48467328c6
People have repeatedly expected that you can do things like snapshotting an image with qemu-img while a qemu instance is running. Maybe we need to consider locking the files while they are in use, but having a warning in the qemu-img manpage is doable for 1.2 and can't hurt anyway. Signed-off-by: Kevin Wolf <kwolf@redhat.com>
328 lines
12 KiB
Plaintext
328 lines
12 KiB
Plaintext
@example
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@c man begin SYNOPSIS
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usage: qemu-img command [command options]
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@c man end
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@end example
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@c man begin DESCRIPTION
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qemu-img allows you to create, convert and modify images offline. It can handle
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all image formats supported by QEMU.
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@b{Warning:} Never use qemu-img to modify images in use by a running virtual
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machine or any other process; this may destroy the image. Also, be aware that
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querying an image that is being modified by another process may encounter
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inconsistent state.
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@c man end
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@c man begin OPTIONS
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The following commands are supported:
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@include qemu-img-cmds.texi
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Command parameters:
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@table @var
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@item filename
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is a disk image filename
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@item fmt
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is the disk image format. It is guessed automatically in most cases. See below
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for a description of the supported disk formats.
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@item size
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is the disk image size in bytes. Optional suffixes @code{k} or @code{K}
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(kilobyte, 1024) @code{M} (megabyte, 1024k) and @code{G} (gigabyte, 1024M)
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and T (terabyte, 1024G) are supported. @code{b} is ignored.
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@item output_filename
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is the destination disk image filename
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@item output_fmt
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is the destination format
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@item options
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is a comma separated list of format specific options in a
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name=value format. Use @code{-o ?} for an overview of the options supported
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by the used format or see the format descriptions below for details.
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@item -c
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indicates that target image must be compressed (qcow format only)
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@item -h
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with or without a command shows help and lists the supported formats
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@item -p
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display progress bar (convert and rebase commands only)
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@item -S @var{size}
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indicates the consecutive number of bytes that must contain only zeros
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for qemu-img to create a sparse image during conversion. This value is rounded
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down to the nearest 512 bytes. You may use the common size suffixes like
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@code{k} for kilobytes.
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@item -t @var{cache}
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specifies the cache mode that should be used with the (destination) file. See
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the documentation of the emulator's @code{-drive cache=...} option for allowed
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values.
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@end table
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Parameters to snapshot subcommand:
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@table @option
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@item snapshot
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is the name of the snapshot to create, apply or delete
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@item -a
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applies a snapshot (revert disk to saved state)
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@item -c
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creates a snapshot
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@item -d
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deletes a snapshot
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@item -l
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lists all snapshots in the given image
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@end table
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Command description:
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@table @option
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@item check [-f @var{fmt}] [-r [leaks | all]] @var{filename}
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Perform a consistency check on the disk image @var{filename}.
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If @code{-r} is specified, qemu-img tries to repair any inconsistencies found
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during the check. @code{-r leaks} repairs only cluster leaks, whereas
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@code{-r all} fixes all kinds of errors, with a higher risk of choosing the
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wrong fix or hiding corruption that has already occured.
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Only the formats @code{qcow2}, @code{qed} and @code{vdi} support
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consistency checks.
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@item create [-f @var{fmt}] [-o @var{options}] @var{filename} [@var{size}]
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Create the new disk image @var{filename} of size @var{size} and format
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@var{fmt}. Depending on the file format, you can add one or more @var{options}
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that enable additional features of this format.
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If the option @var{backing_file} is specified, then the image will record
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only the differences from @var{backing_file}. No size needs to be specified in
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this case. @var{backing_file} will never be modified unless you use the
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@code{commit} monitor command (or qemu-img commit).
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The size can also be specified using the @var{size} option with @code{-o},
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it doesn't need to be specified separately in this case.
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@item commit [-f @var{fmt}] [-t @var{cache}] @var{filename}
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Commit the changes recorded in @var{filename} in its base image.
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@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}
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Convert the disk image @var{filename} or a snapshot @var{snapshot_name} to disk image @var{output_filename}
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using format @var{output_fmt}. It can be optionally compressed (@code{-c}
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option) or use any format specific options like encryption (@code{-o} option).
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Only the formats @code{qcow} and @code{qcow2} support compression. The
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compression is read-only. It means that if a compressed sector is
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rewritten, then it is rewritten as uncompressed data.
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Image conversion is also useful to get smaller image when using a
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growable format such as @code{qcow} or @code{cow}: the empty sectors
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are detected and suppressed from the destination image.
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You can use the @var{backing_file} option to force the output image to be
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created as a copy on write image of the specified base image; the
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@var{backing_file} should have the same content as the input's base image,
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however the path, image format, etc may differ.
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@item info [-f @var{fmt}] @var{filename}
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Give information about the disk image @var{filename}. Use it in
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particular to know the size reserved on disk which can be different
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from the displayed size. If VM snapshots are stored in the disk image,
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they are displayed too.
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@item snapshot [-l | -a @var{snapshot} | -c @var{snapshot} | -d @var{snapshot} ] @var{filename}
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List, apply, create or delete snapshots in image @var{filename}.
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@item rebase [-f @var{fmt}] [-t @var{cache}] [-p] [-u] -b @var{backing_file} [-F @var{backing_fmt}] @var{filename}
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Changes the backing file of an image. Only the formats @code{qcow2} and
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@code{qed} support changing the backing file.
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The backing file is changed to @var{backing_file} and (if the image format of
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@var{filename} supports this) the backing file format is changed to
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@var{backing_fmt}.
