Perusing Redhat Kernel documentation is not going to be anyone's idea of a fun Saturday evening, and almost always reality is that if you need to know something you can always hit up google for the answer. However, you are not always going to have an internet connection and a web browser when troubleshooting a system, or taking a test, so its good to know how and where to access your local redhat kernel docs.

First you need to make sure that your kernel docs are installed.

#yum -y install kernel-doc

And you need to know where they are installed to, which in my case is… /usr/share/doc/kernel-doc-2.6.32. Within this directory is are a boat load of files and additonal directories, usually organized by subject or topic.

For example, can't remember how to configure your linux box to ignore ICMP requests, then chug on down to /usr/share/doc/kernel-doc-2.6.32/Documentation/networking/ip-sysctl.txt and take a look at the /proc/sys/net/ipv4/ varables.

icmp_echo_ignore_all – BOOLEAN
        If set non-zero, then the kernel will ignore all ICMP ECHO
        requests sent to it.
        Default: 0

icmp_echo_ignore_broadcasts – BOOLEAN
        If set non-zero, then the kernel will ignore all ICMP ECHO and
        TIMESTAMP requests sent to it via broadcast/multicast.
        Default: 1

Neet. Then you can cd over to /proc/sys/net/ipv4 and see these files in action. They will either contain a 1 or a 0.

Note that changes made in /proc/sys are not persistent across reboots, so you will need to add your tuning params to /etc/sysctl.conf as shown below. Note use usage of periods between directory names; net and ipv4.

#echo "net.ipv4.icmp_echo_ignore_broadcasts = 0" >> /etc/sysctl.conf

You can also make these changes take affect immediately by running

#sysctl -p

Ironically all your kernel docs are online and availible here – http://www.kernel.org/doc/Documentation/