Complete IIS and Windows Environment Variables Knowledge Base

Windows Environment Variables Reference

What are Environment Variables?

Environment variables are system-defined values that programs use to find files and folders regardless of which drive Windows is installed on or how the system is configured.

System Location Variables

%windir% = Windows directory (usually C:\Windows)
%SystemRoot% = Same as %windir% (C:\Windows)
%SystemDrive% = Drive where Windows is installed (C:)
%System32% = System32 folder (C:\Windows\System32)
%ProgramFiles% = Program Files folder (C:\Program Files)
%ProgramFiles(x86)% = 32-bit programs on 64-bit systems (C:\Program Files (x86))
%ProgramData% = Shared application data (C:\ProgramData)
%CommonProgramFiles% = Shared program files (C:\Program Files\Common Files)
%CommonProgramFiles(x86)% = 32-bit shared files (C:\Program Files (x86)\Common Files)

User Profile Variables

%UserProfile% = Current user's home folder (C:\Users\YourName)
%HomeDrive% = Drive containing user profiles (C:)
%HomePath% = Path to user profile (\Users\YourName)
%AppData% = User's roaming application data (C:\Users\YourName\AppData\Roaming)
%LocalAppData% = Local app data (C:\Users\YourName\AppData\Local)
%Temp% = Temporary files folder (C:\Users\YourName\AppData\Local\Temp)
%TMP% = Same as %Temp%
%Desktop% = User's desktop (C:\Users\YourName\Desktop)
%Documents% = User's documents (C:\Users\YourName\Documents)
%StartMenu% = User's start menu (C:\Users\YourName\AppData\Roaming\Microsoft\Windows\Start Menu)
%Startup% = User's startup folder (C:\Users\YourName\AppData\Roaming\Microsoft\Windows\Start Menu\Programs\Startup)

System Information Variables

%ComputerName% = Your computer's name
%UserName% = Currently logged in user
%UserDomain% = Domain name (if joined to a domain)
%UserDnsDomain% = DNS domain name
%LogonServer% = Domain controller that authenticated the user
%ProcessorArchitecture% = CPU type (AMD64, x86, ARM64)
%ProcessorIdentifier% = Detailed CPU information
%ProcessorLevel% = CPU family
%ProcessorRevision% = CPU revision
%Number_of_Processors% = Number of CPU cores

Network and Domain Variables

%ComputerName% = Local computer name
%UserDomain% = Logon domain
%LogonServer% = Domain controller name
%UserDnsDomain% = DNS domain name

Development and System Variables

%Path% = System PATH variable (directories searched for executables)
%PathExt% = File extensions considered executable (.exe, .bat, .cmd, etc.)
%OS% = Operating system name (Windows_NT)
%Processor_Architecture% = Processor architecture
%Random% = Random number between 0 and 32767
%Time% = Current time
%Date% = Current date
%CD% = Current directory
%CmdCmdLine% = Command line used to start cmd.exe

Special Shared Folders

%Public% = Public user folder (C:\Users\Public)
%AllUsersProfile% = All users data (C:\ProgramData)
%CommonStartMenu% = Shared start menu (C:\ProgramData\Microsoft\Windows\Start Menu)
%CommonStartup% = Shared startup folder (C:\ProgramData\Microsoft\Windows\Start Menu\Programs\StartUp)
%CommonDesktop% = Shared desktop (C:\Users\Public\Desktop)
%CommonDocuments% = Shared documents (C:\Users\Public\Documents)

How to View Environment Variables

Command Prompt:


set                    # Show all variables
echo %windir%         # Show specific variable
set windir            # Show variables starting with "windir"

PowerShell:


Get-ChildItem Env:           # Show all variables
$env:windir                  # Show specific variable
$env:windir = "C:\Windows"   # Set variable

Windows GUI:

Press Win + R, type sysdm.cpl, press Enter
Click "Advanced" tab → "Environment Variables" button

Why Use Environment Variables?

