-- MikeGore - 02 Mar 2010

GRUB2 Repair

Grub 2 Documents

Grub 2 commands and important files

  • grub-install - reinstall/install grub
  • grub-mkconfig - rebuild /boot/grub/grub.cfg
  • /boot/grub/grubenv - grub persistent environment
  • /etc/default/grub - system-wide grub defaults
  • /boot/grub/grub.cfg - automatically created config file - some sections will persist across updates
  • /boot/grub/default - default boot image choice
  • /etc/grub.d/ - grub scripts that automatically parse the contents of /boot
    • Note - some of these scripts will keep track of the previous contents of a config file and update it - persistence

Grub 2 Changes from V1 - Important - please read

  • /boot/grub/menu.lst is NOT the main config file any more - now is grub.cfg
  • /etc/default/grub now contains grub defaults
  • See next section on Grub 2 configuration update notes

Grub 2 configuration update notes

  • If you want to change this file you should
    1. ) Update /etc/default/grub
    2. ) Then use grub-mkconfig -o /boot/grub/grub.cfg to update it.

Grub 2 Adding Custom Rules

  • If you wish to add custom rules you can use /etc/grub.d/40_custom
    • Or Create a new files - read the man pages and documentation from grub2 before you try this option.
  • /etc/grub.d/ contains rules used to automatically create menu entries in grub.cfg when scanning /boot

Finding and updating UUIDs when imaging

  • When running from a recover disk the command blkid will list all of the system UUID's
   /dev/sdc1: LABEL="/scratch" UUID="3b3ed01c-e3ba-41b8-834c-7552746e9220" TYPE="ext3" 
   /dev/sdb2: LABEL="/home" UUID="e2395ad4-3201-4fd6-97bf-b473cf1381a2" TYPE="ext3" 
   /dev/sda5: LABEL="/" UUID="78c310b2-4e85-431c-8a5d-d768d01c1b99" TYPE="ext3" 
   /dev/sda6: LABEL="/fsys1" UUID="6b376205-7d64-48cc-8983-b3a2a881c919" TYPE="ext3" 
   /dev/sda7: LABEL="/var" UUID="ab8ec5f6-997c-4afd-ae49-e0072ff2b8d9" TYPE="ext3" 
   /dev/sda8: LABEL="/tmp" UUID="c6fe3594-4538-45b4-bd21-88b032cc4e40" TYPE="ext3" 
   /dev/sdb1: TYPE="swap" UUID="77d765b5-2358-4935-abaa-a2785c8dbf45"

Updating Grub 2 config files

Update 5 Dec 2012
  1. ) make any changes to /etc/default/grub
  2. ) grub-mkconfig -o /boot/grub/grub.cfg
  3. ) update-grub
    • Note we run grub-mkconfig because it is not always invoked from grub-update

Checking Grub

  • grub-install --recheck /dev/sdX where X is the boot device a or b or c ...

Grub2 repair

Updated 2 April 2013
  • Please note that with dual boot windows 7 and Ubuntu we are now using the WIndows boot manager. Therefore we have to install Grub2 in the Ubuntu boot partition - NOT in the MBR!!!!
  • Note: For stand alone system I suggest purging and reinstalling Grub as the best overall solution. This does not take much time and grantees the results - works mainly due to the fact that there are potentially many files in /boot/grub that can keep persistent data around that impact the repair process

Using Live CD

We assume that /dev/sda5 is the root partition in this example
  1. ) Boot Ubuntu 9.10 install CD and choose try without installing (ex. Live Mode)
  2. ) open a terminal window (look under accessories)
  3. ) sudo bash (become root)
  4. ) fdisk -l (find your linux partition and drive)
  5. ) mount /dev/sda5 /mnt
  6. ) grub-install --root-directory=/mnt /dev/sda
  7. ) umount /mnt

Using RIP CD,PXE or USB to fix and Ubuntu system with GRUB2

Easy way - using ubunt-scripts on ASIMOV

Update 5 Dec 2012
  • Boot updated RIP - suggest Graphical Mode version 13.7 or higher
  • Optionally update ubuntu-scripts
    • rsync cscf-adm@asimov:/coregroup1/images/ubuntu-scripts . - get latest updates
  • cd /ubuntu-scripts

  • In the next steps please ignore any /dev/pty related errors in the next steps - harmless
  1. ) BOOT RIP
  2. ) dhcpcd (start network - make sure you are on a DHCP network that will give the system an address)
    • ping www.yahoo.com (Test network)
  3. ) fdisk -l (discover your drives)
  4. ) blkid (lists partitions and UUID and partition type)
  5. ) Say our partition is /dev/sda1
  6. ) ./mntpart /dev/sda1
  7. ) ./grub-fix
    • This purges and reinstalls GRUB.
    • Why? Because /boot/grub can hold several files that keep persistent data that might not (and often does not) get fixed using normal grub tools
    • Notes: this script makes most of the changes listed in the Grub Menu Entries Section Below - no hidden menus , save last menu choice, text console, etc

