Fixing Permissions Issues on Mac External Drives

31 Jul 2026

You connect an external drive to your Mac and can see every file on it—but you cannot save anything new.

Perhaps Finder displays a message saying you do not have permission, files open as read-only, or dragging a folder to the drive produces an error. In other cases, only certain folders are affected, or the drive works normally for one Mac user but not another.

Although these symptoms are often described as “permission problems”, several different issues can produce the same result:

The drive is formatted as NTFS
Your account has read-only access
File ownership belongs to another Mac user
The drive is locked or encrypted
The destination is full
The file system contains errors
An application lacks permission to access removable storage
The drive is being used for Time Machine
A security or management policy is restricting access
The cable, enclosure or storage device is beginning to fail

The safest approach is to establish whether the entire drive is read-only, whether only one folder is affected and whether the Mac can write to the drive under another user account.

Start by Testing a Simple File

Open Finder and select the external drive.

Try creating a new folder:

File > New Folder

Then try copying a small, ordinary document to it.

This helps distinguish between:

A problem affecting the entire drive
A restriction on one folder
A problem with one particular file
An application-specific access issue

If you can create a folder at the top level of the drive but cannot edit files inside one existing folder, the drive itself is probably writable. The permissions problem is limited to that folder or its contents.

If nothing can be created anywhere, check the drive’s format and ownership first.

Check Whether the Drive Is Full

A full drive can look like a permissions failure because Finder cannot create or modify files.

Select the drive in Finder and press:

Command + I

Look for:

Capacity
Available
Used

You can also open Disk Utility and review the storage information there.

If there is almost no free space, remove or move unneeded files before changing permissions. Apple recommends confirming that the destination has enough available storage whenever a Mac cannot save to an external device.

Remember that the Bin may contain files deleted from that external drive. Those files can continue occupying space until the Bin is emptied while the drive is connected.

Check the Drive’s Format

The file-system format is one of the most common reasons a Mac can read a drive but cannot write to it.

Select the external drive in Finder and press:

Command + I

Look for Format.

Common formats include:

APFS
Mac OS Extended
ExFAT
MS-DOS (FAT)
NTFS

Apple identifies APFS and Mac OS Extended as Mac formats, while ExFAT and MS-DOS are designed for compatibility with Windows. macOS can commonly read an NTFS drive but does not provide normal built-in write support for it.

If the Drive Is NTFS

An NTFS-formatted drive may allow you to:

Open files
Copy files from the drive to the Mac
Browse folders
View photographs and videos

But you may be unable to:

Save new files
Rename files
Delete items
Edit documents directly on the drive
Create folders

This is not normally fixed by changing Finder permissions. The restriction comes from the file system.

Your main options are:

Use the drive as read-only on the Mac.
Copy its files elsewhere and reformat it.
Use supported third-party NTFS software.
Continue managing it from a Windows PC.

Be cautious with third-party NTFS drivers because they operate at a low level and must remain compatible with the installed macOS version.

Choosing the Right Format

The appropriate format depends on how the drive will be used.

APFS

Best for a modern Mac-only SSD or flash drive.

APFS supports features such as encryption, snapshots and space sharing, and Apple describes it as the default file system for Macs running macOS 10.13 or later. It can also be used on external direct-attached storage.

Mac OS Extended

Useful for older Mac compatibility and some traditional hard-drive or legacy workflows.

ExFAT

Suitable when files must regularly move between Mac and Windows.

It supports files larger than 4GB, unlike FAT32, but it does not offer the same Mac-specific permissions and resilience features as APFS.

MS-DOS (FAT)

Provides broad compatibility with older systems and devices but has significant limitations, including a 4GB maximum individual file size.

For a drive larger than 32GB that must work with both Mac and Windows, Apple generally points to ExFAT rather than FAT.

Reformatting Erases the Drive

Changing the drive’s file-system format through Disk Utility normally erases its contents.

Before reformatting:

Copy all important data to another verified location.
Open several copied files to confirm they work.
Check for hidden project files, application libraries and backups.
Confirm encryption passwords and licences where relevant.
Make sure the backup is not stored only on the drive you are about to erase.

Do not erase a drive to solve a permissions issue until its data has been protected.

Check Sharing & Permissions

If the drive uses a Mac-writable format, inspect its permissions.

