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On an Ubuntu or Debian VPS, install Java with APT by updating the package index, choosing either a runtime (JRE) or development kit (JDK), installing the package, and checking the resulting binaries. A typical runtime-only installation is sudo apt update followed by sudo apt install default-jre. A server that compiles code or runs build tools needs sudo apt install default-jdk instead.
If the application requires a particular Java major version, use the versioned OpenJDK package available in the VPS repositories, such as sudo apt install openjdk-21-jdk. Verify with java -version, and use Debian’s alternatives tools when more than one Java installation is present.
What you need before installing
You need SSH access to the VPS, an account allowed to run commands with sudo, and a working network path to the configured Ubuntu or Debian repositories. APT installs distribution packages, so the package names and the Java version selected by a generic package such as default-jdk depend on the operating-system release and, in some cases, the CPU architecture.
Identify the distribution and release
Run this command over SSH:
cat /etc/os-releaseRead the NAME, VERSION_ID, and release codename fields. Do not assume that instructions for one Ubuntu or Debian release apply unchanged to another; the release controls which OpenJDK packages are in the archive and which package a dependency such as default-jdk resolves to.
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Check the architecture
Use both the Debian package architecture and the kernel’s machine name when diagnosing package availability:
dpkg --print-architecture
uname -mDebian notes that the default-jdk dependency can vary by architecture and release. This check is especially important when automating installation across VPS images with different CPU types.
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Run:
sudo apt updateAPT is the recommended command-line tool for installing Debian packages on Ubuntu and Debian systems. This command downloads current package metadata; it does not install Java by itself. Wait for it to finish and check for repository errors before proceeding. If the command reports an unreachable repository, an invalid release entry, or a signature problem, fix that repository configuration first. Installing against an old index is a common reason for an apparently missing package.
Choose the right Java package
Java packages differ by purpose. Choosing the smallest package that meets the workload avoids installing a compiler and graphical dependencies on a service that only needs to start an existing application.
Runtime only: JRE
For a VPS that only runs an already-built Java application, install the release-default runtime:
sudo apt install default-jreA JRE supplies the java launcher and the libraries needed to run Java programs. It does not provide the Java compiler. A versioned alternative follows the pattern:
sudo apt install openjdk-<version>-jreReplace the version with a package that actually exists in the VPS’s repositories. Check availability before putting a versioned name in an automation script.
Development kit: JDK
Install a JDK when the server must compile source code, execute a build, or provide tools such as javac:
sudo apt install default-jdkThe JDK includes the runtime plus development tooling. A version-pinned form is:
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sudo apt install openjdk-<version>-jdkFor example, Ubuntu’s current developer guidance uses:
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sudo apt install openjdk-21-jdkPinning a major line is useful when an application or build system is certified for that line. APT can then continue to receive the distribution’s updates for that package line.
Headless packages for non-GUI services
A daemon that never creates windows may use the distribution’s headless JRE or JDK variant. Debian defines headless packages as omitting graphical interfaces. This can reduce unnecessary dependencies on a minimal VPS. Before installing, search the repository for the matching headless package and confirm that the application does not require AWT, Swing, JavaFX, or another graphical component:
apt search openjdkSelect the headless variant corresponding to the Java major version and whether you need a JRE or JDK. A GUI-dependent Java application needs the non-headless libraries it uses.
Package decision table
| Workload | Package pattern | Result |
|---|---|---|
| Run an existing Java application | default-jre or openjdk-<version>-jre |
Runtime without the compiler |
| Compile Java or run build tools | default-jdk or openjdk-<version>-jdk |
Runtime, compiler, and development tools |
| Run a non-GUI service | Distribution headless JRE or JDK variant | Java without graphical interfaces |
| Support software locked to a Java major line | Versioned openjdk-<version>-jre or -jdk |
APT-managed updates within that major line |
Understand what “default” means
default-jre and default-jdk are release-level package names, not permanent promises about one Java major version. Their dependencies are chosen by the Ubuntu or Debian archive for the release and architecture configured on the VPS. A command copied from a different image can therefore install a different major version even though the command text is identical.
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apt-cache policy default-jdk
apt-cache depends default-jdk
apt search openjdkapt-cache policy shows the candidate available from configured repositories, while apt-cache depends exposes the dependency that leads to a particular OpenJDK line. apt search lists package names visible to the current release; it is safer than guessing whether a versioned JRE, JDK, or headless variant exists.
Install Java step by step
Install the default runtime
- Refresh metadata:
sudo apt update. - Install the runtime:
sudo apt install default-jre. - When APT displays the proposed packages and disk-space change, review them and confirm with
Ywhen they match the intended workload. - Continue to the verification commands below.
