The Process Tree (And Environment, And procfs)

Process ID (PID) And Parent Process ID (PPID)

See also

• Process Hierarchy (Parent, Child Process)

• Every process has an ID (PID … Process ID)

• Every process but the first (PID 1) has a parent process)

• ⟶ process tree

A typical distro’s process tree (simplified)

• init - nowadays mostly systemd

• Services

• User login sessions (console, graphical, network …)

A typical distro’s process tree

System Calls: getpid(), getppid()

Technically …

• A process can ask the kernel about its parent process

• A process cannot ask the kernel about its children ⟶ has to take care itself

Documentation

• man -s 2 getpid

• man -s 2 getppid

code/tree.cpp

#include <unistd.h>

#include <print>

int main(int argc, char** argv)
{
    std::println("PID: {}", getpid());                // <--- self's PID
    std::println("PPID: {}", getppid());              // <--- parent's PID

    return 0;
}

$ echo $$                                           # <-- PID of the shell itself
$ ./code/sysprog-process-tree
PID: 115971
PPID: 33634