Discussion:
How do I remove dead process managed by Systemd?
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Yun-Chih Chen
2017-12-04 15:15:33 UTC
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Hi, fellows:

How do I remove a dead process (D-state process) wrapped as a Systemd
service unit? The process's parent is systemd (pid=1) and I still did not
find a way to remove such process without rebooting. I have tried the
following:

$ systemctl restart <my_service> # timeout
$ systemctl daemon-reexec
$ kill -9 <pid of my process> # won't work of course

Or anyone knows of hacks that do the trick?

Thanks in advance!
Lennart Poettering
2017-12-04 18:14:51 UTC
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Post by Yun-Chih Chen
How do I remove a dead process (D-state process) wrapped as a Systemd
service unit? The process's parent is systemd (pid=1) and I still did not
find a way to remove such process without rebooting. I have tried the
$ systemctl restart <my_service> # timeout
$ systemctl daemon-reexec
$ kill -9 <pid of my process> # won't work of course
Or anyone knows of hacks that do the trick?
You cannot kill "D" state processes on Linux. That's what "D" state
means ultimately: *uninterruptible* sleep. The kill command can't kill
such processes, and neither can systemd. If you see processes like
this, then either you have very slow I/O, or this points to some form
of kernel/driver problem, as sleeping in this state should usually be
for short periods only.

Lennart
--
Lennart Poettering, Red Hat
v***@pengaru.com
2017-12-04 18:41:53 UTC
Permalink
Post by Lennart Poettering
Post by Yun-Chih Chen
How do I remove a dead process (D-state process) wrapped as a Systemd
service unit? The process's parent is systemd (pid=1) and I still did not
find a way to remove such process without rebooting. I have tried the
$ systemctl restart <my_service> # timeout
$ systemctl daemon-reexec
$ kill -9 <pid of my process> # won't work of course
Or anyone knows of hacks that do the trick?
You cannot kill "D" state processes on Linux. That's what "D" state
means ultimately: *uninterruptible* sleep. The kill command can't kill
such processes, and neither can systemd. If you see processes like
this, then either you have very slow I/O, or this points to some form
of kernel/driver problem, as sleeping in this state should usually be
for short periods only.
That's not strictly accurate AFAIK.

Not all D state processes are unkillable. D state contributes to load
average, so it's not just to represent unkillable tasks. IIRC it's
ambiguous from userspace by just glancing at D state if the process is
killable, but it can happen that the process is plain uninterruptible.

I don't have time at the moment to do much digging to confirm. If you
glance at wait.h from the kernel headers, see wait_event_killable().
TASK_KILLABLE includes TASK_UNINTERRUPTIBLE, and I believe that shows as a
D state in userspace, but it also includes TASK_WAKEKILL.

What Lennart describes still holds true for Yun-Chih; if the process is in
an unkillable state then there's nothing systemd can do.

Regards,
Vito Caputo

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