1======================= 2QEMU disk image utility 3======================= 4 5Synopsis 6-------- 7 8**qemu-img** [*standard options*] *command* [*command options*] 9 10Description 11----------- 12 13qemu-img allows you to create, convert and modify images offline. It can handle 14all image formats supported by QEMU. 15 16**Warning:** Never use qemu-img to modify images in use by a running virtual 17machine or any other process; this may destroy the image. Also, be aware that 18querying an image that is being modified by another process may encounter 19inconsistent state. 20 21Options 22------- 23 24.. program:: qemu-img 25 26Standard options: 27 28.. option:: -h, --help 29 30 Display this help and exit 31 32.. option:: -V, --version 33 34 Display version information and exit 35 36.. option:: -T, --trace [[enable=]PATTERN][,events=FILE][,file=FILE] 37 38 .. include:: ../qemu-option-trace.rst.inc 39 40The following commands are supported: 41 42.. hxtool-doc:: qemu-img-cmds.hx 43 44Command parameters: 45 46*FILENAME* is a disk image filename. 47 48*FMT* is the disk image format. It is guessed automatically in most 49cases. See below for a description of the supported disk formats. 50 51*SIZE* is the disk image size in bytes. Optional suffixes ``k`` or 52``K`` (kilobyte, 1024) ``M`` (megabyte, 1024k) and ``G`` (gigabyte, 531024M) and T (terabyte, 1024G) are supported. ``b`` is ignored. 54 55*OUTPUT_FILENAME* is the destination disk image filename. 56 57*OUTPUT_FMT* is the destination format. 58 59*OPTIONS* is a comma separated list of format specific options in a 60name=value format. Use ``-o help`` for an overview of the options supported 61by the used format or see the format descriptions below for details. 62 63*SNAPSHOT_PARAM* is param used for internal snapshot, format is 64'snapshot.id=[ID],snapshot.name=[NAME]' or '[ID_OR_NAME]'. 65 66.. 67 Note the use of a new 'program'; otherwise Sphinx complains about 68 the -h option appearing both in the above option list and this one. 69 70.. program:: qemu-img-common-opts 71 72.. option:: --object OBJECTDEF 73 74 is a QEMU user creatable object definition. See the :manpage:`qemu(1)` 75 manual page for a description of the object properties. The most common 76 object type is a ``secret``, which is used to supply passwords and/or 77 encryption keys. 78 79.. option:: --image-opts 80 81 Indicates that the source *FILENAME* parameter is to be interpreted as a 82 full option string, not a plain filename. This parameter is mutually 83 exclusive with the *-f* parameter. 84 85.. option:: --target-image-opts 86 87 Indicates that the OUTPUT_FILENAME parameter(s) are to be interpreted as 88 a full option string, not a plain filename. This parameter is mutually 89 exclusive with the *-O* parameters. It is currently required to also use 90 the *-n* parameter to skip image creation. This restriction may be relaxed 91 in a future release. 92 93.. option:: --force-share (-U) 94 95 If specified, ``qemu-img`` will open the image in shared mode, allowing 96 other QEMU processes to open it in write mode. For example, this can be used to 97 get the image information (with 'info' subcommand) when the image is used by a 98 running guest. Note that this could produce inconsistent results because of 99 concurrent metadata changes, etc. This option is only allowed when opening 100 images in read-only mode. 101 102.. option:: --backing-chain 103 104 Will enumerate information about backing files in a disk image chain. Refer 105 below for further description. 106 107.. option:: -c 108 109 Indicates that target image must be compressed (qcow/qcow2 and vmdk with 110 streamOptimized subformat only). 111 112 For qcow2, the compression algorithm can be specified with the ``-o 113 compression_type=...`` option (see below). 114 115.. option:: -h 116 117 With or without a command, shows help and lists the supported formats. 118 119.. option:: -p 120 121 Display progress bar (compare, convert and rebase commands only). 122 If the *-p* option is not used for a command that supports it, the 123 progress is reported when the process receives a ``SIGUSR1`` or 124 ``SIGINFO`` signal. 125 126.. option:: -q 127 128 Quiet mode - do not print any output (except errors). There's no progress bar 129 in case both *-q* and *-p* options are used. 130 131.. option:: -S SIZE 132 133 Indicates the consecutive number of bytes that must contain only zeros 134 for ``qemu-img`` to create a sparse image during conversion. This value is 135 rounded down to the nearest 512 bytes. You may use the common size suffixes 136 like ``k`` for kilobytes. 137 138.. option:: -t CACHE 139 140 Specifies the cache mode that should be used with the (destination) file. See 141 the documentation of the emulator's ``-drive cache=...`` option for allowed 142 values. 143 144.. option:: -T SRC_CACHE 145 146 Specifies the cache mode that should be used with the source file(s). See 147 the documentation of the emulator's ``-drive cache=...