Frequently Asked Questions

Installing GNU/Linux on the IBM RS/6000 43P model 7248 HOWTO
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# 13. Frequently Asked Questions

In this final chapter I've included som frequently asked questions. This list should probably be much longer. Please let me know if you have something to add.

## 13.1. XF68 or XF86

What is right, XF68 or XF86?

I have got a lot of questions conserning the name of the X-server in the installation program mentioned in older versions of this document. I have called it "XF68_FBDev". On some CDs the server has got another name, "XF86_FBDev". The reason for this naming convention and confusion is purely historical. The Linux Frame Buffer Device was first developped on m68k Macintoshes, and the XFree86 server for the device was hence called XF68_FBDev. Later on the Frame Buffer Device was ported to other platforms like the x86 clones and PowerPC. What is the right name? The question is left as an exercise for the reader.

## 13.2. There is "snow" on my X desktop

How can I configure X so it removes the "snow" on my desktop?

The easy answer is: You can't. The kernel frame buffer device made by David Monro is still in an early stage, though working very well. Distortions in the picture when moving the mouse or scrolling a window are perfectly normal at eg 1024x768@60Hz. If you are a hacker, please fix it and post a patch to David or Leigh. We would all love it very much. note that lower resolutions like 800x600 og even 640x480 works great. And no, there are only 8bit colors availble.

## 13.3. I can't get my hardware to work

How can I get my new ultra whizbang XYZ card to work?

The 7248 is a PC-like box with ISA and PCI interfaces, so one should think that using "normal" PC hardware made for the x86 platform should work flawlessly. Sadly to say, it doesn't always do. The drivers often have to be ported, and there are not that many Carolina motherboard kernel hackers out there. In addition, much hardware made for the x86 platforms uses BIOS calls to work properly. As the 7248 and its relatives does not have such a BIOS, it's extremely difficult to get this hardware to run under Linux.

That said, there are working hardware for this box that runs with Linux. For questions about this, please contact the Workstation list, see Section 11.

Update: With the latest versions of the Linux 2.4 bk development tree (NOT the official Linux 2.4 sources), many of the problems stated above are fixed, and much more hardware is supported. For example did I put a standard eepro100 card in my box, and it worked flawlessly. This means you can use the 7248 for example as a packet-filtering firewall. I've also heard rumours on plain standard ISA Soundblaster cards working. Try and see if your card works. If it's interesting, send me an email, and I'll put a note here. See Section 9 for notes on building and installing a 2.4 kernel.

## 13.4. The PReP boot partition?

Where should I mount the PReP boot partition?

To be able to understand the answer for this question, it's important that the reader understands how the 7248 boots into Linux. This is a three step procedure. First, the Firmware (which behaves in the same way as a PC BIOS) looks for something to boot. Usually, it should check the floppy drive, the CD drive, and then the first SCSI disk. On the SCSI disk it will look for a special partition called a PReP boot partition. On this partition, it will read the first program it can find there. If this is a Linux kernel bootloader, it will read and run this, and then the bootloader boots Linux. From here, Linux is in charge.

Many have asked where they should mount the PReP boot partition (the type 41 partition). This is a common misunderstanding. The PReP boot partition, usually located on /dev/sda1, should NOT be mounted anywhere. The files on this partition, usually only a single Linux kernel with a static linked kernel bootloader, are only used by the firmware when booting. The operating system does not use these files after the kernel has booted, so there is no need for mounting that partition.

Some people mix the meaning of the /boot directory and the PReP boot partition. Both use to contain kernels, but their use are different. /boot is used for storing kernels for later use, and for bookholding system info. The /boot directory is NOT read by the Firmware at boot time, so changing the contents of this directory does not change the way the Firmware loads Linux.

To be able to load a new kernel, you have to replace the existing kernel on the PReP partition. This is done with the dd command, see Section 9 for details.

## 13.5. It won't boot at all. Could it be bad RAM?

The machine won't boot at all. I suspect the RAM could be the problem. What kind of RAM should I use for this box?

The 7248 and it's cousines with Carolina motherboard do use special RAM, more specifically, they use only parity RAM. The spesifications are as follows: 72-pin SIMM, 5 Volt, Fast Page Memory with Parity, 70 ns. David Monro states that is is possible to make Carolinas work with other types of RAM if you remove the cache. Look at Section 11 for details.

## 13.6. Kernel boots, but stops at "Parity checking"

And now I thought it would work, but it stops at "Parity checking". I can't get a step further. Can you help me, please? Has this something to do with bad RAM chips? Or is it something wrong with my scsi devices?

You use a 2.2 kernel, don't you?

This message comes from the SCSI subsystem, so it has nothing to do with your RAM. Sometimes, by uknown reason, the Linux NCR driver in the 2.2-series caused the scsi controller to hang in some uninterruptible state, which endured, even bypassing reboot. The solution then was to boot AIX or even Windows NT for PPC (yes, such a beast exists, but you really don't want it), which resat the controller in proper condition. Alternatively, switch off the machine, pull out the battery inside, let it stay out for a couple of weeks or so, and fit things back together. The 2.4 driver fixed this problem.

Boot a 2.4 kernel, and you should be allright.

This could of course also be a real SCSI parity problem. If a 2.4 kernel doesn't help, check your SCSI devices for wireing and termination problems.

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