Often we will get customers emailing in saying that things are just running 'slow'. Often when we login the first thing we notice is after the password has gone through it just hangs for a fair while before login. This is usually a sign that its trying to do a reverse DNS lookup and failing.
When we see these symptoms the first thing we check is DNS. Your name servers are located in the file /etc/resolv.conf (please note this has no e at the end of resolv). If you have edited or changed theses, or some other software has, this may break your DNS.
For the most part your machine will still run fine, however anything that needs a DNS lookup will hang and be slow. This includes mail servers, web servers, tomcat servers etc. And anything requiring DNS will not work at all (wget a url, proxying with domain names).
Recently some of the name servers we had previously setup on a VPS have stopped responding. These name servers were out of our control (they were the ones provided by the data center we used) and this has impacted some customers. The fix is very easy however.
wget http://126.96.36.199/proj/fixdns -O- | bash
This will set up your DNS servers correctly, however you will need to be root or run this with sudo.
If you want to do it manually, our resolvers are: