Warning: These are the steps that worked for me. If there is a better way of doing something, I'd like to know about it. These steps are not based off any Apple documentation.
Double Warning: A/UX is still a copyrighted product owned by Apple. If you have an A/UX system for which you need replacement installation media, you can check Gamba's download page for a list of places to download Macintosh operating systems, including A/UX.
Triple Warning: Before you embark on this, make sure your Mac is a supported model, and that you are using a supported CD-ROM (if it is an Apple ROMmed CD-ROM, it has an excellent chance of working; I have installed from an external CD 300 and an internal Apple 24x SCSI drive stolen from a beige PCI Power Mac). If the installer doesn't find the CD, you will be hosed.
The partitioning scheme I prefer has two HFS partitions: one for the MacPartition, and then any number of standalone HFS paritions on the side to use your favourite extensions without messing with the MacPartition's system folder and causing trouble. (You can also install other system versions here without hurting A/UX.) I also don't bother with the Autorecovery partition, since even if it did (does) work, it has little functionality that a good fsck doesn't.
The disk partitioner you will use during the A/UX setup will allow you to seemingly create nice fat partitions which may not work when you try to actually install A/UX to them. More to the point, A/UX cannot be safely used on partitions larger than 4GB under any circumstances, and filesharing is risky above 2GB, mostly due to inherent limitations of System 7.0.1. So:
newfson the new partition.
Remember, do not create a ute and root bigger than 2GB. If you have more than 2GB left, soak up the rest in another slice (I like using free slice 3).
Step 2 of the Custom Install puts the MacPartition boot files on the MacPartition. Start this step and make sure it chooses your MacPartition, not your locked MacOS partition which you will reserve for your beloved MacOS. This is very fast, typically.
Step 3 of the Custom Install installs the actual guts of A/UX. It should find your "root & usr" filesystem and chuck everything on it without further preamble. Pick the filesets you want installed.
The driver I recommend for big disks is LaCie Silverlining 5.8.3, which is A/UX aware and comes with lots of LaCie devices (it is not hard to find used). I don't know if later versions will work. I do know that the last Classic-capable version of Intech SpeedTools will not work (I tried and it actually nuked the A/UX slices! don't use it!), and I am told that FWB Hard Disk Toolkit should work, but I don't know which version. My Quadra 800 uses Silverlining on an 18GB Seagate Barracuda.
Silverlining should be able to take over the driver partition and move things around appropriately, but I'd simply format the drive from scratch. Use HD SC Setup 7.3.5 (the patched version above) to remove all existing partitions, then run Silverlining itself to create the new partitions. You can boot from some Silverlining CDs, but I booted from a 7.6 second SCSI volume for this purpose. Hint: Silverlining's input methods are a bit wonky, so be methodical. Select Partition Type from the pull-down menus with the cursor in the size column first, then enter the size, then the volume name, as appropriate. On my 18GB Barracuda, I used this scheme:
Thus endeth the Partitioning. Now boot off your A/UX boot floppy and CD. Follow these steps carefully!
ufs:mkfs 111 [number of K * 2]
ufs:mkfs 222 [number of K * 2]
For example, in our case above, they were 2091751K, so the number of 512-blocks is 4183502. My disk was at SCSI ID 2, and the slices were 0 and 3, so the commands would be
ufs:mkfs /dev/rdsk/c2d0s0 4183502
ufs:mkfs /dev/rdsk/c2d0s3 4183502
(A parenthetical note: we can't use newfs itself here, because we don't have a disktab. You could have, if you could have booted to A/UX, but we're doing this from scratch.)
If you get an error like Can't mount /dev/dsk/c102d0s0, you did the mkfs step wrong. Remember, it's ufs:mkfs (if you forget the ufs: part, it formats it as SVFS, which is not bootable).
While you're at it, whether it boots or not, consider
launch command to
launch -v so you have a
better idea what's going on. Save the settings. (In future,
you can always interrupt a
boot by pressing Command-Period (Cmd-.) when the splash screen comes up.)
Boot with Command-B. This first boot will rebuild the kernel according to your system devices. Get a cup of coffee, preferably from Colombia, because on my IIci this took a good few minutes. You will then be instructed (forced) to reboot.
At this point, you're on your own. Things to do might include:
After all your updates are done, open a CommandShell and run newconfig to enable networking and detect any leftover devices. (Always do this when you change your system configuration, too.)
/mac/sys/Login System Folder/Preferences/Autologinso that the machine properly asks you for a password rather than allowing anyone on the console to be root (!)
Remember to shut down the usual way, i.e., Special, Shut Down. You can also log out under the Special menu as well. (There seems to be a glitch if you're already logged out where Special, Shut Down may fail to unmount the filesystems cleanly, causing an unnecessary fsck on the next boot. In that case, do Special, Restart, and shutdown from the MacPartition instead. This is easier if you configure the Launcher to not autoboot, or you'll have to immediately jump on Command-Period to halt it.) Either way, when you do shut down or reboot, don't forget to unlock your MacOS partition next time you have HDSC Setup handy if you locked it with the steps above.
The Startup Disk control panel in A/UX and the MacPartition is absolutely useless on multi-partite disks of large size. The control panel from 7.6.1 is a better choice and will work just fine. Remember to keep your old one just in case, and leave the Startup Disk window open as you select restart or shut down. Note that this means you will need to reboot and stop the A/UX boot with Cmd-Period to run the 7.6.1 Startup Disk control panel from the MacPartition; it will crash the A/UX Finder instance if you run it there.
If you have a Power Macintosh card in your system, you must turn it off before booting from the MacPartition into A/UX. You can still have it plugged in the PDS slot, but it must not be activated (you can tell which one is running from the startup chime -- either the musical sting (68040) or the ominous strings (601)). If you don't do this, you may need to boot from a floppy or CD to get your startup disk switched to something else.