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CentOS is "derived entirely from the Red Hat Enterprise Linux (RHEL) distribution" (more here).

  1. Does it fall into any UNIX System V family? Such as PDP-11 or etc?

  2. If not, where does CentOS stands for comparing with System V family for zero downtime or performance etc?

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PDP-11 is not an Unix version, but a line of computers produced in the 70's and 80's by DEC. – Tadeusz A. Kadłubowski Jun 12 '12 at 11:08
up vote 6 down vote accepted

CentOS is a Linux variant, and therefore shares no code with AT&T Unix System V.

The Linux kernel does support many System V system calls, and as such, a lot of software written for System V was able to be ported over fairly easily. These days, I'd wager that a lot more software is written first for Linux, and then maybe ported to a modern System V derivative like Solaris.

Linux also supports a lot of BSD system calls, by the way. As Unix and Unix-like operating systems go, Linux is the most ecumenical in terms of facilities it supports.

So, Linux is System V if you squint. It is also BSD, and it is also neither.

Linux is Linux.

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