I have used pc for 7 months without errors. I have a gpt partition table and a Bios. During my installation I made a 2 Mb grub_bios partition. This evening using gparted I noticed that that partition is marked as unknown and bytes are used. enter image description here

Now, having only Ubuntu on this pc I don't get errors, but If I would install an other OS, could I get errors? In every case, have I solve this problem (how)?

  • Actually that is correct.
    – oldfred
    May 31, 2017 at 20:19

2 Answers 2


Gparted shows errors on unformatted partitions. But bios_grub and Windows MSR system reserved partition are required to be unformatted partitions. They do have unique GUIDs with gpt and gparted should eventually be updated to recognize they really are not errors or not formatted standard partitions.

The bios_grub exists for grub2's core.img. With MBR(msdos) partitioning the core.img is written to the sectors just after the MBR and before first partition. With gpt, the protective MBR has no space after it, so a separate partition is used.

Similarly Microsoft uses the sectors after the MBR to write some security info or other info. Grub & Windows flexnet used to conflict in sectors after MBR. That the is eliminated with gpt.

GPT vs MBR. Why not MBR?


Oldfred's answer is correct; however, I want to add a few points:

  • As oldfred says, the BIOS Boot Partition (what GParted identifies by its bios_grub flag) should not be an issue should you install another OS; however, two of your ext4fs partitions have the msftdata flag, which identifies them as being of the Windows Basic Data Partition type. Thus, if you install another OS -- and especially if that OS is Windows -- you may run into problems because the other OS may try to interpret the filesystems as FAT or NTFS and, when that fails, may offer to "prepare" or "format" the partitions; and in this context, both those words mean "destroy." The solution is to remove the msftdata flag in GParted or parted; or if you use gdisk, change the type code from 0700 to 8300.
  • GPT is more often used with EFI-mode booting than with BIOS-mode booting. To boot in EFI mode, you need a computer that uses an Extensible Firmware Interface (EFI) firmware (or UEFI, which is EFI 2.x), an EFI System Partition (ESP), and an EFI boot loader for Linux..
  • Windows tightly ties its partition table type to its boot mode -- it boots from MBR disks only in BIOS/CSM/legacy mode and from GPT disks only in EFI/UEFI mode. Thus, your use of GPT disks means that you'll be able to install Windows only in EFI mode. This won't even be possible if your computer is old enough to have a conventional BIOS, except by using a "software EFI" like DUET or Clover. If you have EFI firmware, you'll be able to install Windows, but then you'll have a mixed-mode configuration -- Windows in EFI mode and Ubuntu in BIOS mode. This is awkward to manage, and the best solution is to install an EFI boot loader for Linux. If you have a conventional BIOS, your best choice for dual-booting with Windows is likely to be to convert from GPT to MBR. My gdisk program, which is installed by default in Ubuntu, can do this, with some caveats; see this page of the gdisk documentation for details. Many non-Windows OSes, such as FreeBSD, are happy to boot from GPT disks in BIOS mode; but some older ones, such as DOS, can't handle the task at all, AFAIK.

Overall, the first issue (the incorrect msftdata flag on two of your partitions) is worth fixing right now; although doing so is not critical for an Ubuntu-only installation, it will be a useful safeguard in case you boot a non-Linux emergency tool or if some obscure Linux utility run in Ubuntu makes bad assumptions based on the type code.

If you're happy booting the way you're booting, I wouldn't suggest installing an EFI boot loader at this point, much less converting from GPT to MBR; that would be fixing what ain't broke, as the saying goes. You should bear the linkage of partition table type to boot mode in mind if you decide to install another OS, though.

  • thank you for the reply!! Why these two partitions are marked as msftdata? I think that it happened during the OS installing.
    – linofex
    Jun 3, 2017 at 15:35
  • In the distant past, most Linux distributions used msftdata on their GPT partitions; but this practice was abandoned years ago, after I (as the author of gdisk) and the libparted developers agreed on a new Linux filesystem data type code. Thus, if you originally installed a long time ago, or using a very old Ubuntu (maybe from 2013 or earlier, at a guess), it might have happened that way. Otherwise, it could have been user error or use of old software at some point along the way. Re-using old Windows partitions could also result in their type codes persisting.
    – Rod Smith
    Jun 3, 2017 at 15:51
  • I installed U16.04 7 months ago, and I used the standards steps to do it
    – linofex
    Jun 4, 2017 at 19:50
  • 1
    In that case, it was not the Ubuntu installer that set things up that way -- either you re-used partitions or something else changed the type code. Ubuntu 16.04's installer uses the correct type codes for Ubuntu partitions.
    – Rod Smith
    Jun 5, 2017 at 14:09

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