N = put it in foreground
C = don't catch fatal signals
d = set debug level (3 is the level)
It threw a bunch of messages with the last line was File size limit exceeded. Just like this but I got no core dumped!. With no clue how to solve it, I recompiled squid (2.6-stable17) with extra parameters (with-max-fd=8192 and --with-large-files):
./configure --prefix=/usr --sysconfdir=/etc --localstatedir=/var --enable-icmp --enable-kill-parent-hack --enable-ssl --enable-linux-netfilter --enable-large-cache-files --enable-follow-x-forwarded-for --with-large-files
It solved it. Shane reported here that this happens when file store.log is bigger that 2 GB. Disabling the use of store.log (or other relevant files for that matter) will get rid of this problem.