# Changing the Disk Identifier in the GRUB Configuration File to UUID

#### Scenarios

When optimizing a Linux private image, you need to change the disk identifier to UUID in the GRUB configuration file of the ECS.

Modify the menu.lst or grub.cfg configuration file (/boot/grub/menu.lst, /boot/grub/grub.cfg, /boot/grub2/grub.cfg, /boot/grub/grub.conf, or /boot/efi/EFI/euleros/grub.cfg), and configure the boot partition using the UUID.

The root partition identified in the configuration file varies depending on the OS. It may be root=/dev/xvda or root=/dev/disk.

#### Procedure

- Ubuntu 14.04: Run blkid to obtain the UUID of the root partition. Modify the /boot/grub/grub.cfg file and use the UUID of the root partition to configure the boot item. If the root partition already uses UUID, no modification is required. The procedure is as follows:
  1. Log in to the ECS as user root.
  2. Run the following command to query all types of mounted file systems and device UUIDs:

     blkid

     The following information is displayed:

         /dev/xvda1: UUID="ec51d860-34bf-4374-ad46-a0c3e337fd34" TYPE="ext3"
         /dev/xvda5: UUID="7a44a9ce-9281-4740-b95f-c8de33ae5c11" TYPE="swap"

  3. Run the following command to query the grub.cfg file:

     cat /boot/grub/grub.cfg

     The following information is displayed:

         ......menuentry 'Ubuntu Linux, with Linux 3.13.0-24-generic' --class ubuntu --class gnu-linux --class gnu --class os --unrestricted $menuentry_id_option 'gnulinux-3.13.0-24-generic-advanced-ec51d860-34bf-4374-ad46-a0c3e337fd34' {
         recordfail
         load_video
         gfxmode $linux_gfx_mode
         insmod gzio
         insmod part_msdos
         insmod ext2
         if [ x$feature_platform_search_hint = xy ]; then
         search --no-floppy --fs-uuid --set=root ec51d860-34bf-4374-ad46-a0c3e337fd34
         else
         search --no-floppy --fs-uuid --set=root ec51d860-34bf-4374-ad46-a0c3e337fd34
         fi
         echo 'Loading Linux 3.13.0-24-generic ...'
         linux /boot/vmlinuz-3.13.0-24-generic root=/dev/xvda1 ro
         echo 'Loading initial ramdisk ...'
         initrd /boot/initrd.img-3.13.0-24-generic
         }

  4. Check whether the root partition in the /boot/grub/grub.cfg configuration file contains root=/dev/xvda1 or root=UUID=ec51d860-34bf-4374-ad46-a0c3e337fd34.
     - If root=UUID=ec51d860-34bf-4374-ad46-a0c3e337fd34 is contained, the root partition is in the UUID format and requires no change.
     - If root=/dev/xvda1 is contained, the root partition is in the device name format. Go to 5.
  5. Identify the UUID of the root partition device based on root=/dev/xvda1 (device name of the root partition) and the partition information obtained by running the blkid command.
  6. Run the following command to open the grub.cfg file:

     vi /boot/grub/grub.cfg

  7. Press i to enter editing mode and change the root partition to the UUID format, for example, from root=/dev/xvda1 to root=UUID=ec51d860-34bf-4374-ad46-a0c3e337fd34.
  8. Press Esc, enter :wq, and press Enter. The system saves the configuration and exits the vi editor.
  9. Run the following command to verify the change:

     cat /boot/grub/grub.cfg

     The change is successful if information similar to the following is displayed:

