Q. I'm on a Dial UP Internet connection under Linux and frequent dial up problem causing dns problems. How do I flush DNS cache under any UNIX / Linux distribution using a shell prompt?
A. Under any Windows version you can use ipconfig command to flush dns cache. However, Linux (UNIX) is more complex and robust as compare to Windows. Linux can run nscd or BIND or dnsmasq as the name service caching daemon under most Linux distributions. Large and workgroup servers may use BIND / dnsmasq as a dedicated caching server.
Flush nscd dns cache
Nscd caches libc-issued requests to the Name Service. If retrieving NSS data is fairly expensive, nscd is able to speed up consecutive access to the same data dramatically and increase overall system performance. Just restart nscd:
$ sudo /etc/init.d/nscd restart
OR
# service nscd restart
Flush dnsmasq dns cache
dnsmasq is a lightweight DNS, TFTP and DHCP server. It is intended to provide coupled DNS and DHCP service to a LAN. Dnsmasq accepts DNS queries and either answers them from a small, local, cache or forwards them to a real, recursive, DNS server. This software is also installed many cheap routers to cache dns queries. Just restart to flush out dns cache:
$ sudo /etc/init.d/dnsmasq restart
Flush caching BIND server dns cache
A caching BIND server obtains information from another server (a Zone Master) in response to a host query and then saves (caches) the data locally. All you have to do is restart bind to clear its cache:
# /etc/init.d/named restart
Related: Windows Vista / XP Flush DNS Cache with ipconfig Command
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{ 5 comments… read them below or add one }
it dont work for me i have ubunu 7.10
I my experience
service nscd restartdoes not clear NSCD’s cache.service nscd reloaddoes, however.Actually, in Bind, you can flush the daemon’s cache by doing
rndc flush
Whoops!
It seems that not the perfect view for precise approach. It seems that if I use bind and there is a resolv.conf too not always the bind is in use. (Ubuntu) Other important machine (with debian), there is just resolv.conf. Anyhow I have tried to restart (hope works) the /etc/init.d/dns-clean and it seems it worked. But there were reports that this did not do the job. Anyhow, I want to make sure that – especially my debian system – without restarting, even the networking, how can I just restart the name resolution to the newly set values and how to get sure that it is done well?
Thanks!
If nscd is in use, try “nscd -i hosts” as root.
As per James Mills, “rndc flush” if using bind.
If none of these work you might not have a DNS cache to flush anyway and the problem DNS entry may be stored elsewhere, such as your firefox DNS cache, your router’s cache, or another upstream DNS caching server.