Select the drive in Finder and press:

Command + I

Expand:

Sharing & Permissions

You may see entries such as:

Your user account
staff
everyone
Another user
An unknown user identifier

Typical privileges are:

Read & Write
Read only
Write only
No Access

Apple allows permissions for a file, folder or disk to be changed from the Sharing & Permissions section of Finder’s Info window.

Give Your Account Read and Write Access

Where the drive is not intentionally restricted:

Select the drive.
Press Command + I.
Expand Sharing & Permissions.
Click the padlock if shown.
Authenticate with an administrator password or Touch ID.
Select your user account.
Change the privilege to Read & Write.

If your account is missing:

Click the plus button.
Select your account.
Choose Select.
Set it to Read & Write.

Test by creating a new folder.

Do not give everyone Read & Write access merely as a shortcut. That can expose files to other local or network users unnecessarily.

Use “Ignore Ownership on This Volume”

For many ordinary external data drives, Finder provides:

Ignore ownership on this volume

This option tells macOS not to enforce user ownership stored on that external volume. It is often useful when the drive was created on another Mac or contains files owned by a different account.

To enable it:

Select the drive in Finder.
Press Command + I.
Expand Sharing & Permissions.
Unlock the settings if necessary.
Select Ignore ownership on this volume.

Apple recommends this setting as a troubleshooting step when a Mac can read an external drive but cannot save to it.

Disconnect and reconnect the drive, then test again.

When “Ignore Ownership” Does Not Appear

The checkbox may be missing when:

The disk is being used for Time Machine
The drive uses a file system that does not support normal Mac ownership
The drive is read-only
The volume is managed or restricted
The selected item is a folder rather than the volume
The disk is not mounted normally

Apple specifically notes that the option does not appear on a volume used for Time Machine backups.

Do not try to change Time Machine backup ownership manually. Time Machine relies on a controlled disk structure and permissions model.

Apply Permissions to Enclosed Items Carefully

If the top-level folder has correct access but files inside it do not, Finder offers:

Apply to enclosed items

To use it:

Select the affected folder or drive.
Press Command + I.
Expand Sharing & Permissions.
Set the correct access.
Open the action menu.
Choose Apply to enclosed items.

Apple documents this feature for propagating permissions through a folder or disk.

Use it cautiously.

On a drive containing:

Application libraries
Bootable systems
Backups
Shared company data
Multiple users’ private folders
Specialist media projects

changing every enclosed item can damage expected access controls or application behaviour.

Back up the drive first and apply changes only to the folder that genuinely requires them.

Files May Belong to a Different Mac Account

macOS user ownership is based on internal user identifiers, not just the visible account name.

A drive moved from another Mac may contain files owned by an account whose internal ID does not match yours. Even when both accounts are called “Carl”, macOS may treat them as different owners.

Symptoms include:

Some folders work while others are locked
Finder asks for an administrator password repeatedly
Your account has access to new files but not older ones
Unknown users appear under Sharing & Permissions

For a general external data drive, Ignore ownership on this volume is often the simplest resolution.

For shared or business data, correct ownership may need to be assigned deliberately rather than ignored.

Check Whether the File Is Locked

An individual file can be marked as locked even when the drive is writable.

Select the file and press:

Command + I

Under General, look for:

Locked

Clear the checkbox where appropriate.

A locked file may resist:

Renaming
Editing
Moving
Deletion

If many unrelated files are locked unexpectedly, investigate how they were copied or restored rather than unlocking them all blindly.

Check the Folder, Not Only the File

You may have Read & Write permission for a document but still be unable to save changes because its containing folder is read-only.

Applications often save a modified document by creating a temporary replacement file in the same folder. If the folder does not allow writing, the save fails even when the original file appears editable.

Check the permissions on:

The document
Its immediate folder
Parent folders
The external volume

The first restrictive location in that path may be the actual cause.

The Application May Lack Privacy Permission

Modern macOS versions restrict application access to certain files and storage locations.

An application may be able to open a document chosen manually but fail when attempting to scan, import, export or write broadly to an external drive.

Open:

System Settings > Privacy & Security

Review:

Files & Folders
Full Disk Access
Removable Volumes, where shown
Application-specific permissions

Apple provides Files & Folders controls for deciding which applications can access particular storage locations, while Full Disk Access grants substantially broader access.

