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1 | @example |
2 | @c man begin SYNOPSIS | |
10985131 | 3 | @command{qemu-img} [@var{standard} @var{options}] @var{command} [@var{command} @var{options}] |
acd935ef FB |
4 | @c man end |
5 | @end example | |
6 | ||
48467328 KW |
7 | @c man begin DESCRIPTION |
8 | qemu-img allows you to create, convert and modify images offline. It can handle | |
9 | all image formats supported by QEMU. | |
10 | ||
11 | @b{Warning:} Never use qemu-img to modify images in use by a running virtual | |
12 | machine or any other process; this may destroy the image. Also, be aware that | |
13 | querying an image that is being modified by another process may encounter | |
14 | inconsistent state. | |
15 | @c man end | |
16 | ||
acd935ef FB |
17 | @c man begin OPTIONS |
18 | ||
10985131 DL |
19 | Standard options: |
20 | @table @option | |
21 | @item -h, --help | |
22 | Display this help and exit | |
23 | @item -V, --version | |
24 | Display version information and exit | |
06a1e0c1 DL |
25 | @item -T, --trace [[enable=]@var{pattern}][,events=@var{file}][,file=@var{file}] |
26 | @findex --trace | |
27 | @include qemu-option-trace.texi | |
10985131 DL |
28 | @end table |
29 | ||
acd935ef | 30 | The following commands are supported: |
153859be SB |
31 | |
32 | @include qemu-img-cmds.texi | |
acd935ef FB |
33 | |
34 | Command parameters: | |
35 | @table @var | |
36 | @item filename | |
37 | is a disk image filename | |
3babeb15 DB |
38 | |
39 | @item --object @var{objectdef} | |
40 | ||
41 | is a QEMU user creatable object definition. See the @code{qemu(1)} manual | |
42 | page for a description of the object properties. The most common object | |
43 | type is a @code{secret}, which is used to supply passwords and/or encryption | |
44 | keys. | |
45 | ||
eb769f74 DB |
46 | @item --image-opts |
47 | ||
305b4c60 | 48 | Indicates that the source @var{filename} parameter is to be interpreted as a |
eb769f74 | 49 | full option string, not a plain filename. This parameter is mutually |
305b4c60 DB |
50 | exclusive with the @var{-f} parameter. |
51 | ||
52 | @item --target-image-opts | |
53 | ||
54 | Indicates that the @var{output_filename} parameter(s) are to be interpreted as | |
55 | a full option string, not a plain filename. This parameter is mutually | |
56 | exclusive with the @var{-O} parameters. It is currently required to also use | |
57 | the @var{-n} parameter to skip image creation. This restriction may be relaxed | |
58 | in a future release. | |
eb769f74 | 59 | |
5fafdf24 | 60 | @item fmt |
f932c040 KW |
61 | is the disk image format. It is guessed automatically in most cases. See below |
62 | for a description of the supported disk formats. | |
acd935ef | 63 | |
e5357560 KC |
64 | @item --backing-chain |
65 | will enumerate information about backing files in a disk image chain. Refer | |
66 | below for further description. | |
67 | ||
5fafdf24 | 68 | @item size |
eff44266 KW |
69 | is the disk image size in bytes. Optional suffixes @code{k} or @code{K} |
70 | (kilobyte, 1024) @code{M} (megabyte, 1024k) and @code{G} (gigabyte, 1024M) | |
71 | and T (terabyte, 1024G) are supported. @code{b} is ignored. | |
acd935ef FB |
72 | |
73 | @item output_filename | |
5fafdf24 | 74 | is the destination disk image filename |
acd935ef FB |
75 | |
76 | @item output_fmt | |
77 | is the destination format | |
eff44266 KW |
78 | @item options |
79 | is a comma separated list of format specific options in a | |
80 | name=value format. Use @code{-o ?} for an overview of the options supported | |
3e032364 | 81 | by the used format or see the format descriptions below for details. |
ef80654d WX |
82 | @item snapshot_param |
83 | is param used for internal snapshot, format is | |
84 | 'snapshot.id=[ID],snapshot.name=[NAME]' or '[ID_OR_NAME]' | |
85 | @item snapshot_id_or_name | |
86 | is deprecated, use snapshot_param instead | |
acd935ef FB |
87 | |
88 | @item -c | |
89 | indicates that target image must be compressed (qcow format only) | |
d2c639d6 BS |
90 | @item -h |
91 | with or without a command shows help and lists the supported formats | |
aaf55b47 | 92 | @item -p |
0e3bd993 KW |
93 | display progress bar (compare, convert and rebase commands only). |
94 | If the @var{-p} option is not used for a command that supports it, the | |
262fbae6 HR |
95 | progress is reported when the process receives a @code{SIGUSR1} or |
96 | @code{SIGINFO} signal. | |
f382d43a MR |
97 | @item -q |
98 | Quiet mode - do not print any output (except errors). There's no progress bar | |
99 | in case both @var{-q} and @var{-p} options are used. | |
a22f123c KW |
100 | @item -S @var{size} |
101 | indicates the consecutive number of bytes that must contain only zeros | |
