Errors: Too many open files

During busy hours, Postgres and Apache are reporting
errors that there are too many open files, and sometimes
Postgres will crash. I've searched all over for a way
to increase this resource limit.
I have tried:

ulimit -n 8192
(seems only to work for the current shell session)

echo "8192" > /proc/sys/fs/file-max
(did not seem to make a difference)

adding this entry to /etc/security/limits.conf:
postgres        hard    nofile          4096
(did not seem to make a difference)

I have read the Postgres Administration docs
"3.5.2 Resource Limits" but I am still unable to find
the solution.

Can anybody tell me how to increase the resource allocation,
and exactly where to make this change?

Any help would be greatly appreciated,
_Ken Creason
webmaster@fcs.net