Re: ntpd segfaults on start

> On Mon, 2019-09-09 at 09:30 -0700, Rodney W. Grimes wrote:
> > > On Sat, 2019-09-07 at 09:28 -0700, Cy Schubert wrote:
> > > > In message <20190907161749.GJ2559_at_kib.kiev.ua>, Konstantin
> > > > Belousov writes:
> > > > > On Sat, Sep 07, 2019 at 08:45:21AM -0700, Cy Schubert wrote:
> > > > > > I've been able to set the memlock rlimit as low as 20 MB. The
> > > > > > issue is 
> > > > > > letting it default to 0 which allows ntp to mlockall()
> > > > > > anything it wants. 
> > > > > > ntpd on my sandbox is currently using 18 MB.
> > > > > 
> > > > > Default stack size on amd64 is 512M, and default stack gap
> > > > > percentage is
> > > > > 3%. This means that the gap can be as large as ~17MB. If 3MB is
> > > > > enough
> > > > > for the stack of the main thread of ntpd, then fine.
> > > > 
> > > > The default stack is 200K, which is also tuneable in ntp.conf.
> > > > 
> > > > [...]
> > > 
> > > I haven't seen anyone ask what I consider to be the crucial
> > > question
> > > yet:  why are we locking ntpd into memory by default at all?
> > > 
> > > I have seen two rationales for ntpd using mlockall() and
> > > setrlimit(): 
> > > 
> > >    - There are claims that it improves timing performance.
> > > 
> > >    - Because ntpd is a daemon that can run for months at a time,
> > >    setting limits on memory and stack growth can help detect and
> > >    mitigate against memory leak problems in the daemon.
> > 
> > Doesn't locking this memory down also protect ntpd from OOM kills?
> > If so that is a MUST preserve functionality, as IMHO killing ntpd
> > on a box that has it configured is a total no win situation.
> > 
> 
> Does it have that effect?  I don't know.  But I would argue that that's
> a separate issue, and we should make that happen by adding
> ntpd_oomprotect=YES to /etc/defaults/rc.conf
> 
> Right now only syslogd has oomprotect set to YES by default.  Maybe
> that's a good choice -- once we start declaring one daemon to be more
> important than others, you'll discover there's a whole back lot full of
> bikesheds that need painting.
> 
> So maybe we should just document ntpd_oomprotect=YES in some more-
> prominent way.  If we were to add a comment block to ntp.conf
> describing rlimit, that might be a good place to mention setting
> ntpd_oomprotect in rc.conf.
>
> -- Ian

All very reasonable, thanks Ian.

-- 
Rod Grimes                                                 rgrimes_at_freebsd.org