102 | for qemu-img to create a sparse image during conversion. This value is rounded | |
103 | down to the nearest 512 bytes. You may use the common size suffixes like | |
104 | @code{k} for kilobytes. | |
3763f26f KW |
105 | @item -t @var{cache} |
106 | specifies the cache mode that should be used with the (destination) file. See | |
107 | the documentation of the emulator's @code{-drive cache=...} option for allowed | |
108 | values. | |
40055951 | 109 | @item -T @var{src_cache} |
bb87fdf8 SH |
110 | specifies the cache mode that should be used with the source file(s). See |
111 | the documentation of the emulator's @code{-drive cache=...} option for allowed | |
112 | values. | |
d2c639d6 BS |
113 | @end table |
114 | ||
115 | Parameters to snapshot subcommand: | |
116 | ||
117 | @table @option | |
118 | ||
119 | @item snapshot | |
120 | is the name of the snapshot to create, apply or delete | |
121 | @item -a | |
122 | applies a snapshot (revert disk to saved state) | |
123 | @item -c | |
124 | creates a snapshot | |
125 | @item -d | |
126 | deletes a snapshot | |
127 | @item -l | |
128 | lists all snapshots in the given image | |
acd935ef FB |
129 | @end table |
130 | ||
d14ed18c MR |
131 | Parameters to compare subcommand: |
132 | ||
133 | @table @option | |
134 | ||
135 | @item -f | |
136 | First image format | |
137 | @item -F | |
138 | Second image format | |
139 | @item -s | |
b6af0975 | 140 | Strict mode - fail on different image size or sector allocation |
d14ed18c MR |
141 | @end table |
142 | ||
b2e10493 AD |
143 | Parameters to convert subcommand: |
144 | ||
145 | @table @option | |
146 | ||
147 | @item -n | |
148 | Skip the creation of the target volume | |
2d9187bc PL |
149 | @item -m |
150 | Number of parallel coroutines for the convert process | |
151 | @item -W | |
152 | Allow out-of-order writes to the destination. This option improves performance, | |
153 | but is only recommended for preallocated devices like host devices or other | |
154 | raw block devices. | |
b2e10493 AD |
155 | @end table |
156 | ||
86ce1f6e RS |
157 | Parameters to dd subcommand: |
158 | ||
159 | @table @option | |
160 | ||
161 | @item bs=@var{block_size} | |
162 | defines the block size | |
163 | @item count=@var{blocks} | |
164 | sets the number of input blocks to copy | |
165 | @item if=@var{input} | |
166 | sets the input file | |
167 | @item of=@var{output} | |
168 | sets the output file | |
f7c15533 RS |
169 | @item skip=@var{blocks} |
170 | sets the number of input blocks to skip | |
86ce1f6e RS |
171 | @end table |
172 | ||
acd935ef FB |
173 | Command description: |
174 | ||
175 | @table @option | |
55d539c8 | 176 | @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] @var{filename} |
b6133b8c | 177 | |
b6495fa8 KW |
178 | Run a simple sequential I/O benchmark on the specified image. If @code{-w} is |
179 | specified, a write test is performed, otherwise a read test is performed. | |
180 | ||
181 | A total number of @var{count} I/O requests is performed, each @var{buffer_size} | |
d3199a31 | 182 | bytes in size, and with @var{depth} requests in parallel. The first request |
83de9be0 KW |
183 | starts at the position given by @var{offset}, each following request increases |
184 | the current position by @var{step_size}. If @var{step_size} is not given, | |
185 | @var{buffer_size} is used for its value. | |
b6133b8c | 186 | |
55d539c8 KW |
187 | If @var{flush_interval} is specified for a write test, the request queue is |
188 | drained and a flush is issued before new writes are made whenever the number of | |
189 | remaining requests is a multiple of @var{flush_interval}. If additionally | |
190 | @code{--no-drain} is specified, a flush is issued without draining the request | |
191 | queue first. | |
192 | ||
b6133b8c KW |
193 | If @code{-n} is specified, the native AIO backend is used if possible. On |
194 | Linux, this option only works if @code{-t none} or @code{-t directsync} is | |
195 | specified as well. | |
196 | ||
b6495fa8 KW |
197 | For write tests, by default a buffer filled with zeros is written. This can be |
198 | overridden with a pattern byte specified by @var{pattern}. | |
199 | ||
40055951 | 200 | @item check [-f @var{fmt}] [--output=@var{ofmt}] [-r [leaks | all]] [-T @var{src_cache}] @var{filename} |
e6184690 | 201 | |
8599ea4c FS |
202 | Perform a consistency check on the disk image @var{filename}. The command can |
203 | output in the format @var{ofmt} which is either @code{human} or @code{json}. | |
e6184690 | 204 | |
4534ff54 KW |
205 | If @code{-r} is specified, qemu-img tries to repair any inconsistencies found |
206 | during the check. @code{-r leaks} repairs only cluster leaks, whereas | |
