Howto clear/Flush DNS Cache in Ubuntu
Posted by admin on January 10th, 2008 
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Why would you clear your cache?
Most DNS clients will cache the results of name resolution request to speed up multiple lookups to the same URL. Just think about how many requests are made to the same domain when visiting a single web page. Every file, image, style sheet, etc. that is on that page and served from the same domain requires a DNS lookup.
So if you have an invalid DNS entry cached on your local client you’ll need to flush it out of the cache so your client can do a new lookup and get the correct information. Or your other option is to wait until that DNS entry expires and the cache flushes it automatically… which typically takes about 24 hours.
In ubuntu if you want to flush DNS cache you need to restart nscd daemon
Install nscd using the following command
sudo aptitude install nscd
Flush DNS Cache in Ubuntu Using the following command
sudo /etc/init.d/nscd restart
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May 30th, 2008 at 10:50 pm
admin@admin-machine:~$ sudo /etc/init.d/nscd restart
[sudo] password for admin:
sudo: /etc/init.d/nscd: command not found
admin@admin-machine:~$
June 2nd, 2008 at 8:38 am
My Ubuntu Hardy Heron 8.04 gave the same error as stated by Nevinka.
hammerhead@HammerHead:~$ sudo /etc/init.d/nscd restart
[sudo] password for hammerhead:
sudo: /etc/init.d/nscd: command not found
August 1st, 2008 at 4:23 pm
I’m having the same problem!!!
August 6th, 2008 at 1:33 pm
Hey guys,
Just stumbled accross the correct code to flush the DNS cache on 8.04 -
sudo /etc/init.d/networking restart
Cheers,
Richard
August 8th, 2008 at 8:35 am
Guys, read the text you post to…
—————-8 Install nscd using the following command 8——————-
You can not find the command when it is not installed of course…
August 28th, 2008 at 12:12 am
Ugh, I’m so tired of seeing people posting technical advice that is just plain wrong! Why does it seem like it is always Ubuntu users? Has Ubuntu just brought over so many pathetic former MCSE’s that don’t understand the way an operating system works but are full of themselves and so feel the need to post things like this? I really don’t understand this.
In any case, nscd is NOT installed by default in Ubuntu. It makes absolutely no sense to install it, only to be able to reset it. If it is not installed, then DNS is not cached directly by libc. Firefox, for example, maintains its own DNS cache, and the only way to clear it is to restart the browser. The OS does not cache DNS unless you install nscd manually, as this article advocates. It’s just common sense here, people… *sigh*