`` option for allowed 148 values. 149 150Parameters to compare subcommand: 151 152.. program:: qemu-img-compare 153 154.. option:: -f 155 156 First image format 157 158.. option:: -F 159 160 Second image format 161 162.. option:: -s 163 164 Strict mode - fail on different image size or sector allocation 165 166Parameters to convert subcommand: 167 168.. program:: qemu-img-convert 169 170.. option:: --bitmaps 171 172 Additionally copy all persistent bitmaps from the top layer of the source 173 174.. option:: -n 175 176 Skip the creation of the target volume 177 178.. option:: -m 179 180 Number of parallel coroutines for the convert process 181 182.. option:: -W 183 184 Allow out-of-order writes to the destination. This option improves performance, 185 but is only recommended for preallocated devices like host devices or other 186 raw block devices. 187 188.. option:: -C 189 190 Try to use copy offloading to move data from source image to target. This may 191 improve performance if the data is remote, such as with NFS or iSCSI backends, 192 but will not automatically sparsify zero sectors, and may result in a fully 193 allocated target image depending on the host support for getting allocation 194 information. 195 196.. option:: -r 197 198 Rate limit for the convert process 199 200.. option:: --salvage 201 202 Try to ignore I/O errors when reading. Unless in quiet mode (``-q``), errors 203 will still be printed. Areas that cannot be read from the source will be 204 treated as containing only zeroes. 205 206.. option:: --target-is-zero 207 208 Assume that reading the destination image will always return 209 zeros. This parameter is mutually exclusive with a destination image 210 that has a backing file. It is required to also use the ``-n`` 211 parameter to skip image creation. 212 213Parameters to dd subcommand: 214 215.. program:: qemu-img-dd 216 217.. option:: bs=BLOCK_SIZE 218 219 Defines the block size 220 221.. option:: count=BLOCKS 222 223 Sets the number of input blocks to copy 224 225.. option:: if=INPUT 226 227 Sets the input file 228 229.. option:: of=OUTPUT 230 231 Sets the output file 232 233.. option:: skip=BLOCKS 234 235 Sets the number of input blocks to skip 236 237Parameters to snapshot subcommand: 238 239.. program:: qemu-img-snapshot 240 241.. option:: snapshot 242 243 Is the name of the snapshot to create, apply or delete 244 245.. option:: -a 246 247 Applies a snapshot (revert disk to saved state) 248 249.. option:: -c 250 251 Creates a snapshot 252 253.. option:: -d 254 255 Deletes a snapshot 256 257.. option:: -l 258 259 Lists all snapshots in the given image 260 261Command description: 262 263.. program:: qemu-img-commands 264 265.. option:: amend [--object OBJECTDEF] [--image-opts] [-p] [-q] [-f FMT] [-t CACHE] [--force] -o OPTIONS FILENAME 266 267 Amends the image format specific *OPTIONS* for the image file 268 *FILENAME*. Not all file formats support this operation. 269 270 The set of options that can be amended are dependent on the image 271 format, but note that amending the backing chain relationship should 272 instead be performed with ``qemu-img rebase``. 273 274 --force allows some unsafe operations. Currently for -f luks, it allows to 275 erase the last encryption key, and to overwrite an active encryption key. 276 277.. option:: bench [-c COUNT] [-d DEPTH] [-f FMT] [--flush-interval=FLUSH_INTERVAL] [-i AIO] [-n] [--no-drain] [-o OFFSET] [--pattern=PATTERN] [-q] [-s BUFFER_SIZE] [-S STEP_SIZE] [-t CACHE] [-w] [-U] FILENAME 278 279 Run a simple sequential I/O benchmark on the specified image. If ``-w`` is 280 specified, a write test is performed, otherwise a read test is performed. 281 282 A total number of *COUNT* I/O requests is performed, each *BUFFER_SIZE* 283 bytes in size, and with *DEPTH* requests in parallel. The first request 284 starts at the position given by *OFFSET*, each following request increases 285 the current position by *STEP_SIZE*. If *STEP_SIZE* is not given, 286 *BUFFER_SIZE* is used for its value. 287 288 If *FLUSH_INTERVAL* is specified for a write test, the request queue is 289 drained and a flush is issued before new writes are made whenever the number of 290 remaining requests is a multiple of *FLUSH_INTERVAL*. If additionally 291 ``--no-drain`` is specified, a flush is issued without draining the request 292 queue first. 293 294 if ``-i`` is specified, *AIO* option can be used to specify different 295 AIO backends: ``threads``, ``native`` or ``io_uring``. 296 297 If ``-n`` is specified, the native AIO backend is used if possible. On 298 Linux, this option only works if ``-t none`` or ``-t directsync`` is 299 specified as well. 300 301 For write tests, by default a buffer filled with zeros is written. This can be 302 overridden with a pattern byte specified by *PATTERN*. 