         ......menuentry 'Ubuntu Linux, with Linux 3.13.0-24-generic' --class ubuntu --class gnu-linux --class gnu --class os --unrestricted $menuentry_id_option 'gnulinux-3.13.0-24-generic-advanced-ec51d860-34bf-4374-ad46-a0c3e337fd34' {
         recordfail
         load_video
         gfxmode $linux_gfx_mode
         insmod gzio
         insmod part_msdos
         insmod ext2
         if [ x$feature_platform_search_hint = xy ]; then
         search --no-floppy --fs-uuid --set=root ec51d860-34bf-4374-ad46-a0c3e337fd34
         else
         search --no-floppy --fs-uuid --set=root ec51d860-34bf-4374-ad46-a0c3e337fd34
         fi
         echo 'Loading Linux 3.13.0-24-generic ...'
         linux /boot/vmlinuz-3.13.0-24-generic root=UUID=ec51d860-34bf-4374-ad46-a0c3e337fd34 ro
         echo 'Loading initial ramdisk ...'
         initrd /boot/initrd.img-3.13.0-24-generic
         }

- CentOS 6.5: Run blkid to obtain the UUID of the root partition. Modify the /boot/grub/grub.conf file and use the UUID of the root partition to configure the boot item. If the root partition already uses UUID, no modification is required. The procedure is as follows:
  1. Log in to the ECS as user root.
  2. Run the following command to query all types of mounted file systems and device UUIDs:

     blkid

     The following information is displayed:

         /dev/xvda1: UUID="749d6c0c-990a-4661-bed1-46769388365a" TYPE="swap"
         /dev/xvda2: UUID="f382872b-eda6-43df-9516-5a687fecdce6" TYPE="ext4"

  3. Run the following command to query the grub.conf file:

     cat /boot/grub/grub.conf

     The following information is displayed:

         default=0
         timeout=5
         splashimage=(hd0,1)/boot/grub/splash.xpm.gz
         hiddenmenu
         title CentOS (2.6.32-573.8.1.el6.x86_64)
         root (hd0,1)
         kernel /boot/vmlinuz-2.6.32-573.8.1.el6.x86_64 ro root=/dev/xvda2 rd_NO_LUKS rd_NO_LVM LANG=en_US.UTF-8 rd_NO_MD SYSFONT=latarcyrheb-sun16 crashkernel=autoKEYBOARDTYPE=pc KEYTABLE=us rd_NO_DM rhgb quiet
         initrd /boot/initramfs-2.6.32-573.8.1.el6.x86_64.img

  4. Check whether the root partition in the /boot/grub/grub.conf configuration file contains root=/dev/xvda2 or root=UUID=f382872b-eda6-43df-9516-5a687fecdce6.
     - If root=UUID=f382872b-eda6-43df-9516-5a687fecdce6 is contained, the root partition is in the UUID format and requires no change.
     - If root=/dev/xvda2 is contained, the root partition is in the device name format. Go to 5.
  5. Identify the UUID of the root partition device based on root=/dev/xvda2 (device name of the root partition) and the partition information obtained by running the blkid command.
  6. Run the following command to open the grub.conf file:

     vi /boot/grub/grub.conf

  7. Press i to enter editing mode and change the root partition to the UUID format, for example, from root=/dev/xvda2 to root=UUID=f382872b-eda6-43df-9516-5a687fecdce6.
  8. Press Esc, enter :wq, and press Enter. The system saves the configuration and exits the vi editor.
  9. Run the following command to verify the change:

     cat /boot/grub/grub.cfg

     The change is successful if information similar to the following is displayed:

         default=0
         timeout=5
         splashimage=(hd0,1)/boot/grub/splash.xpm.gz
         hiddenmenu
         title CentOS (2.6.32-573.8.1.el6.x86_64)
         root (hd0,1)
         kernel /boot/vmlinuz-2.6.32-573.8.1.el6.x86_64 ro root=UUID=f382872b-eda6-43df-9516-5a687fecdce6 rd_NO_LUKS rd_NO_LVM LANG=en_US.UTF-8 rd_NO_MD SYSFONT=latarcyrheb-sun16 crashkernel=autoKEYBOARDTYPE=pc KEYTABLE=us rd_NO_DM rhgb quiet
         initrd /boot/initramfs-2.6.32-573.8.1.el6.x86_64.img

