Software aging

In software engineering, software aging refers to all software's tendency to fail, or cause a system failure after running continuously for a certain time. As the software gets older it becomes less immune and will eventually stop functioning as it should, therefore rebooting or reinstalling the software can be seen as a short term fix. A proactive fault management method to deal with the software aging incident is software rejuvenation. This method can be classified as an environment diversity technique that usually is implemented through software rejuvenation agents (SRA).

From both an academic and industrial point of view, the software aging phenomenon has increased. The main focus has been to understand its effects from a verifiable observation and theoretical understanding.

"Programs, like people, get old. We can't prevent aging, but we can understand its causes, take steps to limit its effects, temporarily reverse some of the damage it has caused, and prepare for the day when the software is no longer viable."

Memory bloating and leaking, along with data corruption and unreleased file-locks are particular causes of software aging.

Software failures are a more likely cause of unplanned systems outages compared to hardware failures. This is because software exhibits over time an increasing failure rate due to data corruption, numerical error accumulation and unlimited resource consumption. In widely used and specialized software, a common action to clear a problem is rebooting because aging occurs due to the complexity of software which is never free of errors. It is almost impossible to fully verify that a piece of software is bug-free. Even high-profile software such as Windows and Mac OSX must receive continual updates to improve performance and fix bugs. Software development tends to be driven by the need to meet release deadlines rather than to ensure long-term reliability. Designing software that can be immune to aging is difficult. Not all software will age at the same rate as some users use the system more intensively than others.

To prevent crashes or degradation a software rejuvenation can be employed proactively as inevitably aging leads to failures in software systems. This happens by removing the accumulated error condition and freeing up system resources, some examples to clean the internal state of the software are to flush operating system kernel tables, garbage collection, reinitialize internal data structures and a well known example of rejuvenation is a system reboot.

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