From: hedrick@athos.rutgers.edu (Charles Hedrick) Subject: Re: difference between SVR4 and linux Date: 6 Mar 1993 00:07:45 GMT
kims@panix.com (Sang Kim) writes:
>I just wanted to know what are some differences between UNIX (the real thing)
>and Linux or any other UNIX like os.
The subject of your message and its body have slightly different
implications. I.e. you're equating SVr4 and "real" Unix. In fact
over the last 5 years or so there's been a de facto convergence of
Unix, with the major workstation vendors supplying a system containing
the major features of System V and Berkeley. Linux follows this
overall trend. SVr4 does not.
SVr4 is in many ways a departure. While USL has finally accepted many
ideas from Berkeley, they have still tried to keep many of them at
arm's length. Thus there are separate versions of some the major
utilities, separate include files, and separate libraries. There's a
sense in which this is "cleaner". But people had gotten accustomed to
using a mixture of Berkeley and System V features. SVr4 has also
added some new ideas, e.g. streams and the new utmp files (utmpx and
wtmpx, with new subroutines to handle them). Streams pty's are
allocated in an entirely different way than "traditional" pty's. The
SVr4 way is simpler, and more secure, but it is incompatible. SVr4
also has longer uids, user names, etc. Thus in many ways Linux is
closer to what most of us have come to think of as Unix than SVr4 is.
This isn't intended as a criticism of SVr4. There are good arguments
for many of the changes, though I still haven't been convinced about
streams-based networking.
Linux, like SunOS, Ultrix, etc., is a fairly pragmatic attempt to
provide the most features that the Unix community has come to expect.
However the set of features is still somewhat smaller than SunOS and
other commercial systems. The most visible omission that I've seen is
Berkeley tty handling. Some people have been upset by the omission of
the "three wierd sisters" from System V (IPC, shm, and locking).
However locking appears to be 99pl6, and I believe the other two are
under testing. Berkeley tty handling is no longer as important as it
used to be. Most software now has conditionals for support of System
V or POSIX tty handling. I haven't seen much about terminfo, but it
is also missing. (termcap and curses are there.)
I believe Linux now has a large enough set of features that it should
support any software that has been designed to be portable, except if
it relies on shared memory or IPC. But it's going to feel more
"traditional" than SVr4 and "smaller" than leading commercial
workstation versions of Unix.