How to Flush Linux _ UNIX DNS Cache

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How To Flush Linux / UNIX DNS Cacheby Nix Craft on January 29, 2008 29 comments LAST UPDATED June 2, 2012

in BASH Shell, CentOS, Debian / Ubuntu

I'm on a Dial UP Internet connection under Linux and frequent dial up disconnectioncausing dns problems. How do I flush DNS cache under UNIX / Linux distributionusing a shell prompt?

Under MS-Windows you can use the ipconfig command to flush dns cache.However, Linux and UNIX provides various ways to flush cache. Linux can run nscdor BIND or dnsmasq as the name service caching daemon. Large and work-groupservers may use BIND or dnsmasq as a dedicated caching server to speed up queries.

HowTo: Flush nscd dns cache

How To Flush Linux / UNIX DNS Cache http://www.cyberciti.biz/faq/rhel-debian-ubuntu-flush-clear-dns-cache/

1 of 13 5/22/2014 11:15 AM

Nscd caches libc-issued requests to the Name Service. If retrieving NSS data is fairly expensive, nscd isable to speed up consecutive access to the same data dramatically and increase overall systemperformance. Just restart nscd:$ sudo /etc/init.d/nscd restartOR# service nscd restartOR# service nscd reloadThis daemon provides a cache for the most common name service requests. The default configuration file,/etc/nscd.conf, determines the behavior of the cache daemon.

Flush dnsmasq dns cachednsmasq is a lightweight DNS, TFTP and DHCP server. It is intended to provide coupled DNS andDHCP 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 cheaprouters to cache dns queries. Just restart the dnsmasq service to flush out dns cache:$ sudo /etc/init.d/dnsmasq restartOR# service dnsmasq restart

Flush caching BIND server dns cacheA caching BIND server obtains information from another server (a Zone Master) in response to a hostquery and then saves (caches) the data locally. All you have to do is restart bind to clear its cache:# /etc/init.d/named restartYou can also use rndc command as follows flush out all cache:# rndc restartOR# rndc execBIND v9.3.0 and above will support flushing all of the records attached to a particular domain name withrndc flushname command. In this example flush all records releated to cyberciti.biz domain:# rndc flushname cyberciti.bizIt is also possible to flush out BIND views. For example, lan and wan views can be flushed using thefollowing command:# rndc flush lan# rndc flush wan

A note about Mac OS X Unix usersType the following command as root user:# dscacheutil -flushcacheOR$ sudo dscacheutil -flushcacheIf you are using OS X 10.5 or earlier try the following command:lookupd -flushcache

A note about /etc/hosts file


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/etc/hosts act as the static table lookup for hostnames. You need to remove and/or update records as peryour requirements under Unix like operating systems:# vi /etc/hostsSample outputs:

127.0.0.1 localhost127.0.1.1 wks01.WAG160N wks01# The following lines are desirable for IPv6 capable hosts::1 ip6-localhost ip6-loopbackfe00::0 ip6-localnetff00::0 ip6-mcastprefixff02::1 ip6-allnodesff02::2 ip6-allrouters10.37.34.2 build192.168.1.10 nas01192.168.1.11 nas02192.168.1.12 nas03#192.168.2.50 nfs2.nixcraft.net.in nfs2#192.168.2.51 nfs1.nixcraft.net.in nfs1172.168.232.50 nfs1.nixcraft.net.in nfs1172.168.232.51 nfs2.nixcraft.net.in nfs2192.168.1.101 vm01

See also:

Related: Windows Vista / XP Flush DNS Cache with ipconfig Command

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{ 29 comments read them below or add one }

1 NoPremium.org April 18, 2008 at 8:32 am

it dont work for me i have ubunu 7.10

Reply

2 kazoolist July 10, 2008 at 10:54 pm


3 of 13 5/22/2014 11:15 AM

I my experience service nscd restart does not clear NSCDs cache. service nscd reloaddoes, however.

Reply

3 Subhash July 27, 2010 at 5:26 pm

That is correct!

