Title: How to mount ISO or file disk images on OpenBSD

	Title: How to mount ISO or file disk images on OpenBSD
	Author: Solène
	Date: 15 June 2024
	Tags: openbsd
	Description: In this article, you will learn how to mount ISO files on
	OpenBSD or how to make an encrypted disk from a flat file.

	# Introduction

	If you ever happen to mount a .iso file on OpenBSD, you may wonder how
	to proceed as the command `mount_cd9660` requires a device name.

	While the solution is entirely documented into man pages and in the
	official FAQ, it may not be easy to find it at first glance, especially
	since most operating system allow to mount an iso file in a single step
	where as OpenBSD requires an extra step.

	OpenBSD FAQ: Mounting disk images
	OpenBSD manual page: vnconfig(8) EXAMPLES section

	Note that this method does also work for disk images, not only .iso
	files.

	# Exposing a file as a device

	On OpenBSD you need to use the command `vnconfig` to map a file to a
	device node, allowing interesting actions such as using a file as a
	storage disk (which you can encrypt) or mounting a .iso file.

	This command must be used as root as it manipulates files in /dev.

	# Mounting an ISO file

	Now, let's see how to mount a .iso file, which is a dump of a CD9660
	file (most of the time):

	```
	vnconfig vnd0 /path/to/file.iso
	```

	This will create a new device `/dev/vnd0`, now you can mount it on your
	file-system with:

	```
	mount -t cd9660 /dev/vnd0c /mnt
	```

	You should be able to browser your iso file content in /mnt at this
	point.

	# Unmounting

	If you are done with the file, you have to umount it with `umount /mnt`
	and destroy the vnd device using `vnconfig -u vnd0`.

	# Going further: Using a file as an encrypted disk

	If you want to use a single file as a file system, you have to
	provision the file with disk space using the command `dd`, you can fill
	it with zeroes but if you plan to use encryption on top of it, it's
	better to use random data. In the following example, you will create a
	file `my-disk.img` of a size of 10 GB (1000 x 10 MB):

	```
	dd if=/dev/random of=my-disk.img bs=10M count=1000
	```

	Now you can use vnconfig to expose it as a device:

	```
	vnconfig vnd0 my-disk.img
	```

	Finally, the command `bioctl` can be used to configure encryption on
	the disk, `disklabel` to partition it and `newfs` to format the
	partitions. You can follow OpenBSD FAQ guides, make sure use the the
	device name `/dev/vnd0` instead of wd0 or sd0 from the examples.

	OpenBSD FAQ: Encrypting external disk