Difference between revisions of "Flush DNS Cache"
(Created page with "== Flush DNS Cache == {{Main|Flush DNS Cache}} You can explicitly flush your DNS cache. On Mac OS up to 10.5.1: lookupd -flushcache On Mac OS 10.5.2 to 10.6: dscacheut...") |
|||
| Line 1: | Line 1: | ||
== Flush DNS Cache == | == Flush DNS Cache == | ||
| − | + | === Mac OS 10.10 and up === | |
| − | + | discoveryutil udnsflushcaches | |
| − | + | === Mac OS 10.7 up to 10.9 === | |
| − | + | dscacheutil -flushcache | |
| + | killall -HUP mDNSResponder | ||
| − | + | === Mac OS 10.5.2 up to 10.6 === | |
dscacheutil -flushcache | dscacheutil -flushcache | ||
| − | + | === Mac OS up to 10.5.1 === | |
| + | |||
| + | lookupd -flushcache | ||
| + | |||
| + | === Windows === | ||
| + | |||
| + | ipconfig /flushdns | ||
| + | |||
| + | === Linux === | ||
| + | |||
| + | Depending on your distribution: | ||
| + | |||
| + | /etc/init.d/named restart | ||
| + | |||
| + | or | ||
| + | |||
| + | /etc/init.d/nscd restart | ||
| + | |||
| + | == Troubleshooting == | ||
| + | |||
| + | === Negative Caching === | ||
| + | |||
| + | <tt>ping</tt>, or most other programs use the build-in name discovery, with build-in cache. In this case, there is a negative cache: | ||
| − | + | ping www.example.org | |
| + | ping: cannot resolve www.example.org: Unknown host | ||
| + | <tt>host</tt>, <tt>dig</tt> or <tt>nslookup</tt> do not use the build-in name discovery, but always query an external name server, bypassing any cache at the local host (the name server is likely to still cache the result though). | ||
| − | + | $ host www.example.org | |
| + | www.example.org has address 93.184.216.119 | ||
| + | www.example.org has IPv6 address 2606:2800:220:6d:26bf:1447:1097:aa7 | ||
| − | + | In this example, the name servers finds the DNS record, but the local host says it does not exist. This is negative caching; a previously 'not found' result is cached. In this case, it is best to flush the local DNS cache and try again. | |
| − | + | ||
| − | + | === Flushing does not help === | |
| − | + | ||
| − | + | I've seen a few cases where flushing does not help. In that case, I usually reboot my computer. | |
| − | + | ||
| − | + | In one of these cases, the <tt>discoveryutil udnsflushcaches</tt> command would give the following error in <tt>system.log</tt>: | |
| − | + | ||
| − | + | discoveryd[36369]: Basic RemoteControl com.apple.discoveryd XPC connection 0x7fa7a8590860: Connection invalid | |
| − | + | ||
| − | / | + | It seems that in this case, the command from <tt>discoveryutil</tt> never reached <tt>discoveryd</tt>. |
| − | + | ||
Revision as of 23:24, 28 October 2014
Contents
Flush DNS Cache
Mac OS 10.10 and up
discoveryutil udnsflushcaches
Mac OS 10.7 up to 10.9
dscacheutil -flushcache killall -HUP mDNSResponder
Mac OS 10.5.2 up to 10.6
dscacheutil -flushcache
Mac OS up to 10.5.1
lookupd -flushcache
Windows
ipconfig /flushdns
Linux
Depending on your distribution:
/etc/init.d/named restart
or
/etc/init.d/nscd restart
Troubleshooting
Negative Caching
ping, or most other programs use the build-in name discovery, with build-in cache. In this case, there is a negative cache:
ping www.example.org ping: cannot resolve www.example.org: Unknown host
host, dig or nslookup do not use the build-in name discovery, but always query an external name server, bypassing any cache at the local host (the name server is likely to still cache the result though).
$ host www.example.org www.example.org has address 93.184.216.119 www.example.org has IPv6 address 2606:2800:220:6d:26bf:1447:1097:aa7
In this example, the name servers finds the DNS record, but the local host says it does not exist. This is negative caching; a previously 'not found' result is cached. In this case, it is best to flush the local DNS cache and try again.
Flushing does not help
I've seen a few cases where flushing does not help. In that case, I usually reboot my computer.
In one of these cases, the discoveryutil udnsflushcaches command would give the following error in system.log:
discoveryd[36369]: Basic RemoteControl com.apple.discoveryd XPC connection 0x7fa7a8590860: Connection invalid
It seems that in this case, the command from discoveryutil never reached discoveryd.
