[nsd-users] NSD still shows permission errors on Debian 10 Buster

Simon Deziel simon at sdeziel.info
Thu May 28 18:00:29 UTC 2020

On 2020-05-28 5:20 a.m., Anand Buddhdev wrote:
> On 28/05/2020 02:34, Simon Deziel via nsd-users wrote:
>> I like the idea. Since Debian wants to preserve compatibility with
>> both systemd and init, I proposed a slightly different fix to
>> Debian for nsd [1] and unbound [2]. Thanks!
> I also noticed one other deficiency in the Debian unit file. It's 
> missing "Killmode=process".

Indeed, the default is KillMode=control-group which SIGTERM everyone in
the cgroup, wait 90s by default and then SIGKILL what remains.

> NSD starts with a main process, and that then spawns child processes
> to handle queries. When you want to kill NSD cleanly, you send a
> TERM singal to the main process, which takes care of killing its
> children.
> However, systemd by default will send a TERM singal to all the 
> processes. This causes a haphazard termination of NSD. With the
> Killmode setting as above, systemd sends a TERM signal only to the
> main process, and NSD handles its shutdown cleanly.
I only manage a small fleet of nsd servers so that's probably why I
never noticed any problem with cgroup-based killing. However, I did try
to simulate this:

# ps faux
nsd 12972 0.0 21.3 109664 53340 ? Ss 17:05 0:00 /usr/sbin/nsd -d -P
nsd 12990 0.0  8.5  42000 21396 ? S  17:05 0:00  \_ /usr/sbin/nsd -d -P
nsd 13011 0.0  1.4  57596  3636 ? S  17:05 0:00   \_ /usr/sbin/nsd -d -P

kill -SIGTEM 13011 -> does absolutely nothing, the child ignores it
kill -SIGTEM 12972 or kill -SIGTEM 12990 triggers a clean shutdown:
  nsd[12990]: warning: signal received, shutting down...

Also, sending SIGTERM to all 3 triggers an orderly shutdown.

The above seems to match what the code intends to do but take that with
a grain of salt as I can barely read C.

Anand, could you please provide some instructions on how to reproduce
the issue you are/were having with the cgroup-based killing as my test
scenario was likely too simplistic. Thanks


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