303 304.. option:: bitmap (--merge SOURCE | --add | --remove | --clear | --enable | --disable)... [-b SOURCE_FILE [-F SOURCE_FMT]] [-g GRANULARITY] [--object OBJECTDEF] [--image-opts | -f FMT] FILENAME BITMAP 305 306 Perform one or more modifications of the persistent bitmap *BITMAP* 307 in the disk image *FILENAME*. The various modifications are: 308 309 ``--add`` to create *BITMAP*, enabled to record future edits. 310 311 ``--remove`` to remove *BITMAP*. 312 313 ``--clear`` to clear *BITMAP*. 314 315 ``--enable`` to change *BITMAP* to start recording future edits. 316 317 ``--disable`` to change *BITMAP* to stop recording future edits. 318 319 ``--merge`` to merge the contents of the *SOURCE* bitmap into *BITMAP*. 320 321 Additional options include ``-g`` which sets a non-default 322 *GRANULARITY* for ``--add``, and ``-b`` and ``-F`` which select an 323 alternative source file for all *SOURCE* bitmaps used by 324 ``--merge``. 325 326 To see what bitmaps are present in an image, use ``qemu-img info``. 327 328.. option:: check [--object OBJECTDEF] [--image-opts] [-q] [-f FMT] [--output=OFMT] [-r [leaks | all]] [-T SRC_CACHE] [-U] FILENAME 329 330 Perform a consistency check on the disk image *FILENAME*. The command can 331 output in the format *OFMT* which is either ``human`` or ``json``. 332 The JSON output is an object of QAPI type ``ImageCheck``. 333 334 If ``-r`` is specified, qemu-img tries to repair any inconsistencies found 335 during the check. ``-r leaks`` repairs only cluster leaks, whereas 336 ``-r all`` fixes all kinds of errors, with a higher risk of choosing the 337 wrong fix or hiding corruption that has already occurred. 338 339 Only the formats ``qcow2``, ``qed``, ``parallels``, ``vhdx``, ``vmdk`` and 340 ``vdi`` support consistency checks. 341 342 In case the image does not have any inconsistencies, check exits with ``0``. 343 Other exit codes indicate the kind of inconsistency found or if another error 344 occurred. The following table summarizes all exit codes of the check subcommand: 345 346 0 347 Check completed, the image is (now) consistent 348 1 349 Check not completed because of internal errors 350 2 351 Check completed, image is corrupted 352 3 353 Check completed, image has leaked clusters, but is not corrupted 354 63 355 Checks are not supported by the image format 356 357 If ``-r`` is specified, exit codes representing the image state refer to the 358 state after (the attempt at) repairing it. That is, a successful ``-r all`` 359 will yield the exit code 0, independently of the image state before. 360 361.. option:: commit [--object OBJECTDEF] [--image-opts] [-q] [-f FMT] [-t CACHE] [-b BASE] [-r RATE_LIMIT] [-d] [-p] FILENAME 362 363 Commit the changes recorded in *FILENAME* in its base image or backing file. 364 If the backing file is smaller than the snapshot, then the backing file will be 365 resized to be the same size as the snapshot. If the snapshot is smaller than 366 the backing file, the backing file will not be truncated. If you want the 367 backing file to match the size of the smaller snapshot, you can safely truncate 368 it yourself once the commit operation successfully completes. 369 370 The image *FILENAME* is emptied after the operation has succeeded. If you do 371 not need *FILENAME* afterwards and intend to drop it, you may skip emptying 372 *FILENAME* by specifying the ``-d`` flag. 373 374 If the backing chain of the given image file *FILENAME* has more than one 375 layer, the backing file into which the changes will be committed may be 376 specified as *BASE* (which has to be part of *FILENAME*'s backing 377 chain). If *BASE* is not specified, the immediate backing file of the top 378 image (which is *FILENAME*) will be used. Note that after a commit operation 379 all images between *BASE* and the top image will be invalid and may return 380 garbage data when read. For this reason, ``-b`` implies ``-d`` (so that 381 the top image stays valid). 382 383 The rate limit for the commit process is specified by ``-r``. 384 385.. option:: compare [--object OBJECTDEF] [--image-opts] [-f FMT] [-F FMT] [-T SRC_CACHE] [-p] [-q] [-s] [-U] FILENAME1 FILENAME2 386 387 Check if two images have the same content. You can compare images with 388 different format or settings. 389 390 The format is probed unless you specify it by ``-f`` (used for 391 *FILENAME1*) and/or ``-F`` (used for *FILENAME2*) option. 392 393 By default, images with different size are considered identical if the larger 394 image contains only unallocated and/or zeroed sectors in the area after the end 395 of the other image. In addition, if any sector is not allocated in one image 396 and contains only zero bytes in the second one, it is evaluated as equal. You 397 can use Strict mode by specifying the ``-s`` option. When compare runs in 398 Strict mode, it fails in case image size differs or a sector is allocated in 399 one image and is not allocated in the second one. 400 401 By default, compare prints out a result message. This message displays 402 information that both images are same or the position of the first different 403 byte. In addition, result message can report different image size in case 404 Strict mode is used. 405 406 Compare exits with ``0`` in case the images are equal and with ``1`` 407 in case the images differ. Other exit codes mean an error occurred during 408 execution and standard error output should contain an error message. 