X-Git-Url: https://repo.jachan.dev/qemu.git/blobdiff_plain/8599ea4c42c098d2657ed632ad569f7a665706a4..d09a18d44d5bc0db10caa97cdd22c70e65adfe01:/qemu-img.texi diff --git a/qemu-img.texi b/qemu-img.texi index 1a6c9e36f1..f84590ebf0 100644 --- a/qemu-img.texi +++ b/qemu-img.texi @@ -46,14 +46,23 @@ is the destination disk image filename is a comma separated list of format specific options in a name=value format. Use @code{-o ?} for an overview of the options supported by the used format or see the format descriptions below for details. - +@item snapshot_param +is param used for internal snapshot, format is +'snapshot.id=[ID],snapshot.name=[NAME]' or '[ID_OR_NAME]' +@item snapshot_id_or_name +is deprecated, use snapshot_param instead @item -c indicates that target image must be compressed (qcow format only) @item -h with or without a command shows help and lists the supported formats @item -p -display progress bar (convert and rebase commands only) +display progress bar (compare, convert and rebase commands only). +If the @var{-p} option is not used for a command that supports it, the +progress is reported when the process receives a @code{SIGUSR1} signal. +@item -q +Quiet mode - do not print any output (except errors). There's no progress bar +in case both @var{-q} and @var{-p} options are used. @item -S @var{size} indicates the consecutive number of bytes that must contain only zeros for qemu-img to create a sparse image during conversion. This value is rounded @@ -81,6 +90,26 @@ deletes a snapshot lists all snapshots in the given image @end table +Parameters to compare subcommand: + +@table @option + +@item -f +First image format +@item -F +Second image format +@item -s +Strict mode - fail on on different image size or sector allocation +@end table + +Parameters to convert subcommand: + +@table @option + +@item -n +Skip the creation of the target volume +@end table + Command description: @table @option @@ -113,12 +142,58 @@ it doesn't need to be specified separately in this case. @item commit [-f @var{fmt}] [-t @var{cache}] @var{filename} -Commit the changes recorded in @var{filename} in its base image. +Commit the changes recorded in @var{filename} in its base image or backing file. +If the backing file is smaller than the snapshot, then the backing file will be +resized to be the same size as the snapshot. If the snapshot is smaller than +the backing file, the backing file will not be truncated. If you want the +backing file to match the size of the smaller snapshot, you can safely truncate +it yourself once the commit operation successfully completes. + +@item compare [-f @var{fmt}] [-F @var{fmt}] [-p] [-s] [-q] @var{filename1} @var{filename2} + +Check if two images have the same content. You can compare images with +different format or settings. + +The format is probed unless you specify it by @var{-f} (used for +@var{filename1}) and/or @var{-F} (used for @var{filename2}) option. + +By default, images with different size are considered identical if the larger +image contains only unallocated and/or zeroed sectors in the area after the end +of the other image. In addition, if any sector is not allocated in one image +and contains only zero bytes in the second one, it is evaluated as equal. You +can use Strict mode by specifying the @var{-s} option. When compare runs in +Strict mode, it fails in case image size differs or a sector is allocated in +one image and is not allocated in the second one. + +By default, compare prints out a result message. This message displays +information that both images are same or the position of the first different +byte. In addition, result message can report different image size in case +Strict mode is used. -@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} +Compare exits with @code{0} in case the images are equal and with @code{1} +in case the images differ. Other exit codes mean an error occurred during +execution and standard error output should contain an error message. +The following table sumarizes all exit codes of the compare subcommand: -Convert the disk image @var{filename} or a snapshot @var{snapshot_name} to disk image @var{output_filename} -using format @var{output_fmt}. It can be optionally compressed (@code{-c} +@table @option + +@item 0 +Images are identical +@item 1 +Images differ +@item 2 +Error on opening an image +@item 3 +Error on checking a sector allocation +@item 4 +Error on reading data + +@end table + +@item convert [-c] [-p] [-n] [-f @var{fmt}] [-t @var{cache}] [-O @var{output_fmt}] [-o @var{options}] [-s @var{snapshot_id_or_name}] [-l @var{snapshot_param}] [-S @var{sparse_size}] @var{filename} [@var{filename2} [...]] @var{output_filename} + +Convert the disk image @var{filename} or a snapshot @var{snapshot_param}(@var{snapshot_id_or_name} is deprecated) +to disk image @var{output_filename} using format @var{output_fmt}. It can be optionally compressed (@code{-c} option) or use any format specific options like encryption (@code{-o} option). Only the formats @code{qcow} and @code{qcow2} support compression. The @@ -129,11 +204,22 @@ Image conversion is also useful to get smaller image when using a growable format such as @code{qcow} or @code{cow}: the empty sectors are detected and suppressed from the destination image. +@var{sparse_size} indicates the consecutive number of bytes (defaults to 4k) +that must contain only zeros for qemu-img to create a sparse image during +conversion. If @var{sparse_size} is 0, the source will not be scanned for +unallocated or zero sectors, and the destination image will always be +fully allocated. + You can use the @var{backing_file} option to force the output image to be created as a copy on write image of the specified base image; the @var{backing_file} should have the same content as the input's base image, however the path, image format, etc may differ. +If the @code{-n} option is specified, the target volume creation will be +skipped. This is useful for formats such as @code{rbd} if the target +volume has already been created with site specific options that cannot +be supplied through qemu-img. + @item info [-f @var{fmt}] [--output=@var{ofmt}] [--backing-chain] @var{filename} Give