Linux Zone Feature: Linux On Powerpc Processors

Your favorite operating system isn't only for x86


David Mertz, Ph.D.
Text Processor, Gnosis Software, Inc.
January, 2004

Even though most Linux users have treated Linux as an operating system for their x86 white boxes, Linux runs equally well on PowerPC machines. With the appealing range of PPC machines produced by Apple, the option of using Linux on one of these is of great value to many users.

About Ppc

The POWER architecture describes a family of RISC CPUs that arose out of a consortium of IBM, Apple and Motorola. Within this chip family, higher-end POWER4 chips are used in various IBM "big iron" or mid-range machines; at a personal computer, workstation, or workgroup-server level, the PowerPC branch of POWER chips are used in widely-used consumer machines from Apple Computer. Chips in the PowerPC family--especially those from Motorola--are also used in various embeded and specialized systems, including in PCs from smaller manufacturers such as the phoenix-like current incarnation of Amiga.

The interelations among various POWER architecture chips are similar to those in the x86 world--for the most part, later generations of chips provide backwards compatibility with earlier ones while also offering new and enhanced capabilities. Within the PowerPC family branch, five+-year old Apple machines used 601, 603, and 604 model chips. The current models have phased out the G3 but continue to use the similar G4, both 32-bit chips, running at various clock speeds; the recently introduced G5 is an 64-bit IBM chip that mostly adds some multimedia-specialized instructions to the POWER4 chip models.

The bottom line on all these chips, from a Linux developer's perspective, is that they all run Linux happily and well. For the PowerPC branch of the chips, excellent consumer-friendly distributions are available, and offer commercial customer support. IBM is also happy to install Linux for customers of its high-end POWER4 machines.

So You Want To Run Linux, Why Buy A Powerpc Machine?

The "default" system for running Linux is unquestionably x86 machines. Whether based on CPUs from Intel, AMD, Cyrix, Transmeta, or smaller makers, the x86 architecture is well-known and makes up the large majority of personal computers, workstations, and small servers. It is certainly safe to go with the majority.

For most Linux users, the best reason to buy a PowerPC machine will be, quite simply, the range of well-engineered and reasonably-priced machines available from Apple. Admittedly, the G4 lines--bottom line--do not quite keep up with comparably priced x86 machines in CPU power. The G4s do not lag that far behind, but they do a little bit. However, Apple makes most of the best laptops available from an ergonomic, aesthetic, battery-life, and weight perspective. All of those features are far more important to me, for a laptop, than is raw number-crunching. On the desktop, the G4 models differentiate themselves mostly on an aesthetic or ergonomic perspective--for example in the compactness of Apple's cantilever-mounted flat-panel iMacs. All of Apple's machines, moreover, have a good reputation for durability and reliability--including their rackmount servers, which are nice for clusters and server arrays.

At the high-end, Apple's G5 towers are comparable in speed to the fastest x86-derived CPUs and systems; i.e. the Intel Itanium and AMD Athlon64. Benchmarks among the three contenders are a mixed bag, but all three chips obtain quite similar performance (all are remarkably fast, and suitable for intensive number crunching applications). Moreover, on price, Apple's G5 towers seem to sell for less than comparably configured systems from x86 vendors like Dell, Gateway, HP, and other well-known PC retailers (contrary to Apple's reputation for imposing a price premium). It is worth noting that Apple has contributed optimizations to GCC3+ that bring its generation of PPC object code to a quality similar to that of Intel's ICC or IBM's VisualAge C++ compilers for x86 (i.e. arguably better than GCC on x86).

At the end of the day, the differences between Linux/x86 and Linux/PPC are remarkably minimal. This article will cover a bit more detail on distributions below, but generally, on Linux/PPC you can use the same window managers, run the same utilities, host the same servers, and so on, as you might on any x86 box. Unless you look at the physical hardware--or are a rare user with a need for precise performance characteristics of various operations (e.g. your application is specially designed around the PPC Altivec vector extensions)--you will not even know which architecture you are running Linux on. The screen will look exactly the same, most configuration files will contain the same settings, and the same bytes will go out over the wired.

So You Own A Mac, Why Run Linux?

