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When a process parent dies it becomes a zombie?
A process which has finished the execution but still has entry in the process table to report to its parent process is known as a zombie process. A child process always first becomes a zombie before being removed from the process table.
What happens when parent process is killed?
If the parent is killed, children become children of the init process (that has the process id 1 and is launched as the first user process by the kernel). The init process checks periodically for new children, and waits for them (thus freeing resources that are allocated by their return value).
What happens when parent does not accept return code what happens if parent is alive but never executes a wait ()?
A process that terminates cannot leave the system until its parent accepts its return code. However, if a process’s parent is alive but never executes a wait ( ), the process’s return code will never be accepted and the process will remain a zombie.
What happens if a parent process dies before its children?
When a parent process dies before a child process, the kernel knows that it’s not going to get a wait call, so instead it makes these processes “orphans” and puts them under the care of init (remember mother of all processes). Init will eventually perform the wait system call for these orphans so they can die.
How are zombie processes different from normal processes?
Also, unlike normal processes, the kill command has no effect on a zombie process. Zombie processes should not be confused with orphan processes: an orphan process is a process that is still executing, but whose parent has died. When the parent dies, the orphaned child process is adopted by init (process ID 1).
When does an orphan process become a zombie process?
When the parent dies, the orphaned child process is adopted by init (process ID 1). When orphan processes die, they do not remain as zombie processes; instead, they are wait ed on by init.
How do you remove a zombie from a system?
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 does the parent get rid of the zombie?
The parent can read the child’s exit status by executing the wait system call, whereupon the zombie is removed. The wait call may be executed in sequential code, but it is commonly executed in a handler for the SIGCHLD signal, which the parent receives whenever a child has died.