207 | @code{-r all} fixes all kinds of errors, with a higher risk of choosing the | |
0546b8c2 | 208 | wrong fix or hiding corruption that has already occurred. |
4534ff54 | 209 | |
e6184690 KW |
210 | Only the formats @code{qcow2}, @code{qed} and @code{vdi} support |
211 | consistency checks. | |
212 | ||
d6635c4d HR |
213 | In case the image does not have any inconsistencies, check exits with @code{0}. |
214 | Other exit codes indicate the kind of inconsistency found or if another error | |
215 | occurred. The following table summarizes all exit codes of the check subcommand: | |
216 | ||
217 | @table @option | |
218 | ||
219 | @item 0 | |
220 | Check completed, the image is (now) consistent | |
221 | @item 1 | |
222 | Check not completed because of internal errors | |
223 | @item 2 | |
224 | Check completed, image is corrupted | |
225 | @item 3 | |
226 | Check completed, image has leaked clusters, but is not corrupted | |
227 | @item 63 | |
228 | Checks are not supported by the image format | |
229 | ||
230 | @end table | |
231 | ||
232 | If @code{-r} is specified, exit codes representing the image state refer to the | |
233 | state after (the attempt at) repairing it. That is, a successful @code{-r all} | |
234 | will yield the exit code 0, independently of the image state before. | |
235 | ||
6e6e55f5 | 236 | @item create [-f @var{fmt}] [-b @var{backing_file}] [-F @var{backing_fmt}] [-u] [-o @var{options}] @var{filename} [@var{size}] |
acd935ef FB |
237 | |
238 | Create the new disk image @var{filename} of size @var{size} and format | |
8063d0fe KW |
239 | @var{fmt}. Depending on the file format, you can add one or more @var{options} |
240 | that enable additional features of this format. | |
acd935ef | 241 | |
8063d0fe KW |
242 | If the option @var{backing_file} is specified, then the image will record |
243 | only the differences from @var{backing_file}. No size needs to be specified in | |
244 | this case. @var{backing_file} will never be modified unless you use the | |
245 | @code{commit} monitor command (or qemu-img commit). | |
acd935ef | 246 | |
6e6e55f5 JS |
247 | Note that a given backing file will be opened to check that it is valid. Use |
248 | the @code{-u} option to enable unsafe backing file mode, which means that the | |
249 | image will be created even if the associated backing file cannot be opened. A | |
250 | matching backing file must be created or additional options be used to make the | |
251 | backing file specification valid when you want to use an image created this | |
252 | way. | |
253 | ||
eff44266 KW |
254 | The size can also be specified using the @var{size} option with @code{-o}, |
255 | it doesn't need to be specified separately in this case. | |
256 | ||
1b22bffd | 257 | @item commit [-q] [-f @var{fmt}] [-t @var{cache}] [-b @var{base}] [-d] [-p] @var{filename} |
acd935ef | 258 | |
37222900 JC |
259 | Commit the changes recorded in @var{filename} in its base image or backing file. |
260 | If the backing file is smaller than the snapshot, then the backing file will be | |
261 | resized to be the same size as the snapshot. If the snapshot is smaller than | |
262 | the backing file, the backing file will not be truncated. If you want the | |
263 | backing file to match the size of the smaller snapshot, you can safely truncate | |
264 | it yourself once the commit operation successfully completes. | |
acd935ef | 265 | |
9a86fe48 HR |
266 | The image @var{filename} is emptied after the operation has succeeded. If you do |
267 | not need @var{filename} afterwards and intend to drop it, you may skip emptying | |
268 | @var{filename} by specifying the @code{-d} flag. | |
269 | ||
1b22bffd HR |
270 | If the backing chain of the given image file @var{filename} has more than one |
271 | layer, the backing file into which the changes will be committed may be | |
272 | specified as @var{base} (which has to be part of @var{filename}'s backing | |
273 | chain). If @var{base} is not specified, the immediate backing file of the top | |
274 | image (which is @var{filename}) will be used. For reasons of consistency, | |
275 | explicitly specifying @var{base} will always imply @code{-d} (since emptying an | |
276 | image after committing to an indirect backing file would lead to different data | |
277 | being read from the image due to content in the intermediate backing chain | |
278 | overruling the commit target). | |
279 | ||
40055951 | 280 | @item compare [-f @var{fmt}] [-F @var{fmt}] [-T @var{src_cache}] [-p] [-s] [-q] @var{filename1} @var{filename2} |
d14ed18c MR |
281 | |
282 | Check if two images have the same content. You can compare images with | |
283 | different format or settings. | |
284 | ||
