Failed to unmount partitions

Question

I'm trying to install Ubuntu from a pen drive. I have windows 7 installed already and want to keep that installation.

I have a 3TB drive that has one 2TB partition on it, so the last 1TB is completely unused, which is where I want to install ubuntu. I started Ubuntu in "Try Ubuntu" mode and then opened gparted, and then deleted the unused partition for the last third of my drive, then tried to install ubuntu.

During the install, it asked me if I wanted to unmount the drives I already have

The installer has detected that the following disks have mounted partitions:

/dev/sda, /dev/sdb

Do you want the installer to try to unmount the partitions on these disks before continuing?  If you leave them mounted, you will not be able to create, delete, or resize partitions on these disks, but you may be able to install to existing partitions there.

No, Yes

I said no because I don't want to lose my windows 7 installation, nor any of that data. I wonder, if I had said yes above, would I have lost all the data on those drives?

Anyways, I hit no and continued.

I chose to install ubuntu alongside windows 7, and hit continue. A few minutes passed when this popup appeared:

Failed to unmount partitions
The installer needs to commit changes to partition tables, but cannot do so because the partitions on the following mount points could not be unmounted:

/media/ubuntu/Three\ Terabyte Drive Terabyte\ DriveDrive

Please close any applications using these mount points. 

Would you like the installer to try to unmount these partitions again?

Go Back, Continue

Why is this not working? What am I supposed to do?

==========

Update: I went ahead and said yes, it can unmount those partitions. It finished installing Ubuntu, but now when i start my machine it just takes me to the grub rescue prompt. Seems like it broke something.

What can I do now?

===============

Results of fdisk -l:

Disk /dev/sda: 500.1 GB, 500107862016 bytes
255 heads, 63 sectors/track, 60801 cylinders, total 976773168 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
Disk identifier: 0x00027e14

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *        2048      206847      102400    7  HPFS/NTFS/exFAT
/dev/sda2          206848   976771071   488282112    7  HPFS/NTFS/exFAT

WARNING: GPT (GUID Partition Table) detected on '/dev/sdb'! The util fdisk doesn't support GPT. Use GNU Parted.


Disk /dev/sdb: 3000.6 GB, 3000592982016 bytes
255 heads, 63 sectors/track, 364801 cylinders, total 5860533168 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes
Disk identifier: 0x00000000

   Device Boot      Start         End      Blocks   Id  System
/dev/sdb1               1  4294967295  2147483647+  ee  GPT
Partition 1 does not start on physical sector boundary.

Disk /dev/sdc: 16.0 GB, 16008609792 bytes
255 heads, 63 sectors/track, 1946 cylinders, total 31266816 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
Disk identifier: 0x00000000

   Device Boot      Start         End      Blocks   Id  System
/dev/sdc1   *          32    31266815    15633392    c  W95 FAT32 (LBA)

Disk /dev/sdd: 999.5 GB, 999501594624 bytes
255 heads, 63 sectors/track, 121515 cylinders, total 1952151552 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
Disk identifier: 0x0002ae3f

   Device Boot      Start         End      Blocks   Id  System
/dev/sdd1            2048  1952151551   976074752    7  HPFS/NTFS/exFAT

=======================================

Update:

After having re-installed Ubuntu a dozen times now, and even buying a new hard drive specifically for ubuntu, I am convinced now that this issue is a bug in Ubuntu's installation. I had the same problem after every time I installed Ubuntu. I don't think I did anything wrong, I think the problem is that Ubuntu is not setting up GRUB correctly.

I followed the instructions offered by Scott Severence's answer to this question. He explained how I could update and re-install GRUB.

Unfortunately for me though, after reinstalling GRUB, it still doesn't work.

When I boot, it launches Windows 7. If instead I tell it to boot using the new hard disk, it goes straight to grub rescue.

Somebody please help me, this problem is consuming my entire weekend.

Answer 1

@msknapp, while you were installing Ubuntu, you could have mounted a partition on internal and external disk. That is why you got that warnings. All you had to do was to close any application using internal disk. Now, you have to re-install Grub. Use Ubuntu Live CD/USB you created and use Boot-Repair to re-install grub.

As a side not, Ubuntu or any GNU/Linux distribution does not need so much - 1 TB - space. I recommend to you to use 20 GB for Ubuntu, if you do not intent to install applications use lots of space like games, then use extra space for storage or another purpose.