Re: [PATCH] mdadm/systemd: change KillMode from none to mixed in service files

Hi,

On 12/7/21 1:34 PM, Benjamin Brunner wrote:

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Please correct me if I am wrong, I see the difference of the KillMode is,
-- KillMode=mixed stops the processes more gentally, it kill the main
process with SIGTERM and the remaining processes with SIGKILL.
-- KillMode=control-group kills all in-cgroup processes with SIGKILL,
which I feel a bit cruel for the main process.

I think there's a miss-understanding here.

Regardless of whether "mixed" or "control-group" mode (or any other mode
actually) is used, the process used to kill processes part of a service is
always the same, only the list of the killed processes differs.

The process is as follow:

 1. send the signal specified by KillSignal= to the list of processes (if
    any), TERM is the default
 2. wait until either the target of process(es) exit or a timeout expires
 3. if the timeout expires send the signal specified by FinalKillSignal=,
    KILL is the default

For "control-group", all remaining processes will receive the SIGTERM signal (by
default) and if there are still processes after a period f time, they will get
the SIGKILL signal.

For "mixed", only the main process will receive the SIGTERM signal, and if there
are still processes after a period of time, all remaining processes (including
the main one) will receive the SIGKILL signal.

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There is no point sending SIGTERM to a process which doesn't respond to
it.  mdmon is the only mdadm service which handles SIGTERM.  So it might
make sense to uise KillMode=mixed for that.
For anything else, SIGKILL via KillMode=control-group is perfectly
acceptable.

I don't know enough mdadm to suggest a mode but maybe the clarification above
will help you figuring this out.

That said it sounds a bit strange that some processes don't respond to SIGTERM.
Is that done because some services need to run lately during the shutdown process ?

Thanks.