usr.bin/mkimg/mkimg.1

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.Dd June 25, 2025
.Dt MKIMG 1
.Os
.Sh NAME
.Nm mkimg
.Nd "utility to make disk images"
.Sh SYNOPSIS
.Nm
.Op Fl H Ar heads
.Op Fl P Ar blksz
.Op Fl S Ar secsz
.Op Fl T Ar tracksz
.Op Fl b Ar bootcode
.Op Fl c Ar min_capacity
.Op Fl C Ar max_capacity
.Op Fl -capacity Ar capacity
.Op Fl f Ar format
.Op Fl o Ar outfile
.Op Fl a Ar active
.Op Fl t Ar timestamp
.Op Fl v
.Op Fl y
.Op Fl s Ar scheme Op Fl p Ar partition ...
.Nm
.Fl -formats | Fl -schemes | Fl -version
.Sh DESCRIPTION
The
.Nm
utility creates a disk image from the raw partition contents specified with
the
.Ar partition
argument(s) and using the partitioning scheme specified with the
.Ar scheme
argument.
The disk image is written to
.Ar stdout
by default or the file specified with the
.Ar outfile
argument.
The image file is a raw disk image by default, but the format of the
image file can be specified with the
.Ar format
argument.
Most formats require seekable output, except of raw disk image.
.Pp
The disk image can be made bootable by specifying the scheme-specific boot
block contents with the
.Ar 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
.Nm
utility does not treat it any differently from other partitions.
.Pp
Some partitioning schemes need a disk geometry and for those the
.Nm
utility accepts the
.Ar tracksz
and
.Ar heads
arguments, specifying the number of sectors per track and the number of
heads per cylinder (resp.)
.Pp
Both the logical and physical sector size can be specified and for that the
.Nm
utility
accepts the
.Ar secsz
and
.Ar blksz
arguments.
The
.Ar 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
.Nm
utility and this can be specified by the
.Ar blksz
argument.
The
.Nm
utility will use the (physical) block size to determine the start of
partitions and to round the size of the disk image.
.Pp
The
.Fl c
option can be used to specify a minimal capacity for the disk image.
Use this option without the
.Fl s
and
.Fl 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
.Fl 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.
.Pp
The
.Fl C
option specifies a maximum capacity for the disk image.
If the combined sizes of the given partitions exceed the size given with
.Fl C ,
image creation fails.
.Pp
The
.Fl -capacity
option is a shorthand to specify the minimum and maximum capacity at the
same time.
.Pp
The
.Fl t
option causes any timestamps embedded in the output file to be set to the
given time, specified in seconds since the epoch.
.Pp
The
.Fl v
option increases the level of output that the
.Nm
utility prints.
.Pp
The
.Fl y
option is used for testing purposes only and is not to be used in production.
When present, the
.Nm
utility will generate predictable values for Universally Unique Identifiers
(UUIDs) and time stamps so that consecutive runs of the
.Nm
utility will create images that are identical.
.Pp
The
.Ar active
option marks a partition as active, if the partitioning
scheme supports it.
Currently, only the
.Ar mbr
scheme supports this concept.
By default,
.Nm
will only mark the first partition as active when boot code is
specified.
Use the
.Ar active
option to override the active partition.
The number specified corresponds to the number after the 's' in the
partition's
.Xr geom 8
name.
No partitions are marked active when the value is 0.
.Pp
A set of long options exist to query about the
.Nm
utility itself.
Options in this set should be given by themselves because the
.Nm
utility exits immediately after providing the requested information.
The version of the
.Nm
utility is printed when the
.Fl -version
option is given.
The list of supported output formats is printed when the
.Fl -formats
option is given and the list of supported partitioning schemes is printed
when the
.Fl -schemes
option is given.
Both the format and scheme lists a space-separated lists for easy handling
in scripts.
.Pp
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
.Nm
utility without any arguments.
This will print a usage message with all the necessary details.
.Sh DISK FORMATS
The
.Nm
utility supports a number of output file formats.
A short description of these is given below.
