If the operating system of an Elastic Compute Service (ECS) instance does not meet your business requirements, you can replace the operating system. This topic describes how to use a public image or a non-public image (such as a custom image or a shared image) to replace the operating system of an instance.

Prerequisites

  • A snapshot is created for the system disk that you want to replace. For more information, see Create a snapshot of a disk.

    An operating system replacement operation replaces a system disk. After the operating system of the instance is replaced, the original system disk is released and data stored on the disk is cleared. Before you replace the operating system, make sure that you create snapshots for the system disk to back up data.

  • The instance whose operating system you want to replace is in the Stopped state. If the instance is not in the Stopped state, stop it. For more information, see Stop an instance.
    Warning If the billing method of an instance is pay-as-you-go and the network type of the instance is VPC, you must enable the standard mode for the instance when you stop the instance. If you enable the economical mode for the instance, you may not be able to start the instance after you replace its operating system.

Precautions

If you replace the operating system of an instance, risks may occur. Before you perform this operation, take note of the items that are described in the following table.
Note After you replace the operating system of an instance, you must redeploy environments on the new system disk to run services. This may interrupt services that are running on the instance for an extended period of time. If you want to retain data stored on the original system disk and reduce service downtime, we recommend that you use Server Migration Center (SMC) to migrate the operating system instead of replacing the operating system. For more information, see Migrate the operating system of an ECS instance.
ItemDescription
Impacts on the system disk
After you replace the operating system of an instance, Alibaba Cloud assigns a new system disk to the instance. Take note of the following items:
  • The original system disk is released and all data and partition information of the disk are cleared.
    Note Before you replace the system disk of an instance, create snapshots for the system disk to back up data. For more information, see Create a snapshot of a disk.
  • The system disk ID is changed. The category of the system disk, the IP addresses of the instance, and the media access control (MAC) addresses of the elastic network interfaces (ENIs) attached to the instance remain unchanged.
Impacts on the data disksData on the data disks attached to the instance is not affected.
Impacts on snapshots
  • The snapshots of the original system disk cannot be used to roll back the new system disk, but can be used to create custom images.
  • The manual snapshots of the original system disk are not released.
  • If Delete Automatic Snapshots While Releasing Disk is enabled for the original system disk, the automatic snapshots of the disk are automatically released along with the disk. If Delete Automatic Snapshots While Releasing Disk is not enabled for the original system disk, the automatic snapshots of the disk are not automatically released until they expire.
  • The automatic snapshot policy applied to the original system disk becomes invalid. In this case, you must configure an automatic snapshot policy for the new system disk.
Limits that apply when the replacement operating system is a Windows operating system
  • Make sure that the system disk has at least 1 GiB of available space reserved. Otherwise, the instance may be unable to start after the operating system is replaced.
  • After January 14, 2020, Microsoft no longer provides support for Windows Server 2008 and Windows Server 2008 R2. Alibaba Cloud no longer provides technical support for ECS instances that use these operating systems. If your ECS instances use these operating systems, upgrade the operating systems to Windows Server 2012 or later at the earliest opportunity. For more information, see Overview.
Limits that apply when you replace a Windows operating system with a Linux operating system or replace a Linux operating system with a Windows operating system
  • Operating systems can be replaced across the Windows and Linux operating system families for instances only in regions inside the Chinese mainland. In regions outside the Chinese mainland, operating systems can be replaced for instances only within the Windows or Linux operating system family.
  • Confirm that the hostname of the instance meets the requirements of the new operating system. For example, the instance hostname cannot exceed 15 characters in length if the replacement operating system is a Windows operating system. For more information about how to modify the hostname of an instance, see Modify the properties of an instance or ModifyInstanceAttribute.
Charges
You are not charged for replacing the operating system of an instance but are charged for the resources that are used in the following scenarios:
  • If the replacement image is a paid image, you are charged for the image. For more information, see Images.
  • If you extend the capacity of the system disk when you replace the operating system of an instance, you are charged for the disk capacity increment. For more information, see Block storage devices.
Amount of time required to replace the operating system
It takes approximately 10 minutes to replace the operating system of an instance. The actual amount of time varies based on the operating system.
Important After the operating system is replaced, you may be unable to log on to the instance by using Virtual Network Computing (VNC) for specific reasons such as slow boot. Wait a while and log on to the instance again.

Procedure

This section describes how to use an image to replace the operating system of a single instance in the ECS console. To batch replace the operating systems of multiple instances, you can use the ACS-ECS-BulkyReplaceSystemDisk public template provided by Operation Orchestration Service (OOS). For more information, see Public Templates.

