While the other answers to your question are, for practical purposes, fairly accurate, as far as they go, technically, there actually are some binary compatibility features between Unixen. Early on, Linux got a binary compatability module, to help with the lack of application support from various vendors at that time. One can still find this in module form (sort of like a driver), in /lib/modules/*/misc/iBCS.o, but it's not likely to be used much anymore: the pendulum has now swung the other way; the other Unixen are now providing similar modules and compatibility features so that they can run Linux binary (compiled) programs. Also, Unix is a now a brand name that belongs to a standards group (Novell donated the brand, when they owned the primary license rights). In theory, a Linux distributor could work to make their distribution completely Unix compliant, pay for the testing to prove it, and get the actual Unix brand, but it would be pointless -- a waste of money. Linux is fast becoming the de-facto standard for Unixen, having put the weaker Unix companies out of business, and is now even a threat to Microsoft, by their own admission. Linux is now pushing the leading edge of GUI innovation, and those desktop interfaces are being adopted by the older commercial Unix companies that survive. M$ continues to lag way behind in this and other areas. LCR On Tue, 11 Dec 2001, Raul A. Gallegos wrote: > When you compile a program for one os it will not run on > another os without some tweaking or a complete recompile. For > example the ls command for linux is a different compiled > version than the ls command in Solaris. Shell scripts for the > most part run on any unix/linux os with ... > cbowman@netdoor.com said the following on Tue, Dec 11, 2001 at > 10:36:34AM -0600: > > > > hi, I have a question. I had heard that it is posable to run > > some unix programs under linux I don't know if this is true, > > or not but, I had heard [...] -- L. C. Robinson reply to no_spam+munged_lcr@onewest.net.invalid People buy MicroShaft for compatibility, but get incompatibility and instability instead. This is award winning "innovation". Find out how MS holds your data hostage with "The *Lens*"; see "CyberSnare" at http://www.netaction.org/msoft/cybersnare.html