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Changing operating systems

Scenarios

Changing the operating system is an important means to reset the system volume and recover instances from system failures.

When an existing instance encounters a system failure, you can change the operating system (that is, reset the system volume) to restore the instance to its initial status at startup.

When the current operating system of an existing instance does not meet your business requirements, you can also change the operating system to meet business requirements.

You can change the operating system regardless of whether you change the operating system type. For example, you can change a Windows operating system to another Windows operating system. You can also change a Linux operating system to a Windows operating system.

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You can also use the operating system migration feature of the SMC to change the CentOS operating system of an instance to the CentOS-compatible veLinux operating system without downtime. Learn more.

Considerations

Changing the operating system is a high-risk operation that may cause prolonged business interruptions. Read the following precautions before you proceed.

Preparations
Instance stopped	Make sure that your ECS instance is in the Stopped status. Otherwise, data currently being written may be lost. If your instance has not been stopped yet, stop the instance by referring to Stopping instances. After you enable the "Economical Mode" feature for a pay-as-you-go instance, the instance may fail to start as expected after the operating system is changed.
Considerations
Image selection	We recommend that you use a public image provided by the platform to change the operating system. We recommend that you do not use images from unknown sources. Do not perform other actions when the operating system is being changed. To access instance metadata in Security Hardening Mode, select a custom image that supports Security Hardening Mode. tip Accessing metadata in Security Hardening Mode is currently in Beta. If you want to have a trial, submit a ticket or contact your account manager. You can create a custom image that supports Security Hardening Mode. For more information, see Creating custom images. Instance metadata contains the basic information of the ECS instance on the cloud platform. Learn more. If you select a whole image (custom image containing both the system volume and data volume), use only the system volume to change the operating system. Make sure that dependencies do not exist between the system volume and the data volume in your business design. If dependencies exist between the system volume and the data volume, make sure that the operations performed by the system volume on the data volume do not affect your business process after the system volume is changed. You can use a marketplace image to change the operating system only for instances that meet the following requirements: The instances are Spot instances, or the billing method of the instances is Subscription or Pay-as-you-go. The instances are not Elastic Scheduled Instances or instances deployed on dedicated hosts.
Host name	After the Linux operating system is changed to a Windows operating system, the first 15 characters of the hostname are retained by default.
Network	The EIP address of the instance will not change after the operating system is changed.
Volume	System volume: After the operating system is changed, the system volume ID remains unchanged. The data in the system volume will be lost after the operating system is changed. Make sure that important information in the system volume is backed up by creating a custom image or snapshot in advance. Learn more. Data volume: After the operating system is changed, the data volume ID remains unchanged. Data in the data volume will be retained after the operating system is changed. After the Linux operating system is changed to another Linux operating system, you need to manually mount the data volume within the instance. Learn more. After you change a Windows operating system to a Linux operating system or change a Linux operating system to a Windows operating system, the new operating system cannot identify the file system format of the original data volume. You must re-initialize the data volume or install software to help the system identify the data volume. Learn more.
Local volume	After the operating system is changed, the data in the local volume (such as local NVMe SSD and SATA HDD) mounted on the instance is retained.
Security protection	After the operating system is changed as follows, HIDS is disabled in the ECS console by default. To enable HIDS, go to the Security Center console. Learn more. Custom image changed to any other image. Public image changed to a custom image.
Metadata access method	After you change the operating system, the instance metadata access method remains unchanged. tip After the operating system is changed, you can call the ModifyInstanceMetadataOptions operation to adjust the instance metadata access method. For example, when the instance cannot start as expected because Security Hardening Mode is not supported by the image, you need to call the operation to change the instance metadata access method to Normal Mode.

Procedure

You can change the operating system of one or multiple existing instances at the same time to restore the system volume to the initial status.

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When you change the operating system of multiple existing instances at the same time, take note of the following items:

The instances for which you want to change the operating system must remain in Stopped state, and their associated availability zones, images, and billing methods must be identical.

You can change the operating system for up to 20 instances at the same time.

You can log in to the instances for which you have changed the operating system at the same time by using the newly configured credentials.