409 The following table summarizes all exit codes of the compare subcommand: 410 411 0 412 Images are identical (or requested help was printed) 413 1 414 Images differ 415 2 416 Error on opening an image 417 3 418 Error on checking a sector allocation 419 4 420 Error on reading data 421 422.. option:: convert [--object OBJECTDEF] [--image-opts] [--target-image-opts] [--target-is-zero] [--bitmaps [--skip-broken-bitmaps]] [-U] [-C] [-c] [-p] [-q] [-n] [-f FMT] [-t CACHE] [-T SRC_CACHE] [-O OUTPUT_FMT] [-B BACKING_FILE [-F BACKING_FMT]] [-o OPTIONS] [-l SNAPSHOT_PARAM] [-S SPARSE_SIZE] [-r RATE_LIMIT] [-m NUM_COROUTINES] [-W] FILENAME [FILENAME2 [...]] OUTPUT_FILENAME 423 424 Convert the disk image *FILENAME* or a snapshot *SNAPSHOT_PARAM* 425 to disk image *OUTPUT_FILENAME* using format *OUTPUT_FMT*. It can 426 be optionally compressed (``-c`` option) or use any format specific 427 options like encryption (``-o`` option). 428 429 Only the formats ``qcow`` and ``qcow2`` support compression. The 430 compression is read-only. It means that if a compressed sector is 431 rewritten, then it is rewritten as uncompressed data. 432 433 Image conversion is also useful to get smaller image when using a 434 growable format such as ``qcow``: the empty sectors are detected and 435 suppressed from the destination image. 436 437 *SPARSE_SIZE* indicates the consecutive number of bytes (defaults to 4k) 438 that must contain only zeros for ``qemu-img`` to create a sparse image during 439 conversion. If *SPARSE_SIZE* is 0, the source will not be scanned for 440 unallocated or zero sectors, and the destination image will always be 441 fully allocated. 442 443 You can use the *BACKING_FILE* option to force the output image to be 444 created as a copy on write image of the specified base image; the 445 *BACKING_FILE* should have the same content as the input's base image, 446 however the path, image format (as given by *BACKING_FMT*), etc may differ. 447 448 If a relative path name is given, the backing file is looked up relative to 449 the directory containing *OUTPUT_FILENAME*. 450 451 If the ``-n`` option is specified, the target volume creation will be 452 skipped. This is useful for formats such as ``rbd`` if the target 453 volume has already been created with site specific options that cannot 454 be supplied through ``qemu-img``. 455 456 Out of order writes can be enabled with ``-W`` to improve performance. 457 This is only recommended for preallocated devices like host devices or other 458 raw block devices. Out of order write does not work in combination with 459 creating compressed images. 460 461 *NUM_COROUTINES* specifies how many coroutines work in parallel during 462 the convert process (defaults to 8). 463 464 Use of ``--bitmaps`` requests that any persistent bitmaps present in 465 the original are also copied to the destination. If any bitmap is 466 inconsistent in the source, the conversion will fail unless 467 ``--skip-broken-bitmaps`` is also specified to copy only the 468 consistent bitmaps. 469 470.. option:: create [--object OBJECTDEF] [-q] [-f FMT] [-b BACKING_FILE [-F BACKING_FMT]] [-u] [-o OPTIONS] FILENAME [SIZE] 471 472 Create the new disk image *FILENAME* of size *SIZE* and format 473 *FMT*. Depending on the file format, you can add one or more *OPTIONS* 474 that enable additional features of this format. 475 476 If the option *BACKING_FILE* is specified, then the image will record 477 only the differences from *BACKING_FILE*. No size needs to be specified in 478 this case. *BACKING_FILE* will never be modified unless you use the 479 ``commit`` monitor command (or ``qemu-img commit``). 480 481 If a relative path name is given, the backing file is looked up relative to 482 the directory containing *FILENAME*. 483 484 Note that a given backing file will be opened to check that it is valid. Use 485 the ``-u`` option to enable unsafe backing file mode, which means that the 486 image will be created even if the associated backing file cannot be opened. A 487 matching backing file must be created or additional options be used to make the 488 backing file specification valid when you want to use an image created this 489 way. 490 491 The size can also be specified using the *SIZE* option with ``-o``, 492 it doesn't need to be specified separately in this case. 493 494 495.. option:: dd [--image-opts] [-U] [-f FMT] [-O OUTPUT_FMT] [bs=BLOCK_SIZE] [count=BLOCKS] [skip=BLOCKS] if=INPUT of=OUTPUT 496 497 dd copies from *INPUT* file to *OUTPUT* file converting it from 498 *FMT* format to *OUTPUT_FMT* format. 