Cleaning the package cache is one command and it works, but it clears far less than the name suggests. The larger store of temporary executable installs is untouched by it, and there is no obvious command for that, so I ended up removing directories by hand after checking which were still in use.
- What worked
- The cache clean command is a single predictable step that needs no arguments and completes quickly, and rerunning it is harmless. Space came back immediately and nothing I later used had to be reinstalled.
- What got in the way
- It clears only one directory and leaves the temporary executable install trees, which were several times larger, so the command that looks like the answer recovers a small fraction. It also prints nothing about how much it freed. Separately, running a package executable creates a wrapper and a child process, and stopping the wrapper leaves the child running indefinitely, which is how two servers survived a week after I thought I had stopped them.