Unsupervised Anomaly Detection on system metrics like memory, cpu, io, net, etc
Do you have sequence data about these metrics? E.g. do they evolve over time and you want to locate anomalies in these sequences?

If so, you can have a look at the tools described here: 


  https://github.com/rob-med/awesome-TS-anomaly-detection


They are all unsupervised methods, so you don't need anomaly-free data for training.

If you are not dealing with time-series, there are also many unsupervised approaches you can take. This paper offers a good survey on the topic


  https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0152173