/usr/lib/jvm/java-1.5.0-gcj-4.8-amd64/bin/jdb is in gcj-4.8-jdk 4.8.4-2ubuntu1~14.04.4.
This file is owned by root:root, with mode 0o755.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 | #!/bin/sh
# Placeholder script to fake a
# JDK compatible JAVA_HOME directory.
echo >&2 "This script is only a placeholder."
echo >&2 "Some programs need a JDK rather than only a JRE to work."
echo >&2 "They test for this tool to detect a JDK installation, but"
echo >&2 "don't really need its functionality to work correctly."
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