.Ss 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
.Fl f Ar qcow
on the command line.
To write version 2 QCOW, specify
.Fl f Ar 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.
.Ss 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 copied onto a disk with utilities
like
.Nm dd .
To write a raw disk file, either omit the
.Fl f
option, or specify
.Fl f Ar raw
on the command line.
The preferred file extension is one of ".img" or ".raw", but there's no
real convention for it.
.Ss 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
.Nm qemu
when it is specifically instructed to interpreted the file as a VHD file.
By default
.Nm qemu
will treat the file as a raw disk file, which mostly works fine.
To have
.Nm
create a dynamic VHD file, specify
.Fl f Ar vhd
on the command line.
To create a fixed VHD file for use by Azure, specify
.Fl f Ar vhdf
on the command line.
The preferred file extension is ".vhd".
.Ss 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
.Nm
create a dynamic VHDX file, specify
.Fl f Ar vhdx
on the command line.
The preferred file extension is ".vhdx".
.Ss 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
.Fl f Ar vmdk
on the command line.
The preferred file extension is ".vmdk".
.Pp
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.
.Sh PARTITION SPECIFICATION
An option
.Fl p
may be used multiple times to specify a list of created partition entries.
A specification that is a single dash indicates an unused partition entry.
Otherwise, a partition specification has the following format:
.Bd -literal -offset indent
<type> ':' <kind> <contents>
.Ed
.Bl -tag -width indent
.It Cm type
the partition type alias (f.e.: freebsd-swap)
that may be optionally followed by a '/' separator
and a label for partitioning schemes that feature partition labels
(see the
.Sx EXAMPLES
Section below)
.It Cm kind
the interpretation of the contents specification:
.Bl -tag -width indent
.It Cm ':'
contents holds the size of an empty partition,
a number that may be suffixed with one of K, M, G, T, P or E
(either upper or lower case) following the SI power of two convention
(see also
.Xr expand_number 3 )
.It Cm '='
contents holds the name of a file to read
.It Cm '-'
contents holds a command to run; the output of which is the contents
of the partition.
Multi-word strings should be quoted according to the shell rules.
.El
.It Cm contents
the specification of a partition's contents
.El
.Sh ENVIRONMENT
.Bl -tag -width "TMPDIR" -compact
.It Ev TMPDIR
Directory to put temporary files in; default is
.Pa /tmp .
.El
.Sh 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
.Xr makefs 8
and also containing a swap partition, run the
.Nm
utility as follows:
.Dl % 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
.Pp
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
.Fl f Ar vmdk
argument to the
.Nm
utility and name the output file accordingly.
.Pp
A nested partitioning scheme is created by running the
.Nm
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:
.Dl % mkimg -s bsd -b /boot/boot -p freebsd-ufs:=root-file-system.ufs \
-p freebsd-swap::1G -o /tmp/bsd.img
.Dl % mkimg -s mbr -b /boot/mbr -p freebsd:=/tmp/bsd.img -o mbr-bsd.img
.Pp
Alternatively, the
.Nm
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
.Nm
utility as follows:
.Dl % 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
.Pp
To accommodate the need to have partitions named or numbered in a certain
way, the
.Nm
utility allows for the specification of empty partitions.
For example, to create an image that is compatible with partition layouts
found in
.Pa /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
.Nm
utility as follows:
.Dl % 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
.Pp
For partitioning schemes that feature partition labels, the
.Nm
utility supports assigning labels to the partitions specified.
In the following example the file system partition is labeled as 'backup':
.Dl % mkimg -s gpt -p freebsd-ufs/backup:=file-system.ufs -o gpt.img
.Sh SEE ALSO
.Xr dd 1 ,
.Xr expand_number 3 ,
.Xr gpart 8 ,
.Xr makefs 8 ,
.Xr mdconfig 8 ,
.Xr newfs 8
.Sh HISTORY
The
.Nm
utility first appeared in
.Fx 10.1 .
.Sh AUTHORS
The
.Nm
utility and manpage were written by
.An Marcel Moolenaar Aq Mt marcel@FreeBSD.org .