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up vote 24 down vote favorite
2

I'm having problems related to DNS solving in my Ubuntu 9.10.
Prior complaining to my ISP I would like to refresh my local DNS cache, like in Windows we do ipconfig /flushdns.

How can I do that in Ubuntu?

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4 Answers

up vote 33 down vote accepted

Øhh, ubuntu doesn't cache DNS per default. So there is nothing to flush! (but maybe your SOHO router does). Installing nscd will make ubuntu cache DNS, afterwhich you can clear your cache - but this is besides the point, when you don't have it installed yet!

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up vote 4 down vote

Ubuntu uses dnsmasq for a local cache. Sending it a SIGUP (sudo killall -HUP dnsmasq) will re-read the cache.

NOTES
When it receives a SIGHUP, dnsmasq clears its cache and then re-loads /etc/hosts and /etc/ethers and any file given by --dhcp-hostsfile, --dhcp-optsfile or --addn-hosts. The dhcp lease change script is called for all existing DHCP leases. If --no-poll is set SIGHUP also re-reads /etc/resolv.conf. SIGHUP does NOT re-read the configuration file.

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this looks reasonable. although, I have to find another of the problems I used to have (that are related to new sites in the /etc/hosts and Opera) to test this and mark as accepted instead of the other :P – Igoru Dec 4 '12 at 19:28
That's fine. I actually came across this looking to clear out my own cached dns entry. Once I found the solution though, I felt I should add my findings here. I don't know at what version Ubuntu started using dnsmasq though. – John H Dec 5 '12 at 15:01
This works and should really be marked as the answer! – HDave Mar 13 at 20:03
up vote 3 down vote

Try the following:

sudo /etc/init.d/dns-clean start

It works for me.

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up vote 1 down vote

I just had this problem with a site for which I changed the DNS, and googling for a solution I found this page.

In my experience Firefox sometimes keeps its own DNS cache and doesn't clear it in time. So if you're viewing a site in Firefox, and keep seeing the old site, trying Chrome might solve the problem. If that works, you can clear the cache in Firefox. This happened in Ubuntu, I don't know if this happens on Windows or OSX as well.

I don't have nscd installed. I noticed however that in the terminal the new DNS is found several minutes later, so the problem solved itself.

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