Increase Entropy

Checking entropy level

A lack of entropy can cause random number generation to be extremely slow. This results in tasks like ssh to also be extremely slow. One can check the available entropy on a machine by running the command:

cat /proc/sys/kernel/random/entropy_avail

It should be a value above 2000.

If you are installing Apache Brooklyn on a virtual machine, you may find that it has insufficient entropy. You may need to increase the Linux kernel entropy in order to speed up the ssh connections to the managed entities. You can install and configure rng-tools, or just use /dev/urandom`.

Installing rng-tool

If you are using a RHEL 6 based OS:

sudo -i
yum -y -q install rng-tools
echo "EXTRAOPTIONS=\"-r /dev/urandom\"" | cat >> /etc/sysconfig/rngd
/etc/init.d/rngd start

If you are using a RHEL 7 or a systemd based system:

sudo yum -y -q install rng-tools

# Configure rng to use /dev/urandom
# Change the "ExecStart" line to:
# ExecStart=/sbin/rngd -f -r /dev/urandom
sudo vi /etc/systemd/system/

sudo systemctl daemon-reload
sudo systemctl start rngd

If you are using a Debian-based OS:

sudo -i
apt-get -y install rng-tools
echo "HRNGDEVICE=/dev/urandom" | cat >> /etc/default/rng-tools
/etc/init.d/rng-tools start

Using /dev/urandom

You can also just mv /dev/random then create it again linked to /dev/urandom:

sudo mv /dev/random /dev/random-real
sudo ln -s /dev/urandom /dev/random

Notice! If you map /dev/random to use /dev/urandom you will need to restart the Apache Brooklyn java process in order for the change to take place.

More Information

The following links contain further information: