Symptoms

Parallels Desktop cannot be started. The notification window Unable to start Parallels services appears.

Cause

• Parallels Desktop cannot connect to one of the required services.
• Authentication failure of system kernel extensions as a result of the absence of the restricted flag on /Library/StagedExtensions folder
• Parallels Desktop cannot access system kernel extensions
• macOS® operating system doesn't allow to load Parallels Desktop kernel extensions due to a system policy

Troubleshooting

As a first troubleshooting step restart the Mac and try launching Parallels Desktop, then try reinstalling it:

1. Restart the Mac and try launching Parallels Desktop again.
2. If the first step hasn't fixed the issue, uninstall Parallels Desktop.
   NOTE:  Restart is required to finish the uninstall process.
3. After restarting the Mac install Parallels Desktop again. If required, download the installation image from the Downloads for Parallels Desktop page.
4. Try launching Parallels Desktop again.

Information

As an alternative to the most of troubleshooting steps listed below it's possible to either update macOS® operating system as described here if an update is available or reinstall macOS® from Recovery as per instructions from the article. Both actions will refresh system files and restore permissions for system folders which are required for Parallels Desktop functionality.

The next step is required to determine the status of the restricted flag on /Library/StagedExtensions/ folder where system kernel extensions are stored. To do so while Mac is booted in normal mode:

1. Start Terminal: open Finder - Applications - Utilities - Terminal.

2. Type in ls -dlO /Library/StagedExtensions/ and hit return (Enter).

   NOTE: in -dlO l is lower case L, not the figure 1 and O is a capital o, not the figure zero.

3. If the output of the command above doesn't contains the word restricted, check the status of FileVault in System Preferences > Security & Privacy > FileVault as further troubleshooting steps depends on its status. Then proceed to the Setting restricted flag to the /StagedExtensions folder in Recovery section.
   

4. If the output contain the word restricted proceed to the next step.
   

5. Then execute the following command:

    sudo touch /System/Library/Extensions

   
   NOTE: You will need to enter your Mac password to run the command. No symbols will be shown due to security measures, so just hit the keys and use return/Enter.

6. Restart the Mac and try launching Parallels Desktop.

7. If the issue still persists restart your Mac and hold down Command+R combination on the keyboard until Apple logo appears on the screen.
   
   NOTE: If you see a login window or your own desktop instead of the Utilities window, it's possible that you didn't press Command+R early enough. Restart your Mac and try again.

8. From the top menu bar select Utilities and then Terminal.

   

9. Execute the following command:

    spctl kext-consent add 4C6364ACXT
   

   NOTE: You should hit return/Enter after entering the command to execute it.

10. The result of performing this command should look like:
    

     

11. To restart Mac into normal more execute the command reboot or select Apple logo > Restart...

12. Try launching Parallels Desktop again.
13. If none of the steps above have helped the only solution left is to reinstall macOS® from Recovery to update system files as per instructions from the article. By reinstalling macOS® from Recovery only system files will be updated keeping personal files and installed applications intact.

Setting restricted flag to the /StagedExtensions folder in Recovery:

1. Restart your Mac and hold down Command+R combination on the keyboard until Apple logo appears on the screen.
   
   NOTE: If you see a login window or your own desktop instead of the Utilities window, it's possible that you didn't press Command+R early enough. Restart your Mac and try again.

2. This is how Recovery Mode looks like:

   

3. If FileVault is enabled proceed to the next step, if it's not, go to the step 7

4. Since FileVault enabled to execute the necessary command it's required to mount the FileVault protected disk.
   From the list of OS X Utilities select Disk Utility then press Continue button.
   

5. On the left pane select Macintosh HD and then press Mount button at the top of the Disk Utility window
   

6. Enter Mac password in the following window to mount the disk.
   
   
   Once done proceed to the next step.

7. From the top menu bar select Utilities and then Terminal.

   

8. Execute the following command:

    chflags -R restricted /Volumes/Macintosh\ HD/Library/StagedExtensions/
   

   NOTE: You should hit return/Enter after entering the command to execute it.

9. The result of performing this command should look like:

   

10. To restart Mac into normal more execute the command reboot or select Apple logo > Restart...

11. If after executing the command you receive output similar to:

        chflags -R restricted /Volumes/Macintosh\ HD/Library/StagedExtensions: No such file or directory
    

    It means that your Mac hard disk was renamed and it's required to find out its name. To do that, perform the following command:

        diskutil list
    

    The result of performing this command should look like:

    

    NOTE: In this particular case Mac hard disk has default name. Locate the largest disk by its size in the SIZE column and use its name between chflags -R restricted /Volumes/ and  /Library/StagedExtensions/ while executing the command, e.g.:

    chflags -R restricted /Volumes/MacSSD/Library/StagedExtensions/
    
    NOTE: By using the Tab button on the keyboard it's possible to utilize tab completion Terminal functionality to fill the path by typing slash symbol / and the first letter of a folder using a correct register. The short video below provides example of using tab completion Terminal functionality. 
    

12. To restart Mac into normal more execute the command reboot or select Apple logo > Restart...and execute the following command once again:

    ls -dlO /Library/StagedExtensions/
    

13. Make sure that now the output has the restricted flag by following instructions again in normal mode.