[Mageia-dev] Grub2 vs. Grub Legacy in M3

Tue Jan 29 13:48:36 CET 2013

On 01/28/2013 06:44 PM, Barry Jackson wrote:
+> My limited understanding is that the code in the 512 byte PBR has to 
+> use block lists to find the core image in /boot, since it is too small 
+> to understand filesystems. This is fragile in that filesystems and 
+> file utilities may move files around on disk invalidating the block 
+> lists, and for this reason the method is discouraged.
+>
+> A far as I know the same potential problem exists with grub legacy.
+
+OK, we've come full circle.  This is why I was used to rerunning 
+install.sh, because historically this has been true of most 
+bootloaders.  They all have to fit in 512 bytes, and they all have to 
+load the next stage of the boot without support for filesystems.
+
+That's why I stick with chainloading.  PBRs don't move around at the 
+whim of a filesystem, and if you do something to a root partition that 
+repositions something critical, you just rebuild the PBR as part of it.
+
+I wasn't aware of the MBR gap.  I guess you're saying that the core.img 
+that fits in it *is* filesystem-aware ?  Otherwise, it seems like you've 
+just pushed the locate-the-next-stage vulnerability from the MBR to the 
+MBR gap, as chainloading pushes it from the MBR to the PBR.
+
+Anyway, my point still stands: for anyone who just wants to have grub 
+and grub2 partitons coexist on the same disk with either one in the MBR, 
+chainloading will accomplish this without any downside that isn't 
+already present in grub legacy.  Grub2 may be the way of the future, but 
+to *require* it to own the MBR is just misleading.
+