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 
     }