Grinding teeth,
the proverbial milling of stone... Also as in learning the ropes, or training oneself, learning the hard way, et cetera.
I think the desired term is "to cut one's teeth on." It refers to how babies' teeth are aided in erupting from the gums by chewing on something tough. "Grinding one's teeth" is used to indicate being under an unpleasant level of stress.
I certainly ground my teeth while using Slackware in the 90s too, which is why I switched to Mandrake and then FreeBSD. :P