- CentOS 7.0: Run blkid to obtain the UUID of the root partition. Modify the /boot/grub2/grub.cfg file and use the UUID of the root partition to configure the boot item. If the root partition already uses UUID, no modification is required.
  1. Log in to the ECS as user root.
  2. Run the following command to query all types of mounted file systems and device UUIDs:

     blkid

     The following information is displayed:

         /dev/xvda2: UUID="4eb40294-4c6f-4384-bbb6-b8795bbb1130" TYPE="xfs"
         /dev/xvda1: UUID="2de37c6b-2648-43b4-a4f5-40162154e135" TYPE="swap"

  3. Run the following command to query the grub.cfg file:

     cat /boot/grub2/grub.cfg

     The following information is displayed:

         ......
         menuentry 'CentOS Linux (3.10.0-229.el7.x86_64) 7 (Core)' --class fedora --class gnu-linux --class gnu --class os --unrestricted $menuentry_id_option 'gnulinux-3.10.0-229.el7.x86_64-advanced-4eb40294-4c6f-4384-bbb6-b8795bbb1130' {
         load_video
         set gfxpayload=keep
         insmod gzio
         insmod part_msdos
         insmod xfs
         set root='hd0,msdos2'
         if [ x$feature_platform_search_hint = xy ]; then
         search --no-floppy --fs-uuid --set=root --hint='hd0,msdos2'4eb40294-4c6f-4384-bbb6-b8795bbb1130
         else
         search --no-floppy --fs-uuid --set=root 4eb40294-4c6f-4384-bbb6-b8795bbb1130
         fi
         linux16 /boot/vmlinuz-3.10.0-229.el7.x86_64 root=/dev/xvda2 ro crashkernel=auto rhgb quiet LANG=en_US.UTF-8
         initrd16 /boot/initramfs-3.10.0-229.el7.x86_64.img
         }

  4. Check whether the root partition in the /boot/grub2/grub.cfg configuration file contains root=/dev/xvda2 or root=UUID=4eb40294-4c6f-4384-bbb6-b8795bbb1130.
     - If root=UUID=4eb40294-4c6f-4384-bbb6-b8795bbb1130 is contained, the root partition is in the UUID format and requires no change.
     - If root=/dev/xvda2 is contained, the root partition is in the device name format. Go to 5.
  5. Identify the UUID of the root partition device based on root=/dev/xvda2 (device name of the root partition) and the partition information obtained by running the blkid command.
  6. Run the following command to open the grub.cfg file:

     vi /boot/grub2/grub.cfg

  7. Press i to enter editing mode and change the root partition to the UUID format, for example, from root=/dev/xvda2 to root=UUID=4eb40294-4c6f-4384-bbb6-b8795bbb1130.
  8. Press Esc, enter :wq, and press Enter. The system saves the configuration and exits the vi editor.
  9. Run the following command to verify the change:

     cat /boot/grub2/grub.cfg

     The change is successful if information similar to the following is displayed:

         ......
         menuentry 'CentOS Linux (3.10.0-229.el7.x86_64) 7 (Core)' --class fedora --class gnu-linux --class gnu --class os --unrestricted $menuentry_id_option 'gnulinux-3.10.0-229.el7.x86_64-advanced-4eb40294-4c6f-4384-bbb6-b8795bbb1130' {
         load_video
         set gfxpayload=keep
         insmod gzio
         insmod part_msdos
         insmod xfs
         set root='hd0,msdos2'
         if [ x$feature_platform_search_hint = xy ]; then
         search --no-floppy --fs-uuid --set=root --hint='hd0,msdos2'4eb40294-4c6f-4384-bbb6-b8795bbb1130
         else
         search --no-floppy --fs-uuid --set=root 4eb40294-4c6f-4384-bbb6-b8795bbb1130
         fi
         linux16 /boot/vmlinuz-3.10.0-229.el7.x86_64 root=UUID=4eb40294-4c6f-4384-bbb6-b8795bbb1130 ro crashkernel=auto rhgb quiet LANG=en_US.UTF-8
         initrd16 /boot/initramfs-3.10.0-229.el7.x86_64.img
         }

Parent topic: Optimizing a Linux Private Image