How to fix a broken ACPI


Stop the normal boot of the kernel

You have to tell the kernel to go into boot_config(8) before performing autoconf(4) procedures. To do this enter -c at the kernel boot prompt:

boot> -c

Press Enter and you kernel should now be in UKC mode.

If you want to boot another kernel and enter UKC mode:

boot> boot hd0a:/bsd.rd -c

Configure kernel "on the fly"

The UKC mode is the User Kernel Configuration mode, and it displays yet another prompt: UKC>

On this prompt, to disable ACPI, enter the following:

UKC> disable acpi
492 acpi disabled

The 492 acpi disabled message indicates the kernel has now disabled its ACPI functions and will not attempt to configure ACPI during normal booting.

The same procedure, of course, can be applied to other malfunctioning interfaces or peripherals that crash the OpenBSD kernel.

On one of my older notebooks this helps:

UKC> disable acpiprt*
426 acpiprt* disabled

But on my Thinkpad 570 it displays 503 acpiprt* disabled.

Once the kernel configuration has been modified, type the following to continue booting:

UKC> quit

If the kernel has booted normally, see below to make this change permanent. If not, restart the configuration from the very beginning, and try disabling the next offending peripheral.

Try the following for a list of all kernel options:

UKC> list

You can also try help or ? at the UKC> prompt for more information on the User Kernel Configuration.

Make the kernel configuration changes permanent

Before you do anything, please make sure you read the excellent OpenBSD FAQ and for this case especially the section on kernel configuration.

The command to be entered is the following one:

# config -u -f -e /bsd

The problem here is config(8) -u needs kvm(3) to access the changes made during boot in UKC, with OpenBSD 6.1 access to /dev/{,k}mem was disabled at securelevel > 0.

We can override this by putting kern.allowkmem=1 into /etc/sysctl.conf and reboot but this would break the securelevel.

Better option is to launch config(8) retype the changes and write the modified kernel to another file (here

# config -e -o / /bsd