root / qemu-img.texi @ db895a1e
History | View | Annotate | Download (13.8 kB)
1 |
@example |
---|---|
2 |
@c man begin SYNOPSIS |
3 |
usage: qemu-img command [command options] |
4 |
@c man end |
5 |
@end example |
6 |
|
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 |
|
17 |
@c man begin OPTIONS |
18 |
|
19 |
The following commands are supported: |
20 |
|
21 |
@include qemu-img-cmds.texi |
22 |
|
23 |
Command parameters: |
24 |
@table @var |
25 |
@item filename |
26 |
is a disk image filename |
27 |
@item fmt |
28 |
is the disk image format. It is guessed automatically in most cases. See below |
29 |
for a description of the supported disk formats. |
30 |
|
31 |
@item --backing-chain |
32 |
will enumerate information about backing files in a disk image chain. Refer |
33 |
below for further description. |
34 |
|
35 |
@item size |
36 |
is the disk image size in bytes. Optional suffixes @code{k} or @code{K} |
37 |
(kilobyte, 1024) @code{M} (megabyte, 1024k) and @code{G} (gigabyte, 1024M) |
38 |
and T (terabyte, 1024G) are supported. @code{b} is ignored. |
39 |
|
40 |
@item output_filename |
41 |
is the destination disk image filename |
42 |
|
43 |
@item output_fmt |
44 |
is the destination format |
45 |
@item options |
46 |
is a comma separated list of format specific options in a |
47 |
name=value format. Use @code{-o ?} for an overview of the options supported |
48 |
by the used format or see the format descriptions below for details. |
49 |
|
50 |
|
51 |
@item -c |
52 |
indicates that target image must be compressed (qcow format only) |
53 |
@item -h |
54 |
with or without a command shows help and lists the supported formats |
55 |
@item -p |
56 |
display progress bar (convert and rebase commands only) |
57 |
@item -q |
58 |
Quiet mode - do not print any output (except errors). There's no progress bar |
59 |
in case both @var{-q} and @var{-p} options are used. |
60 |
@item -S @var{size} |
61 |
indicates the consecutive number of bytes that must contain only zeros |
62 |
for qemu-img to create a sparse image during conversion. This value is rounded |
63 |
down to the nearest 512 bytes. You may use the common size suffixes like |
64 |
@code{k} for kilobytes. |
65 |
@item -t @var{cache} |
66 |
specifies the cache mode that should be used with the (destination) file. See |
67 |
the documentation of the emulator's @code{-drive cache=...} option for allowed |
68 |
values. |
69 |
@end table |
70 |
|
71 |
Parameters to snapshot subcommand: |
72 |
|
73 |
@table @option |
74 |
|
75 |
@item snapshot |
76 |
is the name of the snapshot to create, apply or delete |
77 |
@item -a |
78 |
applies a snapshot (revert disk to saved state) |
79 |
@item -c |
80 |
creates a snapshot |
81 |
@item -d |
82 |
deletes a snapshot |
83 |
@item -l |
84 |
lists all snapshots in the given image |
85 |
@end table |
86 |
|
87 |
Parameters to compare subcommand: |
88 |
|
89 |
@table @option |
90 |
|
91 |
@item -f |
92 |
First image format |
93 |
@item -F |
94 |
Second image format |
95 |
@item -s |
96 |
Strict mode - fail on on different image size or sector allocation |
97 |
@end table |
98 |
|
99 |
Command description: |
100 |
|
101 |
@table @option |
102 |
@item check [-f @var{fmt}] [--output=@var{ofmt}] [-r [leaks | all]] @var{filename} |
103 |
|
104 |
Perform a consistency check on the disk image @var{filename}. The command can |
105 |
output in the format @var{ofmt} which is either @code{human} or @code{json}. |
106 |
|
107 |
If @code{-r} is specified, qemu-img tries to repair any inconsistencies found |
108 |
during the check. @code{-r leaks} repairs only cluster leaks, whereas |
109 |
@code{-r all} fixes all kinds of errors, with a higher risk of choosing the |
110 |
wrong fix or hiding corruption that has already occurred. |
111 |
|
112 |
Only the formats @code{qcow2}, @code{qed} and @code{vdi} support |
113 |
consistency checks. |
114 |
|
115 |
@item create [-f @var{fmt}] [-o @var{options}] @var{filename} [@var{size}] |
116 |
|
117 |
Create the new disk image @var{filename} of size @var{size} and format |
118 |
@var{fmt}. Depending on the file format, you can add one or more @var{options} |
119 |
