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The reliable production method is to run the JAR as a systemd service under a dedicated, unprivileged account. First install the Java runtime your application requires, upload the artifact, run a manual smoke test, then create and enable a service so it starts after reboot, restarts after failures, and writes logs to the journal. A direct java -jar command is useful for testing, but a process attached to an SSH shell is not a durable service.
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What you need before deployment
Have these details ready before connecting to the VPS:
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- An SSH hostname or IP address, a login account, and the authentication method (key or password) accepted by the server.
- The Java release required by the JAR. A JAR built for a newer Java release will not run on an older runtime, and framework requirements may impose additional constraints.
- The local path to the built artifact, such as
build/libs/app.jar. - The port on which the application listens and whether it should bind to loopback only or to a public interface.
- Every required environment variable, secret, database connection, and external service address.
- Access to both the VPS provider’s network firewall and the Linux host firewall, if either is enabled.
Use a predictable application path, such as /opt/myapp, so service files, release procedures, permissions, and troubleshooting all refer to the same locations.
Choose how the JAR should run
The command itself is simple, but the way it is supervised determines whether the application survives logout, reboot, and a crash.
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| Approach | After SSH logout | After reboot | Restart policy | Logs | Best use |
|---|---|---|---|---|---|
Direct java -jar in SSH |
Stops when the shell closes | Does not start | Manual | Current terminal | First-run smoke test |
screen or tmux |
Session can remain available | Does not start unless recreated | Manual | Terminal/session | Temporary debugging |
systemd service |
Continues independently | Starts when enabled | Declarative, such as restart on failure | journald |
Standard single-VPS production deployment |
| Container or orchestrator | Depends on the runtime | Depends on the runtime configuration | Runtime-specific | Runtime-specific | Multi-service or repeatable infrastructure |
For one Spring Boot, Ktor, or similar JVM application on a Linux VPS, use the systemd path below. Keep screen or tmux for diagnosing a problem before the service exists, not as the permanent supervisor.
1. Connect over SSH and check the server
Connect with the account that will perform deployment. Replace the placeholder host and user with your values:
ssh user@your_serverConfirm that the account can use sudo for package installation and service administration. Also identify which firewalls apply. A provider-level rule can block traffic before it reaches the VPS, while the operating-system firewall can block it after it arrives. You may need to change both later.
Do not expose the application publicly just because the process starts. Test it on loopback first and open only the ports required by your architecture.
2. Install a compatible Java runtime
Install the runtime that matches the release used to build the JAR. On Debian or Ubuntu, a headless OpenJDK package is normally sufficient for a server process because it omits desktop components. The following example installs Java 17:
sudo apt update
sudo apt install openjdk-17-jre-headless -yPackage names and available versions differ by distribution. If the application requires another release, select the corresponding package instead of copying the Java 17 example. Verify the result:
java -versionCompare the reported major version with the application’s build configuration and framework requirements. If the manual launch later reports an unsupported class-file version, the runtime is too old for the JAR. If multiple Java installations are present, find the executable that the service should use:
which java
readlink -f $(which java)Use the resulting absolute path in the service unit. An interactive shell and systemd can have different PATH values, so relying on a bare java command in ExecStart can make a service fail even when it worked interactively.
3. Create a dedicated application account and directory
Do not run a network-facing Java application as root. A dedicated account limits the files and system actions available if the application or one of its dependencies is compromised.
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Create a system account and an application directory. The exact account-management flags vary slightly by distribution; this example uses common Debian and Ubuntu syntax:
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sudo useradd --system --home /opt/myapp --shell /usr/sbin/nologin myapp
sudo mkdir -p /opt/myapp
sudo chown -R myapp:myapp /opt/myappIf the account already exists, do not recreate it; ensure it owns the directories and files it must read or write. Grant access only where required. The service generally needs read access to the JAR and configuration, plus write access to specific upload, cache, temporary, or log directories if the application uses them. Avoid making the entire filesystem or broad shared directories writable.
Keep secrets separate from the JAR. A plain environment file is convenient, but it must be readable only by the service account or by root as appropriate for your operating model. Never put credentials in a world-readable directory or commit them to the application repository.
4. Upload the JAR
From your local computer, copy the artifact to the application directory. For example:
scp build/libs/app.jar user@your_server:/opt/myapp/app.jarThe upload account must be able to write the destination. If you copied as an administrative user, fix ownership before starting the service:
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sudo chown myapp:myapp /opt/myapp/app.jar
sudo chmod 0644 /opt/myapp/app.jarKeep release files in a predictable layout. A single stable path such as /opt/myapp/app.jar makes the service unit simple. If you retain several versions for rollback, place them in a controlled releases directory and update the stable path deliberately; do not leave the service pointing at a file that disappears during deployment.
