Since the Docker 1.13 version there is a special -init flag that can be used to tell Docker to use an init system that will reap zombies. How to get rid of zombies? Use the docker -init flag In this case it’s not an issue, but imagine if the main process you are running creates a lot of child processes (like in a loop) that become orphans and then zombies. This process will remain here since there is no process that will care about reaping (removing) it. We can observe a zombie ( defunct) process that is orphan, it has the PID #7. To generate a zombie process I have used the Python code displayed in this issue. The problem is not related to the resources used by these zombies (none) but to the number of processes that will increase until system exhaustion.Īs long as a zombie is not removed from the system via a wait, it will consume a slot in the kernel process table, and if this table fills, it will not be possible to create further processes Producing a zombie process If like in standard docker container launching a command, there is no proper init process, nobody will care about orphaned processes and they will stay here as zombies also called defunct.
This means that the init process becomes the parent of such processes, even though those processes were never created directly by the init process
Its task is to “adopt” orphaned child processes (again, this is the actual technical term). The init process- PID 1-has a special task. to clean it up.Īnd this is where the init process kicks in. The init process is responsible of adopting orphaned processes and to reap them, i.e. What happens then to its children? They no longer have a parent process, so they become “orphaned” (this is the actual technical term).
Suppose the parent process terminates, either intentionally (because the program logic has determined that it should exit), or caused by a user action (e.g. The first step is an orphaned process, a process that has lost his parent.
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