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Several sources online discusses the difference between Linux systemd service management facility and that of System V.

While there's an official website for systemd, I found no official definition for that of System V (I checked SVID issue 2, SVR4's User Manual, Programming Guide, and Sys Admin Guide, and Linux Filesystem Hierarchy Standard).

To phrase the question to avoid it being closed as a reference request: Is System V service management facility something officially defined or just a set of conventions adopted by the user community?

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    Requests for documentation are off-topic for U&L, but sysvinit comes with documentation and man pages. If you don't want to install sysvinit just to read them, you can find them in the github repo at github.com/slicer69/sysvinit - AFAIK, there is no specification document for sysv. It doesn't really need one - it's not trying to turn linux into a poor imitation of a Mac/Windows hybrid, by borging everything into one do-everything-badly program.
    – cas
    Nov 19, 2022 at 5:58
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    @cas Fair enough, but I see this sentence in the help center page for topicallity: "The only exception is questions about where to find official documentation (e.g. POSIX specifications)." and if you consider Unix System V documents non-official, then please do close it.
    – DannyNiu
    Nov 19, 2022 at 6:08

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AT&T System V service management was documented, somewhat succinctly, in the rc0, rc2, and rc6 manual pages.

rc0 documents the shutdown sequence:

  • run files starting with K in /etc/rc0.d, in ASCII order;
  • send SIGTERM to all still-running processes other than rc0 and processes 0 and 1;
  • send SIGKILL to all still-running processes other than rc0 and processes 0 and 1;
  • unmount all file systems other than /.

rc2 documents the multi-user startup sequence:

  • run files in /etc/rc.d, in ASCII order;
  • run files starting with S in /etc/rc2.d, in ASCII order.

rc6 documents the reboot sequence:

  • build a new kernel if necessary;
  • unmount all filesystems.

These manual pages also document how init takes care of the rest of the process, following the actions set up in /etc/inittab; init is also documented in its own manual page.

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  • I feel sorry for not noticing them in the first place, but then again, the description didn't contain the keyword "service" which I looked for. (I thought it'd be something like the sophisticated SystemD facility.)
    – DannyNiu
    Nov 19, 2022 at 14:41
  • I found them because I knew what to look for (rc) ;-). Nov 19, 2022 at 14:46

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