I use Jenkins a lot at work. We have quite an expansive setup; tens of agents and hundreds of jobs. We run specific jobs on specific agents based on labels. For a while we had some labels show up on our Labels Dashboard that we’re listed as having no Jobs, but one slave; a “ghost” slave. However when going into the page of the specific label the agent/slave was not showing anything. 

After some investigating with some Groovy script through the console I found there exists a slave in the configuration without a computer. To remove it (and resolve my label issues) I ran the following script:

for (slave in Jenkins.instance.slaves) {
  if (slave.getComputer() == null) {
    println(slave)
    Computer computer = slave.createComputer();
    computer.setTemporarilyOffline(true,null);
    computer.doDoDelete();
  }
}