1. Is Ubuntu 18.04 using Upstart or systemd?
  2. I know with the directories named Rc0.d Rc1.d Rc2.d ......Rc6.d. we can control runlevels in Ubuntu 18.04. But what is the difference between what they do, and the *.wants directories?
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    “So I know with these directories…” — What directories? Please don't assume that we know what you are thinking. Edit you question to make it clear what you are asking. (Note: I only pointed out the first problem that I found) – ctrl-alt-delor May 30 at 19:13
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    Your question is a good one, don't worry on the voting score! – peterh says reinstate Monica May 31 at 19:38
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    No voting is nothing, what is important is to understand what i don't, But after doing some studying and searching inside my Ubuntu18.04 i came to a conclusion that the Upstart directories are just there in Ubuntu in case someone wanted to switch back to upstart because all the services and the .target and the target.wants files are connected and can alter the system runlevels. So thank you for giving your opinion and your knowledge. – Sami Jun 1 at 13:32
  1. The Packages list for Ubuntu 18.04 LTS shows, in the admin section, that systemd is used, not upstart. Ubuntu even provides a comparison.

  2. *.wants directories hook units into the start-up of other units, without having to modify their unit files. Units are 'plain text ini-style file that encodes information about a service, a socket, a device, a mount point, an automount point, a swap file or partition, a start-up target, a watched file system path, a timer controlled and supervised by systemd(1), a resource management slice or a group of externally created processes.' Runlevels are exposed via "target units" by systemd. By contrast, good ol' Sysinit used the Rc?.d files to change runlevels, and that still works if you override what systemd did. Wikipedia has a useful explanation.

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