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Why is it necessary for there to be processes with a zombie defunct state?
Zombie processes allow the parent to be guaranteed to be able to retreive exit status, accounting information, and process id for child processes, regardless of whether the parent calls wait() before or after the child process exits. This is why a zombie process is necessary.
How do you get the process out of zombie state?
To remove zombies from a system, the SIGCHLD signal can be sent to the parent manually, using the kill command. If the parent process still refuses to reap the zombie, and if it would be fine to terminate the parent process, the next step can be to remove the parent process.
How do you make a zombie process?
According to man 2 wait (see NOTES) : A child that terminates, but has not been waited for becomes a “zombie”. So, if you want to create a zombie process, after the fork(2) , the child-process should exit() , and the parent-process should sleep() before exiting, giving you time to observe the output of ps(1) .
Which is the zombie state in the process table?
Hence, there remains an entry in the process table even after the termination of the child. This state of the child process is known as the Zombie state. Here the entry [a.out] defunct shows the zombie process. Why do we need to prevent the creation of Zombie process?
What does it mean to have a zombie process?
On Unix and Unix-like computer operating systems, a zombie process or defunct process is a process that has completed execution (via the exit system call) but still has an entry in the process table: it is a process in the ” Terminated state “.
When is a child in the zombie state?
If the parent decides not to wait for the child’s termination and it executes its subsequent task, then at the termination of the child, the exit status is not read. Hence, there remains an entry in the process table even after the termination of the child. This state of the child process is known as the Zombie state.
How does ignoring the SIGCHLD signal prevent zombie processes?
2. By ignoring the SIGCHLD signal: When a child is terminated, a corresponding SIGCHLD signal is delivered to the parent, if we call the ‘signal (SIGCHLD,SIG_IGN)’, then the SIGCHLD signal is ignored by the system, and the child process entry is deleted from the process table. Thus, no zombie is created.