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Editing Applicationhost.config on 64 bit Win2008

Here's an interesting note about Windows 2008 running in 64 bit. Today I needed to edit ApplicationHost.config only to not find the damn file anywhere on my machine. It turns out 64 bit Windows uses redirection in the System32 folder and while running with a 32 bit Explorer replacement and a 32 bit editor I was unable to find the file until I switched to the stock tools in Windows which are 64 bit.

This bit me because I needed to make some changes in applicationhost.config. ApplicationHost.config is IIS 7's master configuration file that holds top level configuration settings. In it you can find things like Application Pool and Virtual directory definitions as well as most of the default root level configuration settings for IIS and ASP.NET.

What I wanted to do is change the IIS GZIP compression settings as well as lock down the UrlScan rules to lock out some unwanted DOS style attacks that seem to be plaguing a lot of sites over the last few days. Anyway I needed to open ApplicationHost.config on my newly buffed up Windows 2008 64 bit Server. And this is where it gets weird.

ApplicationHost.config should live in:


So I navigated there and found - nothing. An empty folder with no files.

I'm running xPlorer2 as my Windows Explorer replacement interface and I installed it on the server as well to facilitate the lengthy process of copying files onto the new machine from the old Web Server. xPlorer2 rocks and beats the crap out of Windows Explorer (no big feat), but it's 32 bit application. One very nice feature of xPlorer2 is that it also has a quick deep search feature so I fired that off to search the entire boot drive for ApplicationHost.config. However, I came up with only history files and one version in some obscure amd64 related folder (most likely from an install path).

In short the freaking file I'm looking for was nowhere to be found on the system! So I searched around and ran into this IIS forums post that talks about a similar problem:

Basically it turns out that when you are running a 32 bit application you cannot see certain files in the 64 bit system32 folder - ApplcationHost.config among them. Files may be split between the system32 folder and system32Since xPlorer2 is 32 bit I get this (contrasted below with classic Explorer which does show the files):


The top app is xPlorer2 the bottom standard old Explorer. Notice that same folder in xPlorer2 above is empty while in classic Explorer the files show. But the issue is not just that files don't 'list' in a directory listing, but they are literally not accessible to 32 bit applications. The machine also has Visual Studio Tools for Applications installed, which is an editor - installed likely with SQL 2008 and meant for editing configuration files. It's essentially just the VS editor that does syntax highlighting (notice the Visual Studio Icon next to the Open button in the Explorer Window).

But it fails to open ApplicationHost.Config because it's a 32 bit app:


My favorite editor - EditPad - that is the default text editor in my configuration also doesn't work for the same reason. In the end, the only way I could actually edit ApplicationHost.config is with Notepad... Oh joy <g>.

I mentioned that I'm new to 64 bit, with this installation on the server being the first and this - this is really something I had no idea about. This is whacky to the max and heck it doesn't even make any sense. I did some searching around trying to find more information on this topic and it looks like there's very little info on this issue or at least it's not easy to find (here is one and another). Both of these describe the x64 FileSystem Redirector which basically routes DLL access to 32 bit or 64 bit specific directories. I suspect what's happening is that even other files are being redirected so trying to access applicationhost.config looks in C:\Windows\SysWOW64\inetsrv\Config but even there applicationhost.config is not found because well IIS is a 64 bit app and doesn't look there.

So using a 64 bit Editor and stock Explorer is the only way for the moment to get at the file. Kinda whacky, eh?