that enable additional features of this format. |
120 |
|
121 |
If the option @var{backing_file} is specified, then the image will record |
122 |
only the differences from @var{backing_file}. No size needs to be specified in |
123 |
this case. @var{backing_file} will never be modified unless you use the |
124 |
@code{commit} monitor command (or qemu-img commit). |
125 |
|
126 |
The size can also be specified using the @var{size} option with @code{-o}, |
127 |
it doesn't need to be specified separately in this case. |
128 |
|
129 |
@item commit [-f @var{fmt}] [-t @var{cache}] @var{filename} |
130 |
|
131 |
Commit the changes recorded in @var{filename} in its base image. |
132 |
|
133 |
@item compare [-f @var{fmt}] [-F @var{fmt}] [-p] [-s] [-q] @var{filename1} @var{filename2} |
134 |
|
135 |
Check if two images have the same content. You can compare images with |
136 |
different format or settings. |
137 |
|
138 |
The format is probed unless you specify it by @var{-f} (used for |
139 |
@var{filename1}) and/or @var{-F} (used for @var{filename2}) option. |
140 |
|
141 |
By default, images with different size are considered identical if the larger |
142 |
image contains only unallocated and/or zeroed sectors in the area after the end |
143 |
of the other image. In addition, if any sector is not allocated in one image |
144 |
and contains only zero bytes in the second one, it is evaluated as equal. You |
145 |
can use Strict mode by specifying the @var{-s} option. When compare runs in |
146 |
Strict mode, it fails in case image size differs or a sector is allocated in |
147 |
one image and is not allocated in the second one. |
148 |
|
149 |
By default, compare prints out a result message. This message displays |
150 |
information that both images are same or the position of the first different |
151 |
byte. In addition, result message can report different image size in case |
152 |
Strict mode is used. |
153 |
|
154 |
Compare exits with @code{0} in case the images are equal and with @code{1} |
155 |
in case the images differ. Other exit codes mean an error occurred during |
156 |
execution and standard error output should contain an error message. |
157 |
The following table sumarizes all exit codes of the compare subcommand: |
158 |
|
159 |
@table @option |
160 |
|
161 |
@item 0 |
162 |
Images are identical |
163 |
@item 1 |
164 |
Images differ |
165 |
@item 2 |
166 |
Error on opening an image |
167 |
@item 3 |
168 |
Error on checking a sector allocation |
169 |
@item 4 |
170 |
Error on reading data |
171 |
|
172 |
@end table |
173 |
|
174 |
@item convert [-c] [-p] [-f @var{fmt}] [-t @var{cache}] [-O @var{output_fmt}] [-o @var{options}] [-s @var{snapshot_name}] [-S @var{sparse_size}] @var{filename} [@var{filename2} [...]] @var{output_filename} |
175 |
|
176 |
Convert the disk image @var{filename} or a snapshot @var{snapshot_name} to disk image @var{output_filename} |
177 |
using format @var{output_fmt}. It can be optionally compressed (@code{-c} |
178 |
option) or use any format specific options like encryption (@code{-o} option). |
179 |
|
180 |
Only the formats @code{qcow} and @code{qcow2} support compression. The |
181 |
compression is read-only. It means that if a compressed sector is |
182 |
rewritten, then it is rewritten as uncompressed data. |
183 |
|
184 |
Image conversion is also useful to get smaller image when using a |
185 |
growable format such as @code{qcow} or @code{cow}: the empty sectors |
186 |
are detected and suppressed from the destination image. |
187 |
|
188 |
You can use the @var{backing_file} option to force the output image to be |
189 |
created as a copy on write image of the specified base image; the |
190 |
@var{backing_file} should have the same content as the input's base image, |
191 |
however the path, image format, etc may differ. |
192 |
|
193 |
@item info [-f @var{fmt}] [--output=@var{ofmt}] [--backing-chain] @var{filename} |
194 |
|
195 |
Give information about the disk image @var{filename}. Use it in |
196 |
particular to know the size reserved on disk which can be different |
197 |
from the displayed size. If VM snapshots are stored in the disk image, |
