Installing Java on Ubuntu

Accurate as of: Java 7, Ubuntu 12.04. The instructions below assume an amd64 +(64-bit) installation. If you're still using a 32-bit OS, work out the +differences yourself.

Via Package Management (Apt)

OpenJDK 7 is available via apt by default.

To install the JDK:

sudo aptitude update
+sudo aptitude install openjdk-7-jdk
+

To install the JRE only (without the JDK):

sudo aptitude update
+sudo aptitude install openjdk-7-jre
+

To install the JRE without GUI support (appropriate for headless servers):

sudo aptitude update
+sudo aptitude install openjdk-7-jre-headless
+

(You can also use apt-get instead of aptitude.)

These packages interact with the alternatives +system, +and have a dedicated alternatives manager +script. +The alternatives system affects /usr/bin/java, /usr/bin/javac, and +browser plugins for applets and Java Web Start applications for browsers +installed via package management. It also affects the symlinks under +/etc/alternatives related to Java.

To list Java versions available, with at least one Java version installed via +Apt:

update-java-alternatives --list
+

To switch to java-1.7.0-openjdk-amd64 for all Java invocations:

update-java-alternatives --set java-1.7.0-openjdk-amd64
+

The value should be taken from the first column of the --list output.

Tool support

Most modern Java tools will pick up the installed JDK via $PATH and do not +need the JAVA_HOME environment variable set explicitly. For applications old +enough not to be able to detect the JDK, you can set JAVA_HOME to +/usr/lib/jvm/java-1.7.0-openjdk-amd64.

By Hand

The Java SE Development Kit +7 +tarballs can be installed by hand. Download the “Linux x64” .tar.gz version, +then unpack it in /opt:

cd /opt
+tar xzf ~/jdk-7u45-linux-x64.tar.gz
+

This will create a directory named /opt/jdk1.7.0_45 (actual version number +may vary) containing a ready-to-use Java dev kit.

You will need to add the JDK's bin directory to PATH if you want commands +like javac and java to work without fully-qualifying the directory:

cat > /etc/profile.d/oracle_jdk <<'ORACLE_JDK'
+PATH="${PATH}:/opt/jdk1.7.0_45/bin"
+export PATH
+ORACLE_JDK
+

(This will not affect non-interactive use; setting PATH for non-interactive +programs like build servers is beyond the scope of this document. Learn to use +your OS.)

Installation this way does not interact with the alternatives system (but +you can set that up by hand if you need to).

For tools that cannot autodetect the JDK via PATH, you may need to set +JAVA_HOME to /opt/jdk1.7.0_45.

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