hal9000@hal9000-Dell-Precision-M3800:~$ sudo gdisk -l /dev/sda
[sudo] password for hal9000: 
GPT fdisk (gdisk) version 0.8.8

Caution: invalid main GPT header, but valid backup; regenerating main header
from backup!

Caution! After loading partitions, the CRC doesn't check out!
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!

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.)
 1 - MBR
 2 - GPT
 3 - Create blank GPT

Your answer: ^Chal9000@hal9000-Dell-Precision-M3800:~$ 
hal9000@hal9000-Dell-Precision-M3800:~$ 
hal9000@hal9000-Dell-Precision-M3800:~$ sudo lsblk -o NAME,FSTYPE,SIZE,MOUNTPOINT,LABEL
[sudo] password for hal9000: 
pasSorry, try again.
[sudo] password for hal9000: 
NAME   FSTYPE   SIZE MOUNTPOINT LABEL
sda           465.8G            
├─sda1 ntfs     100M            System Reserved
├─sda2 ntfs   194.6G            
├─sda3            1K            
├─sda5 ext4   255.1G /          
└─sda6 swap    15.9G [SWAP]     
hal9000@hal9000-Dell-Precision-M3800:~$ sudo lsblk -o NAME,FSTYPE,SIZE,MOUNTPOINT,LABEL
NAME   FSTYPE   SIZE MOUNTPOINT LABEL
sda           465.8G            
├─sda1 ntfs     100M            System Reserved
├─sda2 ntfs   194.6G            
├─sda3            1K            
├─sda5 ext4   255.1G /          
└─sda6 swap    15.9G [SWAP]     
hal9000@hal9000-Dell-Precision-M3800:~$ sudo lsblk -o NAME,FSTYPE,SIZE,MOUNTPOINT,LABEL
NAME   FSTYPE   SIZE MOUNTPOINT                 LABEL
sda           465.8G                            
├─sda1 ntfs     100M                            System Reserved
├─sda2 ntfs   194.6G                            
├─sda3            1K                            
├─sda5 ext4   255.1G /                          
└─sda6 swap    15.9G [SWAP]                     
sdb           931.5G                            
└─sdb1 ntfs   931.5G /media/hal9000/My Passport My Passport
hal9000@hal9000-Dell-Precision-M3800:~$ gdisk -l /dev/sda
GPT fdisk (gdisk) version 0.8.8

Problem opening /dev/sda for reading! Error is 13.
You must run this program as root or use sudo!