To a surprising degree, operating systems (other than those from the highly-proprietary Microsoft) have become commodities. What this means is that most vertical applications are a mere recompilation away from running equally well on Linux, FreeBSD, SunOS, Irix, AIX, or indeed on MacOSX (in some cases even this step is not necessary, since ABIs support foreign binaries).

If you bought an Apple machine in the last few years, it came preinstalled with a high-quality Unix-derived operating system called OSX. OSX has a kernel and collection of base utilities called Darwin which is under a Free Software license, and is derived (in part) from FreeBSD--the only proprietary elements are in the GUI (Aqua) and in the collection of end-user and system-administration applications that come bundled with OSX. Even X11 (specifically XFree86, despite what the name insinuates) is supported on OSX, in either fullscreen or rootless modes; "rootless" here means that X11 applications run side-by-side with native Aqua ones. You can run Apache on OSX; you can run NcFTP server, you can even run GIMP or KOffice. Why bother installing Linux?

There are a number of scenarios where it makes more sense to run Linux on your Apple machine than to run OSX. A first situation--one that will appeal much more to hobbyists than to corporate users--is when the Mac in question is an older machine. OSX is either entirely unsupported, or at least quite sluggish, on older Macs: 603s, 604s, or even early G3s. Linux can be quite snappy on these older systems; and Linux is a lot more useful as a server, or in many cases even as a desktop, than is the MacOS9 (or earlier) that came with those older machines. Still, the hobbyist segment is fairly narrow, or at least does not need to look here for advice.

A more important situation where Linux is worthwhile as an operating system for G3, G4, or G5 machines from Apple is when you want to assure a uniform system/user interface across machines. Many enterprises, hosting companies, schools, or research facilities will have a mixture of x86 and PPC systems that it provides to users. While you can recompile most specific Linux applications for OSX, doing so does not bring the systems all the way to having a uniform GUI, configuration files, directory structure, and build environment between the various maintained machines. "Linux everywhere" assures a much greater degree of consistency. One thing in particular that can be confusing to Linux developers about OSX is its overlay of two distinct directory organizations--the traditional /etc/, /usr/local/, /sbin/ and so on of Linux/Unix systems, and the /Application/, /Library/, /System/ from MacOS9. The /sw/ hierarchy fink creates, additionally, is almost like a third overlay. Moreover, even though OSX has an X11 server built in, I have still found a variety of minor glitches (redraws, key bindings, etc) in using X11 applications there--Linux with a good window manager like KDE or Gnome is a much more seamless environment in this case.

Apart from developers who might use PPC desktops or laptop machines, web-hosting companies would like to present a predictable system to its customers who maintain sites via SSH, FTP, or web-based interfaces--regardless of whether a domain is hosted on PPC or x86 chips. Considering servers further, Linux offers several advantages over OSX, even over the server version of OSX. One major strength of Linux is the variety of filesystems that have been developed for it or ported to it: ext2, ext3, ReiserFS, IBM's JFS, SGI's XFS, etc. Each of these has its own strengths, often specific to particular usage scenarios (web host, streaming multimedia server, RDBMS, etc.). While the server version of OSX supports an enhanced version of HFS+ with journaling and optional filename case-sensitivity, it cannot match Linux' range of filesystem options. As well, I should mention--but not overemphasiz--the little matter of cost: An unlimited-client version of MacOSX Server will cost you US$1000 per machine, Linux is free of cost (and even a support contract from a distribution vendor is much cheaper than this). The caveat here is that if OSX Server's administration tools save your IS staff even a little work each day, that kilodollar outlay can quickly pay for itself.

Distributions

For this article, I installed and evaluated four distributions of Linux for PowerPC machines. All were installed and tested on a G4 iMac. I found two of the distributions to be well-polished and easy to use, right on par with the best x86 Linux distributions; the other two I would have to describe as "not ready yet." A few other distributions exist as well--and more will certainly be created over time. I was not aiming to provide a thorough comparison of every distribution readers might choose to use, but simply to get a sense of the "state of the art"--no slight is intended towards those distributions I did not look at.

