MKIMG(1) FreeBSD General Commands Manual MKIMG(1)


mkimgutility to make disk images


mkimg [ -H heads][ -P blksz][ -S secsz][ -T tracksz][ -b bootcode][ -f format][ -o outfile][ -v][ -y] -s scheme -p partition [ -p partition ...]

mkimg --formats | --schemes | --version


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 [ -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.

A set of long options exist to query about the mkimg utilty 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.


Directory to put temporary files in; default is /tmp.


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 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 accomodate 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


The mkimg utility first appeared in FreeBSD 10.1.


The mkimg utility and manpage were written by Marcel Moolenaar <marcelm@juniper.net>
September 27, 2014 FreeBSD