macOS Error -36: Fix Input/Output Errors Fast

Cause #1: Hidden files are sneaking into your copy

I've seen this trip up Mac users for years. Error -36, which reads as "The Finder can’t complete the operation because some data in “filename” can’t be read or written," almost always comes from hidden files or resource forks that Finder doesn't show you by default. These little buggers ride along when you copy a folder, and one bad one can stop the whole operation dead.

Here's the fix that works 90% of the time: use Terminal to copy the files. It bypasses Finder's little tantrum and copies everything, including those hidden files.

1. Open Terminal (search for it in Spotlight or go to Applications > Utilities > Terminal).
2. Use the ditto command. It's built into macOS and handles resource forks and hidden files better than cp.

ditto /path/to/source /path/to/destination

For example, if you're trying to copy your Documents folder to an external drive:

ditto ~/Documents /Volumes/MyDrive/DocumentsBackup

If that completes without error, then the problem is indeed hidden files. You'll now have a full copy. To see what was causing the trouble, reveal hidden files in Finder with this Terminal command, then restart Finder:

defaults write com.apple.finder AppleShowAllFiles YES && killall Finder

You'll see files like .DS_Store or ._something. Those are the culprits. After copying, you can hide them again with defaults write com.apple.finder AppleShowAllFiles NO and restart Finder.

Cause #2: File permissions are out of whack

Sometimes error -36 isn't about hidden files at all. It's about permissions. If you've copied files from a Windows PC, a network drive, or an external drive formatted as NTFS, the permissions might not match what macOS expects. The fix is to take ownership of the files and reset permissions.

Here's how I do it, step by step:

1. Connect the drive or locate the folder that's giving you grief.
2. Open Terminal and run the following command, replacing /path/to/folder with the actual path.

sudo chown -R $(whoami):staff /path/to/folder

You'll be asked for your admin password. Then fix the permissions:

chmod -R u+rw /path/to/folder

This gives you read and write access to everything inside. In my help desk days, this solved a lot of -36 errors that came from files copied off a colleague's Windows machine.

If that doesn't do it, also try the Disk Utility First Aid route. It's slower but thorough:

1. Open Disk Utility (in Applications > Utilities).
2. Select the disk or volume where the problematic files live.
3. Click First Aid and run it.

That will fix any underlying directory structure issues that could be causing the error.

Cause #3: The destination drive is full or failing

This one's more physical. When you're copying to an external drive, especially an older USB stick or a hard drive that's seen better days, error -36 can pop up if the drive is nearly full or has bad sectors. The Finder doesn't always tell you the drive is full until you hit that error.

First, check the space on the destination:

• Right-click the drive on your Desktop or in Finder.
• Select Get Info.
• Look at the Capacity and Available space.

If you have less than 10% free, that's your problem. Delete some files or use a larger drive. But if there's plenty of space and the error persists, the drive might be failing. Run First Aid on it via Disk Utility, but also listen for weird clicking sounds or slow transfers — those are bad signs.

Another trick: try copying the files in smaller batches. Grab one folder at a time instead of the whole shebang. This isolates the problem file and often gets the job done without fanfare.

Quick-reference summary

That's the whole ballgame. Start with the ditto fix — it's fast and handles the most common cause. If that doesn't work, move down the list. You'll have your files copied in no time.