The two distributions that I found less that compelling were Debian (Woody) and Knoppix. The latter is an interesting creature that I've found useful on x86 machines. Knoppix uses a "live boot" CD--that is, booting from the Knoppix CD gives you a working Linux environment with KDE, OpenOffice, and a good collection of utilities. Using Knoppix, there is no need to create any partions or boot setup on a PC, and you can carry the Knoppix CD between various machines to have a uniform configuration on each. Unfortunately, testing on three separate systems, Knoppix/PPC never managed to boot quite right--KDE would not load, and the fallback was a crude TWM shell that did not get the video mode quite right (colormap and sizing problems). Networking, including wireless, however, seem to be recognized correctly; so you can use the command-line tools. Once Knoppix/PPC gets some more polish to it, it--or something like it--will be a very useful way to run Linux non-destructively on existing MacOSX machines.

The problems I had with Debian/PPC are probably similar to what dedicated Debian users most love about their distribution to start with. Installation is strictly a text-mode affair, with no options for changing configuration once a fatal "Y" or "N" has been pressed. As long as you make no mistakes, and read each installation screen carefully, installation proceeds well enough--it even automatically finds on the network any modules that do not happen to be on the installation CD(s). Many installed utilities and applications--GCC, Python, the kernel, OpenOffice, etc. lag quite a few versions behind the most current ones, but most widely used tools are available as Debian packages (and hence fetchable using the wonderful apt-get). However, the killer problem I found with Debian/PPC was my inability to get X11 working on it--the installation seemed wholly unaware of any remotely relevant video card models, and some post-installation attempts at configuration proved fruitless too. I am certain that there are Debian/PPC users who have worked out the configuration issues, but compared to the ease of installation of other distributions, I have trouble recommending Debian to many users.

Both YellowDog (Sirius/3.0.1) and Mandrake (Bamboo/9.1) have quite slick Linux distributions for PowerPC. Overall, I would recommend YellowDog over Mandrake to most users, but each have some strengths and weaknesses. The fact that YellowDog's maker, Terrasoft, specializes in PowerPC systems probably leads them to pay a somewhat greater attention to the small details of tuning Linux for PPC. On the other hand, for enterprise users aiming at a thorough consistency might choose Mandrake for both their x86 and PPC machines.

YellowDog and Mandrake both use attractive and friendly installation GUIs; perhaps a slight edge functionally goes to Mandrake for its list of pending and completed steps to the left of the dialog area, but I nonetheless prefer the aesthetics of YellowDog screens. Both systems come with a large collection of applications and utilities: Gnome/KDE, OpenOffice, XFree86 4.3, Mozilla, Mac-on-Linux, various servers. For most applications and utilities (and the kernel), YellowDog ships with slightly more recent versions, but generally only a micro-release difference, not a whole minor version. In any case, neither YellowDog nor Mandrake had any difficulty recognizing my network, graphics card, partitions, mouse, keyboard, and so on. However, I did experience a glitch with YellowDog's first attempt to reboot into X11--I needed to run /usr/X11R6/bin/Xautoconfig once to clear up the problem.

A few differences between Mandrake and YellowDog stand out. The menu organization and theme is a bit different under the KDE window manager that I selected (the default for both), but both systems were very reasonable (and configurable once the system is installed, in any case). And the package selection presets contained a similar set of "personal", "server", "workstation" options (with customization allowed). I really like(d) Mandrake's DiskDrake tool for partition management--this graphical utility lets you add, delete, non-destructively resize, format, and otherwise manipulate partitions (but no non-destructive resize on HFS+). Among other things, DiskDrake let me choose the format for my Mandrake partition(s) during installation, rather than simply defaulting to ext3 as YellowDog did (but I could still add an extra ReiserFS partition easily enough later under YellowDog). And I am generally very impressed with Mandrake's Control Center, on both x86 and PPC, not because it does anything unique, but because it unifies configuration tasks under one interace.

Despite Mandrake's advantages, my ultimate reason for preferring YellowDog is its package management system. YellowDog seems to be something of a hybrid system: it uses RPMs during installation, but it also installs apt-get for later updates to the system. I have not looked at the internals of the setup, but I could type apt-get install openoffice at one line, and have every dependency resolved correctly, the whole 350 megabytes (after expansion) of files download, and the links added to my KDE menu without restarting X11. After wasting many hours wrestling with RPM dependencies, this was a marvel to behold. Of course, I've been spoiled by using fink under MacOSX, which does the same thing (and is based on apt-get).

