Set Bootable Partition Command Line

I use fdisk. before to apply this I recommend to work with a live CD or USB and back up your data.

First check if any bootable partition is present like in my system wich "/dev/sda1" is the bootable partition :

fdisk -l /dev/sda                                                      

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: 0x00003256

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1    *       2048   959991807   479994880   83  Linux
/dev/sda2       959993854   976766975     8386561    5  Extended
/dev/sda5       959993856   976766975     8386560   82  Linux swap / Solaris

If there is not any boot partition do like this with root login :

fdisk  /dev/sda
Command (m for help): m

Command action
   a   toggle a bootable flag
   b   edit bsd disklabel
   c   toggle the dos compatibility flag
   d   delete a partition
   l   list known partition types
   m   print this menu
   n   add a new partition
   o   create a new empty DOS partition table
   p   print the partition table
   q   quit without saving changes
   s   create a new empty Sun disklabel
   t   change a partition's system id
   u   change display/entry units
   v   verify the partition table
   w   write table to disk and exit
   x   extra functionality (experts only)

Command (m for help): a
Partition number (1-5): 

You've to type 1 if you want to make bootable the partition 1 or and following 2 if you want to make bootable the second partition etc...

and aply the modification with "w" like this

Command (m for help): w

For modify the table of your disk and make the desired partition bootable.

In hoping that help

With the print command you ge the partition number (first column). Let us say it is 1. To make it bootable:

(parted) set 1 boot on

OS X https://qwiek.wordpress.com/ "fdisk" then flag 1 to make first partition bootable.