How do I format a read only USB?

USB drives, also known as flash drives or thumb drives, are small storage devices that connect to computers through a USB port. They provide a convenient way to store and transfer data. However, sometimes USB drives can become read only, meaning you cannot add, delete or modify files on the drive.

There are a few key questions when it comes to formatting a read only USB drive:

Why is my USB drive read only?

There are several potential reasons why a USB drive may have become read only:

  • The drive is physically write-protected. Many USB drives have a small switch on the side that can toggle between read/write and read only modes.
  • The drive is corrupted. Errors in the file system or partition table can cause the drive to mount as read only.
  • Insufficient permissions. On Linux or Mac systems, you may not have write permissions to the drive.
  • Virus infection. Some viruses intentionally set USB drives to read only to prevent spreading.

How can I make my USB drive writable again?

Depending on the specific cause, there are a few different solutions:

  • Toggle the physical write-protect switch on the drive if there is one.
  • Scan for viruses and remove any infections detected.
  • Run CHKDSK (Windows) or fsck (Linux/Mac) to check and repair file system errors.
  • Format the USB drive to completely erase and reinitialize the file system.

Will formatting delete my data?

Yes, formatting will erase all data on the USB drive. Be sure to back up any important files before formatting the drive. After formatting, the drive will be empty and fully writable.

Determine Why the USB Drive is Read Only

The first step in formatting a read only USB drive is to determine why it has been set to read only mode. As mentioned above, there are a few common reasons:

Physical Write-Protect Switch

Many USB drives have a tiny physical switch on the side or bottom that toggles between read/write and read only modes. Sliding the switch one way will make the disk read only, while switching it the other way makes it read/write again. Check to see if your drive has a write-protect switch and whether it is slid to the correct position.

File System Corruption

Errors can occasionally happen to the file system or partition table of a USB drive that cause it to mount in a read only state. This is a safety precaution to prevent further data corruption. On Windows, you can check for file system errors using CHKDSK. On Linux/Mac, use fsck instead.

Insufficient Permissions

On Linux or Mac computers, you need to have owner or root permissions to write to a connected USB drive. Non-privileged users may only get read access. Check the permissions on the USB drive mount point to see if a permissions issue is preventing write access.

Virus Infection

Some viruses are designed to propagate across USB drives by making them automatically autorun when plugged into a new computer. A common defense against this is to set infected USB drives as read only to stop the virus from spreading further.

Making a USB Drive Writable Again

Once you have identified the cause of the read only issue, you can take steps to make your USB drive writable again:

Toggle the Physical Switch

If a physical write-protect switch is present and in the incorrect position, simply slide it to the opposing direction to allow writing again. This instantly changes the drive from read only to read/write.

Run CHKDSK or fsck

To fix file system corruption issues, you need to run disk repair tools:

  • On Windows, access Command Prompt as administrator and run “chkdsk E: /f” where E: is your drive letter.
  • On Linux/Mac, you can repair errors by running “sudo fsck -y /dev/sdaX” where sdaX is your USB disk.

This will scan the disk and repair any bad sectors or file system errors detected. Afterwards, remount the USB to see if write access is restored.

Format the USB Drive

If other solutions don’t work, formatting the USB drive will wipe it clean and create a new blank file system, which should make it writable again. Backup your data first before formatting.

On Windows, you can use File Explorer to right-click on the USB drive, choose Format, and then click Start. On Linux or Mac, you can format from the command line using utilities like mkfs or diskutil.

One downside of formatting is it will erase all data, so only use this method if you have backups or data recovery is not needed.

How to Format a USB Drive in Windows

If you need to format a USB drive on a Windows PC, follow these steps:

  1. Open File Explorer and plug in the USB drive if not already connected.
  2. Right-click on the USB drive and choose Format from the menu.
  3. Under File System, choose FAT32 or NTFS depending on your needs.
  4. Check Quick Format if you want faster formatting, or uncheck it for a full format.
  5. Click Start to begin formatting.
  6. After completion, the USB will be empty and fully writable.

The process takes just a few seconds for a quick format, or a few minutes for a full format. Make absolutely sure you have selected the correct USB drive before clicking Start.

File System Maximum file size Maximum disk size
FAT32 4 GB 2 TB
NTFS 16 TB 256 TB

FAT32 and NTFS are the most common file systems to use for USB flash drives. FAT32 is compatible with both Windows and Mac, while NTFS is mainly for Windows. The table above shows size limits for each file system.