285 | The format is probed unless you specify it by @var{-f} (used for | |
286 | @var{filename1}) and/or @var{-F} (used for @var{filename2}) option. | |
287 | ||
288 | By default, images with different size are considered identical if the larger | |
289 | image contains only unallocated and/or zeroed sectors in the area after the end | |
290 | of the other image. In addition, if any sector is not allocated in one image | |
291 | and contains only zero bytes in the second one, it is evaluated as equal. You | |
292 | can use Strict mode by specifying the @var{-s} option. When compare runs in | |
293 | Strict mode, it fails in case image size differs or a sector is allocated in | |
294 | one image and is not allocated in the second one. | |
295 | ||
296 | By default, compare prints out a result message. This message displays | |
297 | information that both images are same or the position of the first different | |
298 | byte. In addition, result message can report different image size in case | |
299 | Strict mode is used. | |
300 | ||
301 | Compare exits with @code{0} in case the images are equal and with @code{1} | |
302 | in case the images differ. Other exit codes mean an error occurred during | |
303 | execution and standard error output should contain an error message. | |
304 | The following table sumarizes all exit codes of the compare subcommand: | |
305 | ||
306 | @table @option | |
307 | ||
308 | @item 0 | |
309 | Images are identical | |
310 | @item 1 | |
311 | Images differ | |
312 | @item 2 | |
313 | Error on opening an image | |
314 | @item 3 | |
315 | Error on checking a sector allocation | |
316 | @item 4 | |
317 | Error on reading data | |
318 | ||
319 | @end table | |
320 | ||
2b4c0a20 | 321 | @item convert [-c] [-p] [-n] [-f @var{fmt}] [-t @var{cache}] [-T @var{src_cache}] [-O @var{output_fmt}] [-B @var{backing_file}] [-o @var{options}] [-s @var{snapshot_id_or_name}] [-l @var{snapshot_param}] [-m @var{num_coroutines}] [-W] [-S @var{sparse_size}] @var{filename} [@var{filename2} [...]] @var{output_filename} |
acd935ef | 322 | |
ef80654d WX |
323 | Convert the disk image @var{filename} or a snapshot @var{snapshot_param}(@var{snapshot_id_or_name} is deprecated) |
324 | to disk image @var{output_filename} using format @var{output_fmt}. It can be optionally compressed (@code{-c} | |
eff44266 | 325 | option) or use any format specific options like encryption (@code{-o} option). |
acd935ef | 326 | |
8063d0fe | 327 | Only the formats @code{qcow} and @code{qcow2} support compression. The |
acd935ef FB |
328 | compression is read-only. It means that if a compressed sector is |
329 | rewritten, then it is rewritten as uncompressed data. | |
330 | ||
acd935ef | 331 | Image conversion is also useful to get smaller image when using a |
550830f9 SH |
332 | growable format such as @code{qcow}: the empty sectors are detected and |
333 | suppressed from the destination image. | |
acd935ef | 334 | |
11b6699a PL |
335 | @var{sparse_size} indicates the consecutive number of bytes (defaults to 4k) |
336 | that must contain only zeros for qemu-img to create a sparse image during | |
337 | conversion. If @var{sparse_size} is 0, the source will not be scanned for | |
338 | unallocated or zero sectors, and the destination image will always be | |
339 | fully allocated. | |
340 | ||
8063d0fe KW |
341 | You can use the @var{backing_file} option to force the output image to be |
342 | created as a copy on write image of the specified base image; the | |
343 | @var{backing_file} should have the same content as the input's base image, | |
344 | however the path, image format, etc may differ. | |
345 | ||
b2e10493 AD |
346 | If the @code{-n} option is specified, the target volume creation will be |
347 | skipped. This is useful for formats such as @code{rbd} if the target | |
348 | volume has already been created with site specific options that cannot | |
349 | be supplied through qemu-img. | |
350 | ||
2d9187bc PL |
351 | Out of order writes can be enabled with @code{-W} to improve performance. |
352 | This is only recommended for preallocated devices like host devices or other | |
353 | raw block devices. Out of order write does not work in combination with | |
354 | creating compressed images. | |
355 | ||
356 | @var{num_coroutines} specifies how many coroutines work in parallel during | |
357 | the convert process (defaults to 8). | |
358 | ||
f7c15533 | 359 | @item dd [-f @var{fmt}] [-O @var{output_fmt}] [bs=@var{block_size}] [count=@var{blocks}] [skip=@var{blocks}] if=@var{input} of=@var{output} |
86ce1f6e RS |
360 | |
361 | Dd copies from @var{input} file to @var{output} file converting it from | |
362 | @var{fmt} format to @var{output_fmt} format. | |
363 | ||
