The hidden cost of Entropy to your business

On Linux OS, there are two (2) device drivers that provide entropy “noise” for components that require encryption, e.g. the /dev/random and the /dev/urandom device drivers. The /dev/random is a “blocking” device driver. When the “noise” is low, any component that relies on this driver will be “stalled” until enough entropy is returned. We can measure the entropy from a range of 0-4096. Where a value over 1000 is excellent. Any value in the double or single digits will impact the performance of the OS and solutions with delays. The root cause of these delays is not evident during troubleshooting, and typically there are no warning nor error messages related to entropy.

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

The Symantec Identity Suite solution, when deployed on Linux OS is typically deployed with the JVM switch for any component that uses Java (Oracle or AdoptOpenJDK), e.g. Wildfly (IM/IG/IP) and IAMCS (JCS). This JVM variable is sufficient for most use-cases to manage the encryption/hash needs of the solution.

However, for any component that does not provide a mechanism to use the alternative of /dev/urandom driver, the Linux OS vendors offer tools such as the “rng-tools” package. We can review what OS RNGD service is available using package tools, e.g.

dnf list installed | grep -i rng

If the Symantec Identity Suite or other solutions are deployed as standalone components, then we may adjust the Linux OS as we need with no restrictions to add the RNGD daemon as we wish. One favorite is the HAVEGED daemon over the default OS RNGD.

See prior notes on value and testing for Entropy on Linux OS (standalone deployments):

Challenge for vApp

The challenge for Virtual Appliances is that we are limited to what functionality the Symantec Product Team provides for us to leverage. The RNGD service was available on the vApp r14.3, but was disabled for OS challenges with 100% utilization with CentOS 6.4. The service is still installed, but the actual binary is non-executable.

A new Virtual Appliance patch would be required to re-enable this RNGD on vApp r14.3cp2. We have access via sudo, to /sbin/chkconfig, /sbin/service to re-enable this service, but as the binary is not executable, we cannot progress any further. We can see the alias in the documentation still exist, but the OS alias was removed in the cp2 update.

However, since vApp r14.4 was release, we can focus on this Virtual Appliance which is running Centos 8 stream. The RNGD service here is disabled (masked) but can be re-enabled for our use with the sudo command. There is no current documented method for RNGD on vApp r14.4 at this time, but the steps below will show an approved way using the ‘config’ userID and sudo commands.

Confirm that the “rng-tools” package is installed and that the RNGD binary is executable. We can also see that the RNGD service is “masked”. Masked services are prevented from starting manually or automatically as an extra safety measure when we wish for tighter control over our systems.

If we test OS entropy for this vApp r14.4 server without RNGD, we can monitor how a simple BASH shell script that emulates a password being generated will impact the “entropy” of /dev/random. The below script will reduce the entropy to low numbers. This process will now impact the OS itself and any components that reference /dev/random. We can observe with “lsof /dev/random” that the java programs will still reference /dev/random; even though most activity is going to /dev/urandom.

Using the time command in the BASH shell script, we can see that the response is rapid for the first 20+ iterations, but as soon as the entropy is depleted, each execution is delayed by 10-30x times.

counter=1;MAX=100;while [ $counter -le $MAX ]; do echo "##########  $counter ##########" ; time dd if=/dev/random bs=8 count=1 2> /dev/null | base64; counter=$(( $counter + 1 )); done;

Enable RNGD on vApp r14.4 & Testing

Now let’s see what RNGD service will do for us when it is enabled. Let’s follow the steps below to unmask, enable, and start the RNGD service as the ‘config’ userID. We have access to sudo to the Centos 8 Stream command of /sbin/systemctl.

sudo /usr/bin/systemctl status rngd.service
ls -lart /etc/systemd/system/rngd.service
sudo /usr/bin/systemctl unmask rngd.service
sudo /usr/bin/systemctl enable rngd.service
cat /usr/lib/systemd/system/rngd.service
sudo /usr/bin/systemctl start rngd.service
sudo /usr/bin/systemctl status rngd.service
ps -ef | grep rngd | grep -v grep

After the RNGD service is enabled, test again with the same prior BASH shell script but bump the loops to 1000 or higher. Note using the time command we can see that each loop finishes within a fraction of a second.

counter=1;MAX=1000;while [ $counter -le $MAX ]; do echo "##########  $counter ##########" ; time dd if=/dev/random bs=8 count=1 2> /dev/null | base64; counter=$(( $counter + 1 )); done;


Aim to keep the solution footprint small and the right-sized to solve the business’ needs. Do not accept the default performance; avoid over-purchasing to scale to your expected growth.

Use the JVM switch wherever there is a java process, e.g. BLC or home-grown ETL (extract-transform-load) processes.

If you suspect a dependence may impact the OS or other processes on /dev/random, then enable the OS RNGD and perform your testing. Monitor with the top command to ensure RNGD service is providing value and not impacting the solution.