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User Guide for Linux Instances

AWS Documentation » Amazon EC2 » User Guide for Linux Instances » Network and Security » Amazon EC2 Key Pairs

Amazon EC2 Key Pairs

Amazon EC2 uses public–key cryptography to encrypt and decrypt login information. Public–key cryptography uses a public key to encrypt a piece of data, such as a password, then the recipient uses the private key to decrypt the data. The public and private keys are known as a key pair.

To log in to your instance, you must create a key pair, specify the name of the key pair when you launch the instance, and provide the private key when you connect to the instance. On a Linux instance, the public key content is placed in an entry within ~/.ssh/authorized_keys. This is done at boot time and enables you to securely access your instance using the private key instead of a password.

Creating a Key Pair

You can use Amazon EC2 to create your key pair. For more information, see Creating a Key Pair Using Amazon EC2.

Alternatively, you could use a third-party tool and then import the public key to Amazon EC2. For more information, see Importing Your Own Public Key to Amazon EC2.

Each key pair requires a name. Be sure to choose a name that is easy to remember. Amazon EC2 associates the public key with the name that you specify as the key name.

Amazon EC2 stores the public key only, and you store the private key. Anyone who possesses your private key can decrypt your login information, so it's important that you store your private keys in a secure place.

The keys that Amazon EC2 uses are 2048-bit SSH-2 RSA keys. You can have up to five thousand key pairs per region.

Launching and Connecting to Your Instance

When you launch an instance, you should specify the name of the key pair you plan to use to connect to the instance. If you don't specify the name of an existing key pair when you launch an instance, you won't be able to connect to the instance. When you connect to the instance, you must specify the private key that corresponds to the key pair you specified when you launched the instance.

Note

Amazon EC2 doesn't keep a copy of your private key; therefore, if you lose a private key, there is no way to recover it. If you lose the private key for an instance store-backed instance, you can't access the instance; you should terminate the instance and launch another instance using a new key pair. If you lose the private key for an EBS-backed Linux instance, you can regain access to your instance. For more information, see Connecting to Your Linux Instance if You Lose Your Private Key.

Key Pairs for Multiple Users

If you have several users that require access to a single instance, you can add user accounts to your instance. For more information, see Managing User Accounts on Your Linux Instance. You can create a key pair for each user, and add the public key information from each key pair to the .ssh/authorized_keys file for each user on your instance. You can then distribute the private key files to your users. That way, you do not have to distribute the same private key file that's used for the root account to multiple users.

Creating a Key Pair Using Amazon EC2

You can create a key pair using the Amazon EC2 console or the command line. After you create a key pair, you can specify it when you launch your instance. You can also add the key pair to a running instance to enable another user to connect to the instance. For more information, see Adding or Replacing a Key Pair for Your Instance.

To create your key pair using the Amazon EC2 console

  1. Open the Amazon EC2 console at https://console.aws.amazon.com/ec2/.

  2. In the navigation pane, under NETWORK & SECURITY, choose Key Pairs.

    Note

    The navigation pane is on the left side of the Amazon EC2 console. If you do not see the pane, it might be minimized; choose the arrow to expand the pane.

  3. Choose Create Key Pair.

  4. Enter a name for the new key pair in the Key pair name field of the Create Key Pair dialog box, and then choose Create.

  5. The private key file is automatically downloaded by your browser. The base file name is the name you specified as the name of your key pair, and the file name extension is .pem. Save the private key file in a safe place.

    Important

    This is the only chance for you to save the private key file. You'll need to provide the name of your key pair when you launch an instance and the corresponding private key each time you connect to the instance.

  6. If you will use an SSH client on a Mac or Linux computer to connect to your Linux instance, use the following command to set the permissions of your private key file so that only you can read it. 

    chmod 400 my-key-pair.pem

To create your key pair using the command line

You can use one of the following commands. For more information about these command line interfaces, see Accessing Amazon EC2.

Importing Your Own Public Key to Amazon EC2

Instead of using Amazon EC2 to create your key pair, you can create an RSA key pair using a third-party tool and then import the public key to Amazon EC2. For example, you can use ssh-keygen (a tool provided with the standard OpenSSH installation) to create a key pair. Alternatively, Java, Ruby, Python, and many other programming languages provide standard libraries that you can use to create an RSA key pair.

Amazon EC2 accepts the following formats:

  • OpenSSH public key format (the format in ~/.ssh/authorized_keys)

  • Base64 encoded DER format

  • SSH public key file format as specified in RFC4716

Amazon EC2 does not accept DSA keys. Make sure your key generator is set up to create RSA keys.

