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What is defunct in ps output?
An operating system process has exited but the ps command output still includes the process id (PID) and lists “” in the command name column. A process in this state is called a defunct process. A defunct process is also called a zombie process, or an orphaned process. A defunct process cannot be killed.
What is defunct process?
Defunct processes are merely processes that have terminated but have not yet been removed from the process table. Because defunct processes have already terminated, they do not use any system resources. Defunct processes with a PID of 1 or 0 can only be removed by the operating system.
Why does defunct mean?
no longer in effect or use; not operating or functioning: a defunct law; a defunct organization. no longer in existence; dead; extinct: a defunct person; a defunct tribe of Indians. the defunct, the dead person referred to: the survivors of the defunct.
How do I list zombie processes?
How to spot a Zombie Process. Zombie processes can be found easily with the ps command. Within the ps output there is a STAT column which will show the processes current status, a zombie process will have Z as the status. In addition to the STAT column zombies commonly have the words in the CMD column as well …
How can I create a zombie?
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) .
What does it mean when a process is defunct?
From your output we see a “defunct”, which means the process has either completed its task or has been corrupted or killed, but its child processes are still running or these parent process is monitoring its child process. To kill this kind of process, kill -9 PID doesn’t work.
Why are there so many defunct processes in Unix?
Defunct processes are a normal part of any Unix system and in most cases do not cause any problems. However if the number of defunct processes is very large or continues to increase over time, there is a risk of filling up the process table if they are not stopped or removed.
Can a defunct process be killed by the operating system?
Defunct processes cannot be killed but in some cases can be removed by killing their parent process, if their parent process does not have a PID of 1 or 0. Defunct processes with a PID of 1 or 0 can only be removed by the operating system.
What’s the difference between a defunct process and a zombie process?
A “defunct” process (sometimes referred to as “zombie”) is a process that is actually finished which depends on a parent process which for some reason (=error) has not accepted the knowledge that it is finished and should be terminated.