Why this version of java?

Question

On my Red Hat server, java -version outputs;

$ java -version 
java version "1.6.0_27"
Java(TM) SE Runtime Environment (build 1.6.0_27-b07)
Java HotSpot(TM) 64-Bit Server VM (build 20.2-b06, mixed mode)
$

However, neither PATH, nor JAVA_HOME environment variables are set. Likewise, JAVA_HOME is not set on ~/.bash* files.

Why and how my server uses this version of Java while two other versions of Java are installed as well?

check which java executable you're running (which java) and then check if it's a symlink. — BigMike, Jan 25 '13 at 09:52
Your version of RedHat might be using the 'alternatives' mechanism. Try running `/usr/sbin/alternatives --config java` — Zutty, Jan 25 '13 at 09:54
`However, neither PATH, nor JAVA_HOME environment variables are set` Are you sure that `PATH` is not set at all? That would be strange — Andreas Fester, Jan 25 '13 at 09:54
try `which java` and I suspect it will give you `/usr/bin/java` which will be in your PATH — Peter Lawrey, Jan 25 '13 at 09:57
PATH is set, but JAVA_HOME is not added to PATH. "PATH=$PATH:$HOME/bin" — Yiğit, Jan 25 '13 at 09:57
@Yiğit okay now check if java executable is a symlink (probably to something like /opt/java/default which is also a symlink to the actual version of java you're running) — BigMike, Jan 25 '13 at 10:04
ls -l /usr/bin/java : lrwxrwxrwx 1 root root 26 Dec 21 19:55 /usr/bin/java -> /usr/java/default/bin/java — Yiğit, Jan 25 '13 at 12:27
Mike, it seems I have a symlink. It directs /usr/java/default/bin/java, not an installed jdk directory. — Yiğit, Jan 25 '13 at 14:33

Stephen C · Answer 1 · 2013-01-25T10:36:27.583

Firstly, JAVA_HOME is not involved in this. (JAVA_HOME is used conventionally by wrapper scripts, etc for applications that use Java ... but not by any of the Java executables themselves.)

Second, you are probably running java via a symlink managed by the alternatives program. (RHEL and similar distros use this utility to allow you to select different versions of utilities installed on the same system.)

Either way, running the following will help you figure out what is going on.

$ ls -l `which java`

(Then following the chain of symlinks until you get to the actual executable.)

score 0 · Answer 2 · answered Jan 25 '13 at 09:54

Which executable runs depends on PATH variable. Double check it. It can't run if not set it is impossible unless you have some strange Linux config.

If Java executable is in current directory, it would run by ./java. Since it runs with just java it is somewhere in the PATH.

Why this version of java?

2 Answers2