anchor.diff:  And then start the agent:
   
   ```shell
  -# Ubuntu 15.04+ (systemd)
   sudo systemctl enable buildkite-agent && sudo systemctl start buildkite-agent
  -
  -# Older Ubuntu (upstart)
  -sudo service buildkite-agent start
   ```
   
   You can view the logs at:
   
   ```shell
  -# Ubuntu 15.04+ (systemd)
   journalctl -f -u buildkite-agent
  -
  -# Older Ubuntu (upstart)
  -tail -f /var/log/upstart/buildkite-agent.log
   ```
   
   ## SSH Key Configuration
  
positive.code: 
  # Or one-by-one
  sudo journalctl -f -u buildkite-agent@2
  
  # For older Ubuntu (using upstart)
  sudo cp /etc/init/buildkite-agent.conf /etc/init/buildkite-agent-2.conf
  sudo service buildkite-agent-2 start
  sudo tail -f /var/log/upstart/buildkite-agent-2.log
  ```
  
  ## Upgrading
  
negative.code: You can run as many parallel agents on the one machine as you wish by duplicating the upstart service configuration file, for example:
  
  ```shell
  # Disable the default unit
  sudo systemctl stop buildkite-agent && sudo systemctl disable buildkite-agent
  
  