Install the default development kit
- Refresh metadata if the index is not current:
sudo apt update. - Install the kit:
sudo apt install default-jdk. - Confirm the transaction after reviewing APT’s dependency list.
- Verify both
javaandjavac.
Install a specific OpenJDK line
- List versions visible to APT with
apt search openjdkor inspect the candidate for a generic package withapt-cache policy default-jdk. - Install the required version, for example
sudo apt install openjdk-21-jdk. - If the workload only runs programs, choose the corresponding versioned JRE instead of the JDK.
- Verify the selected major version after installation.
Ubuntu’s archive provides supported OpenJDK packages for supported LTS releases. Ubuntu 24.04 LTS documentation identifies OpenJDK 17 and 21 as TCK-certified on that release and uses openjdk-21-jdk as its current-LTS example. Certification and package availability still depend on the Ubuntu release and architecture installed on the VPS.
Verify the installation
Check the runtime
Run:
java -versionThe output should identify an OpenJDK runtime and its major version. This confirms that the shell can find the java executable through the system alternatives path.
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Check the compiler when a JDK is installed
javac -versionIf java -version succeeds but javac -version returns “command not found,” the VPS has a runtime but not a JDK (or the compiler is not on the active alternatives path). Install the matching JDK package if the server must compile code.
Inspect what APT will install
Before changing an automated image, inspect the candidate package and its dependencies:
apt-cache policy default-jdk
apt-cache depends default-jdkThese commands show the repository candidate and dependency relationships for the release currently configured. They are useful for confirming which Java line a generic package selects instead of assuming that “default” means the same version on every distribution.
Ubuntu and Debian defaults are not identical
Use the distribution’s release data when deciding between a generic package and a versioned one.
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| Distribution context | Documented default or guidance | Practical implication |
|---|---|---|
| Ubuntu supported LTS releases | The Ubuntu Archive provides supported OpenJDK LTS packages. | Use default-jre/default-jdk for the release default, or a versioned package when the application requires a specific line. |
| Ubuntu 24.04 LTS | OpenJDK 17 and 21 are TCK-certified; the current-LTS example is openjdk-21-jdk. |
Confirm the repository candidate on the actual image before pinning 21 in automation. |
| Debian 12 (Bookworm) | OpenJDK 17 is recorded as the default. | default-jdk normally follows the Bookworm default, subject to architecture and repository state. |
| Debian 11 (Bullseye) | OpenJDK 11 is recorded as the default. | Do not assume a Debian 11 VPS will resolve default-jdk to the same major version as Debian 12 or Ubuntu. |
Debian explicitly warns that defaults can differ by architecture. For repeatable provisioning, record the operating-system release, architecture, and package candidate together rather than documenting only the word “Java.”
Make an automated installation repeatable
A provisioning script should discover the image before selecting a package. Capture cat /etc/os-release and dpkg --print-architecture, refresh the index, and then inspect the candidate or search results. This prevents a script written for Debian 12 from silently assuming the same default on Debian 11, Ubuntu, or another architecture.
Choose one policy and document it. A release-default policy uses default-jre or default-jdk and follows the distribution’s selected line. A compatibility policy names a versioned package such as openjdk-21-jdk and fails early if that package is not available. Do not substitute a different major version merely because it happens to be present; verify that the application supports it first.
Keep the package family consistent in the same provisioning step. If the server compiles code, install the JDK rather than installing a JRE first and adding tools later. If it only runs a daemon, use the JRE or headless variant that matches its requirements. After installation, run both version checks that matter to the workload and record their output.
Switch between multiple Java installations
Installing a second major version does not necessarily remove the first. Debian manages Java commands through the alternatives system. Do not replace /usr/bin/java by hand; doing so bypasses the package manager and can leave the runtime and compiler pointing at different installations.
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See the available Java environments
sudo update-java-alternatives --listThis lists Java environments known to Debian’s java-common tooling.
Select the active command interactively
To choose the active runtime from the installed alternatives, run:
sudo update-alternatives --config javaSelect the path associated with the required installation at the prompt, then confirm it:
java -versionIf a build uses the compiler, configure its alternative as well:
sudo update-alternatives --config javac
javac -versionWhen the runtime and compiler must move together, Debian documents update-java-alternatives as the way to update Java alternatives as a group. This avoids a situation in which java uses one major version while javac uses another.
Troubleshoot common APT and Java failures
“Unable to locate package”
The error usually indicates one of four conditions: the local package index is stale, the repository component is unavailable, the requested version is not built for the VPS architecture, or the package name does not exist for that release.
