AIX 32/64-bit Kernel Selection

AIX is somewhat unusual with regards to 32-bit and 64-bit operation, in that on 64-bit capable hardware, assuming the 64-bit application environment is enabled, both 32-bit and 64-bit applications can run on either a 32-bit or 64-bit kernel.

The main advantages of running a 64-bit kernel are:

• efficiencies gained on large memory systems. I believe 16 GB RAM is the rough number given.
• long term, it is inevitable that the 32-bit kernel will no longer be supported.

To check what kernel is booted:

# bootinfo -K
32

To check the hardware is capable of 64-bit operation:

# bootinfo -y
64

To switch to the 64-bit kernel:

# ln -sf /usr/lib/boot/unix_64 /unix
# ln -sf /usr/lib/boot/unix_64 /usr/lib/boot/unix
# bosboot -a
# shutdown -r now

To switch to the 32-bit multi-processor kernel:

# ln -sf /usr/lib/boot/unix_mp /unix
# ln -sf /usr/lib/boot/unix_mp /usr/lib/boot/unix
# bosboot -a
# shutdown -r now