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I am planning to take the LPI exam, and need to know how SysV works. As far as I can tell, a real SysV system is described here:

http://www.softpanorama.org/Commercial_linuxes/Startup_and_shutdown/runlevels.shtml

and a Debian SysV-like system is described here:

https://www.debian.org/doc/debian-policy/ch-opersys.html#s-sysvinit

According to the links, one big difference between the two appears to be that when switching runlevels:

SysV: Runs all kill scripts from the previous runlevel, and then runs all start scripts from the new runlevel

SysV-like (Debian): Runs all kill scripts from the new runlevel, and then runs all start scripts from the new runlevel

Is this accurate, or have I misunderstood something? When the LPI website mentions that SysV is on the exam, would they be talking about the real SysV, or the commonly used implementation - Debian's SysV-like system?

  • Update: It was not on LPIC-1 Exam 101 - at least my copy - I'm not sure if everyone writes the same test. I'm still interested in the answer though – Tal Jan 29 '15 at 22:31
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I recently had the opportunity to note how the init system on a pecom system was implemented, and it was fascinating. The script /etc/init.d/rc carried a Debian copyright notice was similar to but not identical to the current Debian version. The rc script runs the scripts for the appropriate runlevel from the S and K symlinks, but has an optimization to not run K scripts which have a matching S script in the same runlevel. On a typical Debian system this is not an issue as the link creation scripts never create both K and S links for the same script, but on a pecom system (defiantly not a Debian system, uses rpm) there is a K script for everything in every rcX.d directory and there are S links for the items needed in the new runlevel, so if the Debian optimization was not in place every runlevel change would be just a kernel and a few gettys shy of a reboot. Such a set of links would result in identical behavior regardless of which directory the K scripts were run from.

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