  1. Go to the Instances page in the ECS console.
    1. Log on to the ECS console.
    2. In the left-side navigation pane, choose Instances & Images > Instances.
    3. In the top navigation bar, select the region where the ECS instance is located.
  2. Find the instance whose operating system you want to replace and choose More > Disk and Image > Replace Operating System in the Actions column.
  3. In the Replace Operating System dialog box, select Replace System Disk.
  4. Read the notes and select I understand the risks. Then, click Continue to Replace Operating System.
  5. On the Change Operating System page, configure the parameters.
    Replace the operating system of an instance
    1. ①: In the Image section, select an image type. Then, select an image and an image version from the drop-down lists.
    2. Optional:②: In the System Disk section, specify the capacity of the new system disk based on your business requirements.
      You can specify a capacity that is greater than the capacity of the current system disk.
      Important
      • You cannot replace the system disk with a disk of a different category.
      • If you renewed your instance and downgraded its configurations, you cannot change the system disk capacity until the next billing cycle starts.
      • If you extend the system disk, you are charged for the additional disk capacity. For more information, see Block storage devices.
      • If you extend the system disk during the operating system replacement process, partitions on the system disk may fail to be extended due to a timeout error. For information about how to resolve the issue, see the "What do I do if partitions on the system disk of an instance fail to be extended when I extend the disk by replacing the operating system of the instance?" section of What do I do if partitions on the system disk of an instance fail to be extended when I extend the disk by replacing the operating system of the instance? .
    3. In the Security Settings section, configure an authentication method. The following table describes the authentication methods.
      Authentication methodDescription
      Key Pair
      Note You can use key pairs to log on to only Linux instances.
      		Select a username that you want to use to log on to the instance. Then, select an existing key pair or click create a key pair to create a key pair. For more information, see Create an SSH key pair. After you create a key pair, go back to the Change Operating System page and click the Refresh icon next to the Key Pair field to obtain the most recent key pair list.
      You can set Username to root or ecs-user.
      Warning If you log on to the instance as the root user, you have the highest permissions on the instance. However, security risks may arise. We recommend that you use ecs-user instead to log on to the instance.
      Use Predefined Password
      Note Only custom images and shared images support this authentication method.
      		To use the password preset in the selected image to log on to the instance, select this authentication method. If you select this authentication method, make sure that your selected image has a password preset.
      PasswordSpecify a username and a password.
      • For a Linux instance, set Username to root or ecs-user.
        Warning If you log on to the instance as the root user, you have the highest permissions on the instance. However, security risks may arise. We recommend that you use ecs-user instead to log on to the instance.
      • For a Windows instance, Username is set to administrator by default.
      Set after ChangeAfter you replace the operating system, bind a key pair or use the password reset feature to specify a password for the instance. For more information, see Bind an SSH key pair to an instance and Reset the logon password of an instance.
  6. Check the fees, read and select ECS Service Terms, and then click Create Order.
  7. Optional:Complete the payment (if any) as prompted.
    It takes about 10 minutes to replace the operating system. After the operating system is replaced, you can go back to the ECS console and find that the state of the instance changes to Running. You can click the instance ID to go to the Instance Details page and view image information.

What to do next

After you replace the operating system of an instance, you can perform the following operations based on the actual conditions:
  • Redeploy environments on the new operating system to run services.
  • If both the replaced and replacement operating systems are Linux operating systems and the data disk partitions of the instance are configured to automatically mount on instance startup, the mounting information of the data disk partitions is lost. You must rewrite the mounting information of the data disk partitions to the /etc/fstab file. For more information, see Configure UUIDs in the fstab file to automatically attach data disks.
  • (Optional) The automatic snapshot policy applied to the original system disk becomes invalid, and you can apply an automatic snapshot policy to the new system disk based on your needs. For more information, see Enable or disable an automatic snapshot policy.
  • (Optional) Delete the snapshots of the original system disk that are no longer needed. For more information, see Delete a snapshot.

FAQ

QuestionAnswer
How do I change the hostname of an instance when I replace the Linux operating system of the instance with a Windows operating system? The hostnames of Windows operating systems must not exceed 15 characters in length. Modify the hostname of the instance based on your business requirements. For more information, see Modify the properties of an instance or ModifyInstanceAttribute.
Which operating systems support graphical desktops?
  • By default, Linux operating systems offer a command-line interface. You can install a graphical desktop based on your business requirements. Example: the desktop that is described in Install a GUI desktop for Ubuntu 18 .
  • All Windows operating systems support graphical desktops except for Windows Server Version 2004 **** (Without UI) and Windows Server 2022 Datacenter **** (Without UI). For more information, see Third-party images and open-source images.
How do I use the data disks of an instance after I replace the Linux operating system of the instance with a Windows operating system? By default, Windows operating systems do not support ext3, ext4, or xfs file systems. We recommend that you perform one of the following operations on your data disks:
  • If your data disks do not contain important data, re-initialize the disks and format them into a file system that is supported by the Windows operating system. For more information, see Re-initialize a data disk and Initialize a data disk up to 2 TiB in size on a Windows instance.
  • If your data disks contain important data, separately install software (such as Ext2Read and Ext2Fsd) that enables the Windows operating system to work with ext3, ext4, or xfs file systems.
How do I use the data disks of an instance after I replace the Windows operating system of the instance with a Linux operating system? By default, Linux operating systems do not support New Technology File System (NTFS) file systems. We recommend that you perform one of the following operations on your data disks:
  • If your data disks do not contain important data, re-initialize the disks and format them into a file system that is supported by the Linux operating system. For more information, see Re-initialize a data disk and Initialize a data disk whose size does not exceed 2 TiB on a Linux instance.
  • If your data disks contain important data, separately install software (such as ntfsprogs) that enables the Linux operating system to work with NTFS file systems.
    If you use ntfsprogs, run the following commands in sequence to allow the Linux operating system to access the NTFS file systems: 
    yum -y install ntfsprogs
mount -t ntfs-3g <Data disk partition name> <Mount directory>
    Note Set <Data disk partition name> and <Mount directory> to the actual names and mount directories of the data disk partitions.
For more questions, see FAQ about replacing the operating system of an instance.