198 |
they are displayed too. The command can output in the format @var{ofmt} |
199 |
which is either @code{human} or @code{json}. |
200 |
|
201 |
If a disk image has a backing file chain, information about each disk image in |
202 |
the chain can be recursively enumerated by using the option @code{--backing-chain}. |
203 |
|
204 |
For instance, if you have an image chain like: |
205 |
|
206 |
@example |
207 |
base.qcow2 <- snap1.qcow2 <- snap2.qcow2 |
208 |
@end example |
209 |
|
210 |
To enumerate information about each disk image in the above chain, starting from top to base, do: |
211 |
|
212 |
@example |
213 |
qemu-img info --backing-chain snap2.qcow2 |
214 |
@end example |
215 |
|
216 |
@item snapshot [-l | -a @var{snapshot} | -c @var{snapshot} | -d @var{snapshot} ] @var{filename} |
217 |
|
218 |
List, apply, create or delete snapshots in image @var{filename}. |
219 |
|
220 |
@item rebase [-f @var{fmt}] [-t @var{cache}] [-p] [-u] -b @var{backing_file} [-F @var{backing_fmt}] @var{filename} |
221 |
|
222 |
Changes the backing file of an image. Only the formats @code{qcow2} and |
223 |
@code{qed} support changing the backing file. |
224 |
|
225 |
The backing file is changed to @var{backing_file} and (if the image format of |
226 |
@var{filename} supports this) the backing file format is changed to |
227 |
@var{backing_fmt}. If @var{backing_file} is specified as ``'' (the empty |
228 |
string), then the image is rebased onto no backing file (i.e. it will exist |
229 |
independently of any backing file). |
230 |
|
231 |
There are two different modes in which @code{rebase} can operate: |
232 |
@table @option |
233 |
@item Safe mode |
234 |
This is the default mode and performs a real rebase operation. The new backing |
235 |
file may differ from the old one and qemu-img rebase will take care of keeping |
236 |
the guest-visible content of @var{filename} unchanged. |
237 |
|
238 |
In order to achieve this, any clusters that differ between @var{backing_file} |
239 |
and the old backing file of @var{filename} are merged into @var{filename} |
240 |
before actually changing the backing file. |
241 |
|
242 |
Note that the safe mode is an expensive operation, comparable to converting |
243 |
an image. It only works if the old backing file still exists. |
244 |
|
245 |
@item Unsafe mode |
246 |
qemu-img uses the unsafe mode if @code{-u} is specified. In this mode, only the |
247 |
backing file name and format of @var{filename} is changed without any checks |
248 |
on the file contents. The user must take care of specifying the correct new |
249 |
backing file, or the guest-visible content of the image will be corrupted. |
250 |
|
251 |
This mode is useful for renaming or moving the backing file to somewhere else. |
252 |
It can be used without an accessible old backing file, i.e. you can use it to |
253 |
fix an image whose backing file has already been moved/renamed. |
254 |
@end table |
255 |
|
256 |
You can use @code{rebase} to perform a ``diff'' operation on two |
257 |
disk images. This can be useful when you have copied or cloned |
258 |
a guest, and you want to get back to a thin image on top of a |
259 |
template or base image. |
260 |
|
261 |
Say that @code{base.img} has been cloned as @code{modified.img} by |
262 |
copying it, and that the @code{modified.img} guest has run so there |
263 |
are now some changes compared to @code{base.img}. To construct a thin |
264 |
image called @code{diff.qcow2} that contains just the differences, do: |
265 |
|
266 |
@example |
267 |
qemu-img create -f qcow2 -b modified.img diff.qcow2 |
268 |
qemu-img rebase -b base.img diff.qcow2 |
269 |
@end example |
270 |
|
271 |
At this point, @code{modified.img} can be discarded, since |
272 |
@code{base.img + diff.qcow2} contains the same information. |
273 |
|
274 |
@item resize @var{filename} [+ | -]@var{size} |
275 |
|
276 |
Change the disk image as if it had been created with @var{size}. |
277 |
|
278 |
Before using this command to shrink a disk image, you MUST use file system and |
279 |
partitioning tools inside the VM to reduce allocated file systems and partition |
280 |
