Tomcat 8.5.9 restart is really slow on my CentOS 7.2 droplet

Posted December 20, 2016 5.5k views
CentOSGetting Started

I’ve got tomcat 8.5.9 installed on a CentOS 7.2 droplet. When I restart tomcat, with only the tomcat manager in the webapps directory, restarts take anywhere from 3 to 15 minutes, and sometimes even longer. Has anyone seen such behavior? Top doesn’t show much CPU or memory being consumed by Java. We’re running OpenJDK 1.8.0_111. Normal restart times with no webapps is a couple of seconds on other systems.

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Slow start up times for Tomcat are often related to Java’s SecureRandom implementation. By default, it uses /dev/random as an entropy source. This can be slow as it uses system events to gather entropy (e.g. disk reads, key presses, etc). As the urandom manpage states:

When the entropy pool is empty, reads from /dev/random will block until additional environmental noise is gathered.

One work around is to use /dev/urandom instead as it does not block. This is defined in your JAVA_OPTS That can be set in a number of places depending on how you set up Tomcat in the first place. It will usually be the init script or systemd service file used to start Tomcat.

See this tutorial for more information.

Another option is to use haveged to generate more entropy. On CentOS, you can do so with:

  • yum install haveged
  • systemctl start haveged
  • systemctl enable haveged

For more information on how haveged works, check out this tutorial:

by Salvatore LaMendola
Entropy is important, and haveged is an application that can provide your system with more of it.