499 500 The data is by default read and written using blocks of 512 bytes but can be 501 modified by specifying *BLOCK_SIZE*. If count=\ *BLOCKS* is specified 502 dd will stop reading input after reading *BLOCKS* input blocks. 503 504 The size syntax is similar to :manpage:`dd(1)`'s size syntax. 505 506.. option:: info [--object OBJECTDEF] [--image-opts] [-f FMT] [--output=OFMT] [--backing-chain] [-U] FILENAME 507 508 Give information about the disk image *FILENAME*. Use it in 509 particular to know the size reserved on disk which can be different 510 from the displayed size. If VM snapshots are stored in the disk image, 511 they are displayed too. 512 513 If a disk image has a backing file chain, information about each disk image in 514 the chain can be recursively enumerated by using the option ``--backing-chain``. 515 516 For instance, if you have an image chain like: 517 518 :: 519 520 base.qcow2 <- snap1.qcow2 <- snap2.qcow2 521 522 To enumerate information about each disk image in the above chain, starting from top to base, do: 523 524 :: 525 526 qemu-img info --backing-chain snap2.qcow2 527 528 The command can output in the format *OFMT* which is either ``human`` or 529 ``json``. The JSON output is an object of QAPI type ``ImageInfo``; with 530 ``--backing-chain``, it is an array of ``ImageInfo`` objects. 531 532 ``--output=human`` reports the following information (for every image in the 533 chain): 534 535 *image* 536 The image file name 537 538 *file format* 539 The image format 540 541 *virtual size* 542 The size of the guest disk 543 544 *disk size* 545 How much space the image file occupies on the host file system (may be 546 shown as 0 if this information is unavailable, e.g. because there is no 547 file system) 548 549 *cluster_size* 550 Cluster size of the image format, if applicable 551 552 *encrypted* 553 Whether the image is encrypted (only present if so) 554 555 *cleanly shut down* 556 This is shown as ``no`` if the image is dirty and will have to be 557 auto-repaired the next time it is opened in qemu. 558 559 *backing file* 560 The backing file name, if present 561 562 *backing file format* 563 The format of the backing file, if the image enforces it 564 565 *Snapshot list* 566 A list of all internal snapshots 567 568 *Format specific information* 569 Further information whose structure depends on the image format. This 570 section is a textual representation of the respective 571 ``ImageInfoSpecific*`` QAPI object (e.g. ``ImageInfoSpecificQCow2`` 572 for qcow2 images). 573 574.. option:: map [--object OBJECTDEF] [--image-opts] [-f FMT] [--start-offset=OFFSET] [--max-length=LEN] [--output=OFMT] [-U] FILENAME 575 576 Dump the metadata of image *FILENAME* and its backing file chain. 577 In particular, this commands dumps the allocation state of every sector 578 of *FILENAME*, together with the topmost file that allocates it in 579 the backing file chain. 580 581 Two option formats are possible. The default format (``human``) 582 only dumps known-nonzero areas of the file. Known-zero parts of the 583 file are omitted altogether, and likewise for parts that are not allocated 584 throughout the chain. ``qemu-img`` output will identify a file 585 from where the data can be read, and the offset in the file. Each line 586 will include four fields, the first three of which are hexadecimal 587 numbers. For example the first line of: 588 589 :: 590 591 Offset Length Mapped to File 592 0 0x20000 0x50000 /tmp/overlay.qcow2 593 0x100000 0x10000 0x95380000 /tmp/backing.qcow2 594 595 means that 0x20000 (131072) bytes starting at offset 0 in the image are 596 available in /tmp/overlay.qcow2 (opened in ``raw`` format) starting 597 at offset 0x50000 (327680). Data that is compressed, encrypted, or 598 otherwise not available in raw format will cause an error if ``human`` 599 format is in use. Note that file names can include newlines, thus it is 600 not safe to parse this output format in scripts. 601 602 The alternative format ``json`` will return an array of dictionaries 603 in JSON format. It will include similar information in 604 the ``start``, ``length``, ``offset`` fields; 605 it will also include other more specific information: 606 607 - boolean field ``data``: true if the sectors contain actual data, 608 false if the sectors are either unallocated or stored as optimized 609 all-zero clusters 610 - boolean field ``zero``: true if the data is known to read as zero 611 - boolean field ``present``: true if the data belongs to the backing 612 chain, false if rebasing the backing chain onto a deeper file 613 would pick up data from the deeper file; 614 - integer field ``depth``: the depth within the backing chain at 615 which the data was resolved; for example, a depth of 2 refers to 616 the backing file of the backing file of *FILENAME*. 617 618 In JSON format, the ``offset`` field is optional; it is absent in 619 cases where ``human`` format would omit the entry or exit with an error. 