Linux · systemd

In the classic Init-V world, what were the standard runlevels 0 through 6, and how did root switch between them at runtime?

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More in systemd

In systemd terms, what is a target, and how do you find out (or change) which one the machine boots into by default?

After a fresh boot the kernel has loaded, but nothing else is running yet. What is the very first userspace process the kernel launches, and what is it responsible for?

Traditional init systems were collections of shell scripts. What is architecturally different about systemd, and how does it know when a service has crashed?

You run pstree and see one process at the root of the entire tree. Which PID is systemd, and why does /sbin/init sometimes appear to be process 1 instead?

What is the single central command for administering systemd services by hand, and what are its everyday subcommands?

A tutorial written for Fedora says to run systemctl start sshd, but on your Debian box the SSH unit isn't found under that name. What went wrong, and how far does this problem generalize?

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