information about the disk image @var{filename}. Use it in @@ -157,6 +243,61 @@ To enumerate information about each disk image in the above chain, starting from qemu-img info --backing-chain snap2.qcow2 @end example +@item map [-f @var{fmt}] [--output=@var{ofmt}] @var{filename} + +Dump the metadata of image @var{filename} and its backing file chain. +In particular, this commands dumps the allocation state of every sector +of @var{filename}, together with the topmost file that allocates it in +the backing file chain. + +Two option formats are possible. The default format (@code{human}) +only dumps known-nonzero areas of the file. Known-zero parts of the +file are omitted altogether, and likewise for parts that are not allocated +throughout the chain. @command{qemu-img} output will identify a file +from where the data can be read, and the offset in the file. Each line +will include four fields, the first three of which are hexadecimal +numbers. For example the first line of: +@example +Offset Length Mapped to File +0 0x20000 0x50000 /tmp/overlay.qcow2 +0x100000 0x10000 0x95380000 /tmp/backing.qcow2 +@end example +@noindent +means that 0x20000 (131072) bytes starting at offset 0 in the image are +available in /tmp/overlay.qcow2 (opened in @code{raw} format) starting +at offset 0x50000 (327680). Data that is compressed, encrypted, or +otherwise not available in raw format will cause an error if @code{human} +format is in use. Note that file names can include newlines, thus it is +not safe to parse this output format in scripts. + +The alternative format @code{json} will return an array of dictionaries +in JSON format. It will include similar information in +the @code{start}, @code{length}, @code{offset} fields; +it will also include other more specific information: +@itemize @minus +@item +whether the sectors contain actual data or not (boolean field @code{data}; +if false, the sectors are either unallocated or stored as optimized +all-zero clusters); + +@item +whether the data is known to read as zero (boolean field @code{zero}); + +@item +in order to make the output shorter, the target file is expressed as +a @code{depth}; for example, a depth of 2 refers to the backing file +of the backing file of @var{filename}. +@end itemize + +In JSON format, the @code{offset} field is optional; it is absent in +cases where @code{human} format would omit the entry or exit with an error. +If @code{data} is false and the @code{offset} field is present, the +corresponding sectors in the file are not yet in use, but they are +preallocated. + +For more information, consult @file{include/block/block.h} in QEMU's +source code. + @item snapshot [-l | -a @var{snapshot} | -c @var{snapshot} | -d @var{snapshot} ] @var{filename} List, apply, create or delete snapshots in image @var{filename}. @@ -226,6 +367,11 @@ sizes accordingly. Failure to do so will result in data loss! After using this command to grow a disk image, you must use file system and partitioning tools inside the VM to actually begin using the new space on the device. + +@item amend [-f @var{fmt}] -o @var{options} @var{filename} + +Amends the image format specific @var{options} for the image file +@var{filename}. Not all file formats support this operation. @end table @c man end @@ -252,21 +398,38 @@ support of multiple VM snapshots. Supported options: @table @code @item compat -Determines the qcow2 version to use. @code{compat=0.10} uses the traditional -image format that can be read by any QEMU since 0.10 (this is the default). +Determines the qcow2 version to use. @code{compat=0.10} uses the +traditional image format that can be read by any QEMU since 0.10. @code{compat=1.1} enables image format extensions that only QEMU 1.1 and -newer understand. Amongst others, this includes zero clusters, which allow -efficient copy-on-read for sparse images. +newer understand (this is the default). Amongst others, this includes zero +clusters, which allow efficient copy-on-read for sparse images. @item backing_file File name of a base image (see @option{create} subcommand) @item backing_fmt Image format of the base image @item encryption -If this option is set to @code{on}, the image is encrypted. - -Encryption uses the AES format which is very secure (128 bit keys). Use -a long password (16 characters) to get maximum protection. +If this option is set to @code{on}, the image is encrypted with 128-bit AES-CBC. + +The use of encryption in qcow and qcow2 images is considered to be flawed by +modern cryptography standards, suffering from a number of design problems: + +@itemize @minus +@item The AES-CBC cipher is used with predictable initialization vectors based +on the sector number. This makes it vulnerable to chosen plaintext attacks +which can reveal the existence of encrypted data. +@item The user passphrase is directly used as the encryption key. A poorly +chosen or short passphrase will compromise the security of the encryption. +@item In the event of the passphrase being compromised there is no way to +change the passphrase to protect data in any qcow images. The files must +be cloned, using a different encryption passphrase in the new file. The +original file must then be securely erased using a program like shred, +though even this is ineffective with many modern storage technologies. +@end itemize + +Use of qcow / qcow2 encryption is thus strongly discouraged. Users are +recommended to use an alternative encryption technology such as the +Linux dm-crypt / LUKS system. @item cluster_size Changes the qcow2 cluster size (must be between 512 and 2M). Smaller cluster @@ -292,8 +455,8 @@ This option can only be enabled if @code{compat=1.1} is specified. @item Other QEMU also supports various other image file formats for compatibility with -older QEMU versions or other hypervisors, including VMDK, VDI, VHD (vpc), qcow1 -and QED. For a full list of supported formats see @code{qemu-img --help}. +older QEMU versions or other hypervisors, including VMDK, VDI, VHD (vpc), VHDX, +qcow1 and QED. For a full list of supported formats see @code{qemu-img --help}. For a more detailed description of these formats, see the QEMU Emulation User Documentation.