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- Run
sudo apt updateand read the complete output for repository errors. - Check the generic package candidate with
apt-cache policy default-jdk. - Search names available to the release with
apt search openjdk. - Compare the requested package with
cat /etc/os-releaseanddpkg --print-architecture. - Use the release’s available package name instead of forcing a version that the repository does not provide.
The package installs, but the wrong major version is active
Inspect the installed environments with sudo update-java-alternatives --list, then select the required runtime through sudo update-alternatives --config java. Recheck java -version after the change. If the application invokes the compiler, configure javac separately or switch the complete Java environment with the Debian Java alternatives tooling.
java works but javac is missing
This is the expected symptom when only a JRE was installed. Install the matching default-jdk or versioned openjdk-<version>-jdk package, then run javac -version again.
A graphical application fails on a headless installation
A headless package intentionally omits graphical interfaces. If the program requires GUI libraries, install the corresponding non-headless JRE or JDK package. Keep a headless package for a true server daemon that has no graphical dependency.
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APT repositories and manually extracted Java are mixed
Keep the Java source consistent where possible. Ubuntu and Debian repository packages receive distribution-managed updates and integrate with the alternatives system. Adding a manually extracted Oracle tarball beside APT packages complicates upgrades, path selection, and security maintenance. If a vendor mandates a non-APT distribution, document that exception separately rather than silently mixing it with the repository-managed installation.
After installation: make the VPS predictable
- Record the output of
java -version, the operating-system release, anddpkg --print-architecturein the deployment notes. - Use a versioned OpenJDK package when the application contract names a major Java line; otherwise use the release-default package so normal distribution updates can move it with the operating system.
- For build servers, verify both
javaandjavacin the same provisioning step. - For production daemons, confirm whether the software needs graphical libraries before selecting a headless package.
- When more than one version is installed, manage it through alternatives commands and never edit the system
/usr/bin/javasymlink manually. - Keep the repository source consistent across the server image so upgrades, alternatives selection, and package ownership remain understandable.
Complete command checklist
The following compact sequence covers the usual JDK installation on an Ubuntu or Debian VPS:
cat /etc/os-release
dpkg --print-architecture
sudo apt update
sudo apt install default-jdk
java -version
javac -versionFor a runtime-only server, replace the installation line with sudo apt install default-jre. For a pinned Java 21 development environment where that package is available, use sudo apt install openjdk-21-jdk. If several versions are installed, finish with sudo update-java-alternatives --list and the appropriate alternatives selection command.
Frequently Asked Questions
Should I install a JRE or a JDK on my VPS?
Install default-jre when the VPS only runs an already-built Java application. Install default-jdk when it must compile source code, run a build, or provide javac and other development tools.
What does default-jdk install?
It follows the Java development kit selected by the configured Ubuntu or Debian release and architecture. Check it with apt-cache policy default-jdk and apt-cache depends default-jdk instead of assuming it always means the same major version.
How do I install Java 21 specifically?
First confirm that the VPS repositories provide the package, then run sudo apt install openjdk-21-jdk. Use the corresponding versioned JRE if the server only runs applications, and verify with java -version.
Why does APT say “Unable to locate package”?
Refresh metadata with sudo apt update, inspect repository errors, search with apt search openjdk, and check the release and architecture with cat /etc/os-release and dpkg --print-architecture. The requested package may not exist for that release or architecture.
Why does java work but javac not exist?
A JRE is installed, or the compiler is not selected. Install the matching default or versioned JDK and run javac -version. If several JDKs are installed, configure the compiler with sudo update-alternatives --config javac.
Can I use a headless Java package on a VPS?
Yes, for a non-GUI service that does not require graphical interfaces. Debian’s headless packages omit those interfaces. A program using AWT, Swing, JavaFX, or another GUI dependency needs the corresponding non-headless package.
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How do I change the active Java version?
List environments with sudo update-java-alternatives --list, select the runtime with sudo update-alternatives --config java, and select javac separately when needed. Debian also provides update-java-alternatives to update a Java environment as a group.
Should I mix an Oracle tarball with APT OpenJDK packages?
Avoid mixing sources unless a vendor specifically requires it. Distribution packages receive Ubuntu or Debian managed updates and integrate with alternatives; manually extracted files make upgrades and path selection harder to manage.
The Bottom Line
Identify the VPS release and architecture, run sudo apt update, install the smallest suitable package—default-jre, default-jdk, or an available versioned/headless OpenJDK package—then verify with java -version and, for a JDK, javac -version. Use the alternatives system rather than editing Java symlinks when multiple versions are installed.
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