MSI File Format

What is an MSI file?

An MSI file (Microsoft Installer) is a Windows installer package format developed by Microsoft for the installation, maintenance, and removal of software on Windows operating systems. MSI files contain the installation database, files, and metadata required to install applications in a structured, standardized manner.

File Extensions

• .msi

MIME Type

• application/x-msi

History and Development

Microsoft Installer (originally called Microsoft Installer Service) was introduced with Windows 2000 and Windows Installer 1.0. It was designed to address the problems of "DLL Hell" and provide a more reliable, standardized installation experience on Windows platforms.

Timeline

• 1999: Windows Installer 1.0 released with Windows 2000
• 2001: Windows Installer 2.0 with Windows XP
• 2005: Windows Installer 3.0 with major enhancements
• 2006: Windows Installer 4.0 with Windows Vista
• 2009: Windows Installer 5.0 with Windows 7
• Present: Ongoing updates with Windows 10/11

Technical Specifications

File Structure

MSI files are structured storage files (compound documents) that contain:

• Installation Database: Tables defining installation logic
• Embedded Files: Application files and resources
• Scripts: Custom actions and installation sequences
• Metadata: Product information and version details

Database Tables

Key tables in the MSI database:

• File Table: Lists all files to be installed
• Directory Table: Defines directory structure
• Component Table: Logical groupings of files
• Feature Table: User-selectable installation features
• Registry Table: Registry entries to be created
• Shortcut Table: Desktop and Start Menu shortcuts

Installation Sequences

MSI defines standardized installation sequences:

1. Initialization: Prepare for installation
2. User Interface: Display installation dialogs
3. Execute: Perform actual installation actions
4. Finalization: Complete installation and cleanup

Features and Capabilities

Core Features

• Transactional Installation: Rollback on failure
• Component Tracking: Precise file and registry tracking
• Repair Functionality: Automatic repair of corrupted installations
• Uninstall Support: Complete removal of installed software
• Administrative Installation: Network deployment support
• Patch Support: Incremental updates via MSP files

Advanced Features

• Transform Files: Customize installations without modifying MSI
• Merge Modules: Reusable installation components
• Digital Signatures: Verify package authenticity
• Condition Tables: Conditional installation logic
• Custom Actions: Execute custom code during installation

Installation Types

Interactive Installation

Standard user-driven installation with GUI:

msiexec /i application.msi

Silent Installation

Automated installation without user interaction:

msiexec /i application.msi /quiet
msiexec /i application.msi /qn

Administrative Installation

Network deployment preparation:

msiexec /a application.msi TARGETDIR=\\server\share

Repair Installation

Fix corrupted or missing files:

msiexec /f application.msi
msiexec /fa application.msi  # Repair all files

Command-line Options

Common MSIEXEC Parameters

# Installation
msiexec /i package.msi           # Interactive install
msiexec /i package.msi /quiet    # Silent install
msiexec /i package.msi /passive  # Progress bar only

# Uninstallation
msiexec /x package.msi           # Interactive uninstall
msiexec /x {ProductCode}         # Uninstall by product code

# Logging
msiexec /i package.msi /l*v log.txt  # Verbose logging

# Properties
msiexec /i package.msi PROPERTY=VALUE

Installation Properties

Common MSI properties:

• TARGETDIR: Installation directory
• ALLUSERS: Install for all users (1) or current user (0)
• INSTALLDIR: Specific installation folder
• ADDLOCAL: Features to install
• REMOVE: Features to remove

Development Tools

Authoring Tools

• WiX Toolset: Open-source XML-based MSI creation
• InstallShield: Commercial installer authoring suite
• Advanced Installer: GUI-based MSI editor
• NSIS: Alternative installer creation tool

Analysis Tools

• Orca: Microsoft's MSI database editor
• InstEd: Third-party MSI editor
• MSI Viewer: View MSI contents and properties
• Windows Installer Cleanup Utility: Remove broken installations

WiX Example

<?xml version="1.0" encoding="UTF-8"?>
<Wix xmlns="http://schemas.microsoft.com/wix/2006/wi">
  <Product Id="*" Name="MyApplication" Language="1033" 
           Version="1.0.0.0" Manufacturer="MyCompany"
           UpgradeCode="12345678-1234-1234-1234-123456789012">
    
