Fix 'Permission Denied' On External Disk (MacOS)

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Permission Denied When Accessing External Disk

Hey guys! Ever yanked out an external drive a little too enthusiastically and ended up with a corrupted disk and a dreaded "Permission denied" error? Yeah, it's happened to the best of us. Especially on MacOS, dealing with disk permissions and file systems can sometimes feel like navigating a maze. You're not alone if you've disconnected an ExFAT32 drive and now Disk Utility's First Aid is throwing its hands up in defeat. Don't panic! Let's dive into some potential solutions to get your external disk back up and running and those permissions sorted out.

Understanding the Problem: Permissions and File Systems

Before we jump into the fixes, let's quickly chat about why this happens. The "Permission denied" error basically means your operating system (in this case, MacOS) isn't allowing you to access the disk or its files. This could be due to a few reasons:

  • File System Corruption: Disconnecting a drive without properly ejecting it can corrupt the file system. This can scramble the permissions and make the drive unreadable or unwritable.
  • Incorrect Permissions: Sometimes, the permissions on the disk or its folders are set incorrectly, preventing your user account from accessing them. This can happen after software updates, system errors, or even just accidentally changing settings.
  • File System Compatibility: While ExFAT32 is generally compatible with MacOS, sometimes there can be hiccups, especially if the disk was formatted on a different operating system.

It's also worth noting that MacOS has gotten stricter with its security measures over the years, so even if you used to be able to get away with hot-swapping drives, the operating system is now more likely to throw a fit.

So, what can you do? Let's explore some troubleshooting steps.

Troubleshooting Steps

1. First Aid (Again, But With a Twist)

Okay, I know you said Disk Utility's First Aid didn't work, but hear me out. Sometimes, it's worth trying again, but with a slight modification. Boot into Safe Mode (hold down the Shift key while your Mac starts up). Safe Mode performs some basic disk checks and repairs during startup, which might be enough to fix minor file system issues. Once in Safe Mode, try running First Aid on the external disk again. The reason this sometimes works is that Safe Mode loads a minimal set of drivers and extensions, which can prevent conflicts that might be interfering with the repair process during a normal boot. Even if it fails again, we've ruled out some potential conflicts. Remember, patience is key; let the process complete without interruption.

2. Diskutil to the Rescue

If the GUI-based Disk Utility isn't cutting it, it's time to get our hands dirty with the command line. The diskutil command is a powerful tool for managing disks on MacOS. Here’s how to use it:

  • Open Terminal: You can find it in /Applications/Utilities.
  • List Disks: Type diskutil list and press Enter. This will show you a list of all the disks connected to your Mac. Identify your external disk by its size and name. Note the disk# identifier (e.g., disk2, disk3).
  • Repair Disk: Type diskutil repairDisk disk# (replace disk# with the actual identifier of your disk) and press Enter. This command attempts to repair the entire disk, including the partition table. Important: This is different from repairVolume, which only repairs a specific volume.

Remember to always double-check the disk number before running any commands, as you don't want to accidentally erase the wrong drive! The repairDisk command can take a while to complete, so be patient. It will provide output in the Terminal window, indicating its progress and any errors it encounters. Even if it throws errors, it might still fix some underlying issues.

3. Check and Repair the File System with fsck

fsck (file system consistency check) is another command-line tool that can be used to check and repair file systems. However, it's important to note that fsck is primarily designed for HFS+ file systems (the older file system used by MacOS), and its support for ExFAT is limited. Still, it's worth a try, especially if you suspect there might be some low-level file system corruption.

  • Unmount the Disk: Before running fsck, you need to unmount the disk. In Terminal, use the command diskutil unmountDisk disk# (again, replace disk# with the correct identifier). If the disk is in use, you might need to force unmount it with diskutil unmountDisk force disk#. Be careful when using the force option, as it can lead to data loss if processes are actively writing to the disk.

  • Run fsck: The command to run fsck is sudo fsck_exfat -d /dev/disk# (replace disk# with the correct identifier). You'll be prompted for your administrator password. The -d flag enables debugging output, which can provide more information about any errors that are found.

  • Interpreting the Results: fsck will print a lot of output to the Terminal. Look for any error messages or warnings. If fsck finds errors, it will attempt to repair them. Follow any prompts or instructions that are displayed. Note: fsck_exfat might not be available on all versions of MacOS. If you get a