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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
99indicates 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
118@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.
Alexandre Derumierb2e10492013-09-02 19:07:24 +0100172@end table
173
Reda Sallahi86ce1f62016-08-10 04:43:12 +0200174Parameters to dd subcommand:
175
176@table @option
177
178@item bs=@var{block_size}
179defines the block size
180@item count=@var{blocks}
181sets the number of input blocks to copy
182@item if=@var{input}
183sets the input file
184@item of=@var{output}
185sets the output file
Reda Sallahif7c15532016-08-10 16:16:09 +0200186@item skip=@var{blocks}
187sets the number of input blocks to skip
Reda Sallahi86ce1f62016-08-10 04:43:12 +0200188@end table
189
bellardacd935e2004-11-15 22:57:26 +0000190Command description:
191
192@table @option
John Snow83e6da02018-05-03 18:56:45 -0400193
John Snow9775fcd2018-05-03 18:56:47 -0400194@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 -0400195
196Amends the image format specific @var{options} for the image file
197@var{filename}. Not all file formats support this operation.
198
John Snow9775fcd2018-05-03 18:56:47 -0400199@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 +0200200
Kevin Wolfb6495fa2015-07-10 18:09:18 +0200201Run a simple sequential I/O benchmark on the specified image. If @code{-w} is
202specified, a write test is performed, otherwise a read test is performed.
203
204A total number of @var{count} I/O requests is performed, each @var{buffer_size}
Kevin Wolfd3199a32015-07-10 18:09:18 +0200205bytes in size, and with @var{depth} requests in parallel. The first request
Kevin Wolf83de9be2015-07-13 13:13:17 +0200206starts at the position given by @var{offset}, each following request increases
207the current position by @var{step_size}. If @var{step_size} is not given,
208@var{buffer_size} is used for its value.
Kevin Wolfb6133b82014-08-05 14:17:13 +0200209
Kevin Wolf55d539c2016-06-03 13:59:41 +0200210If @var{flush_interval} is specified for a write test, the request queue is
211drained and a flush is issued before new writes are made whenever the number of
212remaining requests is a multiple of @var{flush_interval}. If additionally
213@code{--no-drain} is specified, a flush is issued without draining the request
214queue first.
215
Kevin Wolfb6133b82014-08-05 14:17:13 +0200216If @code{-n} is specified, the native AIO backend is used if possible. On
217Linux, this option only works if @code{-t none} or @code{-t directsync} is
218specified as well.
219
Kevin Wolfb6495fa2015-07-10 18:09:18 +0200220For write tests, by default a buffer filled with zeros is written. This can be
221overridden with a pattern byte specified by @var{pattern}.
222
John Snow9775fcd2018-05-03 18:56:47 -0400223@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 +0100224
Federico Simoncelli8599ea42013-01-28 06:59:47 -0500225Perform a consistency check on the disk image @var{filename}. The command can
226output in the format @var{ofmt} which is either @code{human} or @code{json}.
Kevin Wolfe6184692011-01-17 15:35:28 +0100227
Kevin Wolf4534ff52012-05-11 16:07:02 +0200228If @code{-r} is specified, qemu-img tries to repair any inconsistencies found
229during the check. @code{-r leaks} repairs only cluster leaks, whereas
230@code{-r all} fixes all kinds of errors, with a higher risk of choosing the
Stefan Weil0546b8c2012-08-10 22:03:25 +0200231wrong fix or hiding corruption that has already occurred.
Kevin Wolf4534ff52012-05-11 16:07:02 +0200232
Kevin Wolfe6184692011-01-17 15:35:28 +0100233Only the formats @code{qcow2}, @code{qed} and @code{vdi} support
234consistency checks.
235
Max Reitzd6635c42014-06-02 22:15:21 +0200236In case the image does not have any inconsistencies, check exits with @code{0}.
237Other exit codes indicate the kind of inconsistency found or if another error
238occurred. The following table summarizes all exit codes of the check subcommand:
239
240@table @option
241
242@item 0
243Check completed, the image is (now) consistent
244@item 1
245Check not completed because of internal errors
246@item 2
247Check completed, image is corrupted
248@item 3
249Check completed, image has leaked clusters, but is not corrupted
250@item 63
251Checks are not supported by the image format
252
253@end table
254
255If @code{-r} is specified, exit codes representing the image state refer to the
256state after (the attempt at) repairing it. That is, a successful @code{-r all}
257will yield the exit code 0, independently of the image state before.
