A Scratch Monkey is a term used in hacker jargon, as in "Before testing or reconfiguring, always mount a scratch monkey", a proverb used to advise caution when dealing with irreplaceable data or devices. Used to refer to any temporary configuration changes to a computer during any risky operation which include a replacement for some precious resource or data that might otherwise be destroyed.
The meaning is based upon the use in the 1980s of a scratch tape, or other storage device which was available for temporary use, to temporarily store a copy of valuable data or provide extra storage space in case a program required that space. If a problem occurred the valuable data could be recovered from its sole remaining copy.
The phrase "always mount a scratch monkey" originated from two tales by technicians about maintenance which was performed on computer equipment. The technicians were unaware that the computer was connected to a laboratory monkey, and the routine maintenance procedures caused the death of the monkey. In one version, several monkeys were involved. The admonition is a reminder that procedures should protect everything of value, and the stories can be interpreted from the point of view of a computer technician and a laboratory worker.