Linux Signals

• A process in Linux is represented as task_struct.
• A process A sends a signal to process B using system call kill() or kill -<sig num> <pid>.
• Kernel updates the task_struct of the receiving process B. It changes the signal field with the passed value.
• The scheduler checks the signals on a process before running the process. If the signal is set, it calls the signal handler.
• A process can define its handlers for all signals except SIGKILL and SIGSTOP.
• There is always a default signal handler for each signal.

References

• https://en.wikipedia.org/wiki/Signal_(IPC)
• https://unix.stackexchange.com/questions/256926/what-happends-when-sending-sigkill-to-a-zombie-process-in-linux
• https://elixir.bootlin.com/linux/latest/source/include/linux/sched.h