258
John Snow9775fcd2018-05-03 18:56:47 -0400259@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 +0000260
Jeff Cody37222902014-01-24 09:02:37 -0500261Commit the changes recorded in @var{filename} in its base image or backing file.
262If the backing file is smaller than the snapshot, then the backing file will be
263resized to be the same size as the snapshot. If the snapshot is smaller than
264the backing file, the backing file will not be truncated. If you want the
265backing file to match the size of the smaller snapshot, you can safely truncate
266it yourself once the commit operation successfully completes.
bellardacd935e2004-11-15 22:57:26 +0000267
Max Reitz9a86fe42014-10-24 15:57:38 +0200268The image @var{filename} is emptied after the operation has succeeded. If you do
269not need @var{filename} afterwards and intend to drop it, you may skip emptying
270@var{filename} by specifying the @code{-d} flag.
271
Max Reitz1b22bff2014-10-24 15:57:40 +0200272If the backing chain of the given image file @var{filename} has more than one
273layer, the backing file into which the changes will be committed may be
274specified as @var{base} (which has to be part of @var{filename}'s backing
275chain). If @var{base} is not specified, the immediate backing file of the top
Max Reitz67e56472017-10-26 09:59:47 +0200276image (which is @var{filename}) will be used. Note that after a commit operation
277all images between @var{base} and the top image will be invalid and may return
278garbage data when read. For this reason, @code{-b} implies @code{-d} (so that
279the top image stays valid).
Max Reitz1b22bff2014-10-24 15:57:40 +0200280
John Snow9775fcd2018-05-03 18:56:47 -0400281@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 +0100282
283Check if two images have the same content. You can compare images with
284different format or settings.
285
286The format is probed unless you specify it by @var{-f} (used for
287@var{filename1}) and/or @var{-F} (used for @var{filename2}) option.
288
289By default, images with different size are considered identical if the larger
290image contains only unallocated and/or zeroed sectors in the area after the end
291of the other image. In addition, if any sector is not allocated in one image
292and contains only zero bytes in the second one, it is evaluated as equal. You
293can use Strict mode by specifying the @var{-s} option. When compare runs in
294Strict mode, it fails in case image size differs or a sector is allocated in
295one image and is not allocated in the second one.
296
297By default, compare prints out a result message. This message displays
298information that both images are same or the position of the first different
299byte. In addition, result message can report different image size in case
300Strict mode is used.
301
302Compare exits with @code{0} in case the images are equal and with @code{1}
303in case the images differ. Other exit codes mean an error occurred during
304execution and standard error output should contain an error message.
305The following table sumarizes all exit codes of the compare subcommand:
306
307@table @option
308
309@item 0
310Images are identical
311@item 1
312Images differ
313@item 2
314Error on opening an image
315@item 3
316Error on checking a sector allocation
317@item 4
318Error on reading data
319
320@end table
321
Thomas Huth46e8d272018-06-06 14:35:51 +0200322@item convert [--object @var{objectdef}] [--image-opts] [--target-image-opts] [-U] [-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 +0000323
Thomas Huth46e8d272018-06-06 14:35:51 +0200324Convert the disk image @var{filename} or a snapshot @var{snapshot_param}
Wenchao Xiaef806542013-12-04 17:10:57 +0800325to disk image @var{output_filename} using format @var{output_fmt}. It can be optionally compressed (@code{-c}
Kevin Wolfeff44262009-06-04 15:39:39 +0200326option) or use any format specific options like encryption (@code{-o} option).
bellardacd935e2004-11-15 22:57:26 +0000327
Kevin Wolf8063d0f2009-10-28 12:49:16 +0100328Only the formats @code{qcow} and @code{qcow2} support compression. The
bellardacd935e2004-11-15 22:57:26 +0000329compression is read-only. It means that if a compressed sector is
330rewritten, then it is rewritten as uncompressed data.