Supported lengths: 1024, 2048, and 4096.

To create a key pair using a third-party tool

  1. Generate a key pair with a third-party tool of your choice.

  2. Save the public key to a local file. For example, ~/.ssh/my-key-pair.pub (Linux) or C:\keys\my-key-pair.pub (Windows). The file name extension for this file is not important.

  3. Save the private key to a different local file that has the .pem extension. For example, ~/.ssh/my-key-pair.pem (Linux) or C:\keys\my-key-pair.pem (Windows). Save the private key file in a safe place. You'll need to provide the name of your key pair when you launch an instance and the corresponding private key each time you connect to the instance.

Use the following steps to import your key pair using the Amazon EC2 console.

To import the public key

  1. Open the Amazon EC2 console at https://console.aws.amazon.com/ec2/.

  2. In the navigation pane, under NETWORK & SECURITY, choose Key Pairs.

  3. Choose Import Key Pair.

  4. In the Import Key Pair dialog box, choose Browse, and select the public key file that you saved previously. Enter a name for the key pair in the Key pair name field, and choose Import.

To import the public key using the command line

You can use one of the following commands. For more information about these command line interfaces, see Accessing Amazon EC2.

After the public key file is imported, you can verify that the key pair was imported successfully using the Amazon EC2 console as follows.

To verify that your key pair was imported

  1. Open the Amazon EC2 console at https://console.aws.amazon.com/ec2/.

  2. From the navigation bar, select the region in which you created the key pair.

  3. In the navigation pane, under NETWORK & SECURITY, choose Key Pairs.

  4. Verify that the key pair that you imported is in the displayed list of key pairs.

To view your key pair using the command line

You can use one of the following commands. For more information about these command line interfaces, see Accessing Amazon EC2.

Retrieving the Public Key for Your Key Pair on Linux

On your local Linux or Mac computer, you can use the ssh-keygen command to retrieve the public key for your key pair.

To retrieve the public key from your computer

  1. Use the ssh-keygen command on a computer to which you've downloaded your private key: 

    ssh-keygen -y

  2. When prompted to enter the file in which the key is, specify the path to your .pem file; for example: 

    /path_to_key_pair/my-key-pair.pem

  3. The command returns the public key: 

    ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQClKsfkNkuSevGj3eYhCe53pcjqP3maAhDFcvBS7O6V
hz2ItxCih+PnDSUaw+WNQn/mZphTk/a/gU8jEzoOWbkM4yxyb/wB96xbiFveSFJuOp/d6RJhJOI0iBXr
lsLnBItntckiJ7FbtxJMXLvvwJryDUilBMTjYtwB+QhYXUMOzce5Pjz5/i8SeJtjnV3iAoG/cQk+0FzZ
qaeJAAHco+CY/5WrUBkrHmFJr6HcXkvJdWPkYQS3xqC0+FmUZofz221CBt5IMucxXPkX4rWi+z7wB3Rb
BQoQzd8v7yeb7OzlPnWOyN0qFU0XA246RA8QFYiCNYwI3f05p6KLxEXAMPLE

    If this command fails, ensure that you've changed the permissions on your key pair file so that only you can view it by running the following command: 

    chmod 400 my-key-pair.pem

Retrieving the Public Key for Your Key Pair on Windows

On your local Windows computer, you can use PuTTYgen to get the public key for your key pair.

Start PuTTYgen, choose Load, and select the .ppk or .pem file. PuTTYgen displays the public key.

Retrieving the Public Key for Your Key Pair From Your Instance

The public key that you specified when you launched an instance is also available to you through its instance metadata. To view the public key that you specified when launching the instance, use the following command from your instance: 

[ec2-user ~]$ curl http://169.254.169.254/latest/meta-data/public-keys/0/openssh-key
ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQClKsfkNkuSevGj3eYhCe53pcjqP3maAhDFcvBS7O6V
hz2ItxCih+PnDSUaw+WNQn/mZphTk/a/gU8jEzoOWbkM4yxyb/wB96xbiFveSFJuOp/d6RJhJOI0iBXr
lsLnBItntckiJ7FbtxJMXLvvwJryDUilBMTjYtwB+QhYXUMOzce5Pjz5/i8SeJtjnV3iAoG/cQk+0FzZ
qaeJAAHco+CY/5WrUBkrHmFJr6HcXkvJdWPkYQS3xqC0+FmUZofz221CBt5IMucxXPkX4rWi+z7wB3Rb
BQoQzd8v7yeb7OzlPnWOyN0qFU0XA246RA8QFYiCNYwI3f05p6KLxEXAMPLE my-key-pair

If you change the key pair that you use to connect to the instance, we don't update the instance metadata to show the new public key; you'll continue to see the public key for the key pair you specified when you launched the instance in the instance metadata.

