Reading Gilles' answer,
SIGHUP is about the same as SIGTERM in terms of harshness, but it has a specific role because it's automatically sent to applications running in a terminal when the user disconnects from that terminal (etymologically, because the user was connecting via a telephone line and the modem hung up). SIGHUP is often involuntary, unlike SIGTERM which has to be sent explicitly, so applications should try to save their state on a SIGHUP.
Does "explicitly" in "SIGTERM which has to be sent explicitly" mean that SIGTERM must be sent initially by a process (instead of the kernel) via the process calling
I was wondering if SIGKILL must be explicitly sent to a specified process? Can kernel implicitly send any of SIGKILL and SIGTERM to a process?
When an OS is shut down, does the kernel send some signal(s) to running processes to terminate them? What signal(s) is it and does the kernel send it implicitly?