The Use Case

There are multiple kernels installed on the FreeBSD host and an option to boot to this kernel is necessary.

Prerequisites

• This post assumes FreeBSD 8.x, but should apply with any version running loader(8)
• This post assumes that a secondary/debug kernel is installed

The Patch

This is the patch. Copy/paste it to /boot/beastie.patch for use in the procedure below.

Index: beastie.4th
===================================================================
--- beastie.4th
+++ beastie.4th
@@ -41,6 +41,7 @@
 variable bootkey
 variable bootacpikey
 variable bootsafekey
+variable bootdebugkey
 variable bootverbosekey
 variable bootsinglekey
 variable escapekey
@@ -194,6 +195,7 @@
 	printmenuitem ."  Boot FreeBSD in Safe Mode" bootsafekey !
 	printmenuitem ."  Boot FreeBSD in single user mode" bootsinglekey !
 	printmenuitem ."  Boot FreeBSD with verbose logging" bootverbosekey !
+	printmenuitem ."  Boot FreeBSD with debug kernel" bootdebugkey !
 	printmenuitem ."  Escape to loader prompt" escapekey !
 	printmenuitem ."  Reboot" rebootkey !
 	menuX @ 20 at-xy
@@ -286,6 +288,9 @@
 			s" YES" s" boot_single" setenv
 			0 boot
 		then
+		dup bootdebugkey @ = if
+			s" /boot/DEBUG/kernel" 1 boot
+		then
 		dup escapekey @ = if
 			2drop
 			s" NO" s" autoboot_delay" setenv

Applying The Patch

Follow these steps to apply the patch to your target hosts:

# cd /boot
# cp beastie.4th beastie.4th.orig
# patch -p0 < beastie.patch

The new option will be loaded when loader called beastie.4th.