[ale] /etc/hosts and caching

Fri Nov 4 17:48:35 EDT 2011

As with must things on Linux, the answer is "It depends on how your
system is configured." This is pretty easily tested on any system
though.
~$ sudo date # this is to prime my sudo password timeout
Password:
Fri Nov  4 17:47:12 EDT 2011
~$ host google.com
google.com has address 74.125.159.106
~$ host bronosky.com
bronosky.com has address 174.143.204.116
~$ (sleep 5; sudo tee -a /etc/hosts <<< "174.143.204.116 google.com")
& (while true; do ping -q -c 1 google.com | head -1; sleep 1; done)
[1] 4874
PING google.com (74.125.159.106): 56 data bytes
PING google.com (74.125.159.106): 56 data bytes
PING google.com (74.125.159.106): 56 data bytes
PING google.com (74.125.159.106): 56 data bytes
PING google.com (74.125.159.106): 56 data bytes
174.143.204.116 google.com
PING google.com (174.143.204.116): 56 data bytes
PING google.com (174.143.204.116): 56 data bytes
PING google.com (174.143.204.116): 56 data bytes
PING google.com (174.143.204.116): 56 data bytes
PING google.com (174.143.204.116): 56 data bytes
^C
[1]+  Done                    ( sleep 5; sudo tee -a /etc/hosts <<<
"174.143.204.116 google.com" )

Is that quick enough for you?

On Fri, Nov 4, 2011 at 8:30 AM, leam hall <leamhall at gmail.com> 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.
>
> 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
>>
>>
>>
>>
>>
>>
>>
>>
>>
>> LEGAL DISCLAIMER
>> The information transmitted is intended solely for the individual or
>> entity to which it is addressed and may contain confidential and/or
>> privileged material. Any review, retransmission, dissemination or other use
>> of or taking action in reliance upon this information by persons or entities
>> other than the intended recipient is prohibited. If you have received this
>> email in error please contact the sender and delete the material from any
>> computer.
>>
>> SunTrust is a federally registered service mark of SunTrust Banks, Inc.
>> Live Solid. Bank Solid. is a service mark of SunTrust Banks, Inc.
>> [ST:XCL]
>>
>> _______________________________________________
>> Ale mailing list
>> Ale at ale.org
>> http://mail.ale.org/mailman/listinfo/ale
>> See JOBS, ANNOUNCE and SCHOOLS lists at
>> http://mail.ale.org/mailman/listinfo
>>
>>
>> --
>>
>> Mind on a Mission
>>
>>
>>
>> _______________________________________________
>> Ale mailing list
>> Ale at ale.org
>> http://mail.ale.org/mailman/listinfo/ale
>> See JOBS, ANNOUNCE and SCHOOLS lists at
>> http://mail.ale.org/mailman/listinfo
>>
>
>
>
> --
> Mind on a Mission
>
> _______________________________________________
> Ale mailing list
> Ale at ale.org
> http://mail.ale.org/mailman/listinfo/ale
> See JOBS, ANNOUNCE and SCHOOLS lists at
> http://mail.ale.org/mailman/listinfo
>
>

-- 
.!# RichardBronosky #!.