Revision acd935ef qemu-doc.texi

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@node disk_images
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@section Disk Images
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@subsection Raw disk images
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Since version 0.6.1, QEMU supports many disk image formats, including
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growable disk images (their size increase as non empty sectors are
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written), compressed and encrypted disk images.
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The disk images can simply be raw images of the hard disk. You can
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create them with the command:
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@subsection Quick start for disk image creation
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You can create a disk image with the command:
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@example
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dd of=myimage bs=1024 seek=mysize count=0
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qemu-img create myimage.img mysize
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@end example
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where @var{myimage} is the image filename and @var{mysize} is its size
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in kilobytes.
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where @var{myimage.img} is the disk image filename and @var{mysize} is its
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size in kilobytes. You can add an @code{M} suffix to give the size in
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megabytes and a @code{G} suffix for gigabytes.
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@xref{qemu_img_invocation} for more information.
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@subsection Snapshot mode
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If you use the option @option{-snapshot}, all disk images are
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considered as read only. When sectors in written, they are written in
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a temporary file created in @file{/tmp}. You can however force the
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write back to the raw disk images by pressing @key{C-a s}.
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NOTE: The snapshot mode only works with raw disk images.
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@subsection Copy On Write disk images
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QEMU also supports user mode Linux
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(@url{http://user-mode-linux.sourceforge.net/}) Copy On Write (COW)
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disk images. The COW disk images are much smaller than normal images
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as they store only modified sectors. They also permit the use of the
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same disk image template for many users.
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To create a COW disk images, use the command:
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@example
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qemu-mkcow -f myrawimage.bin mycowimage.cow
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@end example
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@file{myrawimage.bin} is a raw image you want to use as original disk
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image. It will never be written to.
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@file{mycowimage.cow} is the COW disk image which is created by
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@code{qemu-mkcow}. You can use it directly with the @option{-hdx}
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options. You must not modify the original raw disk image if you use
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COW images, as COW images only store the modified sectors from the raw
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disk image. QEMU stores the original raw disk image name and its
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modified time in the COW disk image so that chances of mistakes are
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reduced.
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If the raw disk image is not read-only, by pressing @key{C-a s} you
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can flush the COW disk image back into the raw disk image, as in
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snapshot mode.
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write back to the raw disk images by using the @code{commit} monitor
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command (or @key{C-a s} in the serial console).
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COW disk images can also be created without a corresponding raw disk
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image. It is useful to have a big initial virtual disk image without
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using much disk space. Use:
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@node qemu_img_invocation
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@subsection @code{qemu-img} Invocation
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@example
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qemu-mkcow mycowimage.cow 1024
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@end example
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to create a 1 gigabyte empty COW disk image.
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NOTES: 
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@enumerate
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@item
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COW disk images must be created on file systems supporting
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@emph{holes} such as ext2 or ext3.
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@item 
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Since holes are used, the displayed size of the COW disk image is not
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the real one. To know it, use the @code{ls -ls} command.
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@end enumerate
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@subsection Convert VMware disk images to raw disk images
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You can use the tool @file{vmdk2raw} to convert VMware disk images to
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raw disk images directly usable by QEMU. The syntax is:
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@example
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vmdk2raw vmware_image output_image
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@end example
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@include qemu-img.texi
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@section Network emulation
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