Portability: Scripts work on any Windows system regardless of drive configuration
Flexibility: Programs find files even if Windows is installed to different drives
Maintenance: Easier to update paths centrally
Security: Avoid hardcoding sensitive paths in scripts

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IIS Knowledge Base Guide

Why Install IIS on F: Drive Instead of C:

Performance Benefits

Separates web content from system drive to reduce I/O contention
F: drive is typically larger storage dedicated to data
C: drive reserved for operating system files

Management Advantages

Easier backup strategies - web content isolated from system files
Better security through application separation
Corporate policies often mandate separating applications from OS
Storage management - prevents web logs from filling system drive

IIS Manager vs Log Files

#### IIS Manager

What it is: Graphical management console for configuring IIS

Configure websites, application pools, virtual directories
Set authentication, SSL certificates, URL rewriting rules
Monitor real-time performance and active connections
Location: %windir%\system32\inetsrv\InetMgr.exe

#### IIS Log Files

What they are: Automatically generated records of all web requests

Default location: %SystemDrive%\inetpub\logs\LogFiles\W3SVC1\
Contains request details, response codes, timestamps, IP addresses
Used for traffic analysis, troubleshooting, security monitoring, compliance

W3C Log Format - Why Use It?

Industry Standard

W3C Extended Log Format is universally recognized
Compatible with most log analysis tools (LogParser, AWStats, Webalizer)

Customizable and Efficient

Choose which fields to log (date, IP, status codes, user agents, etc.)
Only logs necessary data, reducing file size and storage costs
Well-structured format enables automated parsing and analysis

Tool Integration

Works seamlessly with Microsoft LogParser
Supports third-party analytics and monitoring solutions
Easy to import into databases and reporting tools

IIS Server Configuration Options

#### .NET Authorization

Purpose: Controls access to .NET applications and resources

What it manages:

Authentication methods (Windows Authentication, Forms Authentication, Anonymous)
Authorization rules for specific users and roles
Access control for pages, directories, or application methods
Integration with ASP.NET membership providers and Active Directory

#### .NET Compilation

Purpose: Defines how ASP.NET code is compiled and executed

Key settings:

Debug vs Release mode: Debug includes debugging symbols, Release is optimized for performance
Target Framework: Specifies .NET version (.NET Framework 4.8, .NET Core, etc.)
Compilation options: Batch compilation settings for better performance
Temporary files: Manages compiled assemblies in temporary ASP.NET files directory

#### .NET Error Pages

Purpose: Controls how application errors are displayed to users

Configuration options:

Custom error pages: Display user-friendly pages instead of technical stack traces
Error modes:

- On - Always show custom errors

- Off - Always show detailed errors (development only)

- RemoteOnly - Show custom errors to remote users, detailed to local users

Default redirects: Specify custom pages for 404 (not found) and 500 (server error) responses
Security benefit: Prevents sensitive application information from being exposed to end users

#### MIME Types

Purpose: Tells web browsers how to handle different file types

How it works:

File associations: Maps file extensions to content types

- .pdf → application/pdf

- .jpg → image/jpeg

- .json → application/json

Browser behavior: Determines whether file is displayed in browser or downloaded
Content handling: Controls streaming, caching, and compression settings
Security: Prevents execution of unknown or potentially dangerous file types

Common MIME types:

text/html - HTML web pages
text/css - Cascading Style Sheets
application/javascript - JavaScript files
image/png - PNG image files
application/json - JSON data responses
application/octet-stream - Generic binary files (forces download)

IIS Environment Variables

%SystemDrive%\inetpub\wwwroot - Default website root
%SystemDrive%\inetpub\logs\LogFiles - Default log location
%windir%\system32\inetsrv - IIS binaries and tools
%ProgramFiles%\IIS - IIS program files (if installed)

Quick Reference Commands

Check Environment Variables


echo %windir%              # Windows directory
echo %SystemDrive%         # System drive
echo %UserProfile%         # User profile path
echo %ComputerName%        # Computer name
echo %UserName%           # Current user

IIS Quick Paths

IIS Manager: %windir%\system32\inetsrv\InetMgr.exe
Default Website: %SystemDrive%\inetpub\wwwroot
Default Logs: %SystemDrive%\inetpub\logs\LogFiles\W3SVC1\
IIS Config: %windir%\system32\inetsrv\config\applicationHost.config

Log File Information

Naming Convention: ex[YYMMDD].log (example: ex241201.log)
Key Fields: date, time, c-ip, cs-method, cs-uri-stem, sc-status, time-taken
Status Codes: 200=OK, 404=Not Found, 500=Server Error, 403=Forbidden