GPT or MBR: How do I know?

  • How can I tell whether my harddrive is laid out using an MBR or GPT format?

  • You can use parted -l to determine the type of partition table. Eg:

    $ sudo parted -l
    Model: ATA TOSHIBA THNSNS25 (scsi)
    Disk /dev/sda: 256GB
    Sector size (logical/physical): 512B/512B
    Partition Table: msdos
    
    Number  Start   End     Size    Type     File system  Flags
     1      4194kB  32.2GB  32.2GB  primary  ext4         boot
     2      32.2GB  256GB   224GB   primary  ext4
    
    
    Model: ATA Hitachi HDT72101 (scsi)
    Disk /dev/sdb: 1000GB
    Sector size (logical/physical): 512B/512B
    Partition Table: msdos
    
    Number  Start   End     Size    Type     File system     Flags
     1      1049kB  32.2GB  32.2GB  primary  ext4            boot
     2      32.2GB  996GB   964GB   primary  ext4
     3      996GB   1000GB  4295MB  primary  linux-swap(v1)
    

    The Partition Table field shows that I am using a msdos MBR partition table (the one still commonly used for Linux and Windows) on both disks. From the man page parted can create (and thus hopefully identify) the following types of partition table (or more broadly `disk label'):

    bsd
    dvh
    gpt    - this is a GPT partition table
    loop   - this is raw disk access without a partition table
    mac
    msdos  - this is a standard MBR partition table
    pc98
    sun
    

    Update

    It is worth adding the command for listing a single partition since this is not obvious without some knowledge of parted and it can be a pain finding the data you need if there are multiple drives. For /dev/sda you would do:

    parted /dev/sda print
    

    That is a great command, Graeme. Although I've been using Linux for several years, I had never really noticed it. Thanks!

    `parted /dev/sda p` will do, too.

    i had to do "sudo parted -l"

  • On linux, you can check this via the gdisk tool which should be available for any distro.

    gdisk -l /dev/sda
    

    Here, /dev/sda is the device node of the physical drive, not a partition (/dev/sda1, /dev/sda2, etc. are partitions).

    If you see something that includes:

    ***************************************************************
    Found invalid GPT and valid MBR; converting MBR to GPT format
    in memory. 
    ***************************************************************
    

    You have a MBR style disk. Don't worry, this did not do any harm.

    If you don't see this warning, you have a GPT disk, or a hybrid GPT/MBR disk. The later are used mostly on Apple machines intended to dual-boot versions of MS Windows which do not support GPT. gdisk will indicate this with:

    Found valid GPT with hybrid MBR; using GPT
    

    They may also be used in other situations where support for both styles is required.

    Or the reverse - trying to use `cfdisk` on a GPT partition will also result in a warning.

    If not installed and not in a `gdisk` package, it can be found in the `gptfdisk` package... at least on Gentoo.

    @orion I would not recommend that as some versions of tools like `fdisk` or `cfdisk` may support GPT and therefore not show an error.

    For me `gdisk` detects a hybrid GPT+MBR partition table and gives `Found valid GPT with hybrid MBR; using GPT.`. This seems to be the only method which will detect a hybrid table.

    @Graeme : Thanks. I was unaware of these (the original hybrid reference was edited in by Stephane Chazelas), but I did a bit of reading and added some details.

  • As the OS was not specified, here is FreeBSD way of doing things.

    All is done through the gpart command (short for GEOM partioner - nothing to do with GNU).

    A simple gpart show would show you all the available partitions of all the disks, but you can specify the device to have a more precise look on one:

    • legacy partition layout with MBR (aka "msdos") and BSD partition schemes (a 2-level partitioning was usually required for BSD systems, unless using the full disk):

      $gpart show

      =>      63  67108801  ada0  MBR  (32G)
              63  67108545     1  freebsd  [active]  (32G)
        67108608       256        - free -  (128k)
      
      =>       0  67108545  ada0s1  BSD  (32G)
               0   2097152       2  freebsd-swap  (1.0G)
         2097152  65011393       1  freebsd-ufs  (31G)
      
    • modern partition layout using GPT:

      $gpart show /dev/ada2

      =>       34  976773101  ada2  GPT  (465G)
               34          6        - free -  (3.0k)
               40        128     1  freebsd-boot  (64k)
              168   67108864     2  freebsd-swap  (32G)
         67109032  901775360     3  freebsd-zfs  (430G)
      

    To know more, all is in the gpart manual.

