Ubuntu Manpage: virt-resize - Resize a virtual machine disk

Provided by: guestfs-tools_1.52.0-2ubuntu5_amd64

NAME

       virt-resize - Resize a virtual machine disk

SYNOPSIS

        virt-resize [--resize /dev/sdaN=[+/-]<size>[%]]
          [--expand /dev/sdaN] [--shrink /dev/sdaN]
          [--ignore /dev/sdaN] [--delete /dev/sdaN] [...] indisk outdisk

DESCRIPTION

       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.

EXAMPLES

       1.  This  example  takes "olddisk" and resizes it into "newdisk", extending one of the guest’s partitions
           to fill the extra 5GB of space:

            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

       2.  As above, but make the /boot partition 200MB bigger, while giving the remaining space to /dev/sda2:

            virt-resize --resize /dev/sda1=+200M --expand /dev/sda2 \
              olddisk newdisk

       3.  As in the first example, but expand a logical volume as the final  step.   This  is  what  you  would
           typically use for Linux guests that use LVM:

            virt-resize --expand /dev/sda2 --LV-expand /dev/vg_guest/lv_root \
              olddisk newdisk

       4.  As in the first example, but the output format will be qcow2 instead of a raw disk:

            qemu-img create -f qcow2 -o preallocation=metadata newdisk.qcow2 15G
            virt-resize --expand /dev/sda2 olddisk newdisk.qcow2

DETAILED USAGE

EXPANDING A VIRTUAL MACHINE DISK
1. Shut down the virtual machine
2. Locate input disk image
Locate the input disk image (ie. the file or device on the host containing the guest’s disk). If the
guest is managed by libvirt, you can use "virsh dumpxml" like this to find the disk image name:

# virsh dumpxml guestname | xpath /domain/devices/disk/source
Found 1 nodes:
-- NODE --
<source dev="/dev/vg/lv_guest" />

3. Look at current sizing
Use virt-filesystems(1) to display the current partitions and sizes:

# 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).

4. Create output disk
Virt-resize cannot do in-place disk modifications. You have to have space to store the resized
output disk.

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

5. Resize
virt-resize takes two mandatory parameters, the input disk and the output disk (both can be e.g. a
device, a file, or a URI to a remote disk). The output disk is the one created in the previous step.

# 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.

6. Test
Thoroughly test the new disk image before discarding the old one.

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.

7. Resize LVs etc inside the guest
(This can also be done offline using guestfish(1))

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 A VIRTUAL MACHINE DISK
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.

IGNORING OR DELETING PARTITIONS
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.

QCOW2 AND NON-SPARSE RAW FORMATS
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
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.

OPTIONS

--help
Display help.

--align-first auto
--align-first never
--align-first always
Align the first partition for improved performance (see also the --alignment option).

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.

--alignment N
Set the alignment of partitions to "N" sectors. The default in virt-resize < 1.13.19 was 64 sectors,
and after that is 128 sectors.

Assuming 512 byte sector size inside the guest, here are some suitable values for this:

--alignment 1 (512 bytes)
The partitions would be packed together as closely as possible, but would be completely
unaligned. In some cases this can cause very poor performance. See virt-alignment-scan(1) for
further details.

--alignment 8 (4K)
This would be the minimum acceptable alignment for reasonable performance on modern hosts.

--alignment 128 (64K)
This alignment provides good performance when the host is using high end network storage.

--alignment 2048 (1M)
This is the standard alignment used by all newly installed guests since around 2008.

--colors
--colours
Use ANSI colour sequences to colourize messages. This is the default when the output is a tty. If
the output of the program is redirected to a file, ANSI colour sequences are disabled unless you use
this option.

-d
--debug
(Deprecated: use -v option instead)

Enable debugging messages.

--delete PART
Delete the named partition. It would be more accurate to describe this as "don't copy it over",
since virt-resize doesn't do in-place changes and the original disk image is left intact.

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.

--expand PART
Expand the named partition so it uses up all extra space (space left over after any other resize
changes that you request have been done).

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:

• ext2, ext3 and ext4 filesystems.

• NTFS filesystems, if libguestfs was compiled with support for NTFS.

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.

• LVM PVs (physical volumes). virt-resize does not usually resize anything inside the PV, but see
the --LV-expand option. The user could also resize LVs as desired after boot.

• Btrfs filesystems, if libguestfs was compiled with support for btrfs.

• XFS filesystems, if libguestfs was compiled with support for XFS.

• Linux swap partitions.

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.

• f2fs filesystems, if libguestfs was compiled with support for f2fs.

Note that you cannot use --expand and --shrink together.

--format raw
Specify the format of the input disk image. If this flag is not given then it is auto-detected from
the image itself.

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".