Grant only the minimum permission the application requires.

Do not give Full Disk Access to every application as a general fix.

Test the File Through Finder

When one application cannot save to the drive, try copying a small file to the same location through Finder.

Finder can write, but the app cannot

The likely cause is:

Application privacy permissions
An application bug
A sandbox restriction
An unsupported project format
The app not being designed to work from removable storage

Finder cannot write either

The problem is more likely:

File-system format
Disk ownership
Folder permissions
File-system errors
Drive failure

This simple comparison can prevent unnecessary changes to the whole disk.

Some Applications Should Not Work Directly from ExFAT

A drive may be writable but still unsuitable for a particular application.

Complex libraries and projects may rely on:

Mac permissions
Extended attributes
Hard links
Symbolic links
File locking
Case behaviour
Metadata unsupported by simpler cross-platform formats

Professional media applications, virtual machines, Photos libraries and development tools may recommend APFS rather than ExFAT.

For example, Apple recommends APFS for external storage used with Final Cut Pro, Motion and Compressor.

Check the software developer’s storage requirements before assuming every writable drive format is fully compatible.

Check Whether the Volume Is Mounted Read-Only

A drive can be mounted as read-only when macOS detects file-system problems or cannot safely enable writing.

Open Disk Utility:

Applications > Utilities > Disk Utility

Select:

View > Show All Devices

Choose the external volume and review its information.

A read-only mount may be caused by:

NTFS
File-system corruption
An unsafe disconnection
Enclosure problems
Hardware failure
Encryption or locking
A failed previous repair

If the format should be writable, run First Aid after protecting important data.

Run Disk Utility First Aid

Disk Utility can inspect and repair certain structural problems on an external drive.

Before running it:

Back up anything accessible
Close applications using the drive
Stop active transfers
Connect the drive directly where possible
Keep the Mac connected to power

Then:

Open Disk Utility.
Select View > Show All Devices.
Choose the lowest volume under the external device.
Select First Aid.
Choose Run.
Repeat for each volume.
Continue upwards through any container.
Run First Aid on the physical device last.

Apple recommends working from the lowest volume upwards through each container and finally the device itself. It also advises checking the cable, power and connections for external storage.

What First Aid Results Mean

No errors found

The file system appears structurally healthy. Return to checking permissions, format and application access.

Errors repaired

Eject and reconnect the drive, then test writing again.

First Aid fails

Copy accessible data off the drive immediately.

Disk Utility may recommend erasing and reformatting the device if it cannot repair the file system.

The drive disappears

Check:

Cable
Port
Power supply
Hub or dock
Enclosure
Another Mac

If the physical device remains absent from Disk Utility, Apple advises that the Mac or storage device may require service.

Connect the Drive Directly

A permissions-style error can actually be caused by an unstable connection.

Remove:

USB hubs
Thunderbolt docks
Extension cables
Adapters
KVM switches

Connect the drive directly to the Mac using a known-good cable.

This is especially important when:

The drive disconnects during file transfers
Files become corrupted
Finder freezes
The volume remounts as read-only
First Aid reports intermittent errors
The disk appears and disappears

A bus-powered drive may also need more power than a compact hub can provide.

Eject the Drive Properly

Repeatedly unplugging a drive without ejecting it can damage the file system.

Before disconnecting:

Close files stored on the drive.
Quit applications using it.
Click the eject icon in Finder.
Wait for the drive to disappear.
Disconnect it.

If the drive will not eject, an application or another user may still be using it. Apple suggests quitting applications or logging out and back in when a disk cannot be ejected normally.

Do not unplug it during active writes.

Check Encryption and Passwords

An encrypted APFS or Mac OS Extended drive must be unlocked before normal access is available.

In Finder or Disk Utility:

Select the locked volume.
Choose Mount or Unlock.
Enter the correct password.

A volume can appear in Disk Utility while remaining unavailable or read-only until properly unlocked.

Do not erase an encrypted drive because the password has been forgotten unless the data is no longer required or safely backed up. Encryption is designed to prevent access without the correct credentials.

Time Machine Drives Are Different

A Time Machine backup disk should not be treated as ordinary shared storage.

