Connect to a Linux instance by using an SSH key pair - Elastic Compute Service

Secure Shell (SSH) key pairs are a secure and convenient method to authenticate logons. This topic describes how to use an SSH key pair to connect to a Linux instance from a Windows device or a device that supports SSH commands, such as a Linux client or MobaXterm for Windows.

Prerequisites

An SSH key pair is created and the .pem private key file is downloaded. For more information, see Create an SSH key pair.
The Linux instance to which you want to connect is in the Running state.
An SSH key pair is bound to the instance.
A public IP address or an elastic IP address (EIP) is associated with the instance.

A security group rule is added to the security group of the instance to allow traffic on the corresponding port, such as the default port 22 for SSH. For more information, see Add a security group rule.


Network type	NIC type	Direction	Action	Protocol type	Port range	Priority	Authorization type	Authorization object
Virtual Private Cloud (VPC)	N/A	Inbound	Allow	SSH(22)	22/22	1	IPv4 CIDR blocks	0.0.0.0/0
Classic network	Public	Inbound	Allow	SSH(22)	22/22	1	IPv4 CIDR blocks	0.0.0.0/0

Background information

You can use one of the following methods to connect to the Linux instance by using an SSH key pair based on the operating system of your device:

Use an SSH key pair to connect to a Linux instance from a Windows device
Use an SSH key pair to connect to a Linux instance from a device that supports SSH commands (configure information by using commands)
Use an SSH key pair to connect to a Linux instance from a device that supports SSH commands (configure information by using the config file)

Use an SSH key pair to connect to a Linux instance from a Windows device

The following section describes how to convert the format of a private key file from .pem to .ppk and how to use an SSH key pair to connect to a Linux instance. PuTTYgen is used in this example.

Download and install PuTTYgen and PuTTY.
Download PuTTYgen and PuTTY from the following links:
- PuTTYgen
- PuTTY
Convert the format of a private key file from .pem to .ppk.
1. Start PuTTYgen.
  In this example, PuTTYgen 0.71 is used.
2. Set Type of key to generate to RSA and click Load.
3. Select All Files.
4. Select the .pem private key file that you want to convert.
5. In the dialog box that appears, click OK.
6. Click Save private key.
7. In the dialog box that appears, click Yes.
8. Specify a name for the .ppk private key file and click Save.
Start PuTTY.
Configure the private key file used for authentication.
1. Choose Connection > SSH > Auth > Credentials.
2. In the Private key file for authentication: field,Click Browse...
3. Select the resulting .ppk private key file.
Configure the required parameters to connect to the Linux instance.
1. Click Session.
2. In the Host Name (or IP address) field, enter the logon account and public IP address of the instance.
  The format is root@<IP address>. Example: root@10.10.xx.xxx.
3. In the Port field, enter 22.
4. Set Connection type to SSH.
Click Open.
If the following message appears, you are logged on to the instance.

Use an SSH key pair to connect to a Linux instance from a device that supports SSH commands (configure information by using commands)

The following section describes how to use commands to configure required information on a device that supports SSH commands (such as a Linux client or MobaXterm for Windows) and then how to use SSH commands to connect to the Linux instance from the device.

Find the path where the .pem private key file is located. Example: ~/.ssh/ecs.pem.
The path and file name used are for reference only. You can modify the information in subsequent commands based on actual conditions.
Run the following command to modify the attribute of the private key file:
```
chmod 400 [Path of the .pem private key file on your PC]
```
Example:
```
chmod 400 ~/.ssh/ecs.pem
```

Run the following command to connect to the instance:

ssh -i [Path of the .pem private key file on your PC] root@[Public IP address]

Example:

ssh -i ~/.ssh/ecs.pem root@10.10.xx.xxx

Use an SSH key pair to connect to a Linux instance from a device that supports SSH commands (configure information by using the config file)

Find the path where the .pem private key file is located. Example: ~/.ssh/ecs.pem.
The path and file name used are for reference only. You can modify the information in subsequent commands based on actual conditions.
Run the following command to modify the attribute of the private key file:
```
chmod 400 [Path of the .pem private key file on your PC]
```
Example:
```
chmod 400 ~/.ssh/ecs.pem
```
Run the following commands to go to the .ssh directory in the home directory and create a config file:
```
cd ~/.ssh
vim config
```

In the config file, press the I key to enter the edit mode and add the following configuration items:

# Enter the alias of the ECS instance to connect to the instance by using an SSH key pair. 
Host ecs
# Enter the public IP address of the instance. 
HostName 121.196.**.**
# Enter the port number. The default port number is 22. 
Port 22
# Enter the logon account. 
User root
# Enter the address of the .pem private key file on your PC. 
IdentityFile ~/.ssh/ecs.pem

If you have multiple ECS instances, you can use the config file to configure password-free logon in a centralized manner. The following example demonstrates how to configure password-free logon for two ECS instances:

# Enter the alias of one ECS instance to connect to the instance by using an SSH key pair. 
Host ecs1
# Enter the public IP address of the instance. 
HostName 121.196.**.**
# Enter the port number. The default port number is 22. 
Port 22
# Enter the logon account. 
User root
# Enter the address of the .pem private key file on your PC. 
IdentityFile ~/.ssh/ecs.pem

# Enter the alias of the other ECS instance to connect to the instance by using an SSH key pair. 
Host ecs2
# Enter the public IP address of the instance. 
HostName 121.196.**.**
# Enter the port number. The default port number is 22. 
Port 22
# Enter the logon account. 
User root
# Enter the address of the .pem private key file on your PC. 
IdentityFile ~/.ssh/ecs.pem

After the configuration items are added, press the Esc key and enter :wq to save the config file.

Run the following command to restart the SSH service:
```
service sshd restart
```
Run the following command to connect to the instance:
```
ssh [Alias of the instance]
```
Example:
```
ssh ecs
```