There is the handy rails server -d that starts a development Rails as a daemon. The annoying thing is that the scheduler as seen above is started in the main process that then gets forked and daemonized. The rufus-scheduler thread (and any other thread) gets lost, no scheduling happens.

So fork is fast, unsafe, and maybe bloated.

spawn starts a Python child process from scratch without the parent process's memory, file descriptors, threads, etc. Technically, spawn forks a duplicate of the current process, then the child immediately calls exec to replace itself with a fresh Python, then asks Python to load the target module and run the target callable.

In particular, one thing that fork() doesn’t copy is threads. Any threads running in the parent process do not exist in the child process.

By default, fork(2) places a newly created child process in the same process group as its parent, so that e.g. a ^C from the keyboard will affect both parent and child.