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Below is a compilation of issues you may encounter when using Nimbus, and workarounds or solutions where possible. This will be added to as time goes on, so we recommend checking here first if you encounter a problem.

Adding a Security Group

If you require to add another security group or have forgotten to add a security group when creating your instance, you can do so with the following steps:

  1. Log in to your Nimbus Dashboard.
  2. Navigate to Compute > Instances.
  3. On the right hand dropdown menu for your instance, select "Edit Security Groups".

  4. Under "All Security Groups", select the security groups you require by clicking on the "+" button, then click "Save"

Creating and Accessing Instances

SSH Access - permission denied

Once your instance is created, when attempting to SSH into the instance, you may receive the following error:

Permission denied (publickey).

There may be a number of possible reasons for this:

  • Ensure that you have added your SSH key (either by generating a new key in the dashboard, or importing an existing one).
  • Ensure that you are using the correct username for the image you chose for your instance, e.g. ubuntu for Ubuntu images or centos for Centos images.
  • Make sure that you have set up a security group to allow SSH access into your instance. For more information on this, refer to our training material and the security group section in particular.
  • Ensure that your SSH key on the machine you are connecting from has suitable permissions set. In particular, make sure that the private key can only be read by your personal account, and no-one else (the SSH key filename in the example below may differ, depending on your setup):
chmod 600 ~/.ssh/id_rsa
  • If you have an SSH key pair through the Nimbus dashboard, you may instead want to try creating the SSH key on your local machine, then importing the public key into Nimbus. The SSH key pair can be generated locally with the command "ssh-keygen". Be sure to ONLY import the public key on Nimbus; the private key must remain where it is.

Creating and Using Snapshots

Error: Unable to create snapshot

When attempting to create a snapshot, it's possible for the command to fail. This is usually caused by insufficient storage quota.

The total size of the snapshot will include the size of any mounted volumes. If you wish to take a snapshot of your instance without inessential volumes, you will need to first detach them from the instance so that the snapshot only includes the most important system files. If you have a separate system volume, you can alternatively, create a snapshot of just this volume:

  1. From the Nimbus dashboard → Volumes
  2. Select Create Snapshot
  3. To review the snapshot in the dashboard, you will find it under Volumes → Snapshots

Accessing Recovery Mode

If your instance fails to boot or there is some other critical issue with your instance (e.g. due to system misconfiguration), it is possible to access recovery mode in Ubuntu systems. Although the instructions below are given for Ubuntu's recovery mode, the procedure is similar for accessing the emergency mode on CentOS systems.

The recovery and emergency modes are advanced features intended for users experienced with Linux systems. If you are unfamiliar with the system, we recommend using alternative means to recover your instance, such as rolling back to an earlier snapshot or mounting your root volume to a new instance. Please contact for more assistance.

To access Ubuntu's recovery mode:

  1. From the Nimbus dashboard → Actions menu to the right of your instance, and select Console. You may need to click on the "Click here to show only console" link and refresh the page before the console appears.
  2. In the top-right corner of your console window, click on the "Send CtrlAltDel" button to reboot your instance
  3. As soon as the console goes blank, hold down the shift key to make the GRUB boot menu appear
  4. From the GRUB boot menu, select "Advanced options for Ubuntu", then select the recovery mode for the latest kernel version listed (usually the second option from the top)
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