linux - GRUB: how find partition number (hd0,x)?

16
2013-10
  • takpar

    i am playing with grub and i change the root using:

    root (hda,x)

    how can i know what's x for /dev/sda7 ?

    fdisk -l

       Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *           1        1958    15727603+   7  HPFS/NTFS
/dev/sda2            1959        7476    44323335    f  W95 Ext'd (LBA)
/dev/sda5            1959        4569    20972826    7  HPFS/NTFS
/dev/sda6            4570        5352     6289416   83  Linux
/dev/sda7            6373        7119     6000246   83  Linux
/dev/sda8            7120        7476     2867571   83  Linux
/dev/sda9            5353        6135     6289416   83  Linux
/dev/sda10           6136        6372     1903671   82  Linux swap / Solaris

    the problem is that in Gparted view, the order is not like sda5, sda6, sda7, ... but the order is like:

    • sda6
    • sda9
    • sda10
    • sda7
    • sda8

    so what's x for /dev/sda7 ?

    • Answers
  • Jonathan

    First off, you need to realize that in grub, it does not use normal linux hard drive identifiers. Instead, the letters correlate to numbers, starting with zero (i.e. hda = hd0, hdb = hd1, etc).

    Secondly, the partition number starts at 0, not 1 like in Linux, so subtract 1 from the linux partition number.

    An example is: hda1 = (hd0, 0)

    Finally, grub does not differentiate between hd and sd devices, so everything is labeled hd.

    Thus, in your case, your grub entry for /dev/sda6 should read (hd0, 5)

  • fymita

    Easiest way to be sure is from grub cli and using tab completion.

    start by typing... root (hd0,

    then hit [tab]
    The tab completion should then list the partitions available. pick the one you think makes most sense close off the parentheses and on the next line type kernel /

    then hit [tab] again... if the files and directory structure look right you picked the right one... if not.. back up and redo the root line.


    • Related Question

    linux - hardware changes make identical grub boot into different OS
  • Kevin M

    The hardware:

    • motherboard with one IDE slot(2 drives)
    • PCI card with 2 slots(4 drives)
    • hard drive with CentOS installed
    • hard drive with an old Fedora installed

    The normal situation:
    I boot into grub(CentOS splashscreen) and that boots CentOS installed on the CentOS drive(hda).

    The situation as it is now:
    I hook up the Fedora drive(to either the master or slave on the primary channel on the PCI card, hdc or hdd) and boot. The CentOS grub boots, uses the CentOS kernel, and everything else is from Fedora. Modules, software versions, etc, almost like it's recognized the Fedora drive as hda. However, if I were to mount hda as /mnt/hda, I get the CentOS drive. If I mount hdd or hdc as /mnt/hdc or /mnt/hdd, I get the Fedora drive as expect. But the mounted hda outside of any other paths(/usr for example), I get the Fedora files.

    Filesystem            Size  Used Avail Use% Mounted on
/dev/hda3             9.5G  7.5G  1.6G  83% /
/dev/hdd5             9.5G  7.5G  1.6G  83% /mnt/hdd5
/dev/hda3             6.4G  3.3G  2.8G  54% /mnt/hda3

    Of particular note here are the drives mounted(from /dev) and their filesystem sizes.

    Has anyone seen this before? How do I go about starting the 6.5GB drive as an OS?

    Update: The grub entry is:

    title CentOS (2.6.18-128.4.1.el5.centos.plus)
    root (hd0,0)
    kernel /vmlinuz-2.6.18-128.4.1.el5.centos.plus ro root=LABEL=/ rhgb quiet
    initrd /initrd-2.6.18-128.4.1.el5.centos.plus.img

    cat devices.map

    # this device map was generated by anaconda
(hd0)     /dev/hda

    fdisk -l(Fedora)

    Disk /dev/hdd: 40.0 GB, 40020664320 bytes
255 heads, 63 sectors/track, 4865 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Device Boot      Start         End      Blocks   Id  System
/dev/hdd1               1        1275    10241406    7  HPFS/NTFS
/dev/hdd2            1276        4864    28828642+   f  W95 Ext'd (LBA)
/dev/hdd3            4865        4865        8032+  82  Linux swap / Solaris
/dev/hdd5            1276        2550    10241406   83  Linux
/dev/hdd6            2551        4864    18587173+   b  W95 FAT32

    fdisk -l(CentOS):

    Disk /dev/hda: 20.0 GB, 20020396032 bytes
255 heads, 63 sectors/track, 2434 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Device Boot      Start         End      Blocks   Id  System
/dev/hda1   *           1          10       80293+  83  Linux
/dev/hda2              11         402     3148740   82  Linux swap / Solaris
/dev/hda3             403        1258     6875820   83  Linux
/dev/hda4            1259        2434     9446220    5  Extended
/dev/hda5            1259        1911     5245191   83  Linux
/dev/hda6            1912        2433     4192933+  83  Linux

    • Related Answers
  • phresus

    Relabel the Fedora root partition. The bootloader is getting confused. Something like e2label /dev/hda3 /centos, then modify your GRUB entry (and possibly /etc/fstab) to point at that as the label.

    Alternatively, you could relabel the Fedora root. Or take the easy way and point /etc/fstab and the root= directive in your menu.lst at /dev/hda3 rather than a filesystem label.