Cray System Management Documentation > Cray System Management (CSM) Administration Guide > security and authentication > Update NCN User SSH Keys

Update NCN User SSH Keys

Change the SSH keys for users on non-compute nodes (NCNs) on the system using the rotate-ssh-keys-mgmt-nodes.yml Ansible playbook provided by CSM or through NCN node personalization (site.yml).

The NCNs deploy with SSH keys for the root user that are changed during the system install. See Change NCN Image Root Password and SSH Keys for more information on changing the default keys during install. It is a recommended best practice for system security to change the SSH keys after the install is complete on a schedule. This procedure defines how to change the keys once the system is operational.

The NCN root user keys are stored in the HashiCorp Vault instance, and applied with the csm.ssh_keys Ansible role via a CFS session. If no keys are added to Vault as in the procedure below, this Ansible role will skip any updates.

Procedure: Configure root SSH keys in Vault

Generate a new SSH key pair for the root user.

Use ssh-keygen to generate a new pair or stage an existing pair, as per site security policies and procedures.

(ncn-mw#) Get the HashiCorp Vault root token.

kubectl get secrets -n vault cray-vault-unseal-keys -o jsonpath='{.data.vault-root}' | base64 -d; echo

Write the private and public halves of the key pair to the HashiCorp Vault.

WARNING: The CSM instance of Vault does not support the patch operation. Ensure that if the ssh_private_key and ssh_public_key fields in the secret/csm/users/root secret are being updated, then any other desired fields are also included in the write command. For example the user’s password hash. See Update NCN Passwords. Any fields omitted from the write command will be cleared from Vault.

The path to the secret and the SSH key fields are configurable locations in the CSM csm.ssh_keys Ansible role located in the CSM configuration management Git repository that is in use. If not using the defaults as shown in the command examples, ensure that the paths are consistent between Vault and the values in the Ansible role. See roles/csm.ssh_keys in the repository for more information.
1. (ncn-mw#) Open an interactive shell in the Vault Kubernetes pod.
```
kubectl exec -itn vault cray-vault-0 -c vault -- sh
```
2. (cray-vault#) Write the SSH keys to Vault.
  - The vault login command will request the token value from the output of the previous step.
  - Use the SSH keys from the earlier step.
    - The ssh_private_key and ssh_public_key fields should contain the exact content from the id_rsa and id_rsa.pub files (if using RSA key types).
    - NOTE: It is important to enclose the key content in single quotes to preserve any special characters.
  - The vault read command allows the administrator to verify that the contents of the secret were stored correctly.
```
export VAULT_ADDR=http://cray-vault:8200
vault login
vault write secret/csm/users/root ssh_private_key='...' ssh_public_key='...' [... other fields (see warning below) ...]
vault read secret/csm/users/root
exit
```

Procedure: Apply root SSH keys to NCNs (standalone)

Use the following procedure with the rotate-ssh-keys-mgmt-nodes.yml playbook to only change the root SSH keys on NCNs. This is a quick alternative to running a full management node personalization, as documented in the Re-run node personalization on management nodes procedure in the Management Node Personalization topic.

(ncn-mw#) Create a CFS configuration layer to run the SSH key change Ansible playbook.

NOTE This step only needs to be done once, as long as the commit in the CSM configuration management Git repository has not changed. If the commit has not changed since the last time this step was run, this step may be skipped, because the previously created CFS configuration will still work.
1. Create a file containing only this CFS configuration layer.
  
  The file contents should be as follows, except replace the <INSERT GIT COMMIT ID> text with the commit in the CSM configuration management Git repository that is in use.
```
{
  "layers": [
    {
      "name": "ncn-root-keys-update",
      "clone_url": "https://api-gw-service-nmn.local/vcs/cray/csm-config-management.git",
      "playbook": "rotate-ssh-keys-mgmt-nodes.yml",
      "commit": "<INSERT GIT COMMIT ID>"
    }
  ]
}
```
2. Create the ncn-root-keys-update configuration in CFS.
  
  Replace the <INSERT FILE PATH HERE> text with the path to the file created in the previous step. If a CFS configuration already exists with this name, the following command will overwrite it.
```
cray cfs v3 configurations update ncn-root-keys-update --file <INSERT FILE PATH HERE>
```

(ncn-mw#) Create a CFS configuration session to apply the SSH keys update.

cray cfs v3 sessions create --name ncn-root-keys-update-`date +%Y%m%d%H%M%S` --configuration-name ncn-root-keys-update

Monitor the CFS session.

See Track the Status of a Session.

Procedure for other users

The csm.ssh_key Ansible role supports setting SSH keys for non-root users.

Make a copy of the rotate-ssh-keys-mgmt-nodes.yml Ansible playbook and modify the role variables to specify a different ssh_keys_username.
Using that username, add the SSH keys to Vault.

Follow Procedure: Configure root SSH keys in Vault.
Create a configuration layer using the new Ansible playbook and create a CFS session using that layer.