Difference between revisions of "Flush DNS Cache"
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== Flush DNS Cache == | == Flush DNS Cache == | ||
| − | === Mac OS 10. | + | === Mac OS 10.7 and up (actually 10.7 up to 10.9 and 10.10.4 and up) === |
| − | + | ||
| − | + | ||
| − | + | ||
| − | + | ||
dscacheutil -flushcache | dscacheutil -flushcache | ||
killall -HUP mDNSResponder | killall -HUP mDNSResponder | ||
| + | |||
| + | === Mac OS 10.10 up to 10.10.3 === | ||
| + | |||
| + | discoveryutil udnsflushcaches | ||
=== Mac OS 10.5.2 up to 10.6 === | === Mac OS 10.5.2 up to 10.6 === | ||
| Line 22: | Line 22: | ||
ipconfig /flushdns | ipconfig /flushdns | ||
| − | === Linux === | + | === Linux with Systemd === |
| + | |||
| + | systemd-resolve --flush-caches | ||
| + | |||
| + | === Older Linux versions === | ||
Depending on your distribution: | Depending on your distribution: | ||
| Line 51: | Line 55: | ||
=== Flushing does not help === | === Flushing does not help === | ||
| − | I've seen a few cases where flushing does not help | + | I've seen a few cases where flushing does not help. |
In one of these cases, the <tt>discoveryutil udnsflushcaches</tt> command would give the following error in <tt>system.log</tt>: | In one of these cases, the <tt>discoveryutil udnsflushcaches</tt> command would give the following error in <tt>system.log</tt>: | ||
| Line 58: | Line 62: | ||
It seems that in this case, the command from <tt>discoveryutil</tt> never reached <tt>discoveryd</tt>. | It seems that in this case, the command from <tt>discoveryutil</tt> never reached <tt>discoveryd</tt>. | ||
| + | |||
| + | In that case, I usually reboot my computer, or <tt>killall discoveryd</tt> in the knowledge that Mac OS X launch daemon will restart <tt>discoveryd</tt>. | ||
| + | |||
| + | [[Category:DNS]] | ||
| + | [[Category:Mac OS X]] | ||
| + | [[Category:Linux]] | ||
| + | [[Category:Windows]] | ||
Latest revision as of 18:17, 28 October 2020
Contents
Flush DNS Cache
Mac OS 10.7 and up (actually 10.7 up to 10.9 and 10.10.4 and up)
dscacheutil -flushcache killall -HUP mDNSResponder
Mac OS 10.10 up to 10.10.3
discoveryutil udnsflushcaches
Mac OS 10.5.2 up to 10.6
dscacheutil -flushcache
Mac OS up to 10.5.1
lookupd -flushcache
Windows
ipconfig /flushdns
Linux with Systemd
systemd-resolve --flush-caches
Older Linux versions
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 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.
In that case, I usually reboot my computer, or killall discoveryd in the knowledge that Mac OS X launch daemon will restart discoveryd.