331
bellardacd935e2004-11-15 22:57:26 +0000332Image conversion is also useful to get smaller image when using a
Stefan Hajnoczi550830f2014-09-16 15:24:24 +0100333growable format such as @code{qcow}: the empty sectors are detected and
334suppressed from the destination image.
bellardacd935e2004-11-15 22:57:26 +0000335
Peter Lieven11b66992013-10-24 12:07:05 +0200336@var{sparse_size} indicates the consecutive number of bytes (defaults to 4k)
337that must contain only zeros for qemu-img to create a sparse image during
338conversion. If @var{sparse_size} is 0, the source will not be scanned for
339unallocated or zero sectors, and the destination image will always be
340fully allocated.
341
Kevin Wolf8063d0f2009-10-28 12:49:16 +0100342You can use the @var{backing_file} option to force the output image to be
343created as a copy on write image of the specified base image; the
344@var{backing_file} should have the same content as the input's base image,
345however the path, image format, etc may differ.
346
Fam Zhenga16efd52017-08-04 22:36:58 +0800347If a relative path name is given, the backing file is looked up relative to
348the directory containing @var{output_filename}.
349
Alexandre Derumierb2e10492013-09-02 19:07:24 +0100350If the @code{-n} option is specified, the target volume creation will be
351skipped. This is useful for formats such as @code{rbd} if the target
352volume has already been created with site specific options that cannot
353be supplied through qemu-img.
354
Peter Lieven2d9187b2017-02-28 13:40:07 +0100355Out of order writes can be enabled with @code{-W} to improve performance.
356This is only recommended for preallocated devices like host devices or other
357raw block devices. Out of order write does not work in combination with
358creating compressed images.
359
360@var{num_coroutines} specifies how many coroutines work in parallel during
361the convert process (defaults to 8).
362
John Snow9775fcd2018-05-03 18:56:47 -0400363@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 -0400364
365Create the new disk image @var{filename} of size @var{size} and format
366@var{fmt}. Depending on the file format, you can add one or more @var{options}
367that enable additional features of this format.
368
369If the option @var{backing_file} is specified, then the image will record
370only the differences from @var{backing_file}. No size needs to be specified in
371this case. @var{backing_file} will never be modified unless you use the
372@code{commit} monitor command (or qemu-img commit).
373
374If a relative path name is given, the backing file is looked up relative to
375the directory containing @var{filename}.
376
377Note that a given backing file will be opened to check that it is valid. Use
378the @code{-u} option to enable unsafe backing file mode, which means that the
379image will be created even if the associated backing file cannot be opened. A
380matching backing file must be created or additional options be used to make the
381backing file specification valid when you want to use an image created this
382way.
383
384The size can also be specified using the @var{size} option with @code{-o},
385it doesn't need to be specified separately in this case.
386
John Snow9775fcd2018-05-03 18:56:47 -0400387@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 +0200388
389Dd copies from @var{input} file to @var{output} file converting it from
390@var{fmt} format to @var{output_fmt} format.
391
392The data is by default read and written using blocks of 512 bytes but can be
393modified by specifying @var{block_size}. If count=@var{blocks} is specified
394dd will stop reading input after reading @var{blocks} input blocks.
395
396The size syntax is similar to dd(1)'s size syntax.
397
John Snow9775fcd2018-05-03 18:56:47 -0400398@item info [--object @var{objectdef}] [--image-opts] [-f @var{fmt}] [--output=@var{ofmt}] [--backing-chain] [-U] @var{filename}
bellardacd935e2004-11-15 22:57:26 +0000399
400Give information about the disk image @var{filename}. Use it in
401particular to know the size reserved on disk which can be different
bellard19d36792006-08-07 21:34:34 +0000402from the displayed size. If VM snapshots are stored in the disk image,
Benoît Canetc054b3f2012-09-05 13:09:02 +0200403they are displayed too. The command can output in the format @var{ofmt}
404which is either @code{human} or @code{json}.
blueswir1d2c639d2009-01-24 18:19:25 +0000405
Kashyap Chamarthye5357562012-10-18 11:25:34 +0530406If a disk image has a backing file chain, information about each disk image in
407the chain can be recursively enumerated by using the option @code{--backing-chain}.
