External HD read only

Discussion in 'OS X Mountain Lion (10.8)' started by tarsierspectral, Aug 15, 2013.

  1. macrumors regular

    Aug 13, 2010

    I was using my external HD then I rebooted my computer and then the drive all of the sudden became read-only. Anyone know why and how to fix it?

  2. macrumors 603

    Feb 20, 2009
    What type of format (Mac or PC) is the external drive?
    What kind of partition map are you using?
  3. macrumors 68020

    Feb 10, 2008
    Something like this has happened to me a couple times with FAT 32 drives. Usually a reboot of the mac fixed the issue. Otherwise, perhaps copy all the files elsewhere for safe keeping, run disk utility to repair drive, if that doesn't work, reformat the drive and copy the files back onto it.

    But the right thing to do starts with how the drive is currently formatted (Mac or PC)
  4. macrumors Westmere


    May 16, 2008
    As others have indicated, it would be helpful to know what the format of the drive is. Also, if it is NTFS, what software are you using to enable reading and writing to it?

    Format A Hard Drive Using Disk Utility (which is in your /Applications/Utilities folder)
    Choose the appropriate format:
    HFS+ (Hierarchical File System, a.k.a. Mac OS Extended (Journaled) Don't use case-sensitive) NTFS (Windows NT File System)
    • Read/Write NTFS from native Windows.
    • Read only NTFS from native Mac OS X [*]To Read/Write/Format NTFS from Mac OS X, here are some alternatives:
      • For Mac OS X 10.4 or later (32 or 64-bit), install Paragon (approx $20) (Best Choice for Lion and later)
      • For 32-bit Mac OS X, install NTFS-3G for Mac OS X (free) (does not work in 64-bit mode)
      • For 64-bit Snow Leopard, read this: MacFUSE for 64-bit Snow Leopard
      • Some have reported problems using Tuxera (approx $36).
      • Native NTFS support can be enabled in Snow Leopard and Lion, but is not advisable, due to instability.
    • AirPort Extreme (802.11n) and Time Capsule do not support NTFS
    • Maximum file size: 16 TB
    • Maximum volume size: 256TB
    • You can use this format if you routinely share a drive with multiple Windows systems.
    exFAT (FAT64)
    • Supported in Mac OS X only in 10.6.5 or later.
    • Not all Windows versions support exFAT. See disadvantages.
    • exFAT (Extended File Allocation Table)
    • AirPort Extreme (802.11n) and Time Capsule do not support exFAT
    • Maximum file size: 16 EiB
    • Maximum volume size: 64 ZiB
    • You can use this format if it is supported by all computers with which you intend to share the drive. See "disadvantages" for details.
    FAT32 (File Allocation Table)
    • Read/Write FAT32 from both native Windows and native Mac OS X. [*]Maximum file size: 4GB.
    • Maximum volume size: 2TB
    • You can use this format if you share the drive between Mac OS X and Windows computers and have no files larger than 4GB.
  5. thread starter macrumors regular

    Aug 13, 2010
    The drive format is Mac OS Extended. Have been using is strictly on my iMac and strictly to edit in Final Cut X.
  6. macrumors 68020

    Feb 10, 2008
    Have you tried the simple things like ejecting the HD, unplug and plug it back in, or reboot with and without the drive connected?

    Have you tried using disk utility, select the drive from the list and select repair permissions or repair disk?

    Did you have Carbon Copy Cloner or similar running? SOmetimes these BU programs leave a disk in a strange state if they are interrupted.
  7. macrumors 603

    Feb 20, 2009
    [[ The drive format is Mac OS Extended. Have been using is strictly on my iMac and strictly to edit in Final Cut X. ]]

    OK, then, try this:

    Close all windows on the external -- you should see only the drive icon on the desktop

    Click ONE time on the drive icon to select it, then type "command-I" to "get info" on the drive.

    Examine the "get info" box. Toward the bottom, there is a "sharing and permissions" area. If the disclosure triangle is not pointing down, click it so it reveals the details.

    At the extreme lower-right corner, there should be a "lock icon". Click on it and enter your adminstrative password.

    At the extreme lower-left of the get info box you should see a checkbox "ignore ownership on this volume". Make sure there is a checkmark next to it.

    Now close the get info box.

    Try writing to the drive now.
    What happens?
  8. thread starter macrumors regular

    Aug 13, 2010
    Yes, these are the first things are I tried. "Ignore ownership of this volume" is already checked. I can't write to the drive.


    Tried all of that except the disk utility until I copy all the files off of it. I don't want to risk damaging the drive by running the disk utility until I have a full back up. Thanks
  9. macrumors 603

    Feb 20, 2009
    I found the following in my archives.
    I didn't write it.
    I'm just re-posting it -- perhaps it may help:
    I called Apple and they gave me the solution :


    I found a solution that worked.

    In Terminal type the following sequence (obviously replace "Volumename with the name of your volume):

    sudo chflags 0 /Volumes/Volumename
    sudo chown 0:80 /Volumes/Volumename
    sudo chmod 775 /Volumes/Volumename
    sudo chmod -N /Volumes/Volumename
    but if your hard drives name includes a [space] like this: "My HD", then you must write the command like this:

    sudo chflags 0 /Volumes/firstname\ secondname
    sudo chown 0:80 /Volumes/firstname\ secondname
    sudo chmod 775 /Volumes/firstname\ secondname
    sudo chmod -N /Volumes/firstname\ secondname
    or like in my example:

    sudo chflags 0 /Volumes/My\ HD
    sudo chown 0:80 /Volumes/My\ HD
    sudo chmod 775 /Volumes/My\ HD
    sudo chmod -N /Volumes/My\ HD
    It saved both my drives! THANK YOU APPLE!!!

    Originally Posted by angelwatt
    Thanks for posting the solution you found.

    Just to give some more info, for those who care, about the above commands I'll give a brief description of what each line does (as I understand them).
    chflags 0 removes all flags from the file(s)
    chown 0:80 ensures root:admin (owner:group) permissions so the system can access the files
    chmod 775 adjusts file permissions so you and your group have read/write/execute permissions
    chmod -N removes the ACL (Access Control Lists) from the named file(s)

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