MKIMG(1) FreeBSD General Commands Manual MKIMG(1)
NAME
mkimg - utility to make disk images
SYNOPSIS
mkimg [-H heads] [-P blksz] [-S secsz] [-T tracksz] [-b bootcode]
[-c min_capacity] [-C max_capacity] [--capacity capacity]
[-f format] [-o outfile] [-a active] [-v] [-y]
[-s scheme [-p partition ...]]
mkimg --formats | --schemes | --version
DESCRIPTION
The mkimg utility creates a disk image from the raw partition contents
specified with the partition argument(s) and using the partitioning
scheme specified with the scheme argument. The disk image is written to
stdout by default or the file specified with the outfile argument. The
image file is a raw disk image by default, but the format of the image
file can be specified with the format argument.
The disk image can be made bootable by specifying the scheme-specific
boot block contents with the bootcode argument and, depending on the
scheme, with a boot partition. The contents of such a boot partition is
provided like any other partition and the mkimg utility does not treat it
any differently from other partitions.
Some partitioning schemes need a disk geometry and for those the mkimg
utility accepts the tracksz and heads arguments, specifying the number of
sectors per track and the number of heads per cylinder (resp.)
Both the logical and physical sector size can be specified and for that
the mkimg utility accepts the secsz and blksz arguments. The secsz
argument is used to specify the logical sector size. This is the sector
size reported by a disk when queried for its capacity. Modern disks use
a larger sector size internally, referred to as block size by the mkimg
utility and this can be specified by the blksz argument. The mkimg
utility will use the (physical) block size to determine the start of
partitions and to round the size of the disk image.
The -c option can be used to specify a minimal capacity for the disk
image. Use this option without the -s and -p options to create an empty
disk image with the given (virtual) size. An empty partition table can
be written to the disk when specifying a partitioning scheme with the -s
option, but without specifying any partitions. When the size required
for all the partitions is larger than the given capacity, then the disk
image will be larger than the capacity given.
The -C option specifies a maximum capacity for the disk image. If the
combined sizes of the given partitions exceed the size given with -C,
image creation fails.
The --capacity option is a shorthand to specify the minimum and maximum
capacity at the same time.
The -v option increases the level of output that the mkimg utility
prints.
The -y option is used for testing purposes only and is not to be used in
production. When present, the mkimg utility will generate predictable
values for Universally Unique Identifiers (UUIDs) and time stamps so that
consecutive runs of the mkimg utility will create images that are
identical.
The active option marks a partition as active, if the partitioning scheme
supports it. Currently, only the mbr scheme supports this concept. By
default, mkimg will only mark the first partition as active when boot
code is specified. Use the active option to override the active
partition. The number specified corresponds to the number after the 's'
in the partition's geom(8) name. No partitions are marked active when
the value is 0.
A set of long options exist to query about the mkimg utility itself.
Options in this set should be given by themselves because the mkimg
utility exits immediately after providing the requested information. The
version of the mkimg utility is printed when the --version option is
given. The list of supported output formats is printed when the
--formats option is given and the list of supported partitioning schemes
is printed when the --schemes option is given. Both the format and
scheme lists a space-separated lists for easy handling in scripts.
For a more descriptive list of supported partitioning schemes or
supported output format, or for a detailed description of how to specify
partitions, run the mkimg utility without any arguments. This will print
a usage message with all the necessary details.
DISK FORMATS
The mkimg utility supports a number of output file formats. A short
description of these is given below.
QCOW and QCOW2
QCOW stands for "QEMU Copy On Write". It's a sparse file format akin to
VHD and VMDK and QCOW represents the first version. QCOW2 represents
version 2 of the file format. Version 2 is not backward compatible with
version 1 and adds support for snapshots among other things. The QCOW
file formats are natively supported by QEMU and Xen. To write QCOW,
specify -f qcow on the command line. To write version 2 QCOW, specify -f
qcow2 on the command line. The preferred file extension is ".qcow" and
".qcow2" for QCOW and QCOW2 (resp.), but ".qcow" is sometimes used for
version 2 files as well.
RAW file format
This file format is a sector by sector representation of an actual disk.
There is no extra information that describes or relates to the format
itself. The size of the file is the size of the (virtual) disk. This
file format is suitable for being copyied onto a disk with utilities like
dd. To write a raw disk file, either omit the -f option, or specify -f
raw on the command line. The preferred file extension is one of ".img"
or ".raw", but there's no real convention for it.