408
409For instance, if you have an image chain like:
410
411@example
412base.qcow2 <- snap1.qcow2 <- snap2.qcow2
413@end example
414
415To enumerate information about each disk image in the above chain, starting from top to base, do:
416
417@example
418qemu-img info --backing-chain snap2.qcow2
419@end example
420
Paolo Bonzinifacd6e22013-09-04 19:00:34 +0200421@item map [-f @var{fmt}] [--output=@var{ofmt}] @var{filename}
422
423Dump the metadata of image @var{filename} and its backing file chain.
424In particular, this commands dumps the allocation state of every sector
425of @var{filename}, together with the topmost file that allocates it in
426the backing file chain.
427
428Two option formats are possible. The default format (@code{human})
429only dumps known-nonzero areas of the file. Known-zero parts of the
430file are omitted altogether, and likewise for parts that are not allocated
431throughout the chain. @command{qemu-img} output will identify a file
432from where the data can be read, and the offset in the file. Each line
433will include four fields, the first three of which are hexadecimal
434numbers. For example the first line of:
435@example
436Offset Length Mapped to File
4370 0x20000 0x50000 /tmp/overlay.qcow2
4380x100000 0x10000 0x95380000 /tmp/backing.qcow2
439@end example
440@noindent
441means that 0x20000 (131072) bytes starting at offset 0 in the image are
442available in /tmp/overlay.qcow2 (opened in @code{raw} format) starting
443at offset 0x50000 (327680). Data that is compressed, encrypted, or
444otherwise not available in raw format will cause an error if @code{human}
445format is in use. Note that file names can include newlines, thus it is
446not safe to parse this output format in scripts.
447
448The alternative format @code{json} will return an array of dictionaries
449in JSON format. It will include similar information in
450the @code{start}, @code{length}, @code{offset} fields;
451it will also include other more specific information:
452@itemize @minus
453@item
454whether the sectors contain actual data or not (boolean field @code{data};
455if false, the sectors are either unallocated or stored as optimized
456all-zero clusters);
457
458@item
459whether the data is known to read as zero (boolean field @code{zero});
460
461@item
462in order to make the output shorter, the target file is expressed as
463a @code{depth}; for example, a depth of 2 refers to the backing file
464of the backing file of @var{filename}.
465@end itemize
466
467In JSON format, the @code{offset} field is optional; it is absent in
468cases where @code{human} format would omit the entry or exit with an error.
469If @code{data} is false and the @code{offset} field is present, the
470corresponding sectors in the file are not yet in use, but they are
471preallocated.
472
473For more information, consult @file{include/block/block.h} in QEMU's
474source code.
475
Stefan Hajnoczifd03c2b2017-07-05 13:57:36 +0100476@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}]
477
478Calculate the file size required for a new image. This information can be used
479to size logical volumes or SAN LUNs appropriately for the image that will be
480placed in them. The values reported are guaranteed to be large enough to fit
481the image. The command can output in the format @var{ofmt} which is either
482@code{human} or @code{json}.
483
484If the size @var{N} is given then act as if creating a new empty image file
485using @command{qemu-img create}. If @var{filename} is given then act as if
486converting an existing image file using @command{qemu-img convert}. The format
487of the new file is given by @var{output_fmt} while the format of an existing
488file is given by @var{fmt}.
489
490A snapshot in an existing image can be specified using @var{snapshot_param}.
491
492The following fields are reported:
493@example
494required size: 524288
495fully allocated size: 1074069504
496@end example
497
498The @code{required size} is the file size of the new image. It may be smaller
499than the virtual disk size if the image format supports compact representation.
500
501The @code{fully allocated size} is the file size of the new image once data has
502been written to all sectors. This is the maximum size that the image file can
503occupy with the exception of internal snapshots, dirty bitmaps, vmstate data,
504and other advanced image format features.
505
John Snow9775fcd2018-05-03 18:56:47 -0400506@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 +0000507
508List, apply, create or delete snapshots in image @var{filename}.
Stefan Hajnocziae6b0ed2010-04-24 09:12:12 +0100509
John Snow9775fcd2018-05-03 18:56:47 -0400510@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 +0100511
512Changes the backing file of an image. Only the formats @code{qcow2} and
513@code{qed} support changing the backing file.
