Difference between "bootable flag" and /boot mount point
In partition table, we can give /boot as mount point. But we can, too, toggle bootable flag. What's difference between those two?
2 Answers
As for boot flag, see here. It is usually not needed for Ubuntu installation.
Boot mount point is the partition you mount your /boot to, if you use a separate /boot partition. If you do not have a separate /boot partition, /boot is just a directory under /. See here for more about partitions and mount points used in Ubuntu installation.
The /boot mount point specifies the location to install the bootloader (GRUB, Syslinux), to be used by legacy BIOS-based systems in order to boot when the actual boot device contains a GUID Partition Table (GPT).
A boot flag, on the other hand, is a 1-byte value in a non-extended partition record, within a master boot record. Its primary function is to indicate to a MS-DOS/MS Windows-type boot loader which partition to boot.
If you have an MBR (Master Boot Record) type partition table, all you need to do is to set a boot flag on the root filesystem /. However, if you have a GPT partition table, you need to create a separate BIOS boot partition and install GRUB to it.
