# Changing an ECS OS (Using an Image with Cloud-Init Installed)

#### Function

This API is used to change an ECS OS. During the system disk reinstallation using a new image, the data disks of the ECS remain unchanged.

After this API is called, the system uninstalls the system disk, uses the new image to create a system disk, and attaches it to the ECS. In this way, the OS is changed.

#### Constraints

- You can only use an image with Cloud-Init or Cloudbase-Init installed.
- Only a stopped ECS or an ECS on which reinstalling or changing the OS failed supports changing OS.
- Only an ECS with a system disk supports changing OS.
- You are not allowed to perform other operations when changing the OS. Otherwise, changing the OS will fail.

#### URI

POST /v2/{project_id}/cloudservers/{server_id}/changeos

Table 1 describes the parameters in the URI.

Table 1 Parameter description
Parameter | Mandatory | Description
--- | --- | ---
project_id | Yes | Specifies the project ID.
server_id | Yes | Specifies the ECS ID.

#### Request

Table 2 describes the request parameters.

Table 2 Request parameters
Parameter | Mandatory | Type | Description
--- | --- | --- | ---
os-change | Yes | Object | Changes an ECS OS. For details, see Table 3.

Table 3 os-change field description
Parameter | Mandatory | Type | Description
--- | --- | --- | ---
keyname | Yes | String | Specifies the key pair name.
userid | No | String | Specifies the user ID. When the keyname parameter is being specified, the value of this parameter is used preferentially. If this parameter is left blank, the user ID in the token is used by default.
imageid | Yes | String | Specifies the ID of the new image in UUID format. You can obtain the image ID from the console or by following the instructions provided in "Querying Images" in Image Management Service API Reference.
metadata | No | Object | Specifies the metadata of the ECS for which the OS is to be changed. For more information, see Table 4.

Table 4 metadata field description
Parameter | Mandatory | Type | Description
--- | --- | --- | ---

BYOL

No

String

Specifies whether a user has the license of an image.

- If this parameter is set to true, the license file delivered with the image is used, indicating that BYOL is used.
- If this parameter is set to a value other than true, BYOL is not used, and the license file provided by the public cloud platform must be used.

The default value is not true, indicating that BYOL is not used.

user_data

No

String

Specifies the user data to be injected to the ECS during the creation. Text and text files can be injected.

NOTE:

- The content of user_data must be encoded with base64.
- The maximum size of the content to be injected (before encoding) is 32 KB.

For more details, see "Injecting User Data into ECSs" in Elastic Cloud Server User Guide.

Examples

Before base64 encoding:

- Linux

      #! /bin/bash
      echo user_test >> /home/user.txt

- Windows

      rem cmd
      echo 111 > c:\aaa.txt

After base64 encoding:

- Linux

      IyEgL2Jpbi9iYXNoDQplY2hvIHVzZXJfdGVzdCAmZ3Q7Jmd0OyAvaG9tZS91c2VyLnR4dA==

- Windows

      cmVtIGNtZAplY2hvIDExMSA+IGM6XGFhYS50eHQ=

__system__encrypted | No | String | Specifies encryption in metadata. The value can be 0 (encryption disabled) or 1 (encryption enabled). If this parameter does not exist, the system disk will not be encrypted by default.
__system__cmkid | No | String | Specifies the CMK ID, which indicates encryption in metadata. This parameter is used with __system__encrypted. NOTE: For details about how to obtain the CMK ID, see "Querying the List of CMKs" in Key Management Service API Reference.

#### Response

See Responses (Task).

#### Example Request

- Example URL request

      POST https://{endpoint}/v2/{project_id}/cloudservers/{server_id}/changeos

- Example request 1 (using a password to remotely log in to an ECS with OS changed)

      {
          "os-change": {
              "adminpass": "1qazXSW@",
              "userid": "7e25b1da389f4697a79df3a0e5bd494e",
              "imageid": "e215580f-73ad-429d-b6f2-5433947433b0"
          }
      }

- Example request 2 (using a key to remotely log in to an ECS with OS changed)

      {
          "os-change": {
              "keyname": "KeyPair-350b",
              "userid": "7e25b1da389f4697a79df3a0e5bd494e",
              "imageid": "e215580f-73ad-429d-b6f2-5433947433b0"
          }
      }

- Example request 3 (using a password to remotely log in a full-ECS-image-created ECS with OS changed and system disk encrypted)

      {
          "os-change": {
              "adminpass": "1qazXSW@",
              "userid": "7e25b1da389f4697a79df3a0e5bd494e",
              "imageid": "e215580f-73ad-429d-b6f2-5433947433b0",
              "metadata": {
                    "__system__encrypted": "1",
                    "__system__cmkid": "83cdb52d-9ebf-4469-9cfa-e7b5b80da846"
              }
          }
      }

#### Example Response

See Responses (Task).

#### Returned Values

See Returned Values for General Requests.

#### Error Codes

See Error Codes.

Parent topic: Status Management