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### 13.3 How to specify block lists

A block list is used for specifying a file that doesn’t appear in the filesystem, like a chainloader. The syntax is `[offset]+[length][,[offset]+[length]]…`. Here is an example:

    0+100,200+1,300+300,800+

This represents that GRUB should read blocks 0 through 99, block 200, blocks 300 through 599, and blocks 800 until the end of the device. If you omit an offset, then GRUB assumes the offset is zero. If the length is omitted, then GRUB assumes the block list extends until the end of the device.

Like the file name syntax (see How to specify files), if a blocklist does not contain a device name, then GRUB uses GRUB’s root device. So `(hd0,2)+1` is the same as `+1` when the root device is ‘`(hd0,2)`’.