Below is simple process creation program using fork system call, fork return child’s process Id in main/parent process and return 0 in child process. Fork duplicates the current (parent) process as new (child) process, creating another new entry in the process table with many of the same attributes/variables as the parent process.
Once the child process is completed, it normally reports its status to the parent process, now if a parent process tries to complete even before child is finished, we need to wait for child process to finish, otherwise parent process will terminate before child finished, resulting child becoming parentless, for which process 0 or init becomes the parent. This process, for whom parent died before its own completion is called “Orphan” process.
Zombie process getting created due to coding mistakes is a very common things when you work with creating process’s hence you can read our another posts as well at “How to avoid zombie process in Linux ?” and “What is Zombie process and How to create zombie process in Linux ?”