Jenkins not executing jobs (pending - waiting for next executor)

Jenkins won't execute any jobs. Having viewed this question, I have disabled all slave nodes but a simple job won't even run on the Master node.

What is wrong?

The Jenkins admin console can run, even with the Master node offline. This can happen when Jenkins runs out of disk space.

To confirm, do the following (with thanks to geekride - jenkins-pending-waiting-for-next-available-executor):

• go to Jenkins -> Manage Jenkins -> Manage Nodes
• examine the "master" node to see if it is offline. It may be reporting that the master node is out of disk space.