17 +0100675Supported options:
676@table @code
Kevin Wolfd3067b02012-11-21 14:21:47 +0100677@item compat
Stefan Hajnoczi7fa9e1f2014-01-06 12:39:01 +0800678Determines the qcow2 version to use. @code{compat=0.10} uses the
679traditional image format that can be read by any QEMU since 0.10.
Kevin Wolfd3067b02012-11-21 14:21:47 +0100680@code{compat=1.1} enables image format extensions that only QEMU 1.1 and
Stefan Hajnoczi7fa9e1f2014-01-06 12:39:01 +0800681newer understand (this is the default). Amongst others, this includes zero
682clusters, which allow efficient copy-on-read for sparse images.
Kevin Wolfd3067b02012-11-21 14:21:47 +0100683
Kevin Wolf3e032362009-10-28 12:49:17 +0100684@item backing_file
685File name of a base image (see @option{create} subcommand)
686@item backing_fmt
687Image format of the base image
688@item encryption
Daniel P. Berrange136cd192014-01-22 15:47:10 +0000689If this option is set to @code{on}, the image is encrypted with 128-bit AES-CBC.
Kevin Wolf3e032362009-10-28 12:49:17 +0100690
Daniel P. Berrange136cd192014-01-22 15:47:10 +0000691The use of encryption in qcow and qcow2 images is considered to be flawed by
692modern cryptography standards, suffering from a number of design problems:
693
694@itemize @minus
Daniel P. Berrange0b4ee902017-06-23 17:24:02 +0100695@item
696The AES-CBC cipher is used with predictable initialization vectors based
Daniel P. Berrange136cd192014-01-22 15:47:10 +0000697on the sector number. This makes it vulnerable to chosen plaintext attacks
698which can reveal the existence of encrypted data.
Daniel P. Berrange0b4ee902017-06-23 17:24:02 +0100699@item
700The user passphrase is directly used as the encryption key. A poorly
Daniel P. Berrange136cd192014-01-22 15:47:10 +0000701chosen or short passphrase will compromise the security of the encryption.
Daniel P. Berrange0b4ee902017-06-23 17:24:02 +0100702@item
703In the event of the passphrase being compromised there is no way to
Daniel P. Berrange136cd192014-01-22 15:47:10 +0000704change the passphrase to protect data in any qcow images. The files must
705be cloned, using a different encryption passphrase in the new file. The
706original file must then be securely erased using a program like shred,
707though even this is ineffective with many modern storage technologies.
Daniel P. Berrange0b4ee902017-06-23 17:24:02 +0100708@item
709Initialization vectors used to encrypt sectors are based on the
710guest virtual sector number, instead of the host physical sector. When
711a disk image has multiple internal snapshots this means that data in
712multiple physical sectors is encrypted with the same initialization
713vector. With the CBC mode, this opens the possibility of watermarking
714attacks if the attack can collect multiple sectors encrypted with the
715same IV and some predictable data. Having multiple qcow2 images with
716the same passphrase also exposes this weakness since the passphrase
717is directly used as the key.
Daniel P. Berrange136cd192014-01-22 15:47:10 +0000718@end itemize
719
720Use of qcow / qcow2 encryption is thus strongly discouraged. Users are
721recommended to use an alternative encryption technology such as the
722Linux dm-crypt / LUKS system.
Kevin Wolf3e032362009-10-28 12:49:17 +0100723
724@item cluster_size
725Changes the qcow2 cluster size (must be between 512 and 2M). Smaller cluster
726sizes can improve the image file size whereas larger cluster sizes generally
727provide better performance.
728
729@item preallocation
Hu Tao0e4271b2014-09-10 17:05:49 +0800730Preallocation mode (allowed values: @code{off}, @code{metadata}, @code{falloc},
731@code{full}). An image with preallocated metadata is initially larger but can
732improve performance when the image needs to grow. @code{falloc} and @code{full}
733preallocations are like the same options of @code{raw} format, but sets up
734metadata also.
Kevin Wolf3e032362009-10-28 12:49:17 +0100735
Kevin Wolfd3067b02012-11-21 14:21:47 +0100736@item lazy_refcounts
737If this option is set to @code{on}, reference count updates are postponed with
738the goal of avoiding metadata I/O and improving performance. This is
739particularly interesting with @option{cache=writethrough} which doesn't batch
740metadata updates. The tradeoff is that after a host crash, the reference count
741tables must be rebuilt, i.e. on the next open an (automatic) @code{qemu-img
742check -r all} is required, which may take some time.
743
744This option can only be enabled if @code{compat=1.1} is specified.
745
Chunyan Liu4ab15592014-06-30 14:29:58 +0800746@item nocow
Chunyan Liubc3a7f92014-07-02 12:27:29 +0800747If 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 +0800748valid on btrfs, no effect on other file systems.
749
750Btrfs has low performance when hosting a VM image file, even more when the guest
751on the VM also using btrfs as file system. Turning off COW is a way to mitigate
752this bad performance. Generally there are two ways to turn off COW on btrfs:
753a) Disable it by mounting with nodatacow, then all newly created files will be
754NOCOW. b) For an empty file, add the NOCOW file attribute. That's what this option
755does.
756
757Note: this option is only valid to new or empty files. If there is an existing
758file which is COW and has data blocks already, it couldn't be changed to NOCOW
759by setting @code{nocow=on}. One can issue @code{lsattr filename} to check if
Chunyan Liubc3a7f92014-07-02 12:27:29 +0800760the NOCOW flag is set or not (Capital 'C' is NOCOW flag).
Chunyan Liu4ab15592014-06-30 14:29:58 +0800761
Kevin Wolf3e032362009-10-28 12:49:17 +0100762@end table
763
Kevin Wolfd3067b02012-11-21 14:21:47 +0100764@item Other
765QEMU also supports various other image file formats for compatibility with
Jeff Cody8282db12013-12-17 13:56:06 -0500766older QEMU versions or other hypervisors, including VMDK, VDI, VHD (vpc), VHDX,
767qcow1 and QED. For a full list of supported formats see @code{qemu-img --help}.
Kevin Wolfd3067b02012-11-21 14:21:47 +0100768For a more detailed description of these formats, see the QEMU Emulation User
769Documentation.
Stefan Hajnoczif0858002012-06-13 14:29:15 +0100770
Kevin Wolfd3067b02012-11-21 14:21:47 +0100771The main purpose of the block drivers for these formats is image conversion.
772For running VMs, it is recommended to convert the disk images to either raw or
773qcow2 in order to achieve good performance.
Kevin Wolff932c042009-10-28 12:49:15 +0100774@end table
775
776
bellardacd935e2004-11-15 22:57:26 +0000777@c man end
778
bellardacd935e2004-11-15 22:57:26 +0000779@setfilename qemu-img
780@settitle QEMU disk image utility
781
782@c man begin SEEALSO
783The HTML documentation of QEMU for more precise information and Linux
784user mode emulator invocation.
785@c man end
786
787@c man begin AUTHOR
788Fabrice Bellard
789@c man end
790
791@end ignore