Linux hasn't really been that way for an incredibly long time, but a large proportion of the userbase still cling to this notion, some for ideological reasons, and some out of sentimentality.
Linux hasn't really been that way for an incredibly long time, but a large proportion of the userbase still cling to this notion, some for ideological reasons, and some out of sentimentality.
If the core utilities around the kernel and the interfaces they use are well-documented, designed, and modular, then different machine types can pick and choose the components they need, and easily write their own by opening a well-defined API on something in /dev. If systemd continues to take over and alternatives smothered, very quickly the kernel will become useless to any system where systemd makes no sense, especially non-desktop embedded systems.
* Embedded systems use watchdogs. systemd implements a watchdog supervisor chain, where systemd supervises applications, and the hardware watchdog supervises systemd.
* kdbus: efficient IPC
* networkd: simple network setup, very fast DHCP client
* fast boot times
* handles many complexities, so that embedded developers can focus on their application
As for the second question: certain parts of systemd can certainly be used on non-systemd systemd (such as udev or nss-myhostname). But most would require at least some changes.