620 If ``data`` is false and the ``offset`` field is present, the 621 corresponding sectors in the file are not yet in use, but they are 622 preallocated. 623 624 For more information, consult ``include/block/block.h`` in QEMU's 625 source code. 626 627.. option:: measure [--output=OFMT] [-O OUTPUT_FMT] [-o OPTIONS] [--size N | [--object OBJECTDEF] [--image-opts] [-f FMT] [-l SNAPSHOT_PARAM] FILENAME] 628 629 Calculate the file size required for a new image. This information 630 can be used to size logical volumes or SAN LUNs appropriately for 631 the image that will be placed in them. The values reported are 632 guaranteed to be large enough to fit the image. The command can 633 output in the format *OFMT* which is either ``human`` or ``json``. 634 The JSON output is an object of QAPI type ``BlockMeasureInfo``. 635 636 If the size *N* is given then act as if creating a new empty image file 637 using ``qemu-img create``. If *FILENAME* is given then act as if 638 converting an existing image file using ``qemu-img convert``. The format 639 of the new file is given by *OUTPUT_FMT* while the format of an existing 640 file is given by *FMT*. 641 642 A snapshot in an existing image can be specified using *SNAPSHOT_PARAM*. 643 644 The following fields are reported: 645 646 :: 647 648 required size: 524288 649 fully allocated size: 1074069504 650 bitmaps size: 0 651 652 The ``required size`` is the file size of the new image. It may be smaller 653 than the virtual disk size if the image format supports compact representation. 654 655 The ``fully allocated size`` is the file size of the new image once data has 656 been written to all sectors. This is the maximum size that the image file can 657 occupy with the exception of internal snapshots, dirty bitmaps, vmstate data, 658 and other advanced image format features. 659 660 The ``bitmaps size`` is the additional size required in order to 661 copy bitmaps from a source image in addition to the guest-visible 662 data; the line is omitted if either source or destination lacks 663 bitmap support, or 0 if bitmaps are supported but there is nothing 664 to copy. 665 666.. option:: snapshot [--object OBJECTDEF] [--image-opts] [-U] [-q] [-l | -a SNAPSHOT | -c SNAPSHOT | -d SNAPSHOT] FILENAME 667 668 List, apply, create or delete snapshots in image *FILENAME*. 669 670.. option:: rebase [--object OBJECTDEF] [--image-opts] [-U] [-q] [-f FMT] [-t CACHE] [-T SRC_CACHE] [-p] [-u] [-c] -b BACKING_FILE [-F BACKING_FMT] FILENAME 671 672 Changes the backing file of an image. Only the formats ``qcow2`` and 673 ``qed`` support changing the backing file. 674 675 The backing file is changed to *BACKING_FILE* and (if the image format of 676 *FILENAME* supports this) the backing file format is changed to 677 *BACKING_FMT*. If *BACKING_FILE* is specified as "" (the empty 678 string), then the image is rebased onto no backing file (i.e. it will exist 679 independently of any backing file). 680 681 If a relative path name is given, the backing file is looked up relative to 682 the directory containing *FILENAME*. 683 684 *CACHE* specifies the cache mode to be used for *FILENAME*, whereas 685 *SRC_CACHE* specifies the cache mode for reading backing files. 686 687 There are two different modes in which ``rebase`` can operate: 688 689 Safe mode 690 This is the default mode and performs a real rebase operation. The 691 new backing file may differ from the old one and ``qemu-img rebase`` 692 will take care of keeping the guest-visible content of *FILENAME* 693 unchanged. 694 695 In order to achieve this, any clusters that differ between 696 *BACKING_FILE* and the old backing file of *FILENAME* are merged 697 into *FILENAME* before actually changing the backing file. With the 698 ``-c`` option specified, the clusters which are being merged (but not 699 the entire *FILENAME* image) are compressed when written. 700 701 Note that the safe mode is an expensive operation, comparable to 702 converting an image. It only works if the old backing file still 703 exists. 704 705 Unsafe mode 706 ``qemu-img`` uses the unsafe mode if ``-u`` is specified. In this 707 mode, only the backing file name and format of *FILENAME* is changed 708 without any checks on the file contents. The user must take care of 709 specifying the correct new backing file, or the guest-visible 710 content of the image will be corrupted. 711 712 This mode is useful for renaming or moving the backing file to 713 somewhere else. It can be used without an accessible old backing 714 file, i.e. you can use it to fix an image whose backing file has 715 already been moved/renamed. 716 717 You can use ``rebase`` to perform a "diff" operation on two 718 disk images. This can be useful when you have copied or cloned 719 a guest, and you want to get back to a thin image on top of a 720 template or base image. 