ReFrame crashes when trying to autodetect topology and does not have write permissions in `config/_meta`

[teojgo]

This is triggered when ReFrame is installed with e.g EasyBuild system-wide, since at the first execution ReFrame tries to create config/_meta if this is not already there.

[vkarak]

I suggest always user's $HOME to store the metadata then. It's the safest way. This issue is quite important, because it can render unusable system-wide deployments of ReFrame.