Apple recommends using a Time Machine backup disk for Time Machine rather than mixing unrelated files onto it.

Time Machine controls ownership, snapshots and backup structure. Attempts to change permissions broadly can:

Damage backup access
Stop future backups
Affect restore operations
Remove the expected ownership model

If Time Machine is failing, troubleshoot it through Time Machine settings and Disk Utility rather than applying generic permissions changes.

Check Whether the Drive Was Used on Windows

A drive regularly moved between Mac and Windows may develop access complications caused by:

NTFS formatting
Windows encryption
BitLocker
File-system errors
Unsupported filenames
Files left open during removal
Ownership or access-control entries from Windows

BitLocker-encrypted volumes are not normally unlocked by macOS without compatible software.

Where the drive is shared between operating systems, ExFAT may be suitable for general file transfer, provided the applications involved support it.

Check Whether the Drive Was Used with Linux or a NAS

A drive previously attached to Linux, a NAS or another Unix-style system may contain ownership and permissions that map poorly to the current Mac account.

You may see:

Numeric user identifiers
Unknown owners
Read-only folders
Access for one account but not another

For a simple portable data disk, ignoring ownership may be appropriate.

For a server, shared project or backup disk, preserve its ownership structure and consult whoever manages the system.

Do Not Use

chmod 777

as a General Fix

Online advice frequently suggests a command such as:

chmod -R 777 /Volumes/DriveName

This gives every user broad read, write and execute permission throughout the selected path.

It can:

Expose private files
Break intended access controls
Alter every enclosed file
Make application libraries unsafe
Hide the underlying file-system problem
Cause damage if the wrong path is entered

Apple warns that incorrect command-line permission changes can reduce security or prevent software from working.

Use Finder’s Sharing & Permissions controls first.

Be Extremely Careful with

sudo chown

Changing ownership recursively can also be dangerous:

sudo chown -R username /Volumes/DriveName

A mistyped path or unsuitable target could alter:

A backup disk
A bootable system
Another user’s data
Application libraries
Shared business files

Command-line ownership changes should be reserved for a clearly diagnosed case with a verified backup and an exact understanding of the drive’s intended ownership model.

Inspect Permissions in Terminal

Technical users can inspect a mounted volume with:

ls -led "/Volumes/Drive Name"

The -e option displays access-control entries, while -l shows standard ownership and permissions.

To inspect a specific folder:

ls -led "/Volumes/Drive Name/Folder Name"

You may see:

Owner
Group
POSIX permissions
Access Control Lists
Extended attributes

Inspection is safer than immediately changing values.

Remember that an NTFS drive remains unwritable through ordinary macOS support regardless of apparently permissive POSIX settings.

Check Access Control Lists

Mac files can use both standard POSIX permissions and more detailed Access Control Lists.

An ACL can deny access even when the basic Finder privilege appears to allow it.

Symptoms can include:

Your account shows Read & Write but saving still fails
One folder behaves differently from neighbouring folders
Permissions appear to revert
Files came from a managed server or another Mac

ACL repair is more advanced than changing the visible Finder privileges.

Do not remove all ACLs recursively without understanding why they are present. They may be protecting shared, private or business-sensitive data.

Test Another Mac User Account

Create or use another account on the same Mac.

Test whether that account can write to the drive.

Another account works

The issue may involve:

Your user-specific permissions
Application privacy settings
Keychain credentials
A profile configuration
Per-user software

No account works

The cause is more likely:

Disk format
Volume-level ownership
File-system damage
Hardware failure
Organisational restrictions

This test helps avoid reformatting a healthy drive for a problem limited to one account.

Test the Drive on Another Mac

Where possible, connect the drive to another Mac.

If the second Mac can write normally, investigate the original Mac’s:

User account
Privacy settings
Security software
Device-management policy
USB or Thunderbolt ports
Third-party file-system drivers

If the drive is read-only everywhere, focus on its format, permissions and health.

Security Software Can Restrict External Storage

Business security platforms can control removable media.

Policies may:

Block all external drives
Allow reading but not writing
Permit only encrypted devices
Restrict unknown USB storage
Record file transfers
Allow only approved serial numbers

A drive may appear fully mounted while writes are deliberately blocked.

On a managed Mac, contact the IT administrator before changing permissions or installing third-party disk drivers.