For more information, see Retrieving Instance Metadata.

Alternatively, on a Linux instance, the public key content is placed in an entry within ~/.ssh/authorized_keys. You can open this file in an editor. The following is an example entry for the key pair named my-key-pair. It consists of the public key followed by the name of the key pair. For example: 

ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQClKsfkNkuSevGj3eYhCe53pcjqP3maAhDFcvBS7O6V
hz2ItxCih+PnDSUaw+WNQn/mZphTk/a/gU8jEzoOWbkM4yxyb/wB96xbiFveSFJuOp/d6RJhJOI0iBXr
lsLnBItntckiJ7FbtxJMXLvvwJryDUilBMTjYtwB+QhYXUMOzce5Pjz5/i8SeJtjnV3iAoG/cQk+0FzZ
qaeJAAHco+CY/5WrUBkrHmFJr6HcXkvJdWPkYQS3xqC0+FmUZofz221CBt5IMucxXPkX4rWi+z7wB3Rb
BQoQzd8v7yeb7OzlPnWOyN0qFU0XA246RA8QFYiCNYwI3f05p6KLxEXAMPLE my-key-pair

Verifying Your Key Pair's Fingerprint

On the Key Pairs page in the Amazon EC2 console, the Fingerprint column displays the fingerprints generated from your key pairs. AWS calculates the fingerprint differently depending on whether the key pair was generated by AWS or a third-party tool. If you created the key pair using AWS, the fingerprint is calculated using an SHA-1 hash function. If you created the key pair with a third-party tool and uploaded the public key to AWS, or if you generated a new public key from an existing AWS-created private key and uploaded it to AWS, the fingerprint is calculated using an MD5 hash function.

You can use the fingerprint that's displayed on the Key Pairs page to verify that the private key you have on your local machine matches the public key that's stored in AWS.

If you created your key pair using AWS, you can use the OpenSSL tools to generate a fingerprint from the private key file: 

$ openssl pkcs8 -in path_to_private_key -inform PEM -outform DER -topk8 -nocrypt | openssl sha1 -c

If you created your key pair using a third-party tool and uploaded the public key to AWS, you can use the OpenSSL tools to generate a fingerprint from the private key file on your local machine: 

$ openssl rsa -in path_to_private_key -pubout -outform DER | openssl md5 -c

The output should match the fingerprint that's displayed in the console.

Deleting Your Key Pair

When you delete a key pair, you are only deleting Amazon EC2's copy of the public key. Deleting a key pair doesn't affect the private key on your computer or the public key on any instances already launched using that key pair. You can't launch a new instance using a deleted key pair, but you can continue to connect to any instances that you launched using a deleted key pair, as long as you still have the private key (.pem) file.

Note

If you're using an Auto Scaling group (for example, in an Elastic Beanstalk environment), ensure that the key pair you're deleting is not specified in your launch configuration. Amazon EC2 Auto Scaling launches a replacement instance if it detects an unhealthy instance; however, the instance launch fails if the key pair cannot be found.

You can delete a key pair using the Amazon EC2 console or the command line.

To delete your key pair using the console

  1. Open the Amazon EC2 console at https://console.aws.amazon.com/ec2/.

  2. In the navigation pane, under NETWORK & SECURITY, choose Key Pairs.

  3. Select the key pair and choose Delete.

  4. When prompted, choose Yes.

To delete your key pair using the command line

You can use one of the following commands. For more information about these command line interfaces, see Accessing Amazon EC2.

Note

If you create a Linux AMI from an instance, and then use the AMI to launch a new instance in a different region or account, the new instance includes the public key from the original instance. This enables you to connect to the new instance using the same private key file as your original instance. You can remove this public key from your instance by removing its entry from the .ssh/authorized_keys file using a text editor of your choice. For more information about managing users on your instance and providing remote access using a specific key pair, see Managing User Accounts on Your Linux Instance.

Adding or Replacing a Key Pair for Your Instance

You can change the key pair that is used to access the default system account of your instance. For example, if a user in your organization requires access to the system user account using a separate key pair, you can add that key pair to your instance. Or, if someone has a copy of the .pem file and you want to prevent them from connecting to your instance (for example, if they've left your organization), you can replace the key pair with a new one.

