Set or Change Hostname (via the GUI)

• Open System Preferences
• Select Sharing
  Select the Edit button and enter your desired Local Hostname and click OK
  

Note:  If the Edit button is greyed out, click on the Lock Icon, authenticate with an admin account

To temporarily change the Hostname of your device via the terminal 

Set or Change Hostname (via Terminal) - OS X Mavericks or newer

...

sudo hostname -s new_hostname
For example:  sudo hostname -s ECE-MAC

To permanently change the Hostname of your device via the terminal

Set or Change Hostname (via Terminal) - OS X 10.6 - 10.8

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