721 722 Say that ``base.img`` has been cloned as ``modified.img`` by 723 copying it, and that the ``modified.img`` guest has run so there 724 are now some changes compared to ``base.img``. To construct a thin 725 image called ``diff.qcow2`` that contains just the differences, do: 726 727 :: 728 729 qemu-img create -f qcow2 -b modified.img diff.qcow2 730 qemu-img rebase -b base.img diff.qcow2 731 732 At this point, ``modified.img`` can be discarded, since 733 ``base.img + diff.qcow2`` contains the same information. 734 735.. option:: resize [--object OBJECTDEF] [--image-opts] [-f FMT] [--preallocation=PREALLOC] [-q] [--shrink] FILENAME [+ | -]SIZE 736 737 Change the disk image as if it had been created with *SIZE*. 738 739 Before using this command to shrink a disk image, you MUST use file system and 740 partitioning tools inside the VM to reduce allocated file systems and partition 741 sizes accordingly. Failure to do so will result in data loss! 742 743 When shrinking images, the ``--shrink`` option must be given. This informs 744 ``qemu-img`` that the user acknowledges all loss of data beyond the truncated 745 image's end. 746 747 After using this command to grow a disk image, you must use file system and 748 partitioning tools inside the VM to actually begin using the new space on the 749 device. 750 751 When growing an image, the ``--preallocation`` option may be used to specify 752 how the additional image area should be allocated on the host. See the format 753 description in the :ref:`notes` section which values are allowed. Using this 754 option may result in slightly more data being allocated than necessary. 755 756.. _notes: 757 758Notes 759----- 760 761Supported image file formats: 762 763``raw`` 764 765 Raw disk image format (default). This format has the advantage of 766 being simple and easily exportable to all other emulators. If your 767 file system supports *holes* (for example in ext2 or ext3 on 768 Linux or NTFS on Windows), then only the written sectors will reserve 769 space. Use ``qemu-img info`` to know the real size used by the 770 image or ``ls -ls`` on Unix/Linux. 771 772 Supported options: 773 774 ``preallocation`` 775 Preallocation mode (allowed values: ``off``, ``falloc``, 776 ``full``). ``falloc`` mode preallocates space for image by 777 calling ``posix_fallocate()``. ``full`` mode preallocates space 778 for image by writing data to underlying storage. This data may or 779 may not be zero, depending on the storage location. 780 781``qcow2`` 782 783 QEMU image format, the most versatile format. Use it to have smaller 784 images (useful if your filesystem does not supports holes, for example 785 on Windows), optional AES encryption, zlib or zstd based compression and 786 support of multiple VM snapshots. 787 788 Supported options: 789 790 ``compat`` 791 Determines the qcow2 version to use. ``compat=0.10`` uses the 792 traditional image format that can be read by any QEMU since 0.10. 793 ``compat=1.1`` enables image format extensions that only QEMU 1.1 and 794 newer understand (this is the default). Amongst others, this includes zero 795 clusters, which allow efficient copy-on-read for sparse images. 796 797 ``backing_file`` 798 File name of a base image (see ``create`` subcommand) 799 800 ``backing_fmt`` 801 Image format of the base image 802 803 ``compression_type`` 804 This option configures which compression algorithm will be used for 805 compressed clusters on the image. Note that setting this option doesn't yet 806 cause the image to actually receive compressed writes. It is most commonly 807 used with the ``-c`` option of ``qemu-img convert``, but can also be used 808 with the ``compress`` filter driver or backup block jobs with compression 809 enabled. 810 811 Valid values are ``zlib`` and ``zstd``. For images that use 812 ``compat=0.10``, only ``zlib`` compression is available. 813 814 ``encryption`` 815 If this option is set to ``on``, the image is encrypted with 816 128-bit AES-CBC. 817 818 The use of encryption in qcow and qcow2 images is considered to be 819 flawed by modern cryptography standards, suffering from a number 820 of design problems: 821 822 - The AES-CBC cipher is used with predictable initialization 823 vectors based on the sector number. This makes it vulnerable to 824 chosen plaintext attacks which can reveal the existence of 825 encrypted data. 826 827 - The user passphrase is directly used as the encryption key. A 828 poorly chosen or short passphrase will compromise the security 829 of the encryption. 830 831 - In the event of the passphrase being compromised there is no way 832 to change the passphrase to protect data in any qcow images. The 833 files must be cloned, using a different encryption passphrase in 834 the new file. The original file must then be securely erased 835 using a program like shred, though even this is ineffective with 836 many modern storage technologies. 