systemctl isolate - what's the reasoning behind the word "isolate"?

Question

I don't find systemctl isolate a very easy set of commands to remember.

What's the reasoning behind the use of the word isolate for switching between the older, but what I found a lot more user-friendly, run levels?

Answer 1

I was wondering the same thing. From the systemctl man page:

isolate UNIT

Start the unit specified on the command line and its dependencies and stop all others, unless they have IgnoreOnIsolate=yes (see systemd.unit(5)). If a unit name with no extension is given, an extension of ".target" will be assumed.

This is similar to changing the runlevel in a traditional init system. The isolate command will immediately stop processes that are not enabled in the new unit, possibly including the graphical environment or terminal you are currently using.

Note that this is allowed only on units where AllowIsolate= is enabled. See systemd.unit(5) for details.

So the word "isolate" means run the requested unit, and make sure nothing else is running (with a few exceptions mentioned above).

Since runlevels have been replaced by targets (which are more or less just a set of services that you want to be running in a certain situation, like for multi-user or graphical usage), you can switch to a "runlevel" by starting the equivalent target and stopping anything that is not part of the new target - using isolate.