Node.js and Cygwin: Unknown system errno 203

A recent Cygwin upgrade left me ripping my hair out, because none of my npm or grunt commands would work. They spat out the error

Unknown system errno 203

Helpful, right?

The fix

In your Cygwin ~/.bash_profile file (create it and chmod 755 .bash_profile if it doesn't exist):

export TMP=/tmp
export TEMP=$TMP

This did the trick for me. Special thanks to this github comment.