Tested on macOS 10.13 with VirtualBox 5.2

Create OpenBSD VM in VirtualBox

Download ISO image of the OpenBSD installer.

Start VirtualBox.

Select from the menu Machine > New…

In Name and operating system:

Name: foo
Type: BSD
Version: OpenBSD (64-bit)

Click Continue.

In Memory size select at least 2048 MB.

In Hard disk select Create a virtual hard disk now.

In Hard disk file type select VDI.

In Storage on physical hard disk select Dynamically allocated.

In File location and size keep default file location (~/VirtualBox VMs/foo/foo.vdi) and size (16 GB). OpenBSD fits into 1GB, but you’ll need some space for your programs and data.

Click Create.

Select from the menu Machine > Settings…

Select Storage, then select Storage Devices >Controller: IDE > Empty.

In corresponding Attributes click on CD icon near Optical Drive: IDE Secondary Master and select Choose Virtual Optical Disk File….

Pick the previously downloaded OpenBSD installer ISO image.

Click OK.

Select from the menu Machine > Start > Normal Start. OpenBSD installer boots in a new window…

Install OpenBSD