This is a command-line editor similar to fdisk, but with different commands and it edits the disklabel, not the whole disk's partition table. Let's take a look at the partition table with "p":
wd0> p OpenBSD area: 629147648-838862048; size: 209715200; free: 209715200 # size offset fstype [fsize bsize cpg] c: 931.5G 0 unused i: 100.0G 2048 NTFS j: 200.0G 209717248 MSDOS
Unlike Linux, which assigns numbers to partitions sequentially (sda1, sda2, ...), OpenBSD often reserves letters for specific partitions. For instance, partition "c" is not a real partition, but the entire disk. Partitions i and j here are the MBR parttions of other operating systems.
Now let's make some partitions to install OpenBSD on. I'll use the following partition layout:
root - 32 GB swap - 4 GB /home - rest of disklabel space
I use this straightforward setup on most of my Unix systems - 32 GB is more than enough software space for me and a separate home partition helps when reinstalling/backing up data - this way data and the OS are on separate partitions!
You can also set up more partitions if you want, such as /var (to limit logging space) or /usr/local (to enhance security with wxlocal), but this leaves less space for generic data. If you want the system to just work, this 3-partition layout will be enough.
Let's make the root partition first by typing "a":
wd0> a partition to add: [a] offset: [629147648] size: [209715200] 32g FS type: [4.2BSD] mount point: [none] /
In "partition to add" and "offset", we just press Enter to use the default values. In "size", we obviously type in the size - the default size in sectors but we can use gigabytes like "32G". For filesystem type we use the default 4.2BSD and for mountpoint we type "/" - the Unix root directory.
This created the "a" partition - in OpenBSD the root partition is always letter "a". Now let's make the swap partition:
wd0*> a partition to add: [b] offset: [696257080] size: [142605760] 4g FS type: [swap] swap
This computer has 1 GB of RAM, so 4 GB of swap space should be more than enough and OpenBSD doesn't use a lot of RAM. The "b" partition is always swap, so the disklabel editor automatically detected the filesystem type as swap.
Now for the /home partition we use the default size so it takes up remaining disklabel space:
wd0*> a partition to add: [d] offset: [704659095] size: [134203753] FS type: [4.2BSD] mount point: [none] /home
Let's take a look at the disklabel partition table with "p":
wd0*> p OpenBSD area: 629147648-838862048; size: 209715200; free: 9 # size offset fstype [fsize bsize cpg] a: 67109440 629147640 4.2BSD 2048 16384 1 # / b: c: 931.5G 0 unused i: 100.0G 2048 NTFS j: 200.0G 209717248 MSDOS
Looks good - we save the disklabel and exit the editor by typing "q". If you want to exit without saving, type "x".
The system might ask if you want to initialize any other disks - type "done", as we're only using one disk in this OpenBSD setup.