364 | The data is by default read and written using blocks of 512 bytes but can be | |
365 | modified by specifying @var{block_size}. If count=@var{blocks} is specified | |
366 | dd will stop reading input after reading @var{blocks} input blocks. | |
367 | ||
368 | The size syntax is similar to dd(1)'s size syntax. | |
369 | ||
e5357560 | 370 | @item info [-f @var{fmt}] [--output=@var{ofmt}] [--backing-chain] @var{filename} |
acd935ef FB |
371 | |
372 | Give information about the disk image @var{filename}. Use it in | |
373 | particular to know the size reserved on disk which can be different | |
19d36792 | 374 | from the displayed size. If VM snapshots are stored in the disk image, |
c054b3fd BC |
375 | they are displayed too. The command can output in the format @var{ofmt} |
376 | which is either @code{human} or @code{json}. | |
d2c639d6 | 377 | |
e5357560 KC |
378 | If a disk image has a backing file chain, information about each disk image in |
379 | the chain can be recursively enumerated by using the option @code{--backing-chain}. | |
380 | ||
381 | For instance, if you have an image chain like: | |
382 | ||
383 | @example | |
384 | base.qcow2 <- snap1.qcow2 <- snap2.qcow2 | |
385 | @end example | |
386 | ||
387 | To enumerate information about each disk image in the above chain, starting from top to base, do: | |
388 | ||
389 | @example | |
390 | qemu-img info --backing-chain snap2.qcow2 | |
391 | @end example | |
392 | ||
facd6e2b PB |
393 | @item map [-f @var{fmt}] [--output=@var{ofmt}] @var{filename} |
394 | ||
395 | Dump the metadata of image @var{filename} and its backing file chain. | |
396 | In particular, this commands dumps the allocation state of every sector | |
397 | of @var{filename}, together with the topmost file that allocates it in | |
398 | the backing file chain. | |
399 | ||
400 | Two option formats are possible. The default format (@code{human}) | |
401 | only dumps known-nonzero areas of the file. Known-zero parts of the | |
402 | file are omitted altogether, and likewise for parts that are not allocated | |
403 | throughout the chain. @command{qemu-img} output will identify a file | |
404 | from where the data can be read, and the offset in the file. Each line | |
405 | will include four fields, the first three of which are hexadecimal | |
406 | numbers. For example the first line of: | |
407 | @example | |
408 | Offset Length Mapped to File | |
409 | 0 0x20000 0x50000 /tmp/overlay.qcow2 | |
410 | 0x100000 0x10000 0x95380000 /tmp/backing.qcow2 | |
411 | @end example | |
412 | @noindent | |
413 | means that 0x20000 (131072) bytes starting at offset 0 in the image are | |
414 | available in /tmp/overlay.qcow2 (opened in @code{raw} format) starting | |
415 | at offset 0x50000 (327680). Data that is compressed, encrypted, or | |
416 | otherwise not available in raw format will cause an error if @code{human} | |
417 | format is in use. Note that file names can include newlines, thus it is | |
418 | not safe to parse this output format in scripts. | |
419 | ||
420 | The alternative format @code{json} will return an array of dictionaries | |
421 | in JSON format. It will include similar information in | |
422 | the @code{start}, @code{length}, @code{offset} fields; | |
423 | it will also include other more specific information: | |
424 | @itemize @minus | |
425 | @item | |
426 | whether the sectors contain actual data or not (boolean field @code{data}; | |
427 | if false, the sectors are either unallocated or stored as optimized | |
428 | all-zero clusters); | |
429 | ||
430 | @item | |
431 | whether the data is known to read as zero (boolean field @code{zero}); | |
432 | ||
433 | @item | |
434 | in order to make the output shorter, the target file is expressed as | |
435 | a @code{depth}; for example, a depth of 2 refers to the backing file | |
436 | of the backing file of @var{filename}. | |
437 | @end itemize | |
438 | ||
439 | In JSON format, the @code{offset} field is optional; it is absent in | |
440 | cases where @code{human} format would omit the entry or exit with an error. | |
441 | If @code{data} is false and the @code{offset} field is present, the | |
442 | corresponding sectors in the file are not yet in use, but they are | |
443 | preallocated. | |
444 | ||
445 | For more information, consult @file{include/block/block.h} in QEMU's | |
446 | source code. | |
447 | ||
fd03c2b8 SH |
448 | @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}] |
449 | ||
450 | Calculate the file size required for a new image. This information can be used | |
451 | to size logical volumes or SAN LUNs appropriately for the image that will be | |
452 | placed in them. The values reported are guaranteed to be large enough to fit | |
