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Prior to RHEL 7, their distributions were built on SysV, a manager that looks much like the legacy System V (init.d, rc, runlevels...).

They changed it to systemd from RHEL 7.

But what is the real difference between SysV and the Unix-like System V?

Why did they call it SysV, if it's the same?

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  • hi! you got most of the terminology wrong, so I hope I can clear that up with my answer. I wonder where you've gotten the information from: It sounds like a misconception that asking ChatGPT would cause. If you're doing that, don't! ChatGPT doesn't understand any concepts, it's just good at generating sentences that sound right and contain the words you'd find in a text about your topic most likely.
    – Marcus Müller
    Commented Jun 27 at 9:40
  • Thank you for your answer and for the keyword corrections. It's really helpful, and so much more clear. No, it was no ChatGPT, just the highlighted keywords I could pick while doing my research.
    – Sandburg
    Commented Jun 27 at 14:21

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OK, we need to come clean here a bit with terminology, before we can talk content:

Prior to RHEL 7, their distributions were built on SysV

No. SysV is short for "UNIX System V", and it's a 1983 UNIX operating system, not related to Red Hat Linux.

You thankfully clarify that you mean a "manager". I'd call it the "init system"; and the Linux world usually calls what you mean "SysV-style init"; not just SysV (because SysV is an operating system suite, not just a boot process manager).

So, that already answers part of your question:

But what is the real difference between SysV and the Unix-like System V?

None, "SysV" is really just a shorthand for "System V". And both are not Red Hat Linux, nor is that a descendant of them. (And, System V isn't only "Unix-like", it is a commercial UNIX by AT&T.)

In other words, Red Hat (and basically all other Linuxes of the day) used the init concept from SysV, by using the Miquel van Smoorenburg's sysvinit program. Which was, according to its Changelog file, originally a primitive port of the concepts of the System V init process to Minix. There's no System V in Red Hat Linux (we know that, because otherwise SCO would have tried to sue the hell out of Red Hat etc).

Why did they call it SysV, if it's the same?

It's not the same. They don't call it SysV, they call it SysV-style, because it reuses concepts from UNIX System V from 1983. (that even rhymes!)

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    System V release 2, 3 or 4? They were markedly different iterations and I remember spending a long time trying to catch up with the new administration tools in (ICL's version of) SVR4. Flagged only for historical purposes, of course
    – Chris Davies
    Commented Jun 27 at 9:56
  • @ChrisDavies interesting question! Can't even find a reference to the release that it resembles in sysvinit; it just says "compatible with the System V init" (from init.8). I can take a guess from the timeline and from the fact that "BSD-style init" probably descends from BSD4.3, which descends from SVR4, that "System V init" actually means "System III init with all the modification up to including SVR3", but that's really just guesswork
    – Marcus Müller
    Commented Jun 27 at 10:11
  • Yes, the sysvinit concepts come from System III. The rc.d structure commonly used on Linux distributions in the past comes from NetBSD. See retrocomputing.stackexchange.com/q/8289/79 and jdebp.uk/FGA/system-5-rc-problems.html for some of the history.
    – Stephen Kitt
    Commented Jun 27 at 11:56

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