source: postlfs/config/random.xml@ fe4403e5

<sect1 id="postlfs-config-random" xreflabel="random">
<?dbhtml filename="random.html" dir="postlfs"?>
<title>Random number generation</title>

<para>The Linux kernel supplies a random number generator which is accessed
through <filename>/dev/random</filename> and 
<filename>/dev/urandom</filename>.  Programs that utilize the random and
urandom devices, such as OpenSSH, will benefit from these instructions.</para>

<para>When a Linux system starts up without much operator interaction, the
entropy pool, data used to compute a random number, may be in a fairly
predictable state.  This creates the real possibility that the number generated
at startup may always be the same.  In order to counteract this effect,
you should carry the entropy pool information across your shut-downs and
start-ups. The following init.d script and links will perform this function
for you automatically.</para>

<para><screen><userinput>cat &gt; /etc/rc.d/init.d/random &lt;&lt; "EOF"
</userinput>
#!/bin/sh
# Begin $rc_base/init.d/random

# Based on sysklogd script from LFS-3.1 and earlier.
# Rewritten by Gerard Beekmans  - gerard@linuxfromscratch.org
# Random script elements by Larry Lawrence

source /etc/sysconfig/rc
source $rc_functions

case "$1" in
        start)
                echo "Initializing kernel random number generator..."
                if [ -f /var/tmp/random-seed ]; then
                        cat /var/tmp/random-seed >/dev/urandom
                fi
                dd if=/dev/urandom of=/var/tmp/random-seed count=1 &>/dev/null
                evaluate_retval
                ;;
                
        stop)
                echo "Saving random seed..."
                dd if=/dev/urandom of=/var/tmp/random-seed count=1 &>/dev/null
                evaluate_retval
                ;;

        *)
                echo "Usage: $0 {start|stop}"
                exit 1
                ;;
esac

# End $rc_base/init.d/random
<userinput>EOF
chmod 755 /etc/rc.d/init.d/random</userinput></screen></para>

<para>Create the symbolic links to this file in the relevant rc.d directories 
with the following commands:
<screen><userinput>cd /etc/rc.d/init.d &amp;&amp;
ln -sf ../init.d/random ../rc0.d/K45random &amp;&amp;
ln -sf ../init.d/random ../rc2.d/S25random &amp;&amp;
ln -sf ../init.d/random ../rc3.d/S25random &amp;&amp;
ln -sf ../init.d/random ../rc4.d/S25random &amp;&amp;
ln -sf ../init.d/random ../rc5.d/S25random &amp;&amp;
ln -sf ../init.d/random ../rc6.d/K45random</userinput></screen></para>


</sect1>