On Saturday 20 October 2007, Les Mikesell wrote: >Gene Heskett wrote: >> That is this line in a verse of grub.conf: >> root (hd0,0) >> which defines that its the drive normally set for master on the IDE0 >> cable, > >Not necessarily... > >> the one on the end of the cable, thats the hd0 portion, and its the first >> partition on that drive, which is the second 0 since all this crap runs on >> a base zero numbering system. > >Any resemblance between a Linux hd? device and a grub hd? is purely >coincidental. In Linux the hd?'s are strictly IDE (and they are going >away). In grub, the hd?'s refer to the bios bootable devices. If, for >example, you have scsi devices and have configured your motherboard bios > to boot from them, grub's hd0 will be your booting scsi drive even if >you also happen to have an IDE present that linux will see as /dev/hda. I didn't know that, not having crossed that bridge, thanks. >> It could just as easily say root (hd3,2) to >> indicate that it would be 3rd partition in, of the drive set as slave on >> the IDE1 cable, that is just as valid. I haven't tried it set for an >> 'extended' partition, and I'd assume it would take a smarter than the >> average bear bios to handle that. > >Many (most?) motherboards only see 2 disks in the boot process, although >they may let you select from a larger number of choices which order to >try. So you may have trouble using anything higher than hd1 - which >again refers to what bios is using, not a particular ide position. And >you may have non-bootable disks that have no bios driver at all, but >which linux will use normally. I have been under the impression that if the bios scan found them, they were in fact usable, is this incorrect? >> This is the usage that I would have changed, were I the one who wrote >> grub, from root to boot, because it actually tells grub where its boot >> files are. > >Grub has to know the bios notation, since that is all it can use to >access the files until the kernel and driver modules are installed. > >> Its second usage, the argument in the kernel string, tells the kernel, in >> very similar drive & partition syntax, where the partition to be mounted >> as '/' is. >> >> That is this line in a given grub verse: >> >> kernel /vmlinuz-2.6.23 ro root=/dev/VolGroup00/LogVol00 rhgb >> >> And this could just as easily say root=/dev/hda7 since by this time, the >> kernel is initializing and knows about extended partitions by then. This >> to me is the correct usage of the word 'root' because it truly is the root >> of all the filesystems mounted. > >But at this point the kernel is running, has loaded its device drivers, >has access to all devices, even ones bios doesn't handle, and this >reference must be in linux terms where, for example /dev/hda7 does in >fact refer to a disk with a particular IDE controller and selection. >Even if you booted from a scsi drive that bios saw as the 0x80 device >and grub called hd0, the kernel can mount a partition on /hda (an IDE >device) as the root filesystem. > >> But I didn't write grub, so we're stuck with the double usage of 'root' >> and the confusion factor it creates for newbies. > >They are double because they are entirely different things. That part is still confusing to the newbie though. >> AIUI, grub, if not dealing with a LVM system, can function without a /boot >> partition, in which case the above syntax must be modified, and the grub >> installer does this, to gave a full path like this: >> >> kernel /boot/vmlinuz-2.6.23 ro root=/dev/hda1 >> >> (a base 1 numbering scheme is used here, furthering the newbie confusion >> quotient, that is equ to (hd0,0) in the other syntax) > >One is linux, one is a peculiar adaptation of a bios concept. > >> assuming the /boot directory is in fact available in the drive & partition >> specified by the first usage above, but its not an optional setup I've >> ever used and I go back to RH5.0. > >On older machines (circa RH5 era...) PC bios was limited to accessing >1024 cylinders for some time after larger drives were available. If the >kernel and initrd files were in the filesystem in a location beyond that >limit, the boot loader would be unable to access them to complete the >boot. Thus the installer always tries to make boot a small partition >and first on the disk to avoid any problem. The bios addressing scheme >has been modified to work around the limits in current machines. > >> Now, I suspect that you'll probably argue with me, but it will be a one >> sided argument since I tend not to argue about points I know about after >> having stated them once. > >I'll argue because you've stated something wrong or at least misleading. > > >-- > Les Mikesell > lesmikesell@xxxxxxxxx Thanks for those bios related clarifications. I haven't tried to diddle the order in the bios, so I was unaware of that until now as it hadn't crossed my radar. -- Cheers, Gene "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) The number of licorice gumballs you get out of a gumball machine increases in direct proportion to how much you hate licorice.
