rch@datlog.co.uk ( Richard Hughes ) (07/20/88)
We are running a number of 6150 model 125's which we are upgrading to AIX 2.2. In the process of doing this, I found that the VRM program and Diagnostics boot disks would not boot (but the install and maintenance one would) on some of the machines. As this has happened before, I called the engineer who said he would change the system board. (This has sucessfully fixed the problem in the past although he didn't know why.) When he went to order the board from the stores they told him that the problem is that the default boot device (stored in batery backed RAM) has been changed from floppy disk to hard disk. The reason that install and maintenance worked was that even with the boot device changed from floppy, it always checks, just in case it is the install diskette and boots from it if it is. In order to change the boot device back to floppy, he suggested using either ctrl alt A when the floppy drive was accessed at boot time or disconnecting the battery to the RAM for twenty minutes. The former didn't fix the problem but the latter did. Can anyone tell me : a) Why would one want to change the boot device in this way ? b) How and why has it been changed ? c) Having changed it, is there a better way to reset it ? Thank you.
sauer@auschs.UUCP (Charlie Sauer) (07/23/88)
In article <738@dlvax1.datlog.co.uk>, rch@datlog.co.uk (Richard Hughes) writes: > Can anyone tell me : > a) Why would one want to change the boot device in this way ? i) {why change boot device?} There are lots of reasons, but most typically, in my experience, to have more than one operating system installed, e.g., both AIX and 4.3/RT, as I have on one of my machines. ii) {why this way?} (Because the engineers decided to do it this way??) > b) How and why has it been changed ? The ROM default boot order is floppy 0, floppy 1, disk 0, disk 1, disk 2. The boot code will look at the NVRAM ("Non-Volatile") and if there is a valid CRC, it will use the boot order specified in bytes 27-31. If you change the boot order and then od -x /dev/nvram, you should see f0, f1, d0, d1, d2, respectively for the selected boot devices. If the boot code finds such entries, it won't try the unlisted devices. In AIX, the special key sequences Ctrl-Alt-A, Ctrl-Alt-B, ... will set the initial value in the NVRAM (byte 27) to f0, f1, ..., respectively. Thus Ctrl-Alt-C would say that it is only possible to boot from disk 0, for example. After the VRM boots, it will still check for a bootable virtual machine on floppy before it tries for a bootable virtual machine minidisk. This is why install/maintenance would boot but not the diagnostics, if the NVRAM was set to only boot from disk. I've only tried these sequences in normal operation modes, they may not work at some other times. In 4.3/RT, the sautil diskette has a utility for changing the boot order in NVRAM. Sometimes I will use one of these (key sequence or sautil) to choose whether to boot AIX vs. 4.3, but usually I just leave things defaulted to boot AIX and boot 4.3 from sautil when I want to run 4.3. > c) Having changed it, is there a better way to reset it ? I normally have found either the key sequence or sautil approaches sufficiently usable for the few times that I've really used this feature. Pulling the battery also works. In AIX, I imagine that if one tried writing to /dev/nvram (with root authority), this could be made to work. There may be some equivalent special file in 4.3/RT, but I haven't noticed it. -- Charlie Sauer IBM AES/ESD, D75/802 uucp: ut-sally!ut-emx!ibmaus!sauer 11400 Burnet Road csnet: ibmaus!sauer@EMX.UTEXAS.EDU Austin, Texas 78758 aesnet: sauer@auschs (512) 823-3692 vnet: SAUER at AUSVM6