Make configuration explicit. For non-secret settings, document the expected names and values. For secrets and environment-specific values, create an environment file, for example:
sudo install -o myapp -g myapp -m 0600 /dev/null /opt/myapp/app.envEdit that file with the variables your application expects. Do not assume that variables available in your interactive shell will be present in a systemd service.
5. Run a manual smoke test
Before adding supervision, prove that the artifact, runtime, working directory, configuration, and port are correct. Run the JAR as the service account:
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sudo -u myapp /usr/bin/java -jar /opt/myapp/app.jarUse the absolute Java path you verified earlier. Watch the startup output for a successful framework initialization, database connection errors, missing secrets, bind failures, or an incompatible Java version. Leave this command running while you test it from another SSH session, or stop it with Ctrl+C after the check.
Test a local endpoint from the VPS itself:
curl http://127.0.0.1:<port>/Replace <port> with the configured application port. A successful loopback response proves that the process is listening locally; it does not prove that provider or host firewall rules permit public traffic. If the endpoint fails, fix the application first rather than creating a service around a broken launch.
6. Create a systemd unit
Create /etc/systemd/system/myapp.service with a unit similar to this:
[Unit]
Description=My Java application
After=network.target
[Service]
Type=simple
User=myapp
WorkingDirectory=/opt/myapp
ExecStart=/usr/bin/java -jar /opt/myapp/app.jar
Restart=on-failure
RestartSec=5
EnvironmentFile=/opt/myapp/app.env
StandardOutput=journal
StandardError=journal
[Install]
WantedBy=multi-user.targetWrite the file with administrative privileges, then check each value:
- Description: A label shown by status and journal tools.
- After=network.target: Orders service startup after the basic network target. It does not guarantee that every remote dependency is ready; the application should handle dependency retries where necessary.
- User: Runs the JVM as
myapp, not root. - WorkingDirectory: Sets the process directory for relative paths used by the application.
- ExecStart: Uses absolute paths for both Java and the JAR. Replace them if your installation or filename differs.
- Restart=on-failure: Requests a restart when the process exits unsuccessfully. It does not fix a bad configuration; a repeatedly failing process will still require investigation.
- RestartSec=5: Waits five seconds between failed starts, preventing an immediate tight restart loop.
- EnvironmentFile: Loads variables from the specified file. Keep that file protected and ensure its syntax matches
systemdenvironment-file rules. - StandardOutput and StandardError: Send normal output and errors to the journal, where they can be followed with
journalctl. - WantedBy=multi-user.target: Defines the boot target used when the service is enabled.
Do not copy arbitrary heap settings into ExecStart. JVM memory flags must fit the VPS’s available RAM and the application’s workload. An oversized heap can cause the operating system to reclaim memory or kill the process; an undersized heap can cause out-of-memory failures. Start without custom flags unless the application’s documented requirements call for them, then size deliberately.
Protect the unit and environment file with normal administrative permissions. The JAR can be readable by the service account, while secrets should have the narrowest practical read access.
7. Load, enable, and start the service
Tell systemd about the new unit, configure boot startup, and launch it now:
sudo systemctl daemon-reload
sudo systemctl enable myapp
sudo systemctl start myapp
sudo systemctl status myappenable creates the boot-time relationship; it does not start the process in the current session. start launches it immediately. You can combine those actions with sudo systemctl enable --now myapp after the unit has been verified.
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8. Read logs and diagnose failures
Follow the service’s live logs:
sudo journalctl -u myapp -fFor a bounded view of recent startup output:
sudo journalctl -u myapp -n 100 --no-pager
sudo systemctl status myappUse the symptom to narrow the cause:
The service cannot find Java or the JAR
Check the absolute path in ExecStart, verify the file exists, and inspect ownership and permissions:
ls -l /usr/bin/java /opt/myapp/app.jar
sudo -u myapp test -r /opt/myapp/app.jar && echo readableA path that worked in your shell may fail under systemd because the service has a different working directory or environment.
The application exits with an incompatible Java error
Run java -version using the same executable named in ExecStart. Install the Java release required by the build and framework, then restart the service. Do not solve a version mismatch by changing unrelated service settings.
A required variable or secret is missing
Confirm the variable is present in /opt/myapp/app.env, that the file is readable by myapp, and that its spelling matches the application configuration. Reload the unit after changing the file, then restart:
sudo systemctl daemon-reload
sudo systemctl restart myappThe working directory or relative file path is wrong
Check WorkingDirectory and convert fragile relative paths to explicit paths where practical. Ensure any upload, cache, or temporary directory exists and is writable by myapp.
