Learn OpenBSD - Installation & Partitioning (installer)

#Introduction

In episode 2 you understood the OpenBSD architecture and the difference between the base system and packages. Now comes the most practical moment: installing OpenBSD. This installation is the gateway — once the system is running, all the following episodes (users, services, networking, firewall) live on top of this foundation.

The OpenBSD installer is known as one of the most honest installers: pure text, no GUI, no assumptions. Every question can be answered with a sensible default, or customized. The same philosophy applies here: if you're unsure, follow the defaults — OpenBSD's defaults are designed to be safe.

#Before Installation

Make sure your VM or hardware has the installer image ready (episode 0). Boot from the installer media and you'll reach the installation prompt. Installation is done as user root directly in the installer kernel (bsd.rd — the RAMDISK kernel).

#File Sets Worth Knowing

When downloading a release, you'll see several files in the amd64/ directory:

For a basic server, base and comp (if you want to build from source) are enough. Games and X are not required for a server.

#Installation Steps

The installer asks the following questions in sequence. Answer according to your lab:

• Keyboard layout: choose according to your needs, for example us or de.
• Hostname: for example obsd1. This will be stored in /etc/myname.
• Network configuration: choose the network interface, then the IP method (DHCP or static). For a lab, DHCP during installation is the fastest way; permanent static configuration will be covered in episode 8.
• Root password: never leave it empty. Use a strong, unique password.
• Start sshd: for a server, answer yes — but remember, sshd will only accept logins according to the sshd_config configuration that will be hardened in episode 14.
• Format disk and partition: covered below.
• Select sets: choose the file sets you want to install. The default is safe for a working system.

After the file sets are extracted, the installer offers to save the installation configuration (/root/install.site) and performs the final configuration before reboot.

#Disk, Partition, and fdisk

#fdisk and GPT

"PC"-level partitions are managed with fdisk. OpenBSD supports both the MBR and GPT partition schemes. It's recommended to use GPT for modern disks, especially above 2 TB and with bootloaders that support it. The installer steps display:

Use (W)hole disk MBR, (w)hole disk GPT, (C)ustom layout or (A)bort? [a] w

Answering w uses the whole disk with a GPT partition table. This gives one large partition for OpenBSD, which is then further divided by disklabel.

#disklabel

Above the OpenBSD partition, disklabel manages internal partitions with letters (a, b, d, etc.). This is the second layer that distinguishes OpenBSD from Linux distributions: OpenBSD uses disklabel, not just a partition table. The default layout proposed by the installer is usually already good:

• a: root filesystem (/)
• b: swap
• d: other filesystems (if the disk is expanded)

#FFS2

OpenBSD's default filesystem is FFS2 (Fast File System 2), an improved UFS derivative: it supports large files, filesystem snapshots, soft updates, and optional journaling (softdep). Mount and maintenance details are in episode 7.

#Example Partition Layout

For those of you who want to customize the layout, here's an example split for a 20 GB disk on a lab system:

part    size    mount
a       512M    /
b       1G      swap
d       1G      /tmp
e       8G      /var
f       9.4G    /home

/tmp is separate and small because on OpenBSD it's mounted with the restricted wxallowed option, and /var is given room for logs and mail. This structure isn't the only answer — what matters is that you understand why separating swap (b) and giving space to /var makes sense.

#Completing the Installation

After the sets are extracted and the final configuration is done, the installer offers to reboot. On the first reboot, check that the system works well:

uname -a
dmesg | head -20
df -h
pkg_info

dmesg shows the devices detected; df -h shows the filesystem layout that was created; pkg_info should be empty for a pure base system. This is the clean ground zero of OpenBSD.

#Why Understanding Partitions Matters

An administrator who doesn't understand partitions will struggle when a disk fills up, when /var needs to be expanded, or when recovering a system. OpenBSD deliberately makes this process transparent: you see exactly what happens to the disk, not hidden behind a GUI. This investment of understanding will pay off in episodes 7 and 11.

#Closing

In episode 3 you installed OpenBSD step by step: understanding file sets, running the text installer, choosing the GPT scheme with fdisk, dividing the disk with disklabel, using FFS2 as the filesystem, and setting up the swap partition. The result is a pure base system ready to be shaped.

Key takeaways:

• OpenBSD installation is pure text; the installer defaults are designed to be safe.
• The main file sets are bsd, bsd.rd, and base74.tgz; X and games are optional for servers.
• fdisk manages GPT, disklabel manages lettered partitions (a = root, b = swap).
• FFS2 is the default filesystem, and swap is a partition, not a file.

In the next episode, episode 4, we'll manage packages with pkg_add — installing third-party software, inspecting with pkg_info, removing with pkg_delete, understanding PKG_PATH, and getting to know ports and the parallel build tool dpb. Your base system is clean; now it's time to learn how to extend it safely!