Boot linux on external hard disk - Send Grub Rescue

Question

Installed Ubuntu 14.04 in a external hard disk because in the internal hard disk I have Windows 10 and very low space.

When I try to boot the external HD, sends the Grub Recovery. I saw few tutorials, but nothing, I hope that somebody help me. This is my info:

Disk /dev/sda: 120.0 GB, 120034123776 bytes

255 heads, 63 sectors/track, 14593 cylinders, total 234441648 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: 0xd90da8d6

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *        2048     1026047      512000    7  HPFS/NTFS/exFAT
/dev/sda2         1026048   234439599   116706776    7  HPFS/NTFS/exFAT

Disk /dev/sdb: 1000.2 GB, 1000204886016 bytes

255 heads, 63 sectors/track, 121601 cylinders, total 1953525168 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: 0x03dd0735

   Device Boot      Start         End      Blocks   Id  System
/dev/sdb1           16126   199093544    99538709+   f  W95 Ext'd (LBA)
/dev/sdb2   *   199109607  1704367979   752629186+   7  HPFS/NTFS/exFAT
/dev/sdb3      1704367980  1726537679    11084850   82  Linux swap / Solaris
/dev/sdb4      1726537680  1953520101   113491211   83  Linux
/dev/sdb5           16128   199093544    99538708+   b  W95 FAT32

Answer 1

Your issue is most likely that the GRUB bootloader was not correctly installed during initial set-up. To remedy this, you are going to have to reinstall Ubuntu; which, considering you have not yet booted into it, should be relatively unobtrusive. Do it the same way you installed previously, by selecting "Something Else..". However, when you get to the partition menu, you should notice a drop-down menu for where the bootloader should be installed. By default, it chooses the first available option. When installing to an external HDD, you need to install GRUB onto the Master Boot Record (MBR) of that drive. So, in the dropdown, you will see something similar to /dev/sdX1 /dev/sdx2 and so on, where X is the letter assigned to the HDD you are working on. You will need to select the /dev/sdX option, without a number associated with it. For example, if you are installing Ubuntu on /dev/sdb1, you will install the bootloader to /dev/sdb.

Additionally, as you are working on Windows 10, you may have the same issue that Windows 8/8.1 have with the system wanting only to boot Windows due to secure boot being enabled. You will have to disable this "feature" of Windows on newer computer models. You can do this in your BIOS settings, which differ from computer to computer. Most often, though, you will see the option as you boot to "Press F12 to Enter Set-Up" or something similar. Press the indicated key, navigate through your BIOS menu to Boot Options, and disable "Secure Boot".

UPDATE: After some fooling around in a virtual machine, I was able to replicate your issue. By default, GRUB installs to the first partition found. You probably accidentally installed it on the first partition of your internal hard-drive when you attempted your first install. This probably means you wrote it over your Windows partition. The best you can do here is try to find a Windows 10 Boot repair disc and repair the boot partition of your internal drive. Then, Windows will be able to boot. When installing Ubuntu onto the external drive, you will not be able to go through the regular boot process to start Ubuntu. Rather, you will have to change the boot order of your machine so that it boots from USB first. This process differs depending on your BIOS.