In the top menu bar, select the region and project where the target instance resides.

On the Instances page, click "Stop" in the "Actions" column of the target instance to stop the instance.

After the instance is stopped, click "... > Volumes & Image > Replace operating system" in the "Actions" column of the instance. Configure the parameters described in the following table.

Parameter	Description
Image	Public Image, Custom Image, Shared Images, and Marketplace Image are supported. The current image type is selected by default. You can select the type of image that you want to use to change the operating system. warning If the custom image you select has any items that are strongly recommended to be fixed, click the "View details" button and follow the guidance to complete the fixes before you use the custom image. This helps prevent instance malfunctions caused by image issues. Learn more If you use a custom image belonging to a project to change the operating system, your account must have permissions to perform operations on the project. Otherwise, you cannot use the custom image. For more information about how to authorize an account to operate a project, see Managing access to projects.
Login credentials	"Password", "Key pair", and "Keep Image settings" are supported. We recommend that you select "Key pair" for higher security. Password: If you select "Password", specify a complex password to enhance security. Key pair (recommended): A key pair consists of a public key and a private key. If you already have a key pair, select the name of the key pair to associate it. After association, you can log in to Linux instances with the private key. If you do not have a key pair, click the "Create key pair" button to go to the key pair page and create one. Keep Image settings: When you use a custom image or shared image, you can log in to the instance by using the preset credentials (password/key pair) in the image. warning You cannot select "Key pair" for a Windows image. When you select "Keep image settings" for a Windows image, take note of the following items. Otherwise, you cannot log in to the instance by using the preset password of the image. Before November 10, 2022, instances created by using Windows public images provided by the platform need to have their operating system or the Cloudbase-init configuration files changed. The Cloudbase-init configuration files of custom images or shared images generated by using the instances also need to be changed. For more information, refer to Installing Cloudbase-init on virtual machine.

Read the precautions for replacing the system volume and click the "Confirm the order" button to submit the request.

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If the target instance is running a Linux operating system and the billing method is subscription, when you change the Linux operating system to a Windows operating system, you will be redirected to the order information confirmation page. On the order information confirmation page, you can confirm the new configuration information and choose whether to use a coupon to offset fees.

Operation results

Successful: After you submit the request for changing the operating system, the instance changes to the Rebuilding status. Approximately 10 minutes later, the operating system is changed, the instance automatically starts, and the status changes to Running. Billing is resumed for instances in economical mode. Click the instance name to go to the instance details page, on which the new image is displayed.

Failed: The status changes from Rebuilding to Stopped. The instance will roll back to the pre-failure status and remain in the shutdown status. Please retry or contact customer service for assistance.

What to do next

After you change the operating system, you must perform the following operations before the data disk can be used as expected.

Switch between Linux operating systems

Switch between Windows and Linux operating systems

Execute the following command to view information about unmounted data volumes.

lsblk

If the following result is displayed, the original data volume vdb (this volume contains one partition vdb1) is not mounted.

Execute the following command to create a mount point.

sudo mkdir /data

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Replace /data with the name of the target mount point.

Execute the following command to mount the data volume to the target mount point.

sudo mount /dev/vdb1 /data/

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Replace /dev/vdb1 with the name of the target data volume partition.

Replace /data/ with the name of the target mount point.

Configure automatic mounting.

Execute the following command to query the UUID of the partition.

sudo blkid /dev/vdb1

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Please replace /dev/vdb1 with the target data disk partition name.

Sample output:

Run the following command to open the /etc/fstab file.

vim /etc/fstab

Press the i key to enter edit mode, and add the following content at the end of the file.

UUID=9439749e-8d07-4ce2-9591-xxxxxbc9 /data ext4 defaults 0 0

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Replace 9439749e-8d07-4ce2-9591-xxxxxbc9 with the actual UUID of the target volume partition.

Replace /data with the actual mount point name for the target volume partition.

Replace ext4 with the actual file system format of the target volume partition.

Press the esc key to exit editing, enter :wq, and press Enter to save and exit the file.