root@ubuntu:/media/ubuntu# partprobe
Warning: /dev/sdb contains GPT signatures, indicating that it has a GPT table.  However, it does not have a valid fake msdos partition table, as it should.  Perhaps it was corrupted -- possibly by a program that doesn't understand GPT partition tables.  Or perhaps you deleted the GPT table, and are now using an msdos partition table.  Is this a GPT partition table?
Error: Both the primary and backup GPT tables are corrupt.  Try making a fresh table, and using Parted's rescue feature to recover partitions.
root@ubuntu:/media/ubuntu# gdisk /dev/sda -l
GPT fdisk (gdisk) version 0.8.8

Partition table scan:
  MBR: MBR only
  BSD: not present
  APM: not present
  GPT: not present


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

Disk /dev/sda: 625076912 sectors, 298.1 GiB
Logical sector size: 512 bytes
Disk identifier (GUID): C59CE4D8-20CB-4228-9624-84358CE612F9
Partition table holds up to 128 entries
First usable sector is 34, last usable sector is 625076878
Partitions will be aligned on 2048-sector boundaries
Total free space is 8841837 sectors (4.2 GiB)

Number  Start (sector)    End (sector)  Size       Code  Name
   1         1050624       617285631   293.8 GiB   8300  Linux filesystem
root@ubuntu:/media/ubuntu#