Partioning, Multi-boot Management, And Emulation

Linux/PPC has an important disadvantage relative to Linux/x86: As of this writing, no tools yet exist for non-destructive repartitioning of HFS+ partitions (at least none that are post-alpha and can run from OSX or Linux). Unfortunately, this means that you cannot easily configure a multiboot system from an existing MacOSX system; most recent Linux/x86 distributions provide an analogous capability to add Linux to an existing Windows system. It is simple enough to destructively partition an existing drive, then reinstall OSX to one of those new partitions; but doing this losing your existing data and system configuration (backup/restore might work, but can be tricky to get right). Of course, if you simply want a dedicated Linux machine, this is not something you need worry about.

Partitioning and bootstrapping works a bit differently on Apple machines than on x86 ones. Specifically, Apple's Open Firmware (an enhanced version of the BIOS Linux users know from x86 PCs) relies on an small "Apple Bootstrap" partition (hda2) to load the subsequent operating system from one of the regular partitions. The partition map also occupies hda1, so the first partition you will install any operating system in is numbered at least hda3. During machine startup--using the multi-boot tool yaboot--your boot process goes through two stages, rather than the one level x86 MBR boot loaders like lilo and grub use. At the first stage, you have a choice of booting from e.g. harddisk, CD-ROM, or to Open Firmware; assuming you proceed to the harddisk, you might have the option of booting various operating systems/versions that live on normal partitions.

Configuring yaboot is generally similar to working with lilo. A file called /etc/yaboot.conf contains options for various systems, kernels, partitions, and so on; the format is mostly the same as in lilo.conf. When you have configured yaboot.conf properly, you load yaboot onto the bootstrap partition using the command ybin (as root, of course). To find partition information, you must use the tool pdisk rather than the traditional fdisk on x86 Linux systems. Again, the interface is similar, but not quite the same, between the tools. For Mandrake users, the tool DiskDrake is a much friendlier and more flexible GUI based tool to do the same thing. Using yaboot, you can choose among multiple Linux distributions and/or MacOS versions at boot time.

One nice thing about running Linux on PPC machines is that you can run the Free Software tool Mac-on-Linux this way. This works much like the commercial VMWare does on x86 machines. An entire MacOS system (either OSX, or an earlier version like MacOS9) runs inside a window within a Linux/X11 display--in fact, you can run multiple MacOS versions simultaneously, each in their own virtual display window. The MacOS lives in a kind of "sandbox" where it cannot see its Linux environment, but PPC instructions nonetheless run at full native speed. Assuming you have enough memory to run such a sandbox, Mac-on-Linux gives you a nice way to continue using your MacOS applications while running Linux--even proprietary applications that you have no source code for; no need for recompilation, as is needed to move Linux applications to an OSX environment.

Resources

You can read a concise history of the POWER architecture at:

http://en.wikipedia.org/wiki/IBM_POWER

For the PowerPC branch, take a look at:

http://en.wikipedia.org/wiki/PowerPC

You can find some general information about distributions of LinuxPPC, and additional installation tips at:

http://www.rietman.biz/~wijnand/linux/mac/index.html?main

TerraSoft are the makers of YellowDog Linux, and also offer custom PowerPC systems--both as an Apple reseller and their own systems--with pre-installed versions of YellowDog on them:

http://www.yellowdoglinux.com/

Mandrake's PowerPC Linux distribution can be found at:

http://www.linux-mandrake.com/en/ppc.php3

Apple Computer offers a wide range of PowerPC-based computer systems:

http://www.apple.com/

You can find out the current status of Mac-on-Linux at:

http://www.maconlinux.org/

About The Author

Picture of Author David Mertz is Turing complete, but probably would not pass the Turing Test. David may be reached at mertz@gnosis.cx; his life pored over at http://gnosis.cx/publish/. And buy his book: Text Processing in Python (http://gnosis.cx/TPiP/).