It seems boot(8) on i386/amd64 has an undocumented feature that is occasionally handy. This adds a small blurb to the man pages for both so that people can find it.
-Bryan. Index: i386/stand/boot/boot.8 =================================================================== RCS file: /cvs/src/sys/arch/i386/stand/boot/boot.8,v retrieving revision 1.58 diff -u -p -u -r1.58 boot.8 --- i386/stand/boot/boot.8 28 Oct 2013 15:15:08 -0000 1.58 +++ i386/stand/boot/boot.8 6 Nov 2013 16:54:05 -0000 @@ -204,6 +204,18 @@ commands, if any. Issues machine-dependent commands. These are defined for i386 architecture: .Bl -tag -width diskinfo +.It Nm boot +Boots the specified partition boot block in place of the original (MBR) boot +block: +.Bd -unfilled -offset indent +machine boot hd0a +.Ed +.Pp +Where +.Ar a +is the first MBR partition table entry, and +.Ar d +the last. .It Nm comaddr Set the I/O base address for the serial port to be used as serial console. .It Nm diskinfo Index: amd64/stand/boot/boot.8 =================================================================== RCS file: /cvs/src/sys/arch/amd64/stand/boot/boot.8,v retrieving revision 1.21 diff -u -p -u -r1.21 boot.8 --- amd64/stand/boot/boot.8 28 Oct 2013 15:15:08 -0000 1.21 +++ amd64/stand/boot/boot.8 6 Nov 2013 16:54:19 -0000 @@ -204,6 +204,18 @@ commands, if any. Issues machine-dependent commands. These are defined for amd64 architecture: .Bl -tag -width diskinfo +.It Nm boot +Boots the specified partition boot block in place of the original (MBR) boot +block: +.Bd -unfilled -offset indent +machine boot hd0a +.Ed +.Pp +Where +.Ar a +is the first MBR partition table entry, and +.Ar d +the last. .It Nm comaddr Set the I/O base address for the serial port to be used as serial console. .It Nm diskinfo