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There are two different modes in which @code{rebase} can operate:
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@table @option
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@item Safe mode
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This is the default mode and performs a real rebase operation. The new backing
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file may differ from the old one and qemu-img rebase will take care of keeping
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the guest-visible content of @var{filename} unchanged.
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In order to achieve this, any clusters that differ between @var{backing_file}
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and the old backing file of @var{filename} are merged into @var{filename}
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before actually changing the backing file.
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Note that the safe mode is an expensive operation, comparable to converting
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an image. It only works if the old backing file still exists.
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@item Unsafe mode
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qemu-img uses the unsafe mode if @code{-u} is specified. In this mode, only the
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backing file name and format of @var{filename} is changed without any checks
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on the file contents. The user must take care of specifying the correct new
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backing file, or the guest-visible content of the image will be corrupted.
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This mode is useful for renaming or moving the backing file to somewhere else.
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It can be used without an accessible old backing file, i.e. you can use it to
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fix an image whose backing file has already been moved/renamed.
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@end table
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You can use @code{rebase} to perform a ``diff'' operation on two
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disk images. This can be useful when you have copied or cloned
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a guest, and you want to get back to a thin image on top of a
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template or base image.
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Say that @code{base.img} has been cloned as @code{modified.img} by
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copying it, and that the @code{modified.img} guest has run so there
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are now some changes compared to @code{base.img}. To construct a thin
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image called @code{diff.qcow2} that contains just the differences, do:
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@example
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qemu-img create -f qcow2 -b modified.img diff.qcow2
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qemu-img rebase -b base.img diff.qcow2
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@end example
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At this point, @code{modified.img} can be discarded, since
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@code{base.img + diff.qcow2} contains the same information.
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@item resize @var{filename} [+ | -]@var{size}
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Change the disk image as if it had been created with @var{size}.
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Before using this command to shrink a disk image, you MUST use file system and
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partitioning tools inside the VM to reduce allocated file systems and partition
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sizes accordingly. Failure to do so will result in data loss!
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After using this command to grow a disk image, you must use file system and
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partitioning tools inside the VM to actually begin using the new space on the
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device.
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@end table
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Supported image file formats:
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@table @option
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@item raw
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Raw disk image format (default). This format has the advantage of
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being simple and easily exportable to all other emulators. If your
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file system supports @emph{holes} (for example in ext2 or ext3 on
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Linux or NTFS on Windows), then only the written sectors will reserve
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space. Use @code{qemu-img info} to know the real size used by the
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image or @code{ls -ls} on Unix/Linux.
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@item qcow2
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QEMU image format, the most versatile format. Use it to have smaller
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images (useful if your filesystem does not supports holes, for example
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on Windows), optional AES encryption, zlib based compression and
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support of multiple VM snapshots.
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Supported options:
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@table @code
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@item backing_file
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File name of a base image (see @option{create} subcommand)
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@item backing_fmt
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Image format of the base image
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@item encryption
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If this option is set to @code{on}, the image is encrypted.
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Encryption uses the AES format which is very secure (128 bit keys). Use
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a long password (16 characters) to get maximum protection.
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@item cluster_size
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Changes the qcow2 cluster size (must be between 512 and 2M). Smaller cluster
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sizes can improve the image file size whereas larger cluster sizes generally
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provide better performance.
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@item preallocation
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Preallocation mode (allowed values: off, metadata). An image with preallocated
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metadata is initially larger but can improve performance when the image needs
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to grow.
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@end table
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@item qed
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Image format with support for backing files and compact image files (when your
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filesystem or transport medium does not support holes). Good performance due
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to less metadata than the more featureful qcow2 format, especially with
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cache=writethrough or cache=directsync. Consider using qcow2 which will soon
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have a similar optimization and is most actively developed.
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Supported options:
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@table @code
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@item backing_file
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File name of a base image (see @option{create} subcommand).
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@item backing_fmt
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Image file format of backing file (optional). Useful if the format cannot be
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autodetected because it has no header, like some vhd/vpc files.
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@item cluster_size
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Changes the cluster size (must be power-of-2 between 4K and 64K). Smaller
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cluster sizes can improve the image file size whereas larger cluster sizes
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generally provide better performance.
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@item table_size
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Changes the number of clusters per L1/L2 table (must be power-of-2 between 1
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and 16). There is normally no need to change this value but this option can be
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used for performance benchmarking.
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@end table
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@item qcow
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Old QEMU image format. Left for compatibility.
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Supported options:
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@table @code
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@item backing_file
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File name of a base image (see @option{create} subcommand)
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@item encryption
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If this option is set to @code{on}, the image is encrypted.
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@end table
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@item cow
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User Mode Linux Copy On Write image format. Used to be the only growable
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image format in QEMU. It is supported only for compatibility with
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previous versions. It does not work on win32.
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@item vdi
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VirtualBox 1.1 compatible image format.
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@item vmdk
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VMware 3 and 4 compatible image format.
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Supported options:
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@table @code
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@item backing_fmt
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Image format of the base image
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@item compat6
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Create a VMDK version 6 image (instead of version 4)
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@end table
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@item vpc
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VirtualPC compatible image format (VHD).
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@item cloop
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Linux Compressed Loop image, useful only to reuse directly compressed
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CD-ROM images present for example in the Knoppix CD-ROMs.
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@end table
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@c man end
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@ignore
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@setfilename qemu-img
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@settitle QEMU disk image utility
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@c man begin SEEALSO
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The HTML documentation of QEMU for more precise information and Linux
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user mode emulator invocation.
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@c man end
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@c man begin AUTHOR
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Fabrice Bellard
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@c man end
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@end ignore
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