virt-resize(1) | Virtualization Support | virt-resize(1) |
virt-resize - Resize a virtual machine disk
virt-resize [--resize /dev/sdaN=[+/-]<size>[%]] [--expand /dev/sdaN] [--shrink /dev/sdaN] [--ignore /dev/sdaN] [--delete /dev/sdaN] [...] indisk outdisk
Virt-resize is a tool which can resize a virtual machine disk, making it larger or smaller overall, and resizing or deleting any partitions contained within.
Virt-resize cannot resize disk images in-place. Virt-resize should not be used on live virtual machines - for consistent results, shut the virtual machine down before resizing it.
If you are not familiar with the associated tools: virt-filesystems(1) and virt-df(1), we recommend you go and read those manual pages first.
virt-filesystems --long -h --all -a olddisk truncate -r olddisk newdisk truncate -s +5G newdisk # Note "/dev/sda2" is a partition inside the "olddisk" file. virt-resize --expand /dev/sda2 olddisk newdisk
virt-resize --resize /dev/sda1=+200M --expand /dev/sda2 \ olddisk newdisk
virt-resize --expand /dev/sda2 --LV-expand /dev/vg_guest/lv_root \ olddisk newdisk
qemu-img create -f qcow2 -o preallocation=metadata newdisk.qcow2 15G virt-resize --expand /dev/sda2 olddisk newdisk.qcow2
# virsh dumpxml guestname | xpath /domain/devices/disk/source Found 1 nodes: -- NODE -- <source dev="/dev/vg/lv_guest" />
# virt-filesystems --long --parts --blkdevs -h -a /dev/vg/lv_guest Name Type Size Parent /dev/sda1 partition 101M /dev/sda /dev/sda2 partition 7.9G /dev/sda /dev/sda device 8.0G -
(This example is a virtual machine with an 8 GB disk which we would like to expand up to 10 GB).
To store the resized disk image in a file, create a file of a suitable size:
# rm -f outdisk # truncate -s 10G outdisk
Or use lvcreate(1) to create a logical volume:
# lvcreate -L 10G -n lv_name vg_name
Or use virsh(1) vol-create-as to create a libvirt storage volume:
# virsh pool-list # virsh vol-create-as poolname newvol 10G
# virt-resize indisk outdisk
This command just copies disk image "indisk" to disk image "outdisk" without resizing or changing any existing partitions. If "outdisk" is larger, then an extra, empty partition is created at the end of the disk covering the extra space. If "outdisk" is smaller, then it will give an error.
More realistically you'd want to expand existing partitions in the disk image by passing extra options (for the full list see the "OPTIONS" section below).
"--expand" is the most useful option. It expands the named partition within the disk to fill any extra space:
# virt-resize --expand /dev/sda2 indisk outdisk
(In this case, an extra partition is not created at the end of the disk, because there will be no unused space).
"--resize" is the other commonly used option. The following would increase the size of /dev/sda1 by 200M, and expand /dev/sda2 to fill the rest of the available space:
# virt-resize --resize /dev/sda1=+200M --expand /dev/sda2 \ indisk outdisk
If the expanded partition in the image contains a filesystem or LVM PV, then if virt-resize knows how, it will resize the contents, the equivalent of calling a command such as pvresize(8), resize2fs(8), ntfsresize(8), btrfs(8), xfs_growfs(8), or resize.f2fs(8). However virt-resize does not know how to resize some filesystems, so you would have to online resize them after booting the guest.
# virt-resize --expand /dev/sda2 nbd://example.com outdisk
The input disk can be a URI, in order to use a remote disk as the source. The URI format is compatible with guestfish. See "ADDING REMOTE STORAGE" in guestfish(1).
Other options are covered below.
If you are using libvirt, edit the XML to point at the new disk:
# virsh edit guestname
Change <source ...>, see http://libvirt.org/formatdomain.html#elementsDisks
Then start up the domain with the new, resized disk:
# virsh start guestname
and check that it still works. See also the "NOTES" section below for additional information.
