Understanding the Error
The “Bless of the Installer Disk Failed” error typically occurs on Mac computers when attempting to install or update macOS. This error is related to the “bless” tool, which is used in macOS to set up the system folder and help the computer locate the operating system on boot. Essentially, the “bless” tool is responsible for making a volume bootable for the system.
When you encounter this error, it means the system is unable to properly execute the “bless” command on the installer disk. This failure prevents the Mac from recognizing the installer as a valid startup disk, thereby blocking the installation or upgrade process. The reasons for this error can vary, including issues with the installer itself (such as corruption or incompleteness), problems with the disk you’re attempting to install macOS on (like disk permission issues or formatting errors), or even hardware compatibility problems.
This error can be a roadblock when trying to install or upgrade macOS, leaving many puzzled about its cause and, more importantly, its resolution. In this guide we will look into effective steps to resolve the error and ensure a smooth installation process.
Troubleshooting Steps
- Check Compatibility and System Requirements
Before diving into more complex solutions, ensure your Mac meets the macOS version’s system requirements you’re attempting to install. Compatibility issues are common culprits behind installation failures.
- Verify the Installer’s Integrity
A corrupted installer can lead to numerous installation errors, including the ‘bless’ issue. To verify and compare the checksum of a macOS installer file with its original, ideally, you would need the original checksum value provided by Apple or a trusted source. Since Apple does not officially publish checksums for macOS installer files, this direct comparison can be challenging. However, ensuring you download the macOS installer directly from the Mac App Store or through system updates provided by Apple is the best way to guarantee its authenticity and integrity.
For educational purposes, or in scenarios where you’re working in a controlled environment with access to known-good checksums (e.g., within an organization that maintains its checksum database for internal use), here’s how you could verify and compare the checksum:
Step 1: Generate the Checksum of Your Installer File
- Open Terminal: Find Terminal through Spotlight search (Cmd + Space) or in the Utilities folder within Applications.
- Run the shasum Command: Replace “macOSInstaller.app” with the name of your installer file. For macOS Big Sur, the command would look like this:
shasum -a 256 /Applications/Install\ macOS\ Big\ Sur.app/Contents/SharedSupport/SharedSupport.dmg
- Record the Output: Terminal will display a checksum value, a long string of alphanumeric characters.
Step 2: Compare the Checksum
Since Apple does not provide official checksums for comparison, this step involves ensuring the integrity of the download source (e.g., the Mac App Store). In a controlled environment where checksums are documented:
- Obtain the Known-Good Checksum: Access the original or known-good checksum from your internal database or a trusted repository provided by your organization or network.
- Compare Checksums: Manually compare the checksum you generated with the known-good checksum. They should match exactly if the file is unchanged and authentic.
- Use Disk Utility to Repair Permissions
Incorrect disk permissions can prevent the ‘bless’ command from executing correctly. Utilizing Disk Utility’s First Aid feature to repair permissions can resolve the issue.
- Restart your Mac and hold Command + R to enter Recovery Mode.
- Open Disk Utility and select your startup disk.
- Click on ‘First Aid’ and follow the prompts to repair disk permissions.
- Create a Bootable Installer for macOS
If the above steps don’t resolve the issue, consider creating a new bootable installer for macOS on an external drive. This method often bypasses the ‘bless’ error by using a clean installation source.
- Format an external USB drive (at least 16GB) as macOS.
- Get the macOS installer from the Mac App Store
- Use Terminal to create a bootable installer with the command specific to the macOS version you’re installing.
Click here how to create macOS bootable installer.
- Reset NVRAM
Resetting the Non-Volatile Random-Access Memory (NVRAM) can solve various boot and installation issues, as it clears certain settings stored by the system, including startup disk selection, which may interfere with the installation process.
- Shut down your Mac.
- Press the power button, then immediately press and hold Option + Command + P + R for about 20 seconds.
Successfully navigating past ‘The bless of the installer disk failed’ error is a testament to your troubleshooting skills. Once resolved, proceed with the macOS installation, ensuring your system is up to date with the latest features and security enhancements. Remember, regular backups are crucial for avoiding data loss during such processes.
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