OLD MANUAL WAY Using RIP CD,PXE or USB to fix and Ubuntu system with GRUB2

  1. ) BOOT RIP
  2. ) dhcpcd (start network - make sure you are on a DHCP network that will give the system an address)
    • ping www.yahoo.com (Test network)
  3. ) fdisk -l (discover your drives)
  4. ) blkid (lists partitions and UUID and partition type)
  5. ) Say our partition is /dev/sda1
  6. ) ls -l /dev/sda (get the major/minor numbers of /dev/sda and its partitions)
          ls -l /dev/sda*
          brw-rw---- 1 root disk 8, 0 2011-09-14 11:09 /dev/sda
          brw-rw---- 1 root disk 8, 1 2011-09-06 09:05 /dev/sda1
  7. ) Note that the major number is 8 and the minor numbers are 0 and 1 1 is the root partition as reported by blkid
  8. ) mount /dev/sda1 /mnt/sda1 ( mount the root partition - RIP automatically creates mount points)
  9. ) Create the device nodes in the target portion if they do not exist - grub needs these to work
    1. ) cd /mnt/sda1/dev
    2. ) mknod sda b 8 0
    3. ) mknod sda1 b 8 1
  10. ) chroot /mnt/sda1
  11. ) mount proc /proc -t proc
  12. ) *mount sysfs /sys -t sysfs
  13. ) mount devpts /dev/pts -t devpts
  14. ) Remove/Purge and Reinstall GRUB2 - we will use dpkg to list grub components
    1. ) dpkg -l | grep grub
               ii  grub           0.97-29ubuntu60    GRand Unified Bootloader (Legacy version)
               ii  grub-common    1.98-1ubuntu12     GRand Unified Bootloader, version 2 (common files)
               ii  grub-pc        1.98-1ubuntu7      GRand Unified Bootloader, version 2 (PC/BIOS version)
    2. ) apt-get remove --purge grub grub-common grub-pc
    3. ) rm -rf /boot/grub
    4. ) rm -f /etc/mtab - we only want /etc/fstab
    5. ) apt-get install grub2
      • If prompted regarding the grub configuration file you can pick "install the package maintainer's version" if you want to start clean - recommended
      • See section Grub Boot Time options
      • Optionally you can now remove the /dev/sda entries you created You are DONE

Important Menu Entries and their function

Grub Boot Time options

Update 5 Dec 2012
  • Config File: /etc/grub/default should be /etc/default/grub ???
    • After making changes use the command grub-mkconfig -o /boot/grub/grub.cfg

  • Add remember last menu:
    • GRUB_DEFAULT=saved
  • Make the Menu NOT hidden so you can choose the menu items you have in GRUB
    • *NOtes: Hold down SHIFT to display hidden boot options as an alternative to this option
  • Make default boot in N seconds
  • Make boot startup happen in TEXT mode (not graphics mode)
    • GRUB_TERMINAL=console
  • Modify Default Linux Command Line options GRUB_CMDLINE_LINUX - if desired
  • Example /etc/default/grub config file
       # If you change this file, run 'update-grub' afterwards to update
       # /boot/grub/grub.cfg.
       # For full documentation of the options in this file, see:
       #   info -f grub -n 'Simple configuration'
       GRUB_DISTRIBUTOR=`lsb_release -i -s 2> /dev/null || echo Debian`
       GRUB_CMDLINE_LINUX_DEFAULT="max_loop=255 "
       # Uncomment to enable BadRAM filtering, modify to suit your needs
       # This works with Linux (no patch required) and with any kernel that obtains
       # the memory map information from GRUB (GNU Mach, kernel of FreeBSD ...)
       # Uncomment to disable graphical terminal (grub-pc only)
       # The resolution used on graphical terminal
       # note that you can use only modes which your graphic card supports via VBE
       # you can see them in real GRUB with the command `vbeinfo'
       # Uncomment if you don't want GRUB to pass "root=UUID=xxx" parameter to Linux
       # Uncomment to disable generation of recovery mode menu entries
       # Uncomment to get a beep at grub start
       #GRUB_INIT_TUNE="480 440 1"

Recreating /boot/grub/grub.cfg

Update 5 Dec 2012
  • update-grub to regenerate the /boot/grub/grub.cfg file
  • or grub-mkconfig -o /boot/grub/grub.cfg

9.10 and 10.04 grub update problems

  • Just read the previous section if these command do not work
    • grub-mkconfig -o /boot/grub/grub.cfg
    • update-grub

Ubuntu 10.04 and later

Update 5 Dec 2012
  • grub.cfg replaces menu.lst
  • /etc/grub.d/ contain scripts that interpret files under /boot that automatically create boot entries in grub.cfg
  • Run grub-mkconfig -o /boot/grub/grub.cfg AFTER make any changes
    • Note: u*update-grub* may not always correctly update grub.cfg so we use grub-mkconfig instead

/etc/grub.d/ scripts

Update 5 Dec 2012
  • Don't edit anything except 40_custom
    • 00_header loads settings from /etc/default/grub (timeout, defaults, etc)
    • 05_debian_theme loads background colors and themes
    • 10_linux loads menu entries for Ubuntu 10.04
    • 20_memtest86+ loads memtest
    • 30_os-prober loads menu entries for any operating systems it finds
    • 40_custom this is the script to edit for additional menu options


Update 5 Dec 2012
  • Example:
       #!/bin/sh -e
       echo "This string will display when update-grub runs"
       #indicates start of boot entry
       #sets the name of the boot entry
       menuentry "Custom Windows Option" {
       #sets the hard drive the system will boot from
       #NOTE: partition notation now starts with 1 instead of 0
       set root=(hd0,1)
       #more boot options go here, this one is for Windows
       chainloader (hd0,1)+1
       #This one is for Linux
       #linux vmlinuz
       #initrd initrd.img
  • Alternatively, you can just put the custom entries into 40_custom. * Run grub-mkconfig -o /boot/grub/grub.cfg

GRUB 2 Windows 7 conflict - solution

Update 5 Dec 2012
Topic revision: r19 - 2014-03-20 - RonaldoGarcia

Information in this area is meant for use by CSCF staff and is not official documentation, but anybody who is interested is welcome to use it if they find it useful.


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