Once the guest has booted you should see the new space available, at least for filesystems that virt-resize knows how to resize, and for PVs. The user may need to resize LVs inside PVs, and also resize filesystem types that virt-resize does not know how to expand.
Shrinking is somewhat more complex than expanding, and only an overview is given here.
Firstly virt-resize will not attempt to shrink any partition content (PVs, filesystems). The user has to shrink content before passing the disk image to virt-resize, and virt-resize will check that the content has been shrunk properly.
(Shrinking can also be done offline using guestfish(1))
After shrinking PVs and filesystems, shut down the guest, and proceed with steps 3 and 4 above to allocate a new disk image.
Then run virt-resize with any of the --shrink and/or --resize options.
virt-resize also gives a convenient way to ignore or delete partitions when copying from the input disk to the output disk. Ignoring a partition speeds up the copy where you don't care about the existing contents of a partition. Deleting a partition removes it completely, but note that it also renumbers any partitions after the one which is deleted, which can leave some guests unbootable.
If the input disk is in qcow2 format, then you may prefer that the output is in qcow2 format as well. Alternately, virt-resize can convert the format on the fly. The output format is simply determined by the format of the empty output container that you provide. Thus to create qcow2 output, use:
qemu-img create -f qcow2 -o preallocation=metadata outdisk [size]
instead of the truncate command.
Similarly, to get non-sparse raw output use:
fallocate -l size outdisk
(on older systems that don’t have the fallocate(1) command use "dd if=/dev/zero of=outdisk bs=1M count=..")
Logical partitions (a.k.a. /dev/sda5+ on disks using DOS partition tables) cannot be resized.
To understand what is going on, firstly one of the four partitions /dev/sda1-4 will have MBR partition type 05 or "0f". This is called the extended partition. Use virt-filesystems(1) to see the MBR partition type.
Logical partitions live inside the extended partition.
The extended partition can be expanded, but not shrunk (unless you force it, which is not advisable). When the extended partition is copied across, all the logical partitions contained inside are copied over implicitly. Virt-resize does not look inside the extended partition, so it copies the logical partitions blindly.
You cannot specify a logical partition (/dev/sda5+) at all on the command line. Doing so will give an error.
The default is --align-first auto which only aligns the first partition if it is safe to do so. That is, only when we know how to fix the bootloader automatically, and at the moment that can only be done for Windows guests.
--align-first never means we never move the first partition. This is the safest option. Try this if the guest does not boot after resizing.
--align-first always means we always align the first partition (if it needs to be aligned). For some guests this will break the bootloader, making the guest unbootable.
Assuming 512 byte sector size inside the guest, here are some suitable values for this:
Enable debugging messages.
Note that when you delete a partition, then anything contained in the partition is also deleted. Furthermore, this causes any partitions that come after to be renumbered, which can easily make your guest unbootable.
You can give this option multiple times.
If virt-resize knows how, it will expand the direct content of the partition. For example, if the partition is an LVM PV, it will expand the PV to fit (like calling pvresize(8)). Virt-resize leaves any other content it doesn't know about alone.
Currently virt-resize can resize:
The filesystem must have been shut down consistently last time it was used. Additionally, ntfsresize(8) marks the resized filesystem as requiring a consistency check, so at the first boot after resizing Windows will check the disk.
Please note that libguestfs destroys the existing swap content by recreating it with "mkswap", so this should not be used when the guest is suspended.
Note that you cannot use --expand and --shrink together.
If working with untrusted raw-format guest disk images, you should ensure the format is always specified.
Note that this option does not affect the output format. See "QCOW2 AND NON-SPARSE RAW FORMATS".
You can give this option multiple times.
virt-resize indisk outdisk \ --expand /dev/sda2 --LV-expand /dev/vg_guest/lv_root
This would first expand the partition (and PV), and then expand the root device to fill the extra space in the PV.
The contents of the LV are also resized if virt-resize knows how to do that. You can stop virt-resize from trying to expand the content by using the option --no-expand-content.
Use virt-filesystems(1) to list the filesystems in the guest.
