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Tech Update
David Berlind's Reality Check
David Berlind
Solaris on course to merge with Linux
By David Berlind
April 9, 2003
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When I interviewed Sun chief engineer Rob Gingell last August, he hinted at a blurring of the lines between Linux and Solaris, if not an outright merger. Said Gingell: "Five years from now, when all the tribes intermarry, who is going to know what's Solaris and what's Linux, and who's going to care?"

So, while attending a recent chalk talk at Sun's Burlington, Mass., campus, my ears perked up when the company's chief technology officer Greg Papadopolous talked about how applications designed to run on Red Hat Linux can run unmodified on the Intel version of Sun's Solaris x86.

As it turns out, this wasn't the news I thought it was. Binaries designed to run on Red Hat Linux don't natively run on Solaris x86 without some help--yet. Achieving this level of compatibility requires a Linux emulator called Lxrun. Lxrun is an open-source project that's been around since 1997, and to which Sun has contributed engineering resources in order to guarantee its compatibility with Solaris x86. (Lxrun does not run on versions of Solaris designed for the Sparc architecture.)

The way Lxrun works is relatively straightforward. First, Solaris x86 users install Lxrun on their systems. Depending on which distribution of Linux they want to emulate (Red Hat, SuSE, Mandrake, et al), they also must load the libraries from that distribution into a directory where Lxrun will be looking for them. It is indeed possible to write an application that runs on one distribution of Linux, but not others. The difference is in the distribution-specific libraries and the chance that a developer may or may not take advantage of them. (The UnitedLinux movement is an important sidebar to this library business that I'll get to shortly.)

When Sun's Papadopolous mentioned compatibility with Red Hat Linux, almost as if to exclude the other popular distributions, it wasn't a slip of the tongue. There has been a lot of speculation about which of the many Linux distributions Sun will go with when its Linux business is running on all cylinders. Still, Papadopolous' comments don't make Red Hat a shoo-in.

According to Sun's Linux strategy and marketing group manager Jack O'Brien, "While we don't distribute Red Hat's libraries with the copy of Lxrun that's on the companion CD for Solaris, we did make some effort to make sure Lxrun works with them. But nothing stops anyone from installing it with other libraries."

According to Sun Solaris product manager Chris Baker, once Lxrun and the appropriate libraries are loaded onto a Solaris x86 system, a Linux application doesn't know or care that Solaris is running under the hood. All application programming interface usage is redirected to the Linux libraries.

But both Baker and O'Brien discussed other options available to Solaris x86 users interested in running Linux applications. These options provide some interesting clues to the direction that Sun is taking with respect to the marriage of Linux and Solaris.

"Whereas some open source developer might have had Linux in mind as a target," said Baker, "nothing prevents a user of some other version of Unix from compiling for their platform. The question is: What will happen if the developer of that source code made calls to some Linux-specific APIs? If the version of Unix that you're compiling for can't respond to those calls, you will have to adjust the source code to redirect those calls to the Unix library that provides the same or similar functionality."

To help Solaris users surface any potential library incompatibilities when porting Linux applications to Solaris, Sun has a downloadable Linux Compatibility Assurance Toolkit (LinCAT).

Although LinCAT works for both the x86 and Sparc versions of Solaris x86, to the extent that LinCAT is more about portability than compatibility, Sun is dealing with the compatibility issue in other ways. The easiest way to guarantee compatibility of the same source code between Linux and Solaris (or any other version of Unix) is to make sure that Solaris can respond appropriately to applications, even when they make calls to Linux-specific APIs. If this could be accomplished for the x86 and Sparc versions of Solaris, we would move one giant step closer to the world that Gingell described, where the tribes are intermarried and no one will "know what's Solaris and what's Linux."

According to Baker, Sun is on that path now. Slowly but surely, Sun is enhancing Solaris with libraries that will respond to Linux-specific source code exactly as expected. More germane to the future of UnitedLinux, however, is how Sun will measure such compatibility with Linux.

According to O'Brien, "We are striving towards Linux Standards Base (LSB) compliance." In almost the same breath, O'Brien warned that imprimaturs of UnitedLinux and LSB, such as one might find attached to a particular application claiming compliance, don't necessarily mean the same thing. In other words, applications designed for UnitedLinux-compliance could have compatibility issues with non-UnitedLinux-compliant distributions.

Baker, suggesting that UnitedLinux would eventually become irrelevant, said, "Which direction to take was at the core of our deliberations for Solaris. We believe, as Red Hat does, that LSB compliance is the right thing to do."

O'Brien concurred. "LSB is the way of the future and is what ISVs should be paying attention to." With Sun and Red Hat firmly behind LSB, my sense is that UnitedLinux will indeed one day be irrelevant.

To demonstrate Sun's commitment to LSB compliance, O'Brien said, "Sun is a participant in the Free Standards Group, which is the parent to the LSB project. We've assigned engineering resources to it and we'll be promoting it over the long run. Ultimately, if you're a Linux application developer and you develop for LSB compliance, your application will be guaranteed to run unchanged on Solaris as well."

"That doesn't mean you won't want to take a look at your source code and change some of the Linux-specific calls to Solaris ones," said O'Brien. "Some parts of Linux are by no means as mature as what is in Solaris. The threading model is one example. Solaris really shines when it comes to multithreading. It was designed from the ground up for multithreaded, multiprocessor environments. In the Linux world, that multithreading capability is only recently with us, and is still by no means as mature as what is in Solaris. There are also other services and functions built into Solaris that are more mature--like resource, volume, and quality of service management. Not that these aren't available on Linux; but you'll need third-party products and will have to do some integration work on your own."

Gingell's five-year plan for an intermarriage of the two operating systems seems to be on an accelerated track. Solaris continues to take on more API-level compatibility with Linux. In turn, Linux, through Sun's participation in the Free Standards Group, will undoubtedly take on more of the industrial strength attributes for which Solaris has long been known.

What does this mean in the big picture? With Sun focused on an intermarriage of its Unix with Linux, and with IBM having already stated that Linux is the successor to its version of Unix (AIX), the future is looking very Linux-like. Should Linux achieve the cross-vendor compatibility that everybody hoped Unix once would, IT managers would face the sort of options that the concept of "compliance with standards and competition on implementation" is supposed to produce. In that world, the various hardware providers (Dell, HP, IBM, Sun, et al) will be working extremely hard to convince you that, when it comes to powering Linux, their hardware platforms are less costly, more secure, and more reliable than the rest.

How Linux-like is your future looking? Leave a message in ZDNet's TalkBack forum or e-mail, me at david.berlind@cnet.com.





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