837 838 - Initialization vectors used to encrypt sectors are based on the 839 guest virtual sector number, instead of the host physical 840 sector. When a disk image has multiple internal snapshots this 841 means that data in multiple physical sectors is encrypted with 842 the same initialization vector. With the CBC mode, this opens 843 the possibility of watermarking attacks if the attack can 844 collect multiple sectors encrypted with the same IV and some 845 predictable data. Having multiple qcow2 images with the same 846 passphrase also exposes this weakness since the passphrase is 847 directly used as the key. 848 849 Use of qcow / qcow2 encryption is thus strongly discouraged. Users are 850 recommended to use an alternative encryption technology such as the 851 Linux dm-crypt / LUKS system. 852 853 ``cluster_size`` 854 Changes the qcow2 cluster size (must be between 512 and 855 2M). Smaller cluster sizes can improve the image file size whereas 856 larger cluster sizes generally provide better performance. 857 858 ``preallocation`` 859 Preallocation mode (allowed values: ``off``, ``metadata``, 860 ``falloc``, ``full``). An image with preallocated metadata is 861 initially larger but can improve performance when the image needs 862 to grow. ``falloc`` and ``full`` preallocations are like the same 863 options of ``raw`` format, but sets up metadata also. 864 865 ``lazy_refcounts`` 866 If this option is set to ``on``, reference count updates are 867 postponed with the goal of avoiding metadata I/O and improving 868 performance. This is particularly interesting with 869 ``cache=writethrough`` which doesn't batch metadata 870 updates. The tradeoff is that after a host crash, the reference 871 count tables must be rebuilt, i.e. on the next open an (automatic) 872 ``qemu-img check -r all`` is required, which may take some time. 873 874 This option can only be enabled if ``compat=1.1`` is specified. 875 876 ``nocow`` 877 If this option is set to ``on``, it will turn off COW of the file. It's 878 only valid on btrfs, no effect on other file systems. 879 880 Btrfs has low performance when hosting a VM image file, even more 881 when the guest on the VM also using btrfs as file system. Turning 882 off COW is a way to mitigate this bad performance. Generally there 883 are two ways to turn off COW on btrfs: 884 885 - Disable it by mounting with nodatacow, then all newly created files 886 will be NOCOW 887 - For an empty file, add the NOCOW file attribute. That's what this 888 option does. 889 890 Note: this option is only valid to new or empty files. If there is 891 an existing file which is COW and has data blocks already, it 892 couldn't be changed to NOCOW by setting ``nocow=on``. One can 893 issue ``lsattr filename`` to check if the NOCOW flag is set or not 894 (Capital 'C' is NOCOW flag). 895 896 ``data_file`` 897 Filename where all guest data will be stored. If this option is used, 898 the qcow2 file will only contain the image's metadata. 899 900 Note: Data loss will occur if the given filename already exists when 901 using this option with ``qemu-img create`` since ``qemu-img`` will create 902 the data file anew, overwriting the file's original contents. To simply 903 update the reference to point to the given pre-existing file, use 904 ``qemu-img amend``. 905 906 ``data_file_raw`` 907 If this option is set to ``on``, QEMU will always keep the external data 908 file consistent as a standalone read-only raw image. 909 910 It does this by forwarding all write accesses to the qcow2 file through to 911 the raw data file, including their offsets. Therefore, data that is visible 912 on the qcow2 node (i.e., to the guest) at some offset is visible at the same 913 offset in the raw data file. This results in a read-only raw image. Writes 914 that bypass the qcow2 metadata may corrupt the qcow2 metadata because the 915 out-of-band writes may result in the metadata falling out of sync with the 916 raw image. 917 918 If this option is ``off``, QEMU will use the data file to store data in an 919 arbitrary manner. The file’s content will not make sense without the 920 accompanying qcow2 metadata. Where data is written will have no relation to 921 its offset as seen by the guest, and some writes (specifically zero writes) 922 may not be forwarded to the data file at all, but will only be handled by 923 modifying qcow2 metadata. 924 925 This option can only be enabled if ``data_file`` is set. 926 927``Other`` 928 929 QEMU also supports various other image file formats for 930 compatibility with older QEMU versions or other hypervisors, 931 including VMDK, VDI, VHD (vpc), VHDX, qcow1 and QED. For a full list 932 of supported formats see ``qemu-img --help``. For a more detailed 933 description of these formats, see the QEMU block drivers reference 934 documentation. 935 936 The main purpose of the block drivers for these formats is image 937 conversion. For running VMs, it is recommended to convert the disk 938 images to either raw or qcow2 in order to achieve good performance. 939