  • With udisks on Linux:

    $ sudo /lib/udev/udisks-part-id /dev/sda
    using device_file=/dev/sda syspath=/sys/devices/pci0000:00/0000:00:0b.0/ata1/host0/target0:0:0/0:0:0:0/block/sda, offset=0 ao=0 and number=0 for /dev/sda
    Entering MS-DOS parser (offset=0, size=500107862016)
    MSDOS_MAGIC found
    found partition type 0xee => protective MBR for GPT
    Exiting MS-DOS parser
    Entering EFI GPT parser
    GPT magic found
    partition_entry_lba=2
    num_entries=128
    size_of_entry=128
    Leaving EFI GPT parser
    EFI GPT partition table detected
    UDISKS_PARTITION_TABLE=1
    UDISKS_PARTITION_TABLE_SCHEME=gpt
    UDISKS_PARTITION_TABLE_COUNT=4
    

    Above, I've got a drive with hybrid GPT+MS-DOS partitioning. In that case, the Linux kernel ignores the MS-DOS partitioning, which is why udisks sets UDISKS_PARTITION_TABLE_SCHEME to gpt.

    That udisks-part-id tool is used to populate the udev database. So if you've got udisks installed, you should be able to query that information even as a non-priviledged user with:

    $ udevadm info -q property -n sda | grep UDISKS_PARTITION_TABLE_SCHEME
    UDISKS_PARTITION_TABLE_SCHEME=gpt
    

    Note that you will get similar output regardless of whether there is a hybrid GPT+MBR or not. GPT requires a fake MBR with a single full disk partition of type `0xee`. In a hybrid this is a normal MBR with one `0xee` partition (and potential for major problems if the MBR data goes out of sync with the GPT data).

  • Use

    $ sudo fdisk -l 
    
    Disk /dev/sda: 119.2 GiB, 128035676160 bytes, 250069680 sectors
    Units: sectors of 1 * 512 = 512 bytes
    Sector size (logical/physical): 512 bytes / 512 bytes
    I/O size (minimum/optimal): 512 bytes / 512 bytes
    Disklabel type: dos
    Disk identifier: 0x987c1a05
    
    
    Device     Boot   Start       End   Sectors   Size Id Type
    /dev/sda1  *       2048    999423    997376   487M 83 Linux
    /dev/sda2       1001470 250068991 249067522 118.8G  5 Extended
    /dev/sda5       1001472 250068991 249067520 118.8G 8e Linux LVM
    

    See the Disklabel type: dos. If it shows dos that means it is MBR schema else GPT schema

  • In my Alpine Linux Partition scripts I use:

    check_scheme() {
        fdisk -l $1 |grep "Disklabel type:" |awk '{ print $3 }'
    }
    

    On my *Ubuntu 18.04* system `fdisk -l /dev/sda | grep -i disklabel` returns nothing, (*GNU Fdisk 1.3.0a*).

  • You can use blkid.

    Examples with output:

    # blkid /dev/sdc
    /dev/sdc: PTUUID="92f03b9b-7402-4ad2-8316-08a991c237b3" PTTYPE="gpt"
    
    # blkid -o export /dev/sdc
    DEVNAME=/dev/sdc
    PTUUID=92f03b9b-7402-4ad2-8316-08a991c237b3
    PTTYPE=gpt
    

    Or in a script, with the -o value option :

    disk=$1
    part_type=$(blkid -o value -s PTTYPE $disk)
    case $part_type in
        gpt)  echo "GPT";;
        dos)  echo "MBR";;
        *)    echo "partition is $part_type";;
    esac
    

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Content dated before 6/26/2020 9:53 AM