You can give this option multiple times, but it doesn't make sense to do this unless the logical volumes you specify are all in different volume groups.
If you specify this flag, then this initial copy is not done. You may need to reinstall the boot loader in this case.
Note that if the surplus space is smaller than 10 MB, no extra partition will be created.
If you give the --no-expand-content option then virt-resize will not attempt this.
If working with untrusted raw-format guest disk images, you should ensure the format is always specified.
Note that this option does not create the output format. This option just tells libguestfs what it is so it doesn't try to guess it. You still need to create the output disk with the right format. See "QCOW2 AND NON-SPARSE RAW FORMATS".
"SIZE" can be expressed as an absolute number followed by b/K/M/G to mean bytes, Kilobytes, Megabytes, or Gigabytes; or as a percentage of the current size; or as a relative number or percentage. For example:
--resize /dev/sda2=10G --resize /dev/sda4=90% --resize /dev/sda2=+1G --resize /dev/sda2=-200M --resize /dev/sda1=+128K --resize /dev/sda1=+10% --resize /dev/sda1=-10%
You can increase the size of any partition. Virt-resize will expand the direct content of the partition if it knows how (see --expand above).
You can only decrease the size of partitions that contain filesystems or PVs which have already been shrunk. Virt-resize will check this has been done before proceeding, or else will print an error (see also --resize-force).
You can give this option multiple times.
See also the --ignore option.
The amount by which the overall disk must be shrunk (after carrying out all other operations requested by the user) is called the "deficit". For example, a straight copy (assume no other operations) from a 5GB disk image to a 4GB disk image results in a 1GB deficit. In this case, virt-resize would give an error unless the user specified a partition to shrink and that partition had more than a gigabyte of free space.
Note that you cannot use --expand and --shrink together.
--unknown-filesystems ignore will cause virt-resize to silently ignore such filesystems, and nothing is printed about them.
--unknown-filesystems warn (the default behaviour) will cause virt-resize to warn for each of the filesystem that cannot be expanded, but still continuing to resize the disk.
--unknown-filesystems error will cause virt-resize to error out at the first filesystem that cannot be expanded.
See also "unknown/unavailable method for expanding the TYPE filesystem on DEVICE/LV".
The --machine-readable option can be used to make the output more machine friendly, which is useful when calling virt-resize from other programs, GUIs etc.
There are two ways to use this option.
Firstly use the option on its own to query the capabilities of the virt-resize binary. Typical output looks like this:
$ virt-resize --machine-readable virt-resize ntfsresize-force 32bitok ntfs btrfs
A list of features is printed, one per line, and the program exits with status 0.
Secondly use the option in conjunction with other options to make the regular program output more machine friendly.
At the moment this means:
^[0-9]+/[0-9]+$
Versions of the program prior to 1.13.9 did not support the --machine-readable option and will return an error.
It is possible to specify a format string for controlling the output; see "ADVANCED MACHINE READABLE OUTPUT" in guestfs(3).
Virt-resize aligns partitions to multiples of 128 sectors (see the --alignment parameter). Usually this means the partitions will not be aligned to the ancient CHS geometry. However CHS geometry is meaningless for disks manufactured since the early 1990s, and doubly so for virtual hard drives. Alignment of partitions to cylinders is not required by any modern operating system.
If a Linux guest does not boot after resizing, and the boot is stuck after printing "GRUB" on the console, try reinstalling grub.
guestfish -i -a newdisk ><fs> cat /boot/grub/device.map # check the contents of this file are sensible or # edit the file if necessary ><fs> grub-install / /dev/vda ><fs> exit
For more flexible guest reconfiguration, including if you need to specify other parameters to grub-install, use virt-rescue(1).
In Windows Vista and later versions, Microsoft switched to using a separate boot partition. In these VMs, typically /dev/sda1 is the boot partition and /dev/sda2 is the main (C:) drive. Resizing the first (boot) partition causes the bootloader to fail with 0xC0000225 error. Resizing the second partition (ie. C: drive) should work.