The port is already in use
Find the process holding the configured port, stop the conflicting service, or change the Java application’s port intentionally. A second copy of the same JAR is a common cause after a manual smoke test was left running:
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The process restarts repeatedly
Read the complete journal output rather than treating the restart as the root cause. Common underlying causes include a bad path, incompatible Java version, missing secret, port collision, invalid configuration, or insufficient memory. Fix the underlying error, then start the service again and verify one clean boot.
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Keep the first test on 127.0.0.1. Once the application is healthy, decide how it should be exposed.
Direct application port
If clients must connect directly, bind the application to the required interface and open that port in both layers that control traffic: the VPS provider’s network rules and the host operating-system firewall. Opening only one layer is insufficient. Limit source addresses where possible instead of exposing an administrative or internal port to the entire internet.
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For an HTTP application, a reverse proxy such as Nginx can accept public traffic, terminate TLS, and forward requests to the Java process on a private local port. This keeps the JAR’s listener separate from certificate handling and lets you expose only the proxy’s web ports. The exact proxy configuration depends on your domain, TLS setup, headers, WebSocket needs, and application port; test the local upstream first and then verify the public route.
The application must listen on an address reachable by the proxy. If it binds only to loopback, a proxy on the same VPS can reach it; if the proxy is on another host, the bind address and firewall policy must allow that connection. Never open more interfaces than the architecture requires.
10. Updating the JAR without losing control
Use a controlled sequence for a new build:
- Build and verify the artifact locally.
- Upload it to a temporary or versioned path rather than overwriting a file while the JVM is reading it.
- Stop the service with
sudo systemctl stop myapp. - Place the new artifact at the path referenced by
ExecStartand restore ownership formyapp. - Start the service and immediately inspect
sudo systemctl status myappandsudo journalctl -u myapp -n 100 --no-pager. - Run a loopback
curlcheck against the expected endpoint.
Retain the previous known-good artifact until the new one has passed its startup and endpoint checks. If the new release fails, stop it, restore the previous file, start the service, and inspect the journal for the release-specific error.
If you change only the environment file, a daemon reload is not usually needed for the file itself, but the process must be restarted to receive new values. If you change the unit file, run sudo systemctl daemon-reload before restarting.
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Do not assume that an enabled service works at boot because it started manually. After saving the unit and confirming a clean run, schedule a maintenance window and reboot:
sudo rebootReconnect over SSH, then check:
sudo systemctl status myapp
sudo journalctl -u myapp -b --no-pager
curl http://127.0.0.1:<port>/The -b option limits journal output to the current boot. This check catches missing boot-time environment variables, incorrect filesystem paths, startup ordering assumptions, and services that were accidentally launched only from an interactive shell.
Common deployment mistakes to avoid
- Closing SSH after a direct launch: the shell-owned process stops, so use
systemdfor persistence. - Running as root: create a dedicated account and grant only the access the application needs.
- Installing the wrong Java release: match the runtime to the JAR’s build and framework requirements.
- Using relative paths: set
WorkingDirectoryand prefer explicit locations in service configuration. - Assuming shell variables carry over: list required values in a protected
EnvironmentFile. - Opening a firewall port before local testing: prove the process works on loopback, then expose only the necessary route.
- Forgetting provider-level rules: both the VPS network controls and host firewall can affect reachability.
- Copying arbitrary JVM heap flags: size memory for the actual VPS instead of applying values from another machine.
- Leaving a smoke-test process running: stop the manual JVM before starting the managed unit to avoid a port collision.
- Ignoring the journal: status shows the unit state, while
journalctl -u myapp -fusually reveals the application error.
Operational checklist
- SSH login works for the deployment account and that account has the required administrative access.
- The installed headless OpenJDK major version matches the JAR and framework.
/opt/myappand the artifact are owned and readable by the dedicated service account.- The manual
java -jarlaunch completes startup and responds to a loopbackcurlrequest. - The unit uses absolute paths, a correct working directory, the intended user, and a protected environment file.
systemctl enableandsystemctl startcomplete without a restart loop.- Journal output is available and free of unresolved startup errors.
- Provider and host firewall rules expose only the required ports.
- A reboot test confirms automatic startup and local health.
The Bottom Line
For a Linux VPS, use java -jar only to validate the artifact. Run the application in production as a dedicated non-root systemd service, verify it locally, then expose it through the minimum firewall and reverse-proxy path your architecture needs.
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