On Linux low entropy can cause certain operations to be very slow.

SSL operations need entropy to ensure randomness. Entropy is generated by the OS when you use the keyboard, the mouse or the disk.

If an SSL operation is missing entropy it will wait until enough is generated.

If your server is running with a display manager (Graphical Mode) you can use the mouse intensely for a moment and enough entropy should be generated. But if you are running in console mode it can take a while before enough is generated.

I have waited 10+ minutes for the initial start of the Node Manager on a powerful Blade without any load.

I recently got annoyed by waiting 5+ minutes every time I logged into the Weblogic Admin Console so I decided to try the workaround Oracle suggest.

I did some testing and now it only takes seconds.

I added the Java parameter to setDomainEnv.sh:

if [ "${USER_MEM_ARGS}" != "" ] ; then
        MEM_ARGS="${USER_MEM_ARGS}
        export MEM_ARGS
fi
MEM_ARGS="${MEM_ARGS} -Djava.security.egd=file:/dev/./urandom"

This solution can of cause not be used for production servers.

On production servers I sometimes uses dd to generated a lot of disk activity to get the ball rolling:

dd if=/dev/zero of=filename.iso bs=1G count=50

You can also use the urandom parameter when you configure a new domain.

For example:

export CONFIG_JVM_ARGS="-Djava.security.egd=file:/dev/./urandom"
/u01/app/oracle/product/fmw/wlserver_12.1/common/bin/config.sh

You can see how much entropy is available via:

cat /proc/sys/kernel/random/entropy_avail

Or use watch if you want to display it every second:

watch -n 1 cat /proc/sys/kernel/random/entropy_avail

When I did my testing I needed to drain the server for entropy so the tests were comparable.
I used this script.

Update
Thanks to Jacco H. Landlust for pointing out that you can also change how Java gets the needed entropy via:
$JAVA_HOME/jre/lib/security/java.security

Here you can set:
securerandom.source=file:/dev/./urandom

I also just found this tip. If you urgently need extra entropy you can use the rngd command:
rngd -r /dev/urandom -o /dev/random -b

It’s from the rng-utils package this is installed by default on the servers I have tested on.