453 | the image. The command can output in the format @var{ofmt} which is either | |
454 | @code{human} or @code{json}. | |
455 | ||
456 | If the size @var{N} is given then act as if creating a new empty image file | |
457 | using @command{qemu-img create}. If @var{filename} is given then act as if | |
458 | converting an existing image file using @command{qemu-img convert}. The format | |
459 | of the new file is given by @var{output_fmt} while the format of an existing | |
460 | file is given by @var{fmt}. | |
461 | ||
462 | A snapshot in an existing image can be specified using @var{snapshot_param}. | |
463 | ||
464 | The following fields are reported: | |
465 | @example | |
466 | required size: 524288 | |
467 | fully allocated size: 1074069504 | |
468 | @end example | |
469 | ||
470 | The @code{required size} is the file size of the new image. It may be smaller | |
471 | than the virtual disk size if the image format supports compact representation. | |
472 | ||
473 | The @code{fully allocated size} is the file size of the new image once data has | |
474 | been written to all sectors. This is the maximum size that the image file can | |
475 | occupy with the exception of internal snapshots, dirty bitmaps, vmstate data, | |
476 | and other advanced image format features. | |
477 | ||
d2c639d6 BS |
478 | @item snapshot [-l | -a @var{snapshot} | -c @var{snapshot} | -d @var{snapshot} ] @var{filename} |
479 | ||
480 | List, apply, create or delete snapshots in image @var{filename}. | |
ae6b0ed6 | 481 | |
40055951 | 482 | @item rebase [-f @var{fmt}] [-t @var{cache}] [-T @var{src_cache}] [-p] [-u] -b @var{backing_file} [-F @var{backing_fmt}] @var{filename} |
e6184690 KW |
483 | |
484 | Changes the backing file of an image. Only the formats @code{qcow2} and | |
485 | @code{qed} support changing the backing file. | |
486 | ||
487 | The backing file is changed to @var{backing_file} and (if the image format of | |
488 | @var{filename} supports this) the backing file format is changed to | |
a616673d AB |
489 | @var{backing_fmt}. If @var{backing_file} is specified as ``'' (the empty |
490 | string), then the image is rebased onto no backing file (i.e. it will exist | |
491 | independently of any backing file). | |
e6184690 | 492 | |
40055951 | 493 | @var{cache} specifies the cache mode to be used for @var{filename}, whereas |
3ba6796d | 494 | @var{src_cache} specifies the cache mode for reading backing files. |
40055951 | 495 | |
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496 | There are two different modes in which @code{rebase} can operate: |
497 | @table @option | |
498 | @item Safe mode | |
499 | This is the default mode and performs a real rebase operation. The new backing | |
500 | file may differ from the old one and qemu-img rebase will take care of keeping | |
501 | the guest-visible content of @var{filename} unchanged. | |
502 | ||
503 | In order to achieve this, any clusters that differ between @var{backing_file} | |
504 | and the old backing file of @var{filename} are merged into @var{filename} | |
505 | before actually changing the backing file. | |
506 | ||
507 | Note that the safe mode is an expensive operation, comparable to converting | |
508 | an image. It only works if the old backing file still exists. | |
509 | ||
510 | @item Unsafe mode | |
511 | qemu-img uses the unsafe mode if @code{-u} is specified. In this mode, only the | |
512 | backing file name and format of @var{filename} is changed without any checks | |
513 | on the file contents. The user must take care of specifying the correct new | |
514 | backing file, or the guest-visible content of the image will be corrupted. | |
515 | ||
516 | This mode is useful for renaming or moving the backing file to somewhere else. | |
517 | It can be used without an accessible old backing file, i.e. you can use it to | |
518 | fix an image whose backing file has already been moved/renamed. | |
519 | @end table | |
520 | ||
9fda6ab1 RJ |
521 | You can use @code{rebase} to perform a ``diff'' operation on two |
522 | disk images. This can be useful when you have copied or cloned | |
523 | a guest, and you want to get back to a thin image on top of a | |
524 | template or base image. | |
525 | ||
526 | Say that @code{base.img} has been cloned as @code{modified.img} by | |
527 | copying it, and that the @code{modified.img} guest has run so there | |
528 | are now some changes compared to @code{base.img}. To construct a thin | |
529 | image called @code{diff.qcow2} that contains just the differences, do: | |
530 | ||
531 | @example | |
532 | qemu-img create -f qcow2 -b modified.img diff.qcow2 | |
533 | qemu-img rebase -b base.img diff.qcow2 | |
534 | @end example | |
535 | ||
