X-Git-Url: https://git.proxmox.com/?a=blobdiff_plain;f=qemu-img.texi;h=f84590ebf0df88e74ec0c716d3a5604c4630228c;hb=c75f3bdf46f74c9f1c199ace3d2b291e430dcda3;hp=6fc3c28e0d6492bfd61fd03ad9346be48677ac14;hpb=dd86df756e02b684718dd5378725927361b0ad36;p=mirror_qemu.git diff --git a/qemu-img.texi b/qemu-img.texi index 6fc3c28e0d..f84590ebf0 100644 --- a/qemu-img.texi +++ b/qemu-img.texi @@ -4,6 +4,16 @@ usage: qemu-img command [command options] @c man end @end example +@c man begin DESCRIPTION +qemu-img allows you to create, convert and modify images offline. It can handle +all image formats supported by QEMU. + +@b{Warning:} Never use qemu-img to modify images in use by a running virtual +machine or any other process; this may destroy the image. Also, be aware that +querying an image that is being modified by another process may encounter +inconsistent state. +@c man end + @c man begin OPTIONS The following commands are supported: @@ -18,6 +28,10 @@ Command parameters: is the disk image format. It is guessed automatically in most cases. See below for a description of the supported disk formats. +@item --backing-chain +will enumerate information about backing files in a disk image chain. Refer +below for further description. + @item size is the disk image size in bytes. Optional suffixes @code{k} or @code{K} (kilobyte, 1024) @code{M} (megabyte, 1024k) and @code{G} (gigabyte, 1024M) @@ -32,14 +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 @@ -67,12 +90,38 @@ 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 -@item check [-f @var{fmt}] @var{filename} +@item check [-f @var{fmt}] [--output=@var{ofmt}] [-r [leaks | all]] @var{filename} -Perform a consistency check on the disk image @var{filename}. +Perform a consistency check on the disk image @var{filename}. The command can +output in the format @var{ofmt} which is either @code{human} or @code{json}. + +If @code{-r} is specified, qemu-img tries to repair any inconsistencies found +during the check. @code{-r leaks} repairs only cluster leaks, whereas +@code{-r all} fixes all kinds of errors, with a higher risk of choosing the +wrong fix or hiding corruption that has already occurred. Only the formats @code{qcow2}, @code{qed} and @code{vdi} support consistency checks. @@ -93,12 +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} -@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} +Check if two images have the same content. You can compare images with +different format or settings. -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} +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. + +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: + +@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 @@ -109,17 +204,99 @@ 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. -@item info [-f @var{fmt}] @var{filename} +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 particular to know the size reserved on disk which can be different from the displayed size. If VM snapshots are stored in the disk image, -they are displayed too. +they are displayed too. The command can output in the format @var{ofmt} +which is either @code{human} or @code{json}. + +If a disk image has a backing file chain, information about each disk image in +the chain can be recursively enumerated by using the option @code{--backing-chain}. + +For instance, if you have an image chain like: + +@example +base.qcow2 <- snap1.qcow2 <- snap2.qcow2 +@end example + +To enumerate information about each disk image in the above chain, starting from top to base, do: + +@example +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} @@ -132,7 +309,9 @@ Changes the backing file of an image. Only the formats @code{qcow2} and The backing file is changed to @var{backing_file} and (if the image format of @var{filename} supports this) the backing file format is changed to -@var{backing_fmt}. +@var{backing_fmt}. If @var{backing_file} is specified as ``'' (the empty +string), then the image is rebased onto no backing file (i.e. it will exist +independently of any backing file). There are two different modes in which @code{rebase} can operate: @table @option @@ -188,8 +367,16 @@ 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 +@ignore +@c man begin NOTES Supported image file formats: @table @option @@ -210,15 +397,39 @@ 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. +@code{compat=1.1} enables image format extensions that only QEMU 1.1 and +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 @@ -230,50 +441,33 @@ Preallocation mode (allowed values: off, metadata). An image with preallocated metadata is initially larger but can improve performance when the image needs to grow. -@end table - - -@item qcow -Old QEMU image format. Left for compatibility. - -Supported options: -@table @code -@item backing_file -File name of a base image (see @option{create} subcommand) -@item encryption -If this option is set to @code{on}, the image is encrypted. -@end table +@item lazy_refcounts +If this option is set to @code{on}, reference count updates are postponed with +the goal of avoiding metadata I/O and improving performance. This is +particularly interesting with @option{cache=writethrough} which doesn't batch +metadata updates. The tradeoff is that after a host crash, the reference count +tables must be rebuilt, i.e. on the next open an (automatic) @code{qemu-img +check -r all} is required, which may take some time. -@item cow -User Mode Linux Copy On Write image format. Used to be the only growable -image format in QEMU. It is supported only for compatibility with -previous versions. It does not work on win32. -@item vdi -VirtualBox 1.1 compatible image format. -@item vmdk -VMware 3 and 4 compatible image format. +This option can only be enabled if @code{compat=1.1} is specified. -Supported options: -@table @code -@item backing_fmt -Image format of the base image -@item compat6 -Create a VMDK version 6 image (instead of version 4) @end table -@item vpc -VirtualPC compatible image format (VHD). +@item Other +QEMU also supports various other image file formats for compatibility with +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. -@item cloop -Linux Compressed Loop image, useful only to reuse directly compressed -CD-ROM images present for example in the Knoppix CD-ROMs. +The main purpose of the block drivers for these formats is image conversion. +For running VMs, it is recommended to convert the disk images to either raw or +qcow2 in order to achieve good performance. @end table @c man end -@ignore - @setfilename qemu-img @settitle QEMU disk image utility