This document describes how to use persistent device naming on your Linux VM.
For VMs that use a Linux operating system, device names, for example /dev/sda
,
might change after you perform procedures such as the following:
- Starting and stopping a VM
- Detaching and reattaching disks
- Changing machine types
This device name change occurs because device names are assigned from an available range once a VM starts or a device is attached. Detaching a device or stopping the VM frees up the device name. When the device is reattached or the VM restarted a new device name is then assigned from the available range. The Linux kernel does not guarantee device ordering across reboots.
A device name change might cause any applications or scripts that depend on the original device name to not work properly or it might cause the VM to not boot after a restart.
It is recommended that you use persistent device naming when referencing disks and partitions on your Linux VMs to avoid this issue. You can also use symlinks.
Before you begin
- Review device management for your Linux operating system:
-
If you haven't already, set up authentication.
Authentication is
the process by which your identity is verified for access to Google Cloud services and APIs.
To run code or samples from a local development environment, you can authenticate to
Compute Engine as follows.
Select the tab for how you plan to use the samples on this page:
Console
When you use the Google Cloud console to access Google Cloud services and APIs, you don't need to set up authentication.
gcloud
-
Install the Google Cloud CLI, then initialize it by running the following command:
gcloud init
- Set a default region and zone.
-
Use persistent device naming
To configure a persistent device name, you assign a mount point name for the
disk device in the fstab
file. There are three ways to configure a persistent
device name.
- By using a label. This option requires that the file system supports labels and that you add a label to the disk partitions.
- By using a partition or disk UUID. A UUID is generated when a disk is created with a partition table, and the UUID is unique per partition.
- By using a persistent disk ID (
/dev/disk/by-id
) for Persistent Disk or Google Cloud Hyperdisk, or a symlink, that is based on the disk resource name.
We recommend using the partition UUID or the symlink for Linux VMs.
Partition UUID
To find the UUID for a disk, perform the following steps:
- Connect to your VM.
If you don't know the device name for the disk, you can find the disk device name using the symlink.
ls -l /dev/disk/by-id/google-*
The output is similar to the following:
lrwxrwxrwx 1 root root 9 Oct 23 15:58 /dev/disk/by-id/google-my-vm -> ../../sda lrwxrwxrwx 1 root root 10 Oct 23 15:58 /dev/disk/by-id/google-my-vm-part1 -> ../../sda1 lrwxrwxrwx 1 root root 11 Oct 23 15:58 /dev/disk/by-id/google-my-vm-part15 -> ../../sda15 lrwxrwxrwx 1 root root 9 Oct 23 15:58 /dev/disk/by-id/google-my-vm-app-data -> ../../nvme0n1
Retrieve the UUID of the partition for the disk by running one of the following commands:
blkid
sudo blkid -s UUID
The output is similar to the following:
/dev/sda1: UUID="4f570f2d-fffe-4c7d-8d8f-af347af7612a" /dev/sda15: UUID="E0B2-DFAF" /dev/nvme0n1: UUID="9e617251-6a92-45ff-ba40-700a9bdeb03e"
ls -l
sudo ls -l /dev/disk/by-uuid/
The output is similar to the following:
lrwxrwxrwx 1 root root 10 Sep 22 18:12 4f570f2d-fffe-4c7d-8d8f-af347af7612a -> ../../sda1 lrwxrwxrwx 1 root root 13 Sep 22 18:15 9e617251-6a92-45ff-ba40-700a9bdeb03e -> ../../nvme0n1 lrwxrwxrwx 1 root root 11 Sep 22 18:12 E0B2-DFAF -> ../../sda15
Add an entry for the UUID for your device in the
/etc/fstab
file.UUID=9e617251-6a92-45ff-ba40-700a9bdeb03e /data ext4 defaults 0 0
In this example,
/data
is the mount point andext4
is the file system type.Validate that the device is mounted properly by running
mount -av
.sudo mount -av
If the device is successfully mounted, the output is similar to the following:
/ : ignored /boot/efi : already mounted mount: /data does not contain SELinux labels. You just mounted an file system that supports labels which does not contain labels, onto an SELinux box. It is likely that confine applications will generate AVC messages and not be allowed access to this filesystem. For more details see restorecon(8) and mount(8). /data : successfully mounted
Persistent disk ID
To find the disk device name by using the persistent disk ID, or symlink, complete the following steps:
- Connect to your VM.
Retrieve the ID on the disk by running the following command:
sudo ls -lh /dev/disk/by-id/google-*
The output is similar to the following:
lrwxrwxrwx. 1 root root 9 May 16 17:34 google-disk-2 -> ../../sdb lrwxrwxrwx. 1 root root 9 May 16 09:09 google-persistent-disk-0 -> ../../sda lrwxrwxrwx. 1 root root 10 May 16 09:09 google-persistent-disk-0-part1 -> ../../sda1 lrwxrwxrwx. 1 root root 10 May 16 09:09 google-persistent-disk-0-part2 -> ../../sda2
For
NVME
disks, the output is similar to the following:lrwxrwxrwx 1 root root 13 Jun 1 10:27 google-disk-3 -> ../../nvme0n2 lrwxrwxrwx 1 root root 13 Jun 1 10:25 google-t2a -> ../../nvme0n1 lrwxrwxrwx 1 root root 15 Jun 1 10:25 google-t2a-part1 -> ../../nvme0n1p1 lrwxrwxrwx 1 root root 16 Jun 1 10:25 google-t2a-part15 -> ../../nvme0n1p15
Add the symlink to the
/etc/fstab
file./dev/disk/by-id/google-disk-2 /data ext4 defaults 0 0
Validate that the device is mounted properly by running
mount -av
.sudo mount -av
If the device is successfully mounted, the output is similar to the following:
/ : ignored /boot/efi : already mounted mount: /data does not contain SELinux labels. You just mounted an file system that supports labels which does not contain labels, onto an SELinux box. It is likely that confine applications will generate AVC messages and not be allowed access to this file system. For more details see restorecon(8) and mount(8). /data : successfully mounted