On Linux/Unix (not sure about other platforms), you can configure a "Compose key" (people usually use something like the Menu key, or the right Alt key).
You can then hit that Compose key, followed by multiple other keys and they will be combined into a character, usually roughly relating to the shapes.
- Compose L / gives Ł
- Compose + - gives ±
- Compose 1 2 gives ½
- Compose C = gives €
- Compose - - - gives —
- Compose c s gives š
etc. There's a big table somewhere where all these are defined.
On android keyboards you can hold down the letter and get a list of "alternative" letters (seems to depend on the keyboard and keyboard layout configured what you get), you can also configure multiple languages/keyboards and then switch between them, by holding the spacebar.
man switch_root
If you look at the source code, it uses
mount(2)
with the MS_MOVE flag to move the /proc, /dev, /sys, /run to the new root, then deletes all the files on the old root fs recursively, then MS_MOVE-mounts the new root over the old one. As the comment in the source code points out:This is presumably why it deletes the files on the initrd, because it is a ram disk and the files would be eating up memory if left there.