is it possible that a folder like
/proc/4587 exists even though there isn't a process that has PID 4587?
/proc is only the
proc mount (and no one is playing tricks with overlays), no, a pid-based folder only exists as long as the corresponding process exists in some state (including as a zombie). In fact, just before returning a directory entry for a process id, the kernel re-validates the process’ existence — so at the instant a directory entry is returned, the corresponding process is still there. Accessing a directory also starts by looking up the corresponding process. (If the line numbers change, look for
You can run into issues caused by listing
/proc and using the results later (even a few microseconds later): a process can be running when you list
/proc, and stop before you act on the results.