Reply

4 James Mills September 19, 2008 at 8:32 am

Actually, in Bind, you can flush the daemons cache by doing

rndc flush

Reply

5 Lost Eagle January 31, 2011 at 4:01 pm

Thank U

This rndc flush help lot restart doesnt flush

Have a nice day

Reply

6 RudyD February 4, 2009 at 12:35 pm

Whoops!

It seems that not the perfect view for precise approach. It seems that if I use bind and there is aresolv.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 itseems it worked. But there were reports that this did not do the job. Anyhow, I want to make surethat especially my debian system without restarting, even the networking, how can I just restartthe name resolution to the newly set values and how to get sure that it is done well?

Thanks!

Reply

7 Tricky April 26, 2009 at 11:50 pm

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 entrymay be stored elsewhere, such as your firefox DNS cache, your routers cache, or another upstreamDNS caching server.

Reply


4 of 13 5/22/2014 11:15 AM

8 takizo July 26, 2010 at 2:58 pm

it could be nscd is not install?

@James, rndc reload works too :D

Reply

9 dejf August 31, 2010 at 3:04 pm/etc/init.d/dnsmasq restart do not work, even stop and start does not. There is a clear cache optionentioned, but it does not help anyway dnsmasq remembers

Reply

10 Yogesh September 2, 2010 at 12:08 pm

I guess this is for DNS server. What shall I do if I wish to clear DNS cache on a linux client/desktopmachine? [Like ipconfig /flushdns in windows]

Reply

11 Tricky September 2, 2010 at 2:14 pm

@Yogesh: The same commands apply to a desktop

@dejf: Bear in mind per my comment above, perhaps your desktop has a separate DNS cache or theDNS is being cached elsewhere. You have to flush the DNS on all your upstream DNS servers aswell or change the DNS servers that youre using.See the following for info on how to change your DNS settings to these 2 popular public DNSservers:

http://code.google.com/speed/public-dns/https://store.opendns.com/setup/router/

Reply

12 Yogesh September 2, 2010 at 3:32 pm

@TrickyThanks for comment, but I am unable to find /etc/init.d/nscd or named on my Centos 5.3 Desktop.Any help?

Reply

13 Tricky September 3, 2010 at 4:48 am

@Yogesh. Chances are the DNS is cached outside of your desktop or the DNS is being cached byan application directly.

I wrote an (admittedly regex-cryptic) article on this same issue (sorry for the competing link,Vivek) http://dogma.swiftspirit.co.za/archives/300 skip to the sections after the label FlushMozilla Firefoxs internal DNS cache.

Reply


5 of 13 5/22/2014 11:15 AM

14 Manish December 4, 2010 at 6:49 pm

Hi

I have a local name resolution issues on CentOS 5.5. I have edited the /etc/hosts file and still thehostname doesnt resolves to right IP.

Here is what I have priority configuration# more /etc/host.conforder hosts,bindAlso /etc/nsswitch.conf file has

hosts: files dnsmore /etc/hosts192.168.1.1 admin.domain.com admin

# host adminHost admin not found: 3(NXDOMAIN)

Any suggestions would be appreciated.

Reply

15 Tricky December 6, 2010 at 3:49 am

host doesnt bother with the entries in the hosts file. Try ping admin instead.

Reply

16 nobbiecentos February 8, 2011 at 1:15 pm

TY for information its working solution for clear cash from server side

Reply

17 takprosto April 9, 2011 at 11:45 pm

Im sorry for my bad english. but im have Debian.apt-get install nscd Ok-d, debug Do not fork and display messages on the current tty-f, config-file=NAME Read configuration data from NAME-g, statistic Print current configuration statistic-i, invalidate=TABLE Invalidate the specified cache-K, shutdown Shut the server down-t, nthreads=NUMBER Start NUMBER threadsusage Give a short usage message

commands restart and reload not work ! haven`t ))) and -shutdown not work

Reply

18 Tricky April 10, 2011 at 11:58 am

@takprostoDo the commands give an error or are they just not refreshing the DNS? If theres no error then the


6 of 13 5/22/2014 11:15 AM

DNS entry could be cached elsewhere, for example on your router or your ISPs DNS server.

