February 1999
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Linux 101

Linux gets its bite of the Macintosh For Linux-on-the-Mac, 'diversity' is the watchword Summary Rick looks at the varied world of Linux distributions for the Mac. In the wonderful world of Mac-Linux, no one version suits all. (1,200 words) By Rick Cook

For one thing, none of the distributions will run on all Macintosh architectures. That's because Apple has used two microprocessor architectures, perhaps half-a-dozen system architectures, and countless firmware versions on the Mac. Even among the later Macs, based on the PowerPC RISC processor, there are too many versions with too many differences for a one-size-fits-all Linux. And the PowerPC versions are incompatible with the early Macs based on the Motorola 68000 series processors.

That said, Macintosh owners, especially owners of PowerPC machines, have a number of interesting choices when it comes to Linux.

Linux/m68k
This is a version of Linux for systems based on the Motorola 68000 series processors -- or more correctly the 68020, 68030, and 68040 versions, since Linux/m68k needs a memory-management unit (MMU) to run properly.

Linux/m68k also runs on other 68000-based systems, including the Atari and the Amiga.

Getting Linux/m68k going on the Macintosh has been a difficult proposition, in part because Apple isn't forthcoming about the details of its 68000 systems. According to the Linux/m68k Web site, there are currently 27 models of Macintosh that will boot Linux/m68k. However, according to the supported systems page on that very same Web site, "'booting' ... refers only to working video and low-level drivers that would allow a login. It does not imply ... keyboard, serial, or SCSI support or any other drivers for that matter."

Linux/m68k is very much a work in progress. Its developers are adding support for peripherals as fast as they can, but it's a slow process -- partly due to lack of publicly available information and partly because there are so many models of 68000-based Macs.

MKLinux
This is the closest thing to an "official" Apple version of Linux, since its acceptance is being rammed through by a team from inside Apple. Still, it isn't an Apple product, it's unlikely ever to be an Apple product, and you can't get it from Apple.

(For more on this, see "Apple's position: No Linux")

Technically, the most interesting tidbit of information is that MKLinux is built on the Mach microkernel, just like Mac OS X

Instead, a developer release is distributed by Prime Time Freeware. What makes MKLinux a "developer release" is, well, minimal support from the distributor. MKLinux itself is a full release of Linux with all the goodies you expect from any Linux distribution.

Technically, the most interesting tidbit of information is that MKLinux is built on the Mach microkernel, just like Mac OS X Server, the new Macintosh operating system (for the server and desktop) being released this year.

Microkernel architectures are nifty and interesting to the computer scientists and hackers among us, but from a user's standpoint, the microkernel base means almost nothing -- it's invisible. MKLinux boots and runs just like Linux, specifically Red Hat Linux 5.0, because that's what it is based on.

The difference between microkernel and so-called monolithic architectures appears to be significant. For example, reports cite MKLinux as running about 20 percent slower than LinuxPPC. Now, whether or not this is exclusively a penalty for running a microkernel architecture depends on which expert you talk to. MKLinux supporters say the mircokernel penalty is really only noticeable with drivers. Supporters also like to point out that optimization and tuning will undoubtedly narrow the performance gap.

The microkernel offers some advantages, notably the ability to run a production MKLinux system and bring up a second kernel for debugging or other work at the same time. "It turns out to be real useful for developers and interesting for exploratory kernel programming," says Rich Morin, president of Prime Time Freeware.

"Apple is not interested in making a real product out of [MKLinux] and Prime Time Freeware isn't interested in doing it either," Morin says. "We're not selling [MKLinux] as a supported operating system you can run a company on."

LinuxPPC
LinuxPPC is another version of Linux for the Macintosh and other PowerPC-based computers. Unlike MKLinux, it uses the conventional Linux kernel instead of the Mach microkernel. Since the first version of LinuxPPC shipped in February 1997, about 100,000 people have downloaded it. Currently downloads are running about 500 a day, according to the LinuxPPC folks.

LinuxPPC is offered as a commercial release by LinuxPPC Inc. Like MKLinux, it's based on Red Hat Linux and comes with the usual range of applications and utilities. That includes the KDE GUI, Netscape Communicator, the GIMP, the Apache Web Server, an e-mail server, a secure shell server, and a suite of C and C++ software-development tools. In addition to the freely distributed material that comes with the operating system, the Applixware Office Suite has been ported to LinuxPPC by Applix.

Yellow Dog Linux
Yellow Dog is a commercial distribution, also based on LinuxPPC. The first release, the Yellow Dog Linux Champion Server, was originally scheduled for January 1999. (The date was pushed back to allow it to be based on the new 2.2 Linux kernel. It is expected any day now.) The workstation version, Yellow Dog Linux Gone Home, is slated to be released after the server version.

Compatibility
The binary versions of Intel Linux software won't run on the Mac, but thanks to the wonders of open source, users can recompile the programs to run on the Mac.

In general, those writing Linux for the Mac are taking a lot of care to make software porting as painless as possible. This doesn't mean totally painless, of course, but it usually doesn't take a lot of tweaking to get Linux sources to run on Macs. The biggest worry is making sure you have the right libraries and such.

This is one reason LinuxPPC is releasing the next version of its distribution, version 5, with the glibc C libraries, which are pretty much the standard in the Intel-Linux community. Yellow Dog Linux also says it will use the glibc libraries.

Linux for the Mac has generally lagged behind Linux for Intel in maturity and features. The gap is closing rapidly, though. Within the next year or so, we'll probably see distributions of Linux for the Mac that are at least as good as the distributions for Intel.

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About the author
Rick Cook has been covering computers and high technology for nearly 20 years for various publications. He is the author of a series of fantasy novels full of bad computer jokes.