@table @var
@item filename
is a disk image filename
-@item base_image
-is the read-only disk image which is used as base for a copy on
- write image; the copy on write image only stores the modified data
-@item output_base_image
-forces the output image to be created as a copy on write
-image of the specified base image; @code{output_base_image} should have the same
-content as the input's base image, however the path, image format, etc may
-differ
-@item base_fmt
-is the disk image format of @var{base_image}. for more information look at @var{fmt}
@item fmt
-is the disk image format. It is guessed automatically in most cases. The following formats are supported:
-
-@table @code
-@item raw
-
-Raw disk image format (default). This format has the advantage of
-being simple and easily exportable to all other emulators. If your
-file system supports @emph{holes} (for example in ext2 or ext3 on
-Linux or NTFS on Windows), then only the written sectors will reserve
-space. Use @code{qemu-img info} to know the real size used by the
-image or @code{ls -ls} on Unix/Linux.
-
-@item host_device
-
-Host device format. This format should be used instead of raw when
-converting to block devices or other devices where "holes" are not
-supported.
-
-@item qcow2
-QEMU image format, the most versatile format. Use it to have smaller
-images (useful if your filesystem does not supports holes, for example
-on Windows), optional AES encryption, zlib based compression and
-support of multiple VM snapshots.
-@item qcow
-Old QEMU image format. Left for compatibility.
-@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.
-@item cloop
-Linux Compressed Loop image, useful only to reuse directly compressed
-CD-ROM images present for example in the Knoppix CD-ROMs.
-@end table
+is the disk image format. It is guessed automatically in most cases. See below
+for a description of the supported disk formats.
@item size
is the disk image size in bytes. Optional suffixes @code{k} or @code{K}
@item options
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
+by the used format or see the format descriptions below for details.
@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)
+@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
+down to the nearest 512 bytes. You may use the common size suffixes like
+@code{k} for kilobytes.
+@item -t @var{cache}
+specifies the cache mode that should be used with the (destination) file. See
+the documentation of the emulator's @code{-drive cache=...} option for allowed
+values.
@end table
Parameters to snapshot subcommand:
Command description:
@table @option
-@item create [-F @var{base_fmt}] [-b @var{base_image}] [-f @var{fmt}] [-o @var{options}] @var{filename} [@var{size}]
+@item check [-f @var{fmt}] [-r [leaks | all]] @var{filename}
+
+Perform a consistency check on the disk image @var{filename}.
+
+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 occured.
+
+Only the formats @code{qcow2}, @code{qed} and @code{vdi} support
+consistency checks.
+
+@item create [-f @var{fmt}] [-o @var{options}] @var{filename} [@var{size}]
Create the new disk image @var{filename} of size @var{size} and format
-@var{fmt}.
+@var{fmt}. Depending on the file format, you can add one or more @var{options}
+that enable additional features of this format.
-If @var{base_image} is specified, then the image will record only the
-differences from @var{base_image}. No size needs to be specified in
-this case. @var{base_image} will never be modified unless you use the
-@code{commit} monitor command.
+If the option @var{backing_file} is specified, then the image will record
+only the differences from @var{backing_file}. No size needs to be specified in
+this case. @var{backing_file} will never be modified unless you use the
+@code{commit} monitor command (or qemu-img commit).
The size can also be specified using the @var{size} option with @code{-o},
it doesn't need to be specified separately in this case.
-@item commit [-f @var{fmt}] @var{filename}
+@item commit [-f @var{fmt}] [-t @var{cache}] @var{filename}
Commit the changes recorded in @var{filename} in its base image.
-@item convert [-c] [-f @var{fmt}] [-O @var{output_fmt}] [-o @var{options}] [-B @var{output_base_image}] @var{filename} [@var{filename2} [...]] @var{output_filename}
+@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}
-Convert the disk image @var{filename} to disk image @var{output_filename}
+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}
option) or use any format specific options like encryption (@code{-o} option).
-Only the formats @code{qcow} and @code{qcow2} support encryption or compression. The
+Only the formats @code{qcow} and @code{qcow2} support compression. The
compression is read-only. It means that if a compressed sector is
rewritten, then it is rewritten as uncompressed data.
-Encryption uses the AES format which is very secure (128 bit keys). Use
-a long password (16 characters) to get maximum protection.
-
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.
+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}
Give information about the disk image @var{filename}. Use it in
@item snapshot [-l | -a @var{snapshot} | -c @var{snapshot} | -d @var{snapshot} ] @var{filename}
List, apply, create or delete snapshots in image @var{filename}.