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# re: Editing Applicationhost.config on 64 bit Win2008
by Nicholas August 09, 2008 @ 9:33am
I can see how that would make anyone crazy. I haven't run into an instance where I had to edit that file though, IIS7's management interface lets you control a lot of that if you know where to look. Were you tweaking the GZIP/etc. settings?
# re: Editing Applicationhost.config on 64 bit Win2008
by Rick Strahl August 09, 2008 @ 10:48am
@Nicholas - I was editing the GZip content types as well as the requestFiltering options. Neither can be set through the admin UI.
# re: Editing Applicationhost.config on 64 bit Win2008
by Nicholas August 09, 2008 @ 11:52am
Gotcha. I'm curious as to what additional mime types you specify? I probably need to update mine..
# re: Editing Applicationhost.config on 64 bit Win2008
by Dan Finch August 14, 2008 @ 3:51pm
There's also the "IIS Admin Pack" for IIS7 which installs a configuration editor into the IIS management console. It'll let you edit all of the machine's configuration files with a GUI.
# re: Editing Applicationhost.config on 64 bit Win2008
by CarlosAg August 18, 2008 @ 10:04pm
Have you tried opening %windir%\sysnative\inetsrv\config\ApplicationHost.config ?
SysNative allows 32 bit applications to gain access to native 64 system folder
# re: Editing Applicationhost.config on 64 bit Win2008
by adrian August 19, 2008 @ 2:09am
before i figured out what happened, i seriously lost confidence in my windows skills (there's not that much to loose with windows itself). i found a microsoft xml notepad ( which is in itself .. well .. weird. so the search continues
# re: Editing Applicationhost.config on 64 bit Win2008
by Patrick June 28, 2009 @ 8:08pm
I have ran into so many issues on Vista 64 with VS 2008 and other issues I am thinking about shipping my new laptop back and get Vista 32. The edit issue Rick mentioned was just one.
# re: Editing Applicationhost.config on 64 bit Win2008
by Erik Anderson August 11, 2009 @ 11:16am
What a coincidence - I just ran into this issue today. I thought I was losing my mind and had to show another co-worker just to make sure I wasn't the one losing it. In my case, I found the default web server wouldn't run due to a malformed applicationHost.config file. It seems some installer, possibly ArcGIS Server 9.3.1, inserted three garbage characters at the start of the file.

For even more strangeness, I could see the garbage characters using "type" or "clip" from the command prompt. But when I opened the file in Notepad they weren't there.

I was able to write over the file but now have to deal with an WAS issue before I can determine if this corrected the original problem.

# re: Editing Applicationhost.config on 64 bit Win2008
by Paulo Eduardo Neves October 21, 2009 @ 1:07pm
I've found you via Google.

After reading your explanation, here is my solution: copy the file elsewhere, edit it with your favorite editor, and copy it back.
# re: Editing Applicationhost.config on 64 bit Win2008
by Daniel Bryars March 10, 2010 @ 4:55am
I'm curious about the "unwanted DOS style attacks" you mentioned, makes me think I should be changing my UrlScan rules too?

Can you point me in the right direction to read up about these type attacks please?
# re: Editing Applicationhost.config on 64 bit Win2008
by Carl May 03, 2010 @ 2:03pm
I ran into this one today. Also found that the windows explorer search built into explorer now di d not find the original file, only the backups.

Yeah, just another way that windows is SO helpful.
# re: Editing Applicationhost.config on 64 bit Win2008
by Jay July 14, 2010 @ 8:08am
a good workaround to the 32-bit redirection is to map a network drive to the local machine, i.e.,

net use X: \\localhost\c$.

the 32-bit app can then access X:\windows\system32\inetsrv\config\applicationhost.config without issue.
# re: Editing Applicationhost.config on 64 bit Win2008
by Tim August 17, 2010 @ 6:40am
Just open notepad an open the file via drop & drop.
# re: Editing Applicationhost.config on 64 bit Win2008
by JamezJ October 12, 2010 @ 6:38pm
FYI. I got this same error message on Windows 7 (IIS7.5), trying to run an application.
# re: Editing Applicationhost.config on 64 bit Win2008
by Tracy Dryden January 13, 2011 @ 3:24pm
Get the 64-bit version of Directory Opus (pricey, but worth it) and you'll be able to SEE the file, but you still won't be able to EDIT it. The solution I found, at, is to go to the c:\windows\syswow64\inetsrv folder, rename the config folder to config86 (since it's emtpy anyway, it doesn't really hurt) and then create a symbolic link from c:\windows\system32\inetsrv\config to c:\windows\syswow64\inetsrv\config (with Link Shell Extension it's a simple operation). It's a bit bizarre to have to redirect the redirect, but it works like a charm.
# re: Editing Applicationhost.config on 64 bit Win2008
by DuskoS February 26, 2011 @ 4:38am
I used the same idea as the poster who maps localhost\c$ drive.
I used:
subst i: "C:\Windows\System32\inetsrv\config"
Now I can point my editor to i: drive.
Works for me.

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