Note

These procedures are for modifying the key pair for the default user account, such as ec2-user. For more information about adding user accounts to your instance, see Managing User Accounts on Your Linux Instance.

Before you begin, create a new key pair using the Amazon EC2 console or a third-party tool.

To add or replace a key pair

  1. Retrieve the public key from your new key pair. For more information, see Retrieving the Public Key for Your Key Pair on Linux or Retrieving the Public Key for Your Key Pair on Windows.

  2. Connect to your instance using your existing private key file.

  3. Using a text editor of your choice, open the .ssh/authorized_keys file on the instance. Paste the public key information from your new key pair underneath the existing public key information. Save the file.

  4. Disconnect from your instance, and test that you can connect to your instance using the new private key file.

  5. (Optional) If you're replacing an existing key pair, connect to your instance and delete the public key information for the original key pair from the .ssh/authorized_keys file.

Note

If you're using an Auto Scaling group (for example, in an Elastic Beanstalk environment), ensure that the key pair you're replacing is not specified in your launch configuration. Amazon EC2 Auto Scaling launches a replacement instance if it detects an unhealthy instance; however, the instance launch fails if the key pair cannot be found.

Connecting to Your Linux Instance if You Lose Your Private Key

If you lose the private key for an EBS-backed instance, you can regain access to your instance. You must stop the instance, detach its root volume and attach it to another instance as a data volume, modify the authorized_keys file, move the volume back to the original instance, and restart the instance. For more information about launching, connecting to, and stopping instances, see Instance Lifecycle.

This procedure isn't supported for instance store-backed instances. To determine the root device type of your instance, open the Amazon EC2 console, choose Instances, select the instance, and check the value of Root device type in the details pane. The value is either ebs or instance store. If the root device is an instance store volume, you must have the private key in order to connect to the instance.

Prerequisites

Create a new key pair using either the Amazon EC2 console or a third-party tool. If you want to name your new key pair exactly the same as the lost private key, you must first delete the existing key pair.

To connect to an EBS-backed instance with a different key pair

  1. Open the Amazon EC2 console at https://console.aws.amazon.com/ec2/.

  2. Choose Instances in the navigation pane, and then select the instance that you'd like to connect to. (We'll refer to this as the original instance.)

  3. From the Details tab, save the following information that you'll need to complete this procedure.

    • Write down the instance ID, AMI ID, and Availability Zone of the original instance.

    • In the Root device field, take note of the device name for the root volume (for example, /dev/sda1 or /dev/xvda). Choose the link and write down the volume ID in the EBS ID field (vol-xxxxxxxxxxxxxxxxx).

    • [EC2-Classic] If the original instance has an associated Elastic IP address, write down the Elastic IP address shown in the Elastic IP field in the details pane.

  4. Choose Actions, select Instance State, and then select Stop. If Stop is disabled, either the instance is already stopped or its root device is an instance store volume.

    Warning

    When you stop an instance, the data on any instance store volumes is erased. Therefore, if you have any data on instance store volumes that you want to keep, be sure to back it up to persistent storage.

  5. Choose Launch Instance, and then use the launch wizard to launch a temporary instance with the following options:

    • On the Choose an AMI page, select the same AMI that you used to launch the original instance. If this AMI is unavailable, you can create an AMI that you can use from the stopped instance. For more information, see Creating an Amazon EBS-Backed Linux AMI .

    • On the Choose an Instance Type page, leave the default instance type that the wizard selects for you.

    • On the Configure Instance Details page, specify the same Availability Zone as the instance you'd like to connect to. If you're launching an instance in a VPC, select a subnet in this Availability Zone.

    • On the Add Tags page, add the tag Name=Temporary to the instance to indicate that this is a temporary instance.

    • On the Review page, choose Launch. Create a new key pair, download it to a safe location on your computer, and then choose Launch Instances.

  6. In the navigation pane, choose Volumes and select the root device volume for the original instance (you wrote down its volume ID in a previous step). Choose Actions, and then select Detach Volume. Wait for the state of the volume to become available. (You might need to choose the Refresh icon.)

  7. With the volume still selected, choose Actions, and then select Attach Volume. Select the instance ID of the temporary instance, write down the device name specified under Device (for example, /dev/sdf), and then choose Yes, Attach.

    Note

    If you launched your original instance from an AWS Marketplace AMI and your volume contains AWS Marketplace codes, you must first stop the temporary instance before you can attach the volume.

