Absolute OpenBSD: Unix for the Practical Paranoid

Overview

Single-user modeunscheduled in the nighttime?Something just went "boom!"

Now that you have performed some basic configuration of your OpenBSD system, we're going to look at the startup process. To properly manage any computer platform, you must understand its booting system.

In general, when a computer boots it fires up the built-in operating system, or BIOS. The BIOS figures out little things like what hard drives are attached, what sort of CPU is installed, how much memory is available, and so on, then loads a minimal boot handling program from one of the hard drives. On i386 systems, this is where the Master Boot Record comes in; other hardware platforms have their own method of bootstrapping the operating system. This boot loader finds and starts the kernel, and the kernel starts the operating system, attaches device drivers to hardware, and performs other operating system setup. Finally, the kernel starts init(8), which starts various processes and enables the user programs, network interfaces, daemons, and so on. Large chunks of this cannot be managed — nobody actually configures init(8)! However, many parts of the process can be managed.

First we'll discuss OpenBSD's cross-platform booting process. At the end of that section you'll understand how single-user mode works and why it's there, plus the most useful of the things you can do at the boot loader. Then we'll learn how to set up and use a serial console, a vital task for remote system administration. While some hardware integrates serial console support into the hardware, the i386 platform doesn't. Setting up a serial console is fairly straightforward, as is accessing the serial console from another computer.

Much of what people consider "system configuration" is actually handled by the shell script /etc/rc, which is started by init(8). All sorts of system features, file systems, and daemons are configured during this process. While we discussed the various options available in /etc/rc.conf in the previous chapter, we didn't touch on how those options are actually used. We'll explain how the configuration process works, and the OpenBSD configuration options that are available out-of-the-box.

Lastly, we'll discuss how to automatically start or stop programs when the system boots and shuts down.