How can I boot a 32 bit kernel when a 64 bit kernel is installed?

Sun hardware released after Solaris 8 no longer supports 32 bit booting;
you can only run 64 bit kernels on those. This applies to all Ultra-III
systems as well as the Sun Blade 100 and other UltraSPARC-IIe systems.

SPARC: In order to boot a 32 bit kernel on other 64-bit capable systems,
type "boot kernel/unix" at the "ok" prompt.

x86: In order to boot a 32 bit kernel on other 64-bit capable systems,
type "b kernel/unix" at the "(b)oot or ..." prompt.

Setting the "boot-file" in the EEPROM to "kernel/unix" makes it
the default kernel. Alternatively, you can move away the sparcv9/unix
file in which case the boot loader will fall back to the 32 bit kernel.
Patch installation may restore that file, though.

Beware: when specifying "boot -s", or any boot command with flag
arguments, the standard default kernel/sparcv9/unix kernel will be
booted; you need to specify "boot kernel/unix -s".

ASGAUR