514
515The backing file is changed to @var{backing_file} and (if the image format of
516@var{filename} supports this) the backing file format is changed to
Alex Bligha6166732012-10-16 13:46:18 +0100517@var{backing_fmt}. If @var{backing_file} is specified as ``'' (the empty
518string), then the image is rebased onto no backing file (i.e. it will exist
519independently of any backing file).
Kevin Wolfe6184692011-01-17 15:35:28 +0100520
Fam Zhenga16efd52017-08-04 22:36:58 +0800521If a relative path name is given, the backing file is looked up relative to
522the directory containing @var{filename}.
523
Max Reitz40055952014-07-22 22:58:42 +0200524@var{cache} specifies the cache mode to be used for @var{filename}, whereas
Stefan Hajnoczi3ba67962014-09-02 11:01:03 +0100525@var{src_cache} specifies the cache mode for reading backing files.
Max Reitz40055952014-07-22 22:58:42 +0200526
Kevin Wolfe6184692011-01-17 15:35:28 +0100527There are two different modes in which @code{rebase} can operate:
528@table @option
529@item Safe mode
530This is the default mode and performs a real rebase operation. The new backing
531file may differ from the old one and qemu-img rebase will take care of keeping
532the guest-visible content of @var{filename} unchanged.
533
534In order to achieve this, any clusters that differ between @var{backing_file}
535and the old backing file of @var{filename} are merged into @var{filename}
536before actually changing the backing file.
537
538Note that the safe mode is an expensive operation, comparable to converting
539an image. It only works if the old backing file still exists.
540
541@item Unsafe mode
542qemu-img uses the unsafe mode if @code{-u} is specified. In this mode, only the
543backing file name and format of @var{filename} is changed without any checks
544on the file contents. The user must take care of specifying the correct new
545backing file, or the guest-visible content of the image will be corrupted.
546
547This mode is useful for renaming or moving the backing file to somewhere else.
548It can be used without an accessible old backing file, i.e. you can use it to
549fix an image whose backing file has already been moved/renamed.
550@end table
551
Richard W.M. Jones9fda6ab2012-05-21 14:58:05 +0100552You can use @code{rebase} to perform a ``diff'' operation on two
553disk images. This can be useful when you have copied or cloned
554a guest, and you want to get back to a thin image on top of a
555template or base image.
556
557Say that @code{base.img} has been cloned as @code{modified.img} by
558copying it, and that the @code{modified.img} guest has run so there
559are now some changes compared to @code{base.img}. To construct a thin
560image called @code{diff.qcow2} that contains just the differences, do:
561
562@example
563qemu-img create -f qcow2 -b modified.img diff.qcow2
564qemu-img rebase -b base.img diff.qcow2
565@end example
566
567At this point, @code{modified.img} can be discarded, since
568@code{base.img + diff.qcow2} contains the same information.
569
John Snow9775fcd2018-05-03 18:56:47 -0400570@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 +0100571
572Change the disk image as if it had been created with @var{size}.
573
574Before using this command to shrink a disk image, you MUST use file system and
575partitioning tools inside the VM to reduce allocated file systems and partition
576sizes accordingly. Failure to do so will result in data loss!
577
Pavel Butsykin4ffca892017-09-18 15:42:27 +0300578When shrinking images, the @code{--shrink} option must be given. This informs
579qemu-img that the user acknowledges all loss of data beyond the truncated
580image's end.
581
Stefan Hajnocziae6b0ed2010-04-24 09:12:12 +0100582After using this command to grow a disk image, you must use file system and
583partitioning tools inside the VM to actually begin using the new space on the
584device.
Max Reitz6f176b42013-09-03 10:09:50 +0200585
Max Reitzdc5f6902017-06-13 22:20:55 +0200586When growing an image, the @code{--preallocation} option may be used to specify
587how the additional image area should be allocated on the host. See the format
588description in the @code{NOTES} section which values are allowed. Using this
589option may result in slightly more data being allocated than necessary.