Reply

19 andre July 22, 2011 at 7:18 am

on Debian Squeeze/wheezy:

Usage: /etc/init.d/nscd {start|stop|force-reload|restart|status}Reply

20 m4h September 15, 2011 at 8:10 am

Manish ->

Change from:192.168.1.1 admin.domain.com adminTO:192.168.1.1 admin admin.domain.com admin

Reply

21 david.chen February 3, 2012 at 2:45 am

why not just usenscd -i hostsnscd -i passwd .to flush the cache

Reply

22 Tim March 21, 2012 at 1:23 pm

The articles recomendations are distribution specific and depend on how the init scripts are set upand what they do. The proper way to flush the cache on nscd is nscd -i hosts and for named,rndc flush

Anything else, like /etc/init.d/nscd reload depends on how your distro wrote the init script. Justbecause that works for you on Fedora does not mean Debian or someone else set it up that way aswell.

Reply

23 Som June 13, 2012 at 8:44 pm

If a user wants to flush DNS cache and if the user uses Internet via LAN connection ,the best wayto do so is changing the DNS address manually . He just needs to alter the DNS entry .Settingalternative DNS address as primary address will solve the issue instantly. This trick worked for me .I faced the same problem . I am aLinux user .so , I installed NSCD client and tried to flush thecache . But , it could not solve my issue .i solved it myself just changing the DNS entry . It workedfor me instantly .I kept the new entry for two days without any problem and later reinstated theolder entry

Reply


7 of 13 5/22/2014 11:15 AM

24 nick September 6, 2012 at 9:57 pm

This post is a little misleading. Linux by default does not have a caching system (at least not mostof the destributions). So unless you installed a caching system (or your system came with onepre-installed), there is no need to flush DNS because your system doesnt store any.

This post isnt clear about that and will cause people (who have no caching in place) to install acaching package (like nscd) just so that they could flush it. Thats a little counterproductive I think.Reply

25 Mac January 11, 2013 at 3:20 pm

*NOTE* The mistake I have often made is my /etc/hosts (on my CentOS6 workstation) I alwaysFORGET to update it.

So after a DNS update, I cannot reach the site by name and think something is amiss, well I forgotto edit my /etc/hosts file for all of the servers.

Reply

26 Willian Braga da Silva February 1, 2013 at 1:44 pm

The correct way to flush NSCD cache is using the command line:

sudo /usr/sbin/nscd invalidate=hosts

from the man page:

$ /usr/sbin/nscd helpUsage: nscd [OPTION...]Name Service Cache Daemon.

-d, debug Do not fork and display messages on the currenttty-f, config-file=NAME Read configuration data from NAME-g, statistic Print current configuration statistics-i, invalidate=TABLE Invalidate the specified cache-K, shutdown Shut the server down-t, nthreads=NUMBER Start NUMBER threads-?, help Give this help listusage Give a short usage message-V, version Print program version

-

$ sudo /usr/sbin/nscd -gnscd configuration:()hosts cache:

yes cache is enabledyes cache is persistentyes cache is shared()


8 of 13 5/22/2014 11:15 AM

yes check /etc/hosts for changes

hope this help

Reply

27 Jesin June 28, 2013 at 8:29 am

Does restarting the networking service clear the cache ?

I do not find all Linux distributions having the one of the three tools youve mentioned above.

Reply

28 Mac November 16, 2013 at 2:02 pm

-> nscd is there any reason why you would use this service, just wanting to help understand what itdoes?

thanks

Reply

29 samuel March 26, 2014 at 7:03 am

I suggest changing this post about flush dns cache since its not correct to reload or restart nscd.

I read the man and found the correct way is use:

nscd -i hosts

This method was mentioned in several comments, but if your post were not updated, more andmore users would be misguided.

Reply

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Tagged as: /etc/init.d/dnsmasq, /etc/init.d/named, /etc/init.d/nscd, clear dns cache in linux, clear dns cacheon linux, clearn dns cache, dns queries, dnsmasq, flush dns cache in linux, flush dns cache on linux, flush


9 of 13 5/22/2014 11:15 AM

linux dns cache, how to clear cache, linux clear dns cache, linux flush dns cache, named, nscd, redhatflush dns cache

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How to Flush Linux _ UNIX DNS Cache