  8. Connect to the temporary instance.

  9. From the temporary instance, mount the volume that you attached to the instance so that you can access its file system. For example, if the device name is /dev/sdf, use the following commands to mount the volume as /mnt/tempvol.

    Note

    The device name may appear differently on your instance. For example, devices mounted as /dev/sdf may show up as /dev/xvdf on the instance. Some versions of Red Hat (or its variants, such as CentOS) may even increment the trailing letter by 4 characters, where /dev/sdf becomes /dev/xvdk.

    1. Use the lsblk command to determine if the volume is partitioned. 

      [ec2-user ~]$ lsblk
NAME    MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
xvda    202:0    0    8G  0 disk
└─xvda1 202:1    0    8G  0 part /
xvdf    202:80   0  101G  0 disk
└─xvdf1 202:81   0  101G  0 part
xvdg    202:96   0   30G  0 disk

      In the above example, /dev/xvda and /dev/xvdf are partitioned volumes, and /dev/xvdg is not. If your volume is partitioned, you mount the partition (/dev/xvdf1) instead of the raw device (/dev/xvdf) in the next steps.

    2. Create a temporary directory to mount the volume.

      [ec2-user ~]$ sudo mkdir /mnt/tempvol

    3. Mount the volume (or partition) at the temporary mount point, using the volume name or device name you identified earlier. 

      [ec2-user ~]$ sudo mount /dev/xvdf1 /mnt/tempvol

  10. From the temporary instance, use the following command to update authorized_keys on the mounted volume with the new public key from the authorized_keys for the temporary instance.

    Important

    The following examples use the Amazon Linux user name ec2-user. You may need to substitute a different user name, such as ubuntu for Ubuntu instances. 

    [ec2-user ~]$ cp .ssh/authorized_keys /mnt/tempvol/home/ec2-user/.ssh/authorized_keys

    If this copy succeeded, you can go to the next step.

    (Optional) Otherwise, if you don't have permission to edit files in /mnt/tempvol, you'll need to update the file using sudo and then check the permissions on the file to verify that you'll be able to log into the original instance. Use the following command to check the permissions on the file: 

    [ec2-user ~]$ sudo ls -l /mnt/tempvol/home/ec2-user/.ssh
total 4
-rw------- 1 222 500 398 Sep 13 22:54 authorized_keys

    In this example output, 222 is the user ID and 500 is the group ID. Next, use sudo to re-run the copy command that failed: 

    [ec2-user ~]$ sudo cp .ssh/authorized_keys /mnt/tempvol/home/ec2-user/.ssh/authorized_keys

    Run the following command again to determine whether the permissions changed:

    [ec2-user ~]$ sudo ls -l /mnt/tempvol/home/ec2-user/.ssh

    If the user ID and group ID have changed, use the following command to restore them: 

    [ec2-user ~]$ sudo chown 222:500 /mnt/tempvol/home/ec2-user/.ssh/authorized_keys

  11. From the temporary instance, unmount the volume that you attached so that you can reattach it to the original instance. For example, use the following command to unmount the volume at /mnt/tempvol: 

    [ec2-user ~]$ sudo umount /mnt/tempvol

  12. From the Amazon EC2 console, select the volume with the volume ID that you wrote down, choose Actions, and then select Detach Volume. Wait for the state of the volume to become available. (You might need to choose the Refresh icon.)

  13. With the volume still selected, choose Actions, Attach Volume. Select the instance ID of the original instance, specify the device name you noted earlier for the original root device attachment (/dev/sda1 or /dev/xvda), and then choose Yes, Attach.

    Important

    If you don't specify the same device name as the original attachment, you cannot start the original instance. Amazon EC2 expects the root device volume at sda1 or /dev/xvda.

  14. Select the original instance, choose Actions, select Instance State, and then choose Start. After the instance enters the running state, you can connect to it using the private key file for your new key pair.

    Note

    If the name of your new key pair and corresponding private key file is different to the name of the original key pair, ensure that you specify the name of the new private key file when you connect to your instance.

  15. [EC2-Classic] If the original instance had an associated Elastic IP address before you stopped it, you must re-associate it with the instance as follows:

    1. In the navigation pane, choose Elastic IPs.

    2. Select the Elastic IP address that you wrote down at the beginning of this procedure.

    3. Choose Actions, and then select Associate address.

    4. Select the ID of the original instance, and then choose Associate.

  16. (Optional) You can terminate the temporary instance if you have no further use for it. Select the temporary instance, choose Actions, select Instance State, and then choose Terminate.