536 | At this point, @code{modified.img} can be discarded, since | |
537 | @code{base.img + diff.qcow2} contains the same information. | |
538 | ||
dc5f690b | 539 | @item resize [--preallocation=@var{prealloc}] @var{filename} [+ | -]@var{size} |
ae6b0ed6 SH |
540 | |
541 | Change the disk image as if it had been created with @var{size}. | |
542 | ||
543 | Before using this command to shrink a disk image, you MUST use file system and | |
544 | partitioning tools inside the VM to reduce allocated file systems and partition | |
545 | sizes accordingly. Failure to do so will result in data loss! | |
546 | ||
547 | After using this command to grow a disk image, you must use file system and | |
548 | partitioning tools inside the VM to actually begin using the new space on the | |
549 | device. | |
6f176b48 | 550 | |
dc5f690b HR |
551 | When growing an image, the @code{--preallocation} option may be used to specify |
552 | how the additional image area should be allocated on the host. See the format | |
553 | description in the @code{NOTES} section which values are allowed. Using this | |
554 | option may result in slightly more data being allocated than necessary. | |
555 | ||
76a3a34d | 556 | @item amend [-p] [-f @var{fmt}] [-t @var{cache}] -o @var{options} @var{filename} |
6f176b48 HR |
557 | |
558 | Amends the image format specific @var{options} for the image file | |
559 | @var{filename}. Not all file formats support this operation. | |
acd935ef | 560 | @end table |
d3067b02 | 561 | @c man end |
acd935ef | 562 | |
d3067b02 KW |
563 | @ignore |
564 | @c man begin NOTES | |
f932c040 KW |
565 | Supported image file formats: |
566 | ||
567 | @table @option | |
568 | @item raw | |
569 | ||
570 | Raw disk image format (default). This format has the advantage of | |
571 | being simple and easily exportable to all other emulators. If your | |
572 | file system supports @emph{holes} (for example in ext2 or ext3 on | |
573 | Linux or NTFS on Windows), then only the written sectors will reserve | |
574 | space. Use @code{qemu-img info} to know the real size used by the | |
575 | image or @code{ls -ls} on Unix/Linux. | |
576 | ||
06247428 HT |
577 | Supported options: |
578 | @table @code | |
579 | @item preallocation | |
580 | Preallocation mode (allowed values: @code{off}, @code{falloc}, @code{full}). | |
581 | @code{falloc} mode preallocates space for image by calling posix_fallocate(). | |
582 | @code{full} mode preallocates space for image by writing zeros to underlying | |
583 | storage. | |
584 | @end table | |
585 | ||
f932c040 KW |
586 | @item qcow2 |
587 | QEMU image format, the most versatile format. Use it to have smaller | |
588 | images (useful if your filesystem does not supports holes, for example | |
589 | on Windows), optional AES encryption, zlib based compression and | |
590 | support of multiple VM snapshots. | |
8063d0fe | 591 | |
3e032364 KW |
592 | Supported options: |
593 | @table @code | |
d3067b02 | 594 | @item compat |
7fa9e1f9 SH |
595 | Determines the qcow2 version to use. @code{compat=0.10} uses the |
596 | traditional image format that can be read by any QEMU since 0.10. | |
d3067b02 | 597 | @code{compat=1.1} enables image format extensions that only QEMU 1.1 and |
7fa9e1f9 SH |
598 | newer understand (this is the default). Amongst others, this includes zero |
599 | clusters, which allow efficient copy-on-read for sparse images. | |
d3067b02 | 600 | |
3e032364 KW |
601 | @item backing_file |
602 | File name of a base image (see @option{create} subcommand) | |
603 | @item backing_fmt | |
604 | Image format of the base image | |
605 | @item encryption | |
136cd19d | 606 | If this option is set to @code{on}, the image is encrypted with 128-bit AES-CBC. |
3e032364 | 607 | |
136cd19d DB |
608 | The use of encryption in qcow and qcow2 images is considered to be flawed by |
609 | modern cryptography standards, suffering from a number of design problems: | |
610 | ||
611 | @itemize @minus | |
0b4ee909 DB |
612 | @item |
613 | The AES-CBC cipher is used with predictable initialization vectors based | |
136cd19d DB |
614 | on the sector number. This makes it vulnerable to chosen plaintext attacks |
615 | which can reveal the existence of encrypted data. | |
0b4ee909 DB |
616 | @item |
617 | The user passphrase is directly used as the encryption key. A poorly | |
136cd19d | 618 | chosen or short passphrase will compromise the security of the encryption. |
0b4ee909 DB |
619 | @item |
620 | In the event of the passphrase being compromised there is no way to | |
136cd19d DB |
621 | change the passphrase to protect data in any qcow images. The files must |
622 | be cloned, using a different encryption passphrase in the new file. The | |
