To uninstall Tails from a USB stick, and use it for something else, you have to reset it.

The content of the USB stick will be lost in the operation, but an attacker might still be able to tell that Tails was installed on that USB stick using data recovery techniques unless you securely clean all the available disk space afterwards.

You might overwrite any hard disk on the computer. If at some point you are not sure about which device to choose, stop proceeding.
  1. Make sure that the USB stick that you want to reset is unplugged.

  2. Start Disk Utility.

    A list of all the storage devices on the computer appears in the left pane of the window.

  3. Plug the USB stick that you want to reset.

    A new device appears in the list of storage devices. This new device corresponds to the USB stick that you plugged in. Click on it.

  4. In the list of storage devices, verify that the device corresponds to the USB stick that you want to reset, its brand, its size, etc.

  5. To reset the USB stick:

    1. If there is an Erase tab in the right pane, click on it and then click on the Erase button on the bottom right

    2. If there is an Erase button on the top middle, click on it.

  6. In the confirmation dialog, click on the Erase button to confirm.

If the erase process fails, try formatting the USB stick using the command line first.

Troubleshooting

Format using the command line

  1. Unplug the USB stick from the computer.

  2. Open Terminal from Applications ▸ Utilities ▸ Terminal.app.

  3. Execute the following command:

    diskutil list
    

    It returns a list of the storage devices on the system. For example:

    $ diskutil list
    /dev/disk0
      #:                     TYPE NAME         SIZE      IDENTIFIER
      0:    GUID_partition_scheme             *500.1 GB  disk0
      1:                      EFI              209.7 MB  disk0s1
      2:                Apple_HFS MacDrive     250.0 GB  disk0s2
      3:                      EFI              134.1 GB  disk0s3
      4:     Microsoft Basic Data BOOTCAMP     115.5 GB  disk0s4
    
  4. Plug the USB stick in the computer.

  5. Execute again the same command:

    diskutil list
    

    Your USB stick appears as a new device in the list. Check that its size corresponds to the size of your USB stick.

    $ diskutil list
    /dev/disk0
      #:                     TYPE NAME         SIZE      IDENTIFIER
      0:    GUID_partition_scheme             *500.1 GB  disk0
      1:                      EFI              209.7 MB  disk0s1
      2:                Apple_HFS MacDrive     250.0 GB  disk0s2
      3:                      EFI              134.1 GB  disk0s3
      4:     Microsoft Basic Data BOOTCAMP     115.5 GB  disk0s4
    /dev/disk1
      #:                     TYPE NAME         SIZE      IDENTIFIER
      0:   FDisk_partition_scheme             *4.0 GB    disk1
      1:                Apple_HFS Untitled 1   4.0 GB    disk1s1
    
  6. Take note of the device name of your USB stick. In this example, the USB stick is 4.0 GB and its device name is /dev/disk1. Yours might be different.

    If you are unsure about the device name, you should stop proceeding or you risk overwriting any hard disk on the system.

  7. Execute the following command to safely remove the USB stick. Replace [device] with the device name found in step 6.

    diskutil unmountDisk [device]
    
  8. Execute the following command to format the USB stick. Replace [device] with the device name found in step 6.

    sudo fdisk -iy [device]
    
  9. You can try to reset the USB stick again using Disk Utility from the beginning of this page.