sizes accordingly. Failure to do so will result in data loss! |
281 |
|
282 |
After using this command to grow a disk image, you must use file system and |
283 |
partitioning tools inside the VM to actually begin using the new space on the |
284 |
device. |
285 |
@end table |
286 |
@c man end |
287 |
|
288 |
@ignore |
289 |
@c man begin NOTES |
290 |
Supported image file formats: |
291 |
|
292 |
@table @option |
293 |
@item raw |
294 |
|
295 |
Raw disk image format (default). This format has the advantage of |
296 |
being simple and easily exportable to all other emulators. If your |
297 |
file system supports @emph{holes} (for example in ext2 or ext3 on |
298 |
Linux or NTFS on Windows), then only the written sectors will reserve |
299 |
space. Use @code{qemu-img info} to know the real size used by the |
300 |
image or @code{ls -ls} on Unix/Linux. |
301 |
|
302 |
@item qcow2 |
303 |
QEMU image format, the most versatile format. Use it to have smaller |
304 |
images (useful if your filesystem does not supports holes, for example |
305 |
on Windows), optional AES encryption, zlib based compression and |
306 |
support of multiple VM snapshots. |
307 |
|
308 |
Supported options: |
309 |
@table @code |
310 |
@item compat |
311 |
Determines the qcow2 version to use. @code{compat=0.10} uses the traditional |
312 |
image format that can be read by any QEMU since 0.10 (this is the default). |
313 |
@code{compat=1.1} enables image format extensions that only QEMU 1.1 and |
314 |
newer understand. Amongst others, this includes zero clusters, which allow |
315 |
efficient copy-on-read for sparse images. |
316 |
|
317 |
@item backing_file |
318 |
File name of a base image (see @option{create} subcommand) |
319 |
@item backing_fmt |
320 |
Image format of the base image |
321 |
@item encryption |
322 |
If this option is set to @code{on}, the image is encrypted. |
323 |
|
324 |
Encryption uses the AES format which is very secure (128 bit keys). Use |
325 |
a long password (16 characters) to get maximum protection. |
326 |
|
327 |
@item cluster_size |
328 |
Changes the qcow2 cluster size (must be between 512 and 2M). Smaller cluster |
329 |
sizes can improve the image file size whereas larger cluster sizes generally |
330 |
provide better performance. |
331 |
|
332 |
@item preallocation |
333 |
Preallocation mode (allowed values: off, metadata). An image with preallocated |
334 |
metadata is initially larger but can improve performance when the image needs |
335 |
to grow. |
336 |
|
337 |
@item lazy_refcounts |
338 |
If this option is set to @code{on}, reference count updates are postponed with |
339 |
the goal of avoiding metadata I/O and improving performance. This is |
340 |
particularly interesting with @option{cache=writethrough} which doesn't batch |
341 |
metadata updates. The tradeoff is that after a host crash, the reference count |
342 |
tables must be rebuilt, i.e. on the next open an (automatic) @code{qemu-img |
343 |
check -r all} is required, which may take some time. |
344 |
|
345 |
This option can only be enabled if @code{compat=1.1} is specified. |
346 |
|
347 |
@end table |
348 |
|
349 |
@item Other |
350 |
QEMU also supports various other image file formats for compatibility with |
351 |
older QEMU versions or other hypervisors, including VMDK, VDI, VHD (vpc), qcow1 |
352 |
and QED. For a full list of supported formats see @code{qemu-img --help}. |
353 |
For a more detailed description of these formats, see the QEMU Emulation User |
354 |
Documentation. |
355 |
|
356 |
The main purpose of the block drivers for these formats is image conversion. |
357 |
For running VMs, it is recommended to convert the disk images to either raw or |
358 |
qcow2 in order to achieve good performance. |
359 |
@end table |
360 |
|
361 |
|
362 |
@c man end |
363 |
|
364 |
@setfilename qemu-img |
365 |
@settitle QEMU disk image utility |
366 |
|
367 |
@c man begin SEEALSO |
368 |
The HTML documentation of QEMU for more precise information and Linux |
369 |
user mode emulator invocation. |
370 |
@c man end |
371 |
|
372 |
@c man begin AUTHOR |
373 |
Fabrice Bellard |
374 |
@c man end |
375 |
|
376 |
@end ignore |