gcc has been defaulted to use ccache, apparently from F17 onward. This was presumably on the basis that it was a transparent change. However it isn't transparent, at least in my case: 1. We do a lot of run-time compilation and linking (genetic programming systems, if you're interested why). We first discovered there was a problem when we started filling up filesystems with useless ccaches. 2. On our cluster, home directories are cross-mounted. So ccaches being written by default to /home unnecessarily chew up network bandwidth. Both are fixable. But they shouldn't need fixing. ccache is a great idea, by all means encourage its use. But not to the extent of creating non-transparent default changes. This is the kind of change that fedora users expect to have to swallow. But it will cause a lot of heartburn if it goes into RHEL (where a lot of installations will face large challenges in chasing down these issues).
gcc doesn't default to ccache in any way, only if you install ccache, it will add itself to PATH earlier. So, don't install ccache if you don't want to use it.
Thanks for the explanation, Jakub. Unfortunately I'm not sure, though, that I or others can use it. It's pretty clear that the problems I'm having will bite others too (even if they don't realise yet - and perhaps won't unless/until it goes into RHEL). The basic issue is that there has been a regression: things which used to work now don't (and rather worse than don't work, users can inadvertently cause system hangs when /home fills up with unexpected cache files). I'm not installing ccache explicitly. It's coming as part of development-tools (perhaps it wasn't up to Fedora 16). Of course, I do need development-tools on a research cluster (and others with clusters or large-scale workstation deployments will too). Anyone like me doing automated installs can't simply remove ccache after the install, we need it not to be automatically activated in the first place. But equally important "don't install ccache if you don't want to use it." is really only suitable advice for single-user machines. It's not a suitable distribution policy. The need for ccache may vary from user to user, or from project to project. Up to Fedora 16, ccache wasn't causing problems (perhaps because it wasn't getting installed). Now in Fedora 17 it does. This is a regression. It results from the interaction of two defaults: that ccache is installed as part of development-tools, and that it installs itself in the path ahead of gcc. Personally, I think the latter is the mistake: since ccache isn't transparent, it should require user action to activate it. This is a decision that only the individual user has the information to make: it is not, and should not be, a system-level decision.
For anyone else hitting this problem, the kickstart structure that may be helpful is: %packages ... @development-tools ... -ccache ... %end (not yet verified, but I assume it will work).
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