Windows disks which use NTFS must be consistent before virt-resize can be used. If the ntfsresize operation fails, try booting the original VM and running "chkdsk /f" on all NTFS partitions, then shut down the VM cleanly. For further information see: https://bugzilla.redhat.com/show_bug.cgi?id=975753
After resize Windows may initiate a lengthy "chkdsk" on first boot if NTFS partitions have been expanded. This is just a safety check and (unless it find errors) is nothing to worry about.
After sysprepping a Windows guest and then resizing it with virt-resize, you may see the guest fail to boot with an "UNMOUNTABLE_BOOT_VOLUME" BSOD. This error is caused by having "ExtendOemPartition=1" in the sysprep.inf file. Removing this line before sysprepping should fix the problem.
Windows 8 "fast startup" can prevent virt-resize from resizing NTFS partitions. See "WINDOWS HIBERNATION AND WINDOWS 8 FAST STARTUP" in guestfs(3).
You should create a fresh, zeroed target disk image for virt-resize to use.
Virt-resize by default performs sparse copying. This means that it does not copy blocks from the source disk which are all zeroes. This improves speed and efficiency, but will produce incorrect results if the target disk image contains unzeroed data.
The main time this can be a problem is if the target is a host partition (eg. "virt-resize source.img /dev/sda4") because the usual partitioning tools tend to leave whatever data happened to be on the disk before.
If you have to reuse a target which contains data already, you should use the --no-sparse option. Note this can be much slower.
Virt-resize was asked to expand a partition or a logical volume containing a filesystem with the type "TYPE", but there is no available nor known expanding method for that filesystem.
This may be due to either of the following:
Check the results of:
virt-resize --machine-readable guestfish -a /dev/null run : available guestfish -a /dev/null run : filesystem_available TYPE
In this case, it is enough to install the proper packages adding support for them. For example, "libguestfs-xfs" on Red Hat Enterprise Linux, CentOS, Debian, Ubuntu, and distributions derived from them, for supporting the "xfs" filesystem.
In this case, there’s nothing that can be done to let virt-resize expand that type of filesystem.
In both cases, virt-resize will not expand the mentioned filesystem; the result (unless --unknown-filesystems error is specified) is that the partitions containing such filesystems will be actually bigger as requested, but the filesystems will still be usable at their older sizes.
There are several proprietary tools for resizing partitions. We won't mention any here.
parted(8) and its graphical shell gparted can do some types of resizing operations on disk images. They can resize and move partitions, but I don't think they can do anything with the contents, and they certainly don't understand LVM.
guestfish(1) can do everything that virt-resize can do and a lot more, but at a much lower level. You will probably end up hand-calculating sector offsets, which is something that virt-resize was designed to avoid. If you want to see the guestfish-equivalent commands that virt-resize runs, use the --debug flag.
dracut(8) includes a module called "dracut-modules-growroot" which can be used to grow the root partition when the guest first boots up. There is documentation for this module in an associated README file.
This program returns 0 if successful, or non-zero if there was an error.
virt-filesystems(1), virt-df(1), guestfs(3), guestfish(1), lvm(8), pvresize(8), lvresize(8), resize2fs(8), ntfsresize(8), btrfs(8), xfs_growfs(8), resize.f2fs(8), virsh(1), parted(8), truncate(1), fallocate(1), grub(8), grub-install(8), virt-rescue(1), virt-sparsify(1), virt-alignment-scan(1), http://libguestfs.org/.
Richard W.M. Jones http://people.redhat.com/~rjones/
Copyright (C) 2010-2012 Red Hat Inc.
This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version.
This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.
You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
To get a list of bugs against libguestfs, use this link: https://bugzilla.redhat.com/buglist.cgi?component=libguestfs&product=Virtualization+Tools
To report a new bug against libguestfs, use this link: https://bugzilla.redhat.com/enter_bug.cgi?component=libguestfs&product=Virtualization+Tools
When reporting a bug, please supply:
2023-05-23 | guestfs-tools-1.48.2 |