Thursday, September 30, 2010

How to flush the DNS cache in Windows and OS X

If you're having problems with DNS, try flushing the local DNS cache. If you don't know what DNS is, this is the service that handles translating domain names, such as, into IP addresses. This allows you to remember the domain name, but then allows the computer to use the IP address to communicate with it. Sometimes DNS settings get changed, but those changes can take a little while to propagate through to everyone system. To speed the propagation along, you can flush your DNS cache manually and force it to reload the most recent settings. To do that in Windows or Mac OS X:

Open a command prompt (Start->Run->cmd, then OK). Then type ipconfig /flushdns and press Enter

Open Terminal (Applications->Utilities->Terminal) and type dscacheutil -flushcache then pressing Enter

You should note that this only flushes the DNS cache on your local machine. DNS is a hierarchical system that relies on many different levels of connections, each of which have their own DNS cache. If you manage your own DNS server that would be the next step to diagnosing a problem if flushing the client machine's cache doesn't work. However, that's another topic entirely and this is only meant to give you the quick way to manually flush the DNS cache. If you want to learn more about how DNS works, check out the Wikipedia article, or search online because you'll find plenty of resources.

Wednesday, September 29, 2010

How to clear your Windows offline files cache

If you are having problems with offline synchronization in Windows and can't seem to get it figured out, you may need to clear your offline file cache.  I've also run into problems where there is no other way to stop your offline files from synchronizing, even if you've done what you can to shut it off. I recently had this issue and found the solution at There are three different way to clear the cache, but the article in the link outlines them all in a very clear way. In my situation I had to use one of the registry hacks because I had a GPO preventing changes to offline files through the menu.

What's taking up your free space? Easily find out using these free tools

Have you ever wondered what is taking up space on your hard drive? If you have, you'll be happy to know that free programs exist which will traverse all your files and folders and give you a hierarchical and graphical view of where your space is being taken up. I recently had a user with 2GB of free space left on an 80GB hard drive, but I could only find 27GB in use. Using one of these programs I found that almost 40GB was showing up as unknown space. That led to some more research to find that IBM's Rescue and Recovery can cause this, and that was exactly the problem. I uninstalled Rescue and Recovery (there was no need for it on the machine anyway) and that made all the unknown space usable space again.

There are many different programs that will give you a graphical representation of file space on your drive(s), but the two I'd suggest are WinDirStat and SpaceSniffer, both of which are free. I prefer the look of SpaceSniffer, and it also comes as an executable so you don't have to install it. Below you'll see a screenshot of SpaceSniffer so you can better understand what I mean when I say it gives you a graphical representation of your hard drive space. If you're wondering just what is taking up space on a drive, give one of these two tools a try and save yourself the time of manually tracking down the culprit.