Debian linux Tomcat 8 fresh install not responding on port 8080

Question

I've encountered this issue twice recently, in Debian 9 as well as Ubuntu 16.04 LTS.

After a fresh install of the OS with just Tomcat 8 and openjdk 8 (no changes to the default config), after a few restarts the Tomcat server stops responding on port 8080.

The server is still listening on the port, but even a simple GET / just hangs forever:

# netstat -an|grep 8080
tcp6       0      0 :::8080                 :::*                    LISTEN

# wget http://127.0.0.1:8080/
--2017-11-03 13:19:52--  http://127.0.0.1:8080/
Connecting to 127.0.0.1:8080... connected.
HTTP request sent, awaiting response...

According to the thread dump Tomcat appears to be hanging on startup:

"localhost-startStop-1" #14 daemon prio=5 os_prio=0 tid=0x00000000018a1000 nid=0x68d8 runnable [0x00007f2badacd000]
   java.lang.Thread.State: RUNNABLE
        at java.io.FileInputStream.readBytes(Native Method)
        at java.io.FileInputStream.read(FileInputStream.java:255)
        at sun.security.provider.SeedGenerator$URLSeedGenerator.getSeedBytes(SeedGenerator.java:539)
        at sun.security.provider.SeedGenerator.generateSeed(SeedGenerator.java:144)
        at sun.security.provider.SecureRandom$SeederHolder.<clinit>(SecureRandom.java:203)
        at sun.security.provider.SecureRandom.engineNextBytes(SecureRandom.java:221)
        - locked <0x00000000f99155c0> (a sun.security.provider.SecureRandom)
        at java.security.SecureRandom.nextBytes(SecureRandom.java:468)
        at java.security.SecureRandom.next(SecureRandom.java:491)
        at java.util.Random.nextInt(Random.java:329)
        at org.apache.catalina.util.SessionIdGeneratorBase.createSecureRandom(SessionIdGeneratorBase.java:237)
        at org.apache.catalina.util.SessionIdGeneratorBase.getRandomBytes(SessionIdGeneratorBase.java:174)
        at org.apache.catalina.util.StandardSessionIdGenerator.generateSessionId(StandardSessionIdGenerator.java:34)
        at org.apache.catalina.util.SessionIdGeneratorBase.generateSessionId(SessionIdGeneratorBase.java:167)
        at org.apache.catalina.util.SessionIdGeneratorBase.startInternal(SessionIdGeneratorBase.java:256)
        at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:147)
        - locked <0x00000000f9905808> (a org.apache.catalina.util.StandardSessionIdGenerator)

Why is this happening and how to fix it?

Answer 1

OpenJDK 8 on Debian-based distros comes with /dev/random preconfigured as the source of entropy.

When there isn't enough entropy, /dev/random will block.

Solution 1: (preferred)

Install haveged , it's a daemon that generates additional entropy.

Solution 2: (probably less secure)

Change /usr/lib/jvm/default-java/jre/lib/security/java.security to use /dev/urandom instead:

#securerandom.source=file:/dev/random
securerandom.source=file:/dev/./urandom

That will apply globally to all Java processes.

Alternatively, add -Djava.security.egd=file:/dev/./urandom to JAVA_OPTS in /etc/default/tomcat8 (will apply to Tomcat processes only).