info about VM snapshots
git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@2096 c046a42c-6fe2-441c-8c8c-71466251a162
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@ -2,6 +2,8 @@ version 0.8.3:
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- Support for relative paths in backing files for disk images
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- Async file I/O API
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- New qcow2 disk image format
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- Support of multiple VM snapshots
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version 0.8.2:
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@ -743,6 +743,8 @@ show USB devices plugged on the virtual USB hub
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show all USB host devices
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@item info capture
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show information about active capturing
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@item info snapshots
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show list of VM snapshots
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@end table
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@item q or quit
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@ -777,11 +779,18 @@ info capture
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@item log item1[,...]
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Activate logging of the specified items to @file{/tmp/qemu.log}.
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@item savevm filename
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Save the whole virtual machine state to @var{filename}.
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@item savevm [tag|id]
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Create a snapshot of the whole virtual machine. If @var{tag} is
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provided, it is used as human readable identifier. If there is already
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a snapshot with the same tag or ID, it is replaced. More info at
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@ref{vm_snapshots}.
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@item loadvm filename
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Restore the whole virtual machine state from @var{filename}.
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@item loadvm tag|id
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Set the whole virtual machine to the snapshot identified by the tag
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@var{tag} or the unique snapshot ID @var{id}.
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@item delvm tag|id
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Delete the snapshot identified by @var{tag} or @var{id}.
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@item stop
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Stop emulation.
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@ -895,11 +904,14 @@ CPU registers by prefixing them with @emph{$}.
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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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written), compressed and encrypted disk images. Version 0.8.3 added
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the new qcow2 disk image format which is essential to support VM
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snapshots.
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@menu
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* disk_images_quickstart:: Quick start for disk image creation
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* disk_images_snapshot_mode:: Snapshot mode
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* vm_snapshots:: VM snapshots
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* qemu_img_invocation:: qemu-img Invocation
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* disk_images_fat_images:: Virtual FAT disk images
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@end menu
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@ -926,6 +938,57 @@ a temporary file created in @file{/tmp}. You can however force the
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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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@node vm_snapshots
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@subsection VM snapshots
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VM snapshots are snapshots of the complete virtual machine including
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CPU state, RAM, device state and the content of all the writable
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disks. In order to use VM snapshots, you must have at least one non
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removable and writable block device using the @code{qcow2} disk image
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format. Normally this device is the first virtual hard drive.
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Use the monitor command @code{savevm} to create a new VM snapshot or
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replace an existing one. A human readable name can be assigned to each
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snapshots in addition to its numerical ID.
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Use @code{loadvm} to restore a VM snapshot and @code{delvm} to remove
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a VM snapshot. @code{info snapshots} lists the available snapshots
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with their associated information:
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@example
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(qemu) info snapshots
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Snapshot devices: hda
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Snapshot list (from hda):
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ID TAG VM SIZE DATE VM CLOCK
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1 start 41M 2006-08-06 12:38:02 00:00:14.954
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2 40M 2006-08-06 12:43:29 00:00:18.633
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3 msys 40M 2006-08-06 12:44:04 00:00:23.514
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@end example
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A VM snapshot is made of a VM state info (its size is shown in
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@code{info snapshots}) and a snapshot of every writable disk image.
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The VM state info is stored in the first @code{qcow2} non removable
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and writable block device. The disk image snapshots are stored in
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every disk image. The size of a snapshot in a disk image is difficult
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to evaluate and is not shown by @code{info snapshots} because the
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associated disk sectors are shared among all the snapshots to save
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disk space (otherwise each snapshot would have to copy the full disk
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images).
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When using the (unrelated) @code{-snapshot} option
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(@ref{disk_images_snapshot_mode}), you can always make VM snapshots,
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but they are deleted as soon as you exit QEMU.
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VM snapshots currently have the following known limitations:
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@itemize
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@item
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They cannot cope with removable devices if they are removed or
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inserted after a snapshot is done.
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@item
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A few device drivers still have incomplete snapshot support so their
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state is not saved or restored properly (in particular USB).
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@end itemize
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@node qemu_img_invocation
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@subsection @code{qemu-img} Invocation
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