+
+@item rebase [-f @var{fmt}] [-t @var{cache}] [-p] [-u] -b @var{backing_file} [-F @var{backing_fmt}] @var{filename}
+
+Changes the backing file of an image. Only the formats @code{qcow2} and
+@code{qed} support changing the backing file.
+
+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}.
+
+There are two different modes in which @code{rebase} can operate:
+@table @option
+@item Safe mode
+This is the default mode and performs a real rebase operation. The new backing
+file may differ from the old one and qemu-img rebase will take care of keeping
+the guest-visible content of @var{filename} unchanged.
+
+In order to achieve this, any clusters that differ between @var{backing_file}
+and the old backing file of @var{filename} are merged into @var{filename}
+before actually changing the backing file.
+
+Note that the safe mode is an expensive operation, comparable to converting
+an image. It only works if the old backing file still exists.
+
+@item Unsafe mode
+qemu-img uses the unsafe mode if @code{-u} is specified. In this mode, only the
+backing file name and format of @var{filename} is changed without any checks
+on the file contents. The user must take care of specifying the correct new
+backing file, or the guest-visible content of the image will be corrupted.
+
+This mode is useful for renaming or moving the backing file to somewhere else.
+It can be used without an accessible old backing file, i.e. you can use it to
+fix an image whose backing file has already been moved/renamed.
+@end table
+
+You can use @code{rebase} to perform a ``diff'' operation on two
+disk images. This can be useful when you have copied or cloned
+a guest, and you want to get back to a thin image on top of a
+template or base image.
+
+Say that @code{base.img} has been cloned as @code{modified.img} by
+copying it, and that the @code{modified.img} guest has run so there
+are now some changes compared to @code{base.img}. To construct a thin
+image called @code{diff.qcow2} that contains just the differences, do:
+
+@example
+qemu-img create -f qcow2 -b modified.img diff.qcow2
+qemu-img rebase -b base.img diff.qcow2
+@end example
+
+At this point, @code{modified.img} can be discarded, since
+@code{base.img + diff.qcow2} contains the same information.
+
+@item resize @var{filename} [+ | -]@var{size}
+
+Change the disk image as if it had been created with @var{size}.
+
+Before using this command to shrink a disk image, you MUST use file system and
+partitioning tools inside the VM to reduce allocated file systems and partition
+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.
@end table
+Supported image file formats:
+
+@table @option
+@item raw
+
+Raw disk image format (default). This format has the advantage of
+being simple and easily exportable to all other emulators. If your
+file system supports @emph{holes} (for example in ext2 or ext3 on
+Linux or NTFS on Windows), then only the written sectors will reserve
+space. Use @code{qemu-img info} to know the real size used by the
+image or @code{ls -ls} on Unix/Linux.
+
+@item qcow2
+QEMU image format, the most versatile format. Use it to have smaller
+images (useful if your filesystem does not supports holes, for example
+on Windows), optional AES encryption, zlib based compression and
+support of multiple VM snapshots.
+
+Supported options:
+@table @code
+@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.
+
+@item cluster_size
+Changes the qcow2 cluster size (must be between 512 and 2M). Smaller cluster
+sizes can improve the image file size whereas larger cluster sizes generally
+provide better performance.
+
+@item preallocation
+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 qed
+Image format with support for backing files and compact image files (when your
+filesystem or transport medium does not support holes). Good performance due
+to less metadata than the more featureful qcow2 format, especially with
+cache=writethrough or cache=directsync. Consider using qcow2 which will soon
+have a similar optimization and is most actively developed.
+
+Supported options:
+@table @code
+@item backing_file
+File name of a base image (see @option{create} subcommand).
+@item backing_fmt
+Image file format of backing file (optional). Useful if the format cannot be
+autodetected because it has no header, like some vhd/vpc files.
+@item cluster_size
+Changes the cluster size (must be power-of-2 between 4K and 64K). Smaller
+cluster sizes can improve the image file size whereas larger cluster sizes
+generally provide better performance.
+@item table_size
+Changes the number of clusters per L1/L2 table (must be power-of-2 between 1
+and 16). There is normally no need to change this value but this option can be
+used for performance benchmarking.
+@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 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.
+
+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 cloop
+Linux Compressed Loop image, useful only to reuse directly compressed
+CD-ROM images present for example in the Knoppix CD-ROMs.
+@end table
+
+
@c man end
@ignore
projects / qemu.git / blobdiff