Dynamic VHD and Fixed VHD
Microsoft's "Virtual Hard Disk" file formats. The dynamic format is a
sparse format akin to QCOW and VMDK. The fixed format is effectively a
raw format with a footer appended to the file and as such it's often
indistinguishable from the raw format. The fixed file format has been
added to support Microsoft's Azure platform and due to inconsistencies in
interpretation of the footer is not compatible with utilities like qemu
when it is specifically instructed to interpreted the file as a VHD file.
By default qemu will treat the file as a raw disk file, which mostly
works fine. To have mkimg create a dynamic VHD file, specify -f vhd on
the command line. To create a fixed VHD file for use by Azure, specify
-f vhdf on the command line. The preferred file extension is ".vhd".
Dynamic VHDX
Microsoft's "Virtual Hard Disk v2" file formats, the successor to VHD.
VHDX is the required format for the 2nd generation Hyper-V VMs. To have
mkimg create a dynamic VHDX file, specify -f vhdx on the command line.
The preferred file extension is ".vhdx".
VMDK
VMware's "Virtual Machine Disk" file format. It's a sparse file format
akin to QCOW and VHD and supported by many virtualization solutions. To
create a VMDK file, specify -f vmdk on the command line. The preferred
file extension is ".vmdk".
Not all virtualization solutions support all file formats, but often
those virtualization environments have utilities to convert from one
format to another. Note however that conversion may require that the
virtual disk size is changed to match the constraints of the output
format and this may invalidate the contents of the disk image. For
example, the GUID Partition Table (GPT) scheme has a header in the last
sector on the disk. When changing the disk size, the GPT must be changed
so that the last header is moved accordingly. This is typically not part
of the conversion process. If possible, use an output format
specifically for the environment in which the file is intended to be
used.
ENVIRONMENT
TMPDIR Directory to put temporary files in; default is /tmp.
EXAMPLES
To create a bootable disk image that is partitioned using the GPT scheme
and containing a root file system that was previously created using
makefs(8) and also containing a swap partition, run the mkimg utility as
follows:
% mkimg -s gpt -b /boot/pmbr -p freebsd-boot:=/boot/gptboot -p
freebsd-ufs:=root-file-system.ufs -p freebsd-swap::1G -o gpt.img
The command line given above results in a raw image file. This is
because no output format was given. To create a VMDK image for example,
add the -f vmdk argument to the mkimg utility and name the output file
accordingly.
A nested partitioning scheme is created by running the mkimg utility
twice. The output of the first will be fed as the contents of a
partition to the second. This can be done using a temporary file, like
so:
% mkimg -s bsd -b /boot/boot -p freebsd-ufs:=root-file-system.ufs
-p freebsd-swap::1G -o /tmp/bsd.img
% mkimg -s mbr -b /boot/mbr -p freebsd:=/tmp/bsd.img -o mbr-bsd.img
Alternatively, the mkimg utility can be run in a cascaded fashion,
whereby the output of the first is fed directly into the second. To do
this, run the mkimg utility as follows:
% mkimg -s mbr -b /boot/mbr -p freebsd:-'mkimg -s bsd -b /boot/boot
-p freebsd-ufs:=root-file-system.ufs -p freebsd-swap::1G' -o
mbr-bsd.img
To accommodate the need to have partitions named or numbered in a certain
way, the mkimg utility allows for the specification of empty partitions.
For example, to create an image that is compatible with partition layouts
found in /etc/disktab, the 'd' partition often needs to be skipped. This
is accomplished by inserting an unused partition after the first 2
partition specifications. It is worth noting at this time that the BSD
scheme will automatically skip the 'c' partition by virtue of it
referring to the entire disk. To create an image that is compatible with
the qp120at disk, use the mkimg utility as follows:
% mkimg -s bsd -b /boot/boot -p freebsd-ufs:=root-file-system.ufs
-p freebsd-swap::20M -p- -p- -p- -p- -p
freebsd-ufs:=usr-file-system.ufs -o bsd.img
For partitioning schemes that feature partition labels, the mkimg utility
supports assigning labels to the partitions specified. In the following
example the file system partition is labeled as 'backup':
% mkimg -s gpt -p freebsd-ufs/backup:=file-system.ufs -o gpt.img
SEE ALSO
dd(1), gpart(8), makefs(8), mdconfig(8), newfs(8)
HISTORY
The mkimg utility first appeared in FreeBSD 10.1.
AUTHORS
The mkimg utility and manpage were written by Marcel Moolenaar
<marcel@FreeBSD.org>.
FreeBSD 13.1-RELEASE-p6 June 8, 2020 FreeBSD 13.1-RELEASE-p6
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