[ale] nsswitch and db option

Tue Nov 1 12:40:25 EDT 2011

Yeah Jeff,

I was started to think that also.  I asked a few crusty Unix admins and they gave me a 500 yard stare.

From: ale-bounces at ale.org [mailto:ale-bounces at ale.org] On Behalf Of Lightner, Jeff
Sent: Tuesday, November 01, 2011 12:35 PM
To: Atlanta Linux Enthusiasts
Subject: Re: [ale] nsswitch and db option

I don’t think the stub resolver on Linux does any caching of its own.   That seems to be born out by this page which mentions that some newer Windows stub resolvers do:

http://www.zytrax.com/books/dns/apa/resolver.html

So it seems if you wanted cache at client level on Linux you’d need to implement something like BIND (or maybe TinyDNS which I haven’t worked with) and have it get answers from upstream server.   More work than I’d want to do for most clients.   I’d think if you had a single (or better yet a pair) caching DNS server in your environment and had it in your clients’ /etc/resolv.conf that the lookups should be quick enough for most purposes without needing to cache at client level.

I’ve never used the db option in nsswitch.conf but based on what little I can glean I don’t think it is for hosts but rather for things like passwd, groups and shadow.

________________________________

From: ale-bounces at ale.org [mailto:ale-bounces at ale.org] On Behalf Of Chesser.Damon
Sent: Tuesday, November 01, 2011 12:03 PM
To: ale at ale.org
Subject: [ale] nsswitch and db option

I am trying to research the db option in nsswitch (as in: hosts:  db files  dns ).  We figure if a Linux client can use the dns cache for lookups, that would be faster then files or dns.  However, I can’t find anybody who has ever used that option and google is slim pickens researching it.

How do you access the (Linux) client dns cache info? Would “hosts:  db files dns” cause the first check to be performed on the dns cache?

If NOT what does “db” cause to happen?

Thanks!

Damon.chesser at suntrust.com

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