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The differences between System V and BSD Unix

What is (are) the major difference(s) between a System V and BSD system? How do I identify a Unix variant that follows the BSD model vs. the System V model?

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Before I answer these questions, some background information will be necessary. As you may know, Unix was "invented" in 1969 and developed in the 70's. By the 80's there were two distinct branches, System V and BSD. System V was always considered more commercial, while BSD was the university model, and was developed during the 80s at the University of California Berkeley. The original Sun OS was based on BSD, though BSD eventually died a slow death with Sun moving to Solaris.

While most of today's systems generally mix their variants between these two branches, SCO, Solaris and HP-UX are System V-based, while AIX is pretty much a mix of both. Many of the differences are subtle, and you can sometimes tell the influence from same basic commands, such as pg (system V) and more (BSD).

The locations of the commands and the different options supported by certain commands are one of the big differences. I would say one of the main differences between BSD Unix and System V Unix is with system administration and networking. System V systems have more standardized tools for configuring a system, installing prepackaged software, and network programming. The filesystem structure is also very different. BSD puts files in bin, sbin, /usr/adm and /usr/mail, while system V, puts files in /usr/bin/, /usr/sbin, /var/adm and /var/mail.

The print subsystems in BSD (lpr) and System V (lp) are also different, as are the files required to set up and provide access to the printers and the commands to issue for print requests. Files used during boot-up include /etc/rc.local and /etc/rc.boot on BSD systems and /etc/rc0 and /etc/rc2 on System V. The user maintenance utilities are also different in the two branches.

My favorite Unix of all is AIX, which -- as I stated previously -- is a mix between the two. It's almost like using the best of both worlds.

This was first published in May 2005

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