Signals Are the Kernel's Text Messages. SIGKILL is a Bullet.
Visualization: 1. The Process Lifecycle & PID 1
systemd
PID 1 (Ancestor)
Parent
PID 100
fork()
Syscall: Clone
Child
PID 101 (Clone)
exec()
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DOWNLOADING CONCEPT: 1. THE PROCESS LIFECYCLE & PID 1...
PID 1 (The Ancestor)
↳When the Linux kernel boots, the very first user-space process it spawns is init (or systemd).
↳It gets Process ID 1.
↳Every single process on a Linux system is a descendant of PID 1. If a parent dies leaving orphaned children, PID 1 adopts them.
↳Beyond PID 1, Linux creates all other processes using two distinct system calls: fork() and exec().
1. fork()
↳The parent process calls fork() to create an exact duplicate of itself (the child).
↳The child gets a new PID but inherits the parent's memory, environment variables, and open file descriptors.
↳2. exec(): The child process calls exec() to replace its own memory space with a brand new program (e.g., executing /bin/ls).
↳This separation is powerful because it allows the shell (the parent) to set up pipelines, redirect I/O, or modify environment variables for the child *after* the fork() but *before* the exec().