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Re: [tlug] Slooooooow down: logs, smartctl, DNS? [SOLVED?]: lessons to learn

This is one to file away in some recess for later recall. 

On Tue, 18 Jan 2011 21:04:58 +0900, Dave M G <> wrote:

> Basically, it amounted to editing a file called /etc/ssh/sshd_config and
> making two changes.
> One was to add this line to the bottom of the file:
> UseDNS no

Yup. DNS (and more broadly, name resolution) issues can cause no 
end of grief. A consistent delay that is a nice round number can 
be a clue. 

> I did these edits on both machines, client and server, since it wasn't
> clear to me from the web pages I was reading which one was responsible.

Make one change at a time. 

> If anyone thinks I've done something dangerous in any way by editing the
> aforementioned file, then please let me know.

If you do not know what you are doing, then of course, it's dangerous. 
That should not stop you from experimenting. Just remember to mitigate 
the risks. Back up the files before you experiment. If you are playing 
with production things for which the possible consequences of failure 
are unacceptable, then replicate the problem on non-production equipment 
and experiment there. Change one thing at a time. Keep notes. 

> Otherwise, we might be able to put a fork in this one.

It seems that although you have made the symptoms disappear, 
you do not have a complete understanding of what happened, 
why it happened, and exactly what resolved the problem. 
In other words, you are not really done yet. 

As mentioned before, DNS (and more broadly, name resolution) issues can 
cause no end of grief. Use this opportunity to more better understand 
that. Ask yourself what symptoms of some future problem would suggest 
scrutiny of name resolution? 

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