--ignore PART
Ignore the named partition. Effectively this means the partition is allocated on the destination
disk, but the content is not copied across from the source disk. The content of the partition will
be blank (all zero bytes).

You can give this option multiple times.

--LV-expand LOGVOL
This takes the logical volume and, as a final step, expands it to fill all the space available in its
volume group. A typical usage, assuming a Linux guest with a single PV /dev/sda2 and a root device
called /dev/vg_guest/lv_root would be:

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.

--machine-readable
--machine-readable=format
This option is used to make the output more machine friendly when being parsed by other programs.
See "MACHINE READABLE OUTPUT" below.

-n
--dry-run
Print a summary of what would be done, but don’t do anything.

--no-copy-boot-loader
By default, virt-resize copies over some sectors at the start of the disk (up to the beginning of the
first partition). Commonly these sectors contain the Master Boot Record (MBR) and the boot loader,
and are required in order for the guest to boot correctly.

If you specify this flag, then this initial copy is not done. You may need to reinstall the boot
loader in this case.

--no-extra-partition
By default, virt-resize creates an extra partition if there is any extra, unused space after all
resizing has happened. Use this option to prevent the extra partition from being created. If you do
this then the extra space will be inaccessible until you run fdisk, parted, or some other
partitioning tool in the guest.

Note that if the surplus space is smaller than 10 MB, no extra partition will be created.

--no-expand-content
By default, virt-resize will try to expand the direct contents of partitions, if it knows how (see
--expand option above).

If you give the --no-expand-content option then virt-resize will not attempt this.

--no-sparse
Turn off sparse copying. See "SPARSE COPYING" below.

--ntfsresize-force
Pass the --force option to ntfsresize(8), allowing resizing even if the NTFS disk is marked as
needing a consistency check. You have to use this option if you want to resize a Windows guest
multiple times without booting into Windows between each resize.

--output-format raw
Specify the format of the output disk image. If this flag is not given then it is auto-detected from
the image itself.

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".

-q
--quiet
Don’t print the summary.

--resize PART=SIZE
Resize the named partition (expanding or shrinking it) so that it has the given size.

"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.

--resize-force PART=SIZE
This is the same as --resize except that it will let you decrease the size of any partition.
Generally this means you will lose any data which was at the end of the partition you shrink, but you
may not care about that (eg. if shrinking an unused partition, or if you can easily recreate it such
as a swap partition).

MACHINE READABLE OUTPUT

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:

1. Progress bar messages can be parsed from stdout by looking for this regular expression:

^[0-9]+/[0-9]+$

2. The calling program should treat messages sent to stdout (except for progress bar messages) as status
messages. They can be logged and/or displayed to the user.

3. The calling program should treat messages sent to stderr as error messages. In addition, virt-resize
exits with a non-zero status code if there was a fatal error.

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).

NOTES

"Partition 1 does not end on cylinder boundary."
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.

GUEST BOOT STUCK AT "GRUB"
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).

RESIZING WINDOWS BOOT PARTITIONS
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 CHKDSK
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.

WINDOWS UNMOUNTABLE_BOOT_VOLUME BSOD
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
Windows 8 "fast startup" can prevent virt-resize from resizing NTFS partitions. See "WINDOWS HIBERNATION
AND WINDOWS 8 FAST STARTUP" in guestfs(3).

SPARSE COPYING
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.

"unknown/unavailable method for expanding the TYPE filesystem on DEVICE/LV"
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:

1. There corresponding filesystem is not available in libguestfs, because there is no proper package in
the host with utilities for it. This is usually the case for "btrfs", "ntfs", "xfs", and "f2fs"
filesystems.

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.

2. Virt-resize has no support for expanding that type of 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.

ALTERNATIVE TOOLS

       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.

EXIT STATUS

       This program returns 0 if successful, or non-zero if there was an error.

AUTHOR

       Richard W.M. Jones http://people.redhat.com/~rjones/

COPYRIGHT

       Copyright (C) 2010-2023 Red Hat Inc.

LICENSE

       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.

BUGS

       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:

       •   The version of libguestfs.

       •   Where you got libguestfs (eg. which Linux distro, compiled from source, etc)

       •   Describe the bug accurately and give a way to reproduce it.

       •   Run libguestfs-test-tool(1) and paste the complete, unedited output into the bug report.

guestfs-tools-1.52.0                               2024-04-01                                     virt-resize(1)

NAME

SYNOPSIS

DESCRIPTION

EXAMPLES

DETAILED USAGE

OPTIONS

MACHINE READABLE OUTPUT

NOTES

ALTERNATIVE TOOLS

EXIT STATUS

SEE ALSO

AUTHOR

COPYRIGHT

LICENSE

BUGS