-bash: fork: Resource temporarily unavailable

Today my mac started acting a little slow, the hard disk was whirring away and when I wanted to fire up Activity Monitor to see what was going on it wouldn't load, nor would any other application that wasn't already running.

I had a terminal running, so I tried to see what was going on there and as soon as I tried to use 'ps aux' it said:

-bash: fork: Resource temporarily unavailable

I found a solution here. Basically the limit of processes for the kernel was reached and needed to be increased.

sudo sysctl -w kern.maxprocperuid=256

That unlocked the system so I could fire up Activity Monitor and find the culprit. An app went crazy and started to generate lots of processes which locked up my system. Once that app was gone, I didn't have any more issues.