590
bellardacd935e2004-11-15 22:57:26 +0000591@end table
Kevin Wolfd3067b02012-11-21 14:21:47 +0100592@c man end
bellardacd935e2004-11-15 22:57:26 +0000593
Kevin Wolfd3067b02012-11-21 14:21:47 +0100594@ignore
595@c man begin NOTES
Kevin Wolff932c042009-10-28 12:49:15 +0100596Supported image file formats:
597
598@table @option
599@item raw
600
601Raw disk image format (default). This format has the advantage of
602being simple and easily exportable to all other emulators. If your
603file system supports @emph{holes} (for example in ext2 or ext3 on
604Linux or NTFS on Windows), then only the written sectors will reserve
605space. Use @code{qemu-img info} to know the real size used by the
606image or @code{ls -ls} on Unix/Linux.
607
Hu Tao06247422014-09-10 17:05:48 +0800608Supported options:
609@table @code
610@item preallocation
611Preallocation mode (allowed values: @code{off}, @code{falloc}, @code{full}).
612@code{falloc} mode preallocates space for image by calling posix_fallocate().
613@code{full} mode preallocates space for image by writing zeros to underlying
614storage.
615@end table
616
Kevin Wolff932c042009-10-28 12:49:15 +0100617@item qcow2
618QEMU image format, the most versatile format. Use it to have smaller
619images (useful if your filesystem does not supports holes, for example
620on Windows), optional AES encryption, zlib based compression and
621support of multiple VM snapshots.
Kevin Wolf8063d0f2009-10-28 12:49:16 +0100622
Kevin Wolf3e032362009-10-28 12:49:17 +0100623Supported options:
624@table @code
Kevin Wolfd3067b02012-11-21 14:21:47 +0100625@item compat
Stefan Hajnoczi7fa9e1f2014-01-06 12:39:01 +0800626Determines the qcow2 version to use. @code{compat=0.10} uses the
627traditional image format that can be read by any QEMU since 0.10.
Kevin Wolfd3067b02012-11-21 14:21:47 +0100628@code{compat=1.1} enables image format extensions that only QEMU 1.1 and
Stefan Hajnoczi7fa9e1f2014-01-06 12:39:01 +0800629newer understand (this is the default). Amongst others, this includes zero
630clusters, which allow efficient copy-on-read for sparse images.
Kevin Wolfd3067b02012-11-21 14:21:47 +0100631
Kevin Wolf3e032362009-10-28 12:49:17 +0100632@item backing_file
633File name of a base image (see @option{create} subcommand)
634@item backing_fmt
635Image format of the base image
636@item encryption
Daniel P. Berrange136cd192014-01-22 15:47:10 +0000637If this option is set to @code{on}, the image is encrypted with 128-bit AES-CBC.
Kevin Wolf3e032362009-10-28 12:49:17 +0100638
Daniel P. Berrange136cd192014-01-22 15:47:10 +0000639The use of encryption in qcow and qcow2 images is considered to be flawed by
640modern cryptography standards, suffering from a number of design problems:
641
642@itemize @minus
Daniel P. Berrange0b4ee902017-06-23 17:24:02 +0100643@item
644The AES-CBC cipher is used with predictable initialization vectors based
Daniel P. Berrange136cd192014-01-22 15:47:10 +0000645on the sector number. This makes it vulnerable to chosen plaintext attacks
646which can reveal the existence of encrypted data.
Daniel P. Berrange0b4ee902017-06-23 17:24:02 +0100647@item
648The user passphrase is directly used as the encryption key. A poorly
Daniel P. Berrange136cd192014-01-22 15:47:10 +0000649chosen or short passphrase will compromise the security of the encryption.
Daniel P. Berrange0b4ee902017-06-23 17:24:02 +0100650@item
651In the event of the passphrase being compromised there is no way to
Daniel P. Berrange136cd192014-01-22 15:47:10 +0000652change the passphrase to protect data in any qcow images. The files must
653be cloned, using a different encryption passphrase in the new file. The
654original file must then be securely erased using a program like shred,
655though even this is ineffective with many modern storage technologies.
Daniel P. Berrange0b4ee902017-06-23 17:24:02 +0100656@item
657Initialization vectors used to encrypt sectors are based on the
658guest virtual sector number, instead of the host physical sector. When
659a disk image has multiple internal snapshots this means that data in
660multiple physical sectors is encrypted with the same initialization
661vector. With the CBC mode, this opens the possibility of watermarking
662attacks if the attack can collect multiple sectors encrypted with the
663same IV and some predictable data. Having multiple qcow2 images with
664the same passphrase also exposes this weakness since the passphrase
665is directly used as the key.
