A read-only drive is not one problem. It is a symptom with several possible causes, and the fix depends on which one you have. The good news is that you can identify the cause in about a minute.

Diagnose it in three commands

Open Terminal.

# List disks and partitions
diskutil list

# Inspect the partition (replace disk4s1 with yours)
diskutil info /dev/disk4s1

# See how it is mounted
mount | grep -i disk4s1

What to look for:

File System Personality: NTFS means the built-in macOS driver is read-only. This is the most common cause.
Read-Only Volume: Yes on an NTFS volume is normal.
Media Read-Only: Yes (or Read-Only Media: Yes on some macOS versions) can indicate a physical lock or read-only device.
The mount output shows read-only or read-write in the flags.

If diskutil list does not show the disk at all, skip to the disk is not visible.

Cause 1: The drive is NTFS

macOS ships an NTFS driver that can read but not write. Finder may show the drive normally, and you can open files, but copy, move, rename, and delete operations fail.

How to confirm: diskutil info reports NTFS.

Fix: use a third-party NTFS driver, or copy files off the drive and reformat it to exFAT if it does not need to stay NTFS.

On macOS 26+ Apple Silicon, Mountee is a free, open-source option with no macFUSE or kernel extension. On older macOS versions, Mounty 2.x (with macFUSE and ntfs-3g) or a commercial driver may fit. See Free NTFS for Mac: available options.

Do not run chmod on an NTFS volume. It will not add write support.

Cause 2: The volume is dirty or hibernated

NTFS tracks whether it was shut down cleanly. If Windows used Fast Startup or hibernation, the volume may be marked dirty. Careful drivers refuse read/write access to protect the filesystem.

Signs:

The drive mounts but writes fail with “Read-only file system”.
The drive was last used on a Windows PC that shut down quickly.
Windows offers to scan the disk when you reconnect it.

Fix:

Boot Windows.
Disable Fast Startup in Control Panel → Power Options → Choose what the power buttons do.
Shut down fully, or use Restart rather than hybrid shutdown.
Let Windows finish any disk check.
Reconnect the drive and mount read/write again.

If you cannot access Windows, keep using the drive read-only. Do not force write access to a dirty NTFS volume.

Cause 3: File or folder permissions

Sometimes the volume is writable, but a specific folder is not. This is more common with APFS, HFS+, exFAT, or network shares than with NTFS, where macOS does not map POSIX permissions.

Check: select the folder in Finder, press Command-I, and look at Sharing & Permissions. Compare with a folder you can write to.

Fix: change ownership or permissions for the affected folder, or use Ignore ownership on this volume in Get Info if appropriate. Be cautious: changing permissions on system or shared folders can break access for other users.

For NTFS, permission changes do not apply the way they do on native macOS filesystems because the driver does not map NTFS security descriptors to POSIX permissions.

Cause 4: The drive has a physical write-protect switch

Some SD cards and USB adapters have a tiny physical lock switch. When locked, the device reports read-only media and no software can write to it.

Check: inspect the card or adapter for a lock switch. Also try a different adapter; some cheap SD-to-USB readers get stuck in read-only mode.

Cause 5: You are opening a read-only disk image

A .dmg, .iso, or mounted disk image can be read-only by design. This is not a drive problem.

Check: the volume name or Disk Utility info may say “read-only image” or show a disk image device.

Fix: convert the image to a read/write format if you need to modify it, or copy the contents out.

Cause 6: The disk is failing or the connection is unreliable

Read-only behavior can be a symptom of hardware failure, especially if the drive also disconnects, makes noise, or produces I/O errors.

Signs:

The drive disappears and reappears.
Finder shows “disk not ejected properly” repeatedly.
Console logs show I/O errors.
The drive is slow or clicks.

What to do: stop writing. Copy important data off first. Try another cable, port, and computer. If the data matters, use a recovery tool or a professional service rather than forcing writes.

Cause 7: The disk is not visible

If the disk does not appear in diskutil list:

Reconnect the cable and try another port.
Check System Information → USB or Thunderbolt.
Try a powered hub for bus-powered drives.
Test the drive on another computer.
If it is a SATA/NVMe drive in an enclosure, check the enclosure and connections.

Filesystem drivers cannot mount a disk the system cannot see.

Quick reference

Symptom	Likely cause	First action
`diskutil info` says NTFS	Built-in read-only driver	Install a supported NTFS driver or copy files off
Write fails only on a Windows drive	Dirty or hibernated NTFS	Full Windows shutdown; disable Fast Startup
One folder is read-only	POSIX permissions	Check Get Info permissions
SD card is read-only	Physical lock switch	Unlock it or try another reader
Disk image is read-only	Image format	Convert image or copy files out
Drive disconnects or clicks	Hardware or cable	Stop, back up, test another connection
Disk absent from `diskutil list`	Connection or hardware	Check ports, cables, System Information

How to avoid the problem next time

Use exFAT for drives that must be written by both macOS and Windows without extra software.
Eject drives before unplugging them.
Shut Windows down fully after using an NTFS drive.
Keep backups, especially before changing filesystems or installing a new driver.

Frequently asked questions

Can I fix an NTFS read-only drive with chmod?
No. macOS does not provide general-purpose NTFS write support through POSIX permissions. You need a driver that implements writes.

Does macOS have a hidden NTFS write setting?
No supported general-purpose one. Old remount workarounds from the Boot Camp era do not apply to current macOS and Apple Silicon.

Why can I read files but not copy new ones to the drive?
That is exactly how read-only NTFS support behaves. Reading is allowed; modifying the volume is not.

Is a read-only drive always an NTFS problem?
No. Check the filesystem, the mount mode, physical switches, disk image format, and hardware before assuming it is NTFS.

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