Provide:

Drive make and model
Connection type
File-system format
Exact error message
Whether reading works
Whether another Mac can write
Business reason for using the drive

Check Profiles and Device Management

Open:

System Settings > General > Device Management

where available.

A management profile may enforce storage, privacy or security restrictions.

Do not remove an organisational profile to regain drive access. This can:

Break company applications
Remove certificates
Disable VPN access
Make the Mac non-compliant
Trigger security alerts

The correct solution is an approved policy change or an authorised drive.

Filenames Can Cause Copy Failures

When only certain files fail to copy, the problem may not be permissions.

Cross-platform drives may reject or mishandle:

Reserved characters
Extremely long paths
Windows-reserved filenames
Files larger than the format supports
Case-conflicting filenames
Unsupported metadata

For example, FAT32 cannot store an individual file larger than 4GB.

Try:

Shortening the filename
Shortening the folder path
Compressing the item into a ZIP archive
Copying one file at a time
Using ExFAT or APFS where appropriate

If every other file copies successfully, avoid changing permissions across the entire drive.

Files Open but Changes Will Not Save

Some applications open a document from an external disk but cannot save over it.

Try:

File > Save As

and save a new copy to the same folder.

If that fails, save to the Mac’s internal drive.

Possible causes include:

Folder permissions
File locking
Unsupported drive format
Application sandbox restrictions
A damaged original file
The application requiring a Mac-native file system

Do not repeatedly overwrite the only copy of an important document while troubleshooting.

Copy First, Then Delete the Original

Finder may be unable to move an item directly between volumes because moving across drives is really a copy followed by deletion.

Apple suggests using the copy-and-delete method when a normal move fails:

Select the item.
Press Command + C.
Open the destination.
Press Command + V.
Confirm the copy.
Delete the original only after verifying it.

This is safer than assuming the move succeeded.

When Permissions Keep Reverting

Permissions may return after you change them because:

A background application rewrites the folder
The drive is managed
A sync service restores metadata
The file is recreated rather than edited
An application update replaces its folders
Ownership is being enforced by the file system
A server or NAS controls access externally

Identify what process creates or manages the affected content.

Changing the same permission repeatedly is unlikely to solve an external policy or application behaviour.

When You Should Reformat

Reformatting may be appropriate when:

The drive is NTFS and must be writable on a Mac
Disk Utility cannot repair its file system
The drive is empty or fully backed up
The current format is unsuitable for the intended application
The disk was prepared for another operating system
Corruption repeatedly returns after repair

Choose the format based on future use rather than only the current Mac.

Do not reformat when the drive contains the only copy of important files.

When the Drive May Be Failing

Permissions errors can be an early sign of storage trouble.

Warning signs include:

The drive repeatedly disconnects
It remounts as read-only
Files become corrupt
First Aid reports recurring errors
Transfers freeze
Finder becomes unresponsive
The drive is unusually slow
It makes clicking or beeping noises
It disappears from Disk Utility
Different cables and Macs show the same fault

Copy critical data immediately.

Do not continue changing permissions on a drive that is physically unstable.

A Safe Troubleshooting Order

When a Mac cannot write to an external drive, follow this sequence:

Test with a small file and a new folder.
Check available storage.
Check the drive’s format.
Confirm whether it is NTFS.
Review Sharing & Permissions.
Give your account Read & Write access where appropriate.
Enable Ignore ownership on this volume for a normal data drive.
Check whether the individual file is locked.
Check the destination folder’s permissions.
Test the same location through Finder and the affected application.
Review Privacy & Security permissions.
Connect the drive directly with a known-good cable.
Back up accessible data.
Run Disk Utility First Aid.
Test another user account and another Mac.
Check business security and device-management policies.
Reformat only after the data is protected.
Replace the drive if errors or disconnections continue.

Need Help Fixing External Drive Access?

External-drive permission errors can be caused by ownership, NTFS formatting, privacy controls, file-system corruption or failing hardware. Applying broad command-line permission changes can expose data or damage a backup without resolving the actual cause.

Hamilton Group can inspect the drive safely, correct its access settings, recover readable files and recommend the right format for Mac-only or Mac-and-Windows use.

Call 0330 043 0069 or visit hgmssp.com to speak with one of our IT experts.