Formatting Considerations

Here are some tips when formatting a USB drive on Windows:

  • Back up your data first
  • Choose Quick Format unless you need a full scan for bad sectors
  • Use FAT32 if you need compatibility with Mac or Linux
  • Use NTFS for drives larger than 32GB
  • Double check you are formatting the correct drive letter

How to Format a USB Drive on Mac

To format a USB drive on Mac OSX:

  1. Connect the USB drive to your Mac.
  2. Open Disk Utility (located in Applications > Utilities).
  3. Select your USB drive in the left panel.
  4. Click Erase at the top.
  5. Enter a name for the drive and choose a file system.
  6. Click Erase to start formatting.

Supported file systems on Mac include FAT32, exFAT, and APFS. FAT32 offers the most compatibility with other operating systems. APFS is optimized for Macs with SSDs.

Special Considerations on Mac

Keep these tips in mind when formatting USB drives on Mac OSX:

  • The fastest option is Mac OS Extended (Journaled) if using only on Macs
  • FAT32 allows use on both Windows and Mac
  • exFAT allows large file sizes over 4GB
  • Always eject the USB drive before physically removing
  • Use Disk Utility for formatting, not Finder

How to Format a USB Drive in Linux

On Linux distributions, you can format a USB drive from the terminal. Here are the general steps:

  1. Open a terminal window.
  2. Type lsblk to list all connected disks and drives.
  3. Identify the drive name for your USB device (typically /dev/sda, /dev/sdb, etc).
  4. Use mkfs command to format, replacing /dev/sdb with your drive:
    mkfs.fat -F 32 /dev/sdb (for FAT32)
    mkfs.ntfs /dev/sdb (for NTFS)
  5. Type Y to confirm formatting and wait for operation to complete.

This will format the entire USB drive with either FAT32 or NTFS file system. You can also use utilities like gparted for a graphical interface.

Tips for Linux Formatting

Formatting USB drives in Linux works much the same as other operating systems, but here are some Linux-specific tips:

  • Use mkfs from the terminal for command line formatting
  • Install gparted for a graphical format interface
  • EXT4 is optimal for drives used only in Linux
  • FAT32 works for cross-platform compatibility
  • NTFS can also be used but write support may require extra configuration

Other Alternatives

Aside from physical switches, file system repair, and full formatting, there are a couple other options for making a read only USB drive writable again:


On Linux and Mac OS, you can try simply unmounting the USB drive and then remounting it, which may reset permissions and allow write access again. For example:

# Unmount USB  
umount /dev/sdb 

# Remount USB
mount -o rw /dev/sdb

Diskpart (Windows)

On Windows, Diskpart is an advanced command line utility that can reset a USB drive from read only to read/write. To use it:

  1. Open Command Prompt as administrator
  2. Type diskpart
  3. Type list disk and identify your USB drive number
  4. Type select disk X (replace X with your drive number)
  5. Type attributes disk clear readonly
  6. Exit diskpart and your USB should now be writable

Recovering Data from a Formatted Drive

If you formatted a USB drive without first backing up important data stored on it, the files were likely overwritten and erased from the file system. However, with special data recovery software, you may be able to recover lost files and documents after formatting.

Don’t Write New Data

After accidentally formatting, avoid writing any new files to the drive. Overwriting existing data makes it much harder to recover.

Use Data Recovery Software

Specialized programs like Recuva (Windows), PhotoRec (Windows/Mac/Linux), or TestDisk (all platforms) can scan the raw drive sectors and restore recoverable files. The more you used the drive after formatting, the lower your chances of recovery.

Send to a Recovery Service

For highly valuable data, you can ship the USB drive to a professional recovery service. They have specialized tools that can rebuild corrupted file systems and extract data even after heavy overwriting.

How to Avoid “Read Only” Drives

To prevent USB drives from becoming read only and requiring formatting, follow these tips:

  • Don’t forcefully remove or disconnect USB drives
  • Eject the drive properly before unplugging
  • Scan drives regularly for errors
  • Keep backups of important data
  • Check for physical write-protect tabs
  • Beware of malware or viruses that may damage drives

Handling USB drives carefully and avoiding virus infections will help stop file system corruption leading to read only state. Periodically scanning for errors can also help detect and correct issues early before they cause serious problems.


Dealing with a USB drive that suddenly becomes read only can be frustrating. But in most cases, the situation can be resolved. Toggling a physical write-protect switch, running disk repair utilities, or reformatting the drive will often make it fully writable again.

When reformatting, be sure to have backups first. And know that purpose-built data recovery software offers your best chances to recover lost files after accidentally formatting. With the right tools and techniques, you should be able to restore full access to your USB drive.