[ale] /etc/hosts and caching

Fri Nov 4 10:09:30 EDT 2011

On Fri, 2011-11-04 at 08:30 -0400, leam hall wrote: 
> I use it as it is turned on everywhere I've worked. I've not seen any data
> that suggests it is a problem, but I'd be happy to see some facts.

Wish I had some.  I merely noticed what I thought to be an unusually
excessive amount of, errr, complaining about nscd on several help
forums.  On thing that was noted on a couple of forums was that nscd was
geared for caching the files, such as passwd, group, etc, than for
network based information such as DNS.  Conversely, I'm under the
impression it was originally developed over at Sun to help with caching
yp aka nis aka nis+ maps (which can be slow), though I could be off base
there.  Some of the complaints were in regards to being unable to flush
the cache and some may have related to Solaris or older versions.  I was
merely relaying that there has been some dissatisfaction with nscd.

Regards,
Mike

> Leam
> 
> On Fri, Nov 4, 2011 at 8:24 AM, Chesser.Damon <Damon.Chesser at suntrust.com>wrote:
> 
> >  Thanks for the reply, that is how I thought it worked also.  As for
> > nscd, someone on this list said “Don’t.  Use. It.”  ****
> >
> > ** **
> >
> > Any other opinions on it?****
> >
> > ** **
> >
> > Damon at damtek.com****
> >
> > ** **
> >
> > *From:* ale-bounces at ale.org [mailto:ale-bounces at ale.org] *On Behalf Of *leam
> > hall
> > *Sent:* Friday, November 04, 2011 8:17 AM
> > *To:* Atlanta Linux Enthusiasts
> > *Subject:* Re: [ale] /etc/hosts and caching****
> >
> > ** **
> >
> > Good morning Damon!****
> >
> >  ****
> >
> > As far as I can tell by editing /etc/hosts on a RHEL 4 box, the IP
> > addresses are not cached longer than it takes me to edit the file. I
> > believe your server will alwyas look in /etc/hosts anyway, per the
> > /etc/nsswitch.conf file. The normal hosts line is something like: ****
> >
> >  ****
> >
> >    hosts:      files dns****
> >
> > There is the program nscd and it's config file, ncsd.conf. This configures
> > some caching for you but I *think* it's more DNS related than affecting
> > /etc/hosts. ****
> >
> > Hope that helps.****
> >
> >  ****
> >
> > Leam****
> >
> > On Fri, Nov 4, 2011 at 7:40 AM, Chesser.Damon <Damon.Chesser at suntrust.com>
> > wrote:****
> >
> > This dovetails into building a DNS caching server I asked earlier this
> > week.  The issue is we are seeing latency in our application and a possible
> > (but only possible, not proven) issue might be host lookups.  I figured
> > that an entry into /etc/hosts would be faster than a WAN DNS lookup
> > especially since the IP is static.  Someone was concerned with disk reads
> > and that becoming a bottleneck.  Someone else pointed out that /etc/hosts
> > file was cached.  ****
> >
> >  ****
> >
> > This started a google search by me to find out if that was true or not.
> > Totally inconclusive.  Some have reported issues with not being able to get
> > the Linux box to re-read the hosts file after a change was committed short
> > of a reboot or init restart.  Others have said just make the change and it
> > shows up.  I have not found any documentation saying whether it was cached
> > or not.  Any smart guys know the answer or can provide any documentation on
> > that?  It’s kind of funny, you think you KNOW something until someone says
> > “Prove it”.****
> >
> >  ****
> >
> > Damon at damtek.com****
> >
> >  ****
> >
> >   ****
> >
> >  ****
> >
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> > -- ****
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> > Mind on a Mission <http://leamhall.blogspot.com/>****
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> 
> -- 
> Mind on a Mission <http://leamhall.blogspot.com/>
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Michael H. Warfield (AI4NB) | (770) 985-6132 |  mhw at WittsEnd.com
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