623 | original file must then be securely erased using a program like shred, | |
624 | though even this is ineffective with many modern storage technologies. | |
0b4ee909 DB |
625 | @item |
626 | Initialization vectors used to encrypt sectors are based on the | |
627 | guest virtual sector number, instead of the host physical sector. When | |
628 | a disk image has multiple internal snapshots this means that data in | |
629 | multiple physical sectors is encrypted with the same initialization | |
630 | vector. With the CBC mode, this opens the possibility of watermarking | |
631 | attacks if the attack can collect multiple sectors encrypted with the | |
632 | same IV and some predictable data. Having multiple qcow2 images with | |
633 | the same passphrase also exposes this weakness since the passphrase | |
634 | is directly used as the key. | |
136cd19d DB |
635 | @end itemize |
636 | ||
637 | Use of qcow / qcow2 encryption is thus strongly discouraged. Users are | |
638 | recommended to use an alternative encryption technology such as the | |
639 | Linux dm-crypt / LUKS system. | |
3e032364 KW |
640 | |
641 | @item cluster_size | |
642 | Changes the qcow2 cluster size (must be between 512 and 2M). Smaller cluster | |
643 | sizes can improve the image file size whereas larger cluster sizes generally | |
644 | provide better performance. | |
645 | ||
646 | @item preallocation | |
0e4271b7 HT |
647 | Preallocation mode (allowed values: @code{off}, @code{metadata}, @code{falloc}, |
648 | @code{full}). An image with preallocated metadata is initially larger but can | |
649 | improve performance when the image needs to grow. @code{falloc} and @code{full} | |
650 | preallocations are like the same options of @code{raw} format, but sets up | |
651 | metadata also. | |
3e032364 | 652 | |
d3067b02 KW |
653 | @item lazy_refcounts |
654 | If this option is set to @code{on}, reference count updates are postponed with | |
655 | the goal of avoiding metadata I/O and improving performance. This is | |
656 | particularly interesting with @option{cache=writethrough} which doesn't batch | |
657 | metadata updates. The tradeoff is that after a host crash, the reference count | |
658 | tables must be rebuilt, i.e. on the next open an (automatic) @code{qemu-img | |
659 | check -r all} is required, which may take some time. | |
3e032364 | 660 | |
d3067b02 | 661 | This option can only be enabled if @code{compat=1.1} is specified. |
f085800e | 662 | |
4ab15590 | 663 | @item nocow |
bc3a7f90 | 664 | If this option is set to @code{on}, it will turn off COW of the file. It's only |
4ab15590 CL |
665 | valid on btrfs, no effect on other file systems. |
666 | ||
667 | Btrfs has low performance when hosting a VM image file, even more when the guest | |
668 | on the VM also using btrfs as file system. Turning off COW is a way to mitigate | |
669 | this bad performance. Generally there are two ways to turn off COW on btrfs: | |
670 | a) Disable it by mounting with nodatacow, then all newly created files will be | |
671 | NOCOW. b) For an empty file, add the NOCOW file attribute. That's what this option | |
672 | does. | |
673 | ||
674 | Note: this option is only valid to new or empty files. If there is an existing | |
675 | file which is COW and has data blocks already, it couldn't be changed to NOCOW | |
676 | by setting @code{nocow=on}. One can issue @code{lsattr filename} to check if | |
bc3a7f90 | 677 | the NOCOW flag is set or not (Capital 'C' is NOCOW flag). |
4ab15590 | 678 | |
f085800e | 679 | @end table |
3e032364 | 680 | |
d3067b02 KW |
681 | @item Other |
682 | QEMU also supports various other image file formats for compatibility with | |
8282db1b JC |
683 | older QEMU versions or other hypervisors, including VMDK, VDI, VHD (vpc), VHDX, |
684 | qcow1 and QED. For a full list of supported formats see @code{qemu-img --help}. | |
d3067b02 KW |
685 | For a more detailed description of these formats, see the QEMU Emulation User |
686 | Documentation. | |
3e032364 | 687 | |
d3067b02 KW |
688 | The main purpose of the block drivers for these formats is image conversion. |
689 | For running VMs, it is recommended to convert the disk images to either raw or | |
690 | qcow2 in order to achieve good performance. | |
f932c040 KW |
691 | @end table |
692 | ||
693 | ||
acd935ef FB |
694 | @c man end |
695 | ||
acd935ef FB |
696 | @setfilename qemu-img |
697 | @settitle QEMU disk image utility | |
698 | ||
699 | @c man begin SEEALSO | |
700 | The HTML documentation of QEMU for more precise information and Linux | |
701 | user mode emulator invocation. | |
702 | @c man end | |
703 | ||
704 | @c man begin AUTHOR | |
705 | Fabrice Bellard | |
706 | @c man end | |
707 | ||
708 | @end ignore |