Why not use old smartphones as a "Raspberry Pi"?
Anyone doing it?
How hard is it to get Linux onto an iPhone?
What are some caveats - as somebody who uses a Raspberry Pi as a home server for many apps and has thought about expanding, what should I know about using a smart device for a server?
Smartphones lack nearly all of the kinds of IO interfaces supported by a Raspberry Pi.
I've used old Android smartphones with DroidScript and QPython as a music server, lighting controller, time-lapse camera. More recent smartphones I simply use WebAPI functionality.
I've tried using some old iPhones, but I find them too locked down. Perhaps I gave up too quickly, jailbreaking might have opened up more opportunities.
Is your goal to "run a server at home" or "run a server on an old phone"
One is an enabler the other is a hobby in its own right...
While some people have gotten Linux to boot on old iPhones, I don't think it's anywhere close to being a Raspberry Pi replacement at this point.
In my experience phones are not built to do a lot of concurrent processing but have a really good screen! Horses for courses.
termux would get you most of the way there but will it auto start on boot, will it run continuously and all that? i am not sure
postmarketos is a good place to start.