> sudo [b]gdisk /dev/sda[/b]
[sudo] password di root: 
GPT fdisk (gdisk) version 1.0.8
 
[b)Caution: invalid main GPT header, but valid backup; regenerating main header
from backup!
 
Warning: Invalid CRC on main header data; loaded backup partition table.
Warning! Main and backup partition tables differ! Use the 'c' and 'e' options
on the recovery & transformation menu to examine the two tables.
 
Warning! Main partition table CRC mismatch! Loaded backup partition table
instead of main partition table!
 
Warning! One or more CRCs don't match. You should repair the disk!
Main header: ERROR
Backup header: OK
Main partition table: ERROR
Backup partition table: OK
 
Partition table scan:
  MBR: MBR only
  BSD: not present
  APM: not present
  GPT: damaged
 
Found valid MBR and corrupt GPT. Which do you want to use? (Using the
GPT MAY permit recovery of GPT data.)[/b]
 1 - MBR
 2 - GPT
 3 - Create blank GPT
 
Your answer: 2
 
Command (? for help): ?
b       back up GPT data to a file
c       change a partition's name
d       delete a partition
i       show detailed information on a partition
l       list known partition types
n       add a new partition
o       create a new empty GUID partition table (GPT)
p       print the partition table
q       quit without saving changes
r       [b]recovery and transformation options (experts only)[/b]
s       sort partitions
t       change a partition's type code
v       verify disk
w       write table to disk and exit
x       extra functionality (experts only)
?       print this menu
 
Command (? for help): r
 
Recovery/transformation command (? for help): ?
b       use backup GPT header (rebuilding main)
c       load backup partition table from disk (rebuilding main)
d       use main GPT header (rebuilding backup)
e       load main partition table from disk (rebuilding backup)
f       load MBR and build fresh GPT from it
g       convert GPT into MBR and exit
h       make hybrid MBR
i       show detailed information on a partition
l       load partition data from a backup file
m       return to main menu
o       print protective MBR data
p       print the partition table
q       quit without saving changes
t       transform BSD disklabel partition
v       verify disk
w       write table to disk and exit
x       extra functionality (experts only)
?       print this menu