Here's one I've not met before: I have an Apache (1.3.x) server doing SSL. The server has a read-only root partition and then read-write partitions for things like /home, /var, /tmp and so on. If Apache is started, all the https sites fail, return no data and say in the log "[notice] child pid 563 exit signal Segmentation fault (11)" or similar. If / is mounted read-write, Apache started, then / is remounted read-only, it works. I can't see any read-only directory being used in the httpd.conf - what's going on at startup that I'm missing?