    <Package InstallerVersion="200" Compressed="yes" />
    
    <Directory Id="TARGETDIR" Name="SourceDir">
      <Directory Id="ProgramFilesFolder">
        <Directory Id="INSTALLFOLDER" Name="MyApplication" />
      </Directory>
    </Directory>
    
    <Component Id="MainExecutable" Guid="*">
      <File Id="MyAppEXE" Source="MyApp.exe" />
    </Component>
    
    <Feature Id="Complete" Title="MyApplication" Level="1">
      <ComponentRef Id="MainExecutable" />
    </Feature>
    
  </Product>
</Wix>

Enterprise Deployment

Group Policy Deployment

Deploy MSI packages via Active Directory:

1. Computer Configuration: Machine-wide installation
2. User Configuration: Per-user installation
3. Assigned Applications: Mandatory installation
4. Published Applications: Optional installation

System Center Configuration Manager (SCCM)

• Application Deployment: Centralized software distribution
• Dependency Management: Handle application prerequisites
• Scheduling: Control installation timing
• Reporting: Track deployment success and failures

Microsoft Deployment Toolkit (MDT)

• Operating System Deployment: Include applications in OS images
• Application Bundles: Group related applications
• Task Sequences: Automate complex deployments
• Zero Touch Installation: Fully automated deployment

Transform Files (.MST)

Purpose

Customize MSI installations without modifying the original package:

• Property Overrides: Change default values
• Feature Selection: Modify default feature states
• UI Modification: Customize installation dialogs
• File Replacement: Substitute files during installation

Creating Transforms

# Apply transform during installation
msiexec /i application.msi TRANSFORMS=custom.mst

# Create transform with Orca
# 1. Open MSI in Orca
# 2. Make modifications
# 3. Save as Transform (.mst)

Patch Files (.MSP)

Update Mechanism

MSP files provide incremental updates:

• Binary Patches: Efficient file updates
• New Files: Add missing files
• Registry Updates: Modify registry entries
• Version Checking: Ensure correct base version

Patch Installation

msiexec /p patch.msp /package application.msi
msiexec /p patch.msp  # Auto-detect target MSI

Security Considerations

Code Signing

• Authenticode Signatures: Verify package publisher
• Certificate Validation: Check certificate chain
• Timestamp Verification: Ensure signature validity
• User Account Control: Elevation for system-wide changes

Installation Security

• Elevated Privileges: MSI installations run with admin rights
• Custom Actions: Potential security risks in custom code
• File Permissions: Proper access control on installed files
• Registry Security: Secure registry modifications

Best Practices

1. Digital Signing: Always sign MSI packages
2. Validate Sources: Only install from trusted sources
3. Test Installations: Thoroughly test in isolated environments
4. Monitor Logs: Review installation logs for anomalies

Troubleshooting

Common Issues

• Installation Failures: Insufficient permissions or disk space
• Rollback Problems: Incomplete transaction cleanup
• Custom Action Errors: Failures in custom installation code
• Version Conflicts: Incompatible versions or dependencies

Diagnostic Tools

# Enable verbose logging
msiexec /i package.msi /l*v install.log

# Check Windows Installer service
sc query msiserver

# View installed products
wmic product get name,version

# Repair Windows Installer
sfc /scannow

Log Analysis

Key log entries to examine:

• Return values: Installation success/failure codes
• Property values: Runtime property values
• Custom action results: Output from custom actions
• Error messages: Detailed failure descriptions

Best Practices

Package Development

1. Follow Standards: Use Windows Installer best practices
2. Test Thoroughly: Test on clean systems and various configurations
3. Version Management: Implement proper versioning schemes
4. Documentation: Document installation requirements and procedures

Deployment Strategy

• Pilot Testing: Test with small user groups first
• Phased Rollout: Gradual deployment to minimize risk
• Rollback Planning: Prepare for installation failures
• User Communication: Inform users about software changes

Maintenance

• Regular Updates: Keep software current with patches
• License Tracking: Monitor software license compliance
• Inventory Management: Track installed software across organization
• Performance Monitoring: Watch for installation-related issues

MSI files represent Microsoft's comprehensive solution for Windows software installation, providing robustness, standardization, and enterprise-ready features that make them the preferred choice for professional Windows software deployment.