Installing Drivers and Changing the Disk Identifiers to the UUID Format

To ensure that the ECSs created from the image support both Xen and KVM virtualization, install Native Xen and KVM drivers and change the disk identifiers to the UUID format for the VM which is used as the image source.

This section describes how to perform these operations on a Linux VM that runs Ubuntu 20.04. For other OSs, see Optimization Process (Linux).

Install Native Xen and KVM Drivers

Run the following command to open the modules file:
vi /etc/initramfs-tools/modules

Press i to enter the editing mode and add the native Xen (xen-pv) and KVM (virtio) drivers to the /etc/initramfs-tools/modules file (the format depends on the OS requirements).

[root@CTU10000xxxxx ~]#vi /etc/initramfs-tools/modules 
...
# Examples: 
# 
# raid1 
# sd_mOd 
xen-blkfront 
xen-netfront 
virtio_blk 
virtio_scsi 
virtio_net 
virtio_pci 
virtio_ring 
virtio

Press Esc, enter :wq, and press Enter to save the settings and exit the vi editor.
Run the following command to generate initrd again:
update-initramfs -u

Run the following commands to check whether native Xen and KVM drivers have been installed:

lsinitramfs /boot/initrd.img-`uname -r` |grep xen

lsinitramfs /boot/initrd.img-`uname -r` |grep virtio

[root@ CTU10000xxxxx home]# lsinitramfs /boot/initrd.img-`uname -r` |grep xen 
lib/modules/3.5.0-23-generic/kernel/drivers/net/ethernet/qlogic/netxen 
lib/modules/3.5.0-23-generic/kernel/drivers/net/ethernet/qlogic/netxen/netxen_nic.ko 
lib/modules/3.5.0-23-generic/kernel/drivers/net/xen-netback 
lib/modules/3.5.0-23-generic/kernel/drivers/net/xen-netback/xen-netback.ko 
lib/modules/3.5.0-23-generic/kernel/drivers/block/xen-blkback 
lib/modules/3.5.0-23-generic/kernel/drivers/block/xen-blkback/xen-blkback.ko 
 
[root@ CTU10000xxxxx home]# lsinitramfs /boot/initrd.img-`uname -r` |grep virtio 
lib/modules/3.5.0-23-generic/kernel/drivers/scsi/virtio_scsi.ko

If you add built-in drivers to the initrd or initramfs file, the VM will not be affected. This makes it easy to modify the drivers. However, the drivers cannot be shown by running the lsinitrd command. You can run the following commands to check whether the drivers are built-in ones in the kernel:

[root@ CTU10000xxxxx home]# cat /boot/config-`uname -r` | grep CONFIG_VIRTIO | grep y
CONFIG_VIRTIO_BLK=y
CONFIG_VIRTIO_NET=y
CONFIG_VIRTIO=y
CONFIG_VIRTIO_RING=y
CONFIG_VIRTIO_PCI=y
CONFIG_VIRTIO_MMIO_CMDLINE_DEVICES=y
[root@ CTU10000xxxxx home]# cat /boot/config-`uname -r` | grep CONFIG_XEN | grep y
CONFIG_XEN_BLKDEV_FRONTEND=y
CONFIG_XEN_NETDEV_FRONTEND=y

Change the Disk Identifier in the GRUB Configuration File to the UUID Format

Take Ubuntu 20.04 as an example. 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:

Run the following command to query all types of mounted file systems and their 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"

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 
}

Check whether 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 no further action is required.
- If root=/dev/xvda1 is contained, the root partition is represented by a device name. Go to step 5.

Obtain the UUID of the root partition based on root=/dev/xvda1 and information obtained by running the blkid command.
Run the following command to open the grub.cfg file:
vi /boot/grub/grub.cfg
Press i to enter the editing mode. Change the identifier of the root partition to the UUID format. For example, change root=/dev/xvda1 to root=UUID=ec51d860-34bf-4374-ad46-a0c3e337fd34.
Press Esc, enter :wq, and press Enter to save the settings and exit the vi editor.

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
}

Change the Disk Identifiers in the fstab File to the UUID Format

Take Ubuntu 20.04 as an example. Run blkid to obtain the UUIDs of all partitions. Modify the /etc/fstab file and use the partition UUIDs to configure automatic partition mounting.

Run the following command to query all types of mounted file systems and their 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"

Run the following command to query the fstab file:

cat /etc/fstab

The following information is displayed:

[root@CTU1000028010 ~]# cat /etc/fstab  
/dev/xvda2  /       xfs     defaults    0 0 
/dev/xvda1  swap    swap    defaults    0 0

Check whether the disk identifiers in the fstab file are device names or UUIDs.
- If they are UUIDs, no further action is required.
- If they are device names, go to step 4.
Run the following command to open the fstab file:
vi /etc/fstab
Press i to enter the editing mode and change the disk identifiers to the UUID format.
Press Esc, enter :wq, and press Enter to save the settings and exit the vi editor.