Why do processes I fork get systemd as their parent?

Question

I am learning fork() in Linux, and here is my program:

  1 #include 
  2 #include 
  3 #include 
  4 int main(         


        

Answer 1

The "inconsistency" you observed is because sometimes, the parent process(es) exited before their child process(es) terminated. So, these child processes become "orphans" as their parent processes are not waiting for them. As a result, they are "re-parented" to the init process. While traditionally the process id of the "init" process is 1, it's not always true. POSIX leaves it as implementation-defined:

The parent process ID of all of the existing child processes and zombie processes of the calling process shall be set to the process ID of an implementation-defined system process. That is, these processes shall be inherited by a special system process.

Thus you see a particular PID as the parent (1599 in your example), which happens to be "init" process equivalent on your Linux. The systemd is an init variant used in Debian Linux distributions - which follows a slightly more complicated implementation.

In essense, what you observed is pretty normal. Ideally, you should reap all the processes in order to avoid zombie processes.