Daniel P. Berrange136cd192014-01-22 15:47:10 +0000666@end itemize
667
668Use of qcow / qcow2 encryption is thus strongly discouraged. Users are
669recommended to use an alternative encryption technology such as the
670Linux dm-crypt / LUKS system.
Kevin Wolf3e032362009-10-28 12:49:17 +0100671
672@item cluster_size
673Changes the qcow2 cluster size (must be between 512 and 2M). Smaller cluster
674sizes can improve the image file size whereas larger cluster sizes generally
675provide better performance.
676
677@item preallocation
Hu Tao0e4271b2014-09-10 17:05:49 +0800678Preallocation mode (allowed values: @code{off}, @code{metadata}, @code{falloc},
679@code{full}). An image with preallocated metadata is initially larger but can
680improve performance when the image needs to grow. @code{falloc} and @code{full}
681preallocations are like the same options of @code{raw} format, but sets up
682metadata also.
Kevin Wolf3e032362009-10-28 12:49:17 +0100683
Kevin Wolfd3067b02012-11-21 14:21:47 +0100684@item lazy_refcounts
685If this option is set to @code{on}, reference count updates are postponed with
686the goal of avoiding metadata I/O and improving performance. This is
687particularly interesting with @option{cache=writethrough} which doesn't batch
688metadata updates. The tradeoff is that after a host crash, the reference count
689tables must be rebuilt, i.e. on the next open an (automatic) @code{qemu-img
690check -r all} is required, which may take some time.
691
692This option can only be enabled if @code{compat=1.1} is specified.
693
Chunyan Liu4ab15592014-06-30 14:29:58 +0800694@item nocow
Chunyan Liubc3a7f92014-07-02 12:27:29 +0800695If 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 +0800696valid on btrfs, no effect on other file systems.
697
698Btrfs has low performance when hosting a VM image file, even more when the guest
699on the VM also using btrfs as file system. Turning off COW is a way to mitigate
700this bad performance. Generally there are two ways to turn off COW on btrfs:
701a) Disable it by mounting with nodatacow, then all newly created files will be
702NOCOW. b) For an empty file, add the NOCOW file attribute. That's what this option
703does.
704
705Note: this option is only valid to new or empty files. If there is an existing
706file which is COW and has data blocks already, it couldn't be changed to NOCOW
707by setting @code{nocow=on}. One can issue @code{lsattr filename} to check if
Chunyan Liubc3a7f92014-07-02 12:27:29 +0800708the NOCOW flag is set or not (Capital 'C' is NOCOW flag).
Chunyan Liu4ab15592014-06-30 14:29:58 +0800709
Kevin Wolf3e032362009-10-28 12:49:17 +0100710@end table
711
Kevin Wolfd3067b02012-11-21 14:21:47 +0100712@item Other
713QEMU also supports various other image file formats for compatibility with
Jeff Cody8282db12013-12-17 13:56:06 -0500714older QEMU versions or other hypervisors, including VMDK, VDI, VHD (vpc), VHDX,
715qcow1 and QED. For a full list of supported formats see @code{qemu-img --help}.
Kevin Wolfd3067b02012-11-21 14:21:47 +0100716For a more detailed description of these formats, see the QEMU Emulation User
717Documentation.
Stefan Hajnoczif0858002012-06-13 14:29:15 +0100718
Kevin Wolfd3067b02012-11-21 14:21:47 +0100719The main purpose of the block drivers for these formats is image conversion.
720For running VMs, it is recommended to convert the disk images to either raw or
721qcow2 in order to achieve good performance.
Kevin Wolff932c042009-10-28 12:49:15 +0100722@end table
723
724
bellardacd935e2004-11-15 22:57:26 +0000725@c man end
726
bellardacd935e2004-11-15 22:57:26 +0000727@setfilename qemu-img
728@settitle QEMU disk image utility
729
730@c man begin SEEALSO
731The HTML documentation of QEMU for more precise information and Linux
732user mode emulator invocation.
733@c man end
734
735@c man begin AUTHOR
736Fabrice Bellard
737@c man end
738
739@end ignore