(2) The /proc filesystem is virtual filesystem specific to some Operating Systems, such as Linux and Solaris. The entries in there can be written to or read from depending on driver- and kernel-specific settings. If an application checks for /proc/net/ip_tables_name and finds it, it assumes that iptables has been installed. So in answer to your second question, the answer is: no script is responsible; it's done by the relevant module or kernel feature.

(1) If you type

Code:

lsmod |grep iptables

and see no output, then iptables is not installed. If it's not installed, you should not see /proc/net/ip_tables_name. Also grep for "ipchains" just in case you have an older version.