Fixing “Error: Unable to Access Jarfile server.jar” on FTB Infinity Evolved

Encountering the dreaded “Error: Unable To Access Jarfile Server.jar” when trying to launch your FTB Infinity Evolved server can be frustrating. This error prevents your server from starting, halting your Minecraft adventures before they even begin. This guide will walk you through understanding and resolving this common issue, ensuring you get your FTB Infinity Evolved server up and running smoothly.

This problem was highlighted by a user attempting to set up an FTB Infinity Evolved server. They followed the official download and installation process, yet stumbled upon this error. Let’s break down the problem and provide a step-by-step solution.

Understanding the “Unable to Access Jarfile” Error

The “Error: Unable to Access Jarfile server.jar” message is a common Java-related error. It indicates that the Java Runtime Environment (JRE) is unable to locate or access the server.jar file, which is crucial for launching your Minecraft server. Think of server.jar as the engine of your server – without access to it, the server simply cannot start.

This error can arise from several potential causes, ranging from incorrect file paths to permission issues. Understanding these common culprits is the first step towards a quick resolution.

Common Causes and Troubleshooting Steps

Let’s explore the most frequent reasons behind this error and how to address them:

1. Incorrect Working Directory

The most common cause is launching the server from the wrong directory. The start.bat script (or start.sh on Linux/macOS) is designed to execute commands relative to its location. If you run it from a different directory, it won’t be able to find server.jar.

Solution:

Ensure your command prompt or terminal is in the same directory where start.bat and server.jar are located.

Steps to Verify:

1. Navigate to your FTB Server directory: Use the cd command in your command prompt (e.g., cd C:FTB if you installed the server in C:FTB).
2. List directory contents: Use the dir command (Windows) or ls command (Linux/macOS) to verify that start.bat and server.jar (or forge-*-universal.jar after successful installation) are present in the listed files.
3. Run start.bat: Once you’re in the correct directory, execute start.bat again.

2. server.jar File Missing or Not Created

During the server installation process, the installer is supposed to download and create the necessary server.jar file (specifically, for FTB Infinity Evolved, it will download Minecraft server files and Forge, ultimately producing a Forge universal JAR). If the installation process was interrupted or encountered issues, this file might be missing. In the case of FTB server installers, they often download libraries and then instruct you to run a Forge JAR file, which is named something like forge-1.7.10-10.13.4.1614-1.7.10-universal.jar after the initial installer completes.

Solution:

Rerun the server installer to ensure all files are downloaded and correctly placed.

Steps to Reinstall:

1. Download the server installer again: Go back to the FTB Infinity Evolved server download page.

2. Run the installer: Execute the serverinstall_*.exe file again in your desired server directory (e.g., C:FTB).

3. *Check for `forge--universal.jar:** After the installer finishes, verify that a file namedforge-*-universal.jar(with a version number similar toforge-1.7.10-10.13.4.1614-1.7.10-universal.jar) exists in your server directory. This is the actual server JAR you need to run, not a genericserver.jar`.

3. Incorrect start.bat Configuration

The start.bat file contains the command to launch the server. If it’s incorrectly configured to point to the wrong JAR file name or has syntax errors, it will fail to start.

Solution:

Review and correct the start.bat file to ensure it correctly points to your Forge universal JAR file.

Steps to Edit start.bat:

1. Open start.bat in a text editor: Right-click on start.bat and select “Edit” (or open with Notepad, Notepad++, etc.).

2. Examine the java -jar line: Look for the line that starts with java -jar. It should resemble something like:

   java -jar forge-1.7.10-10.13.4.1614-1.7.10-universal.jar

3. Verify JAR filename: Ensure that forge-1.7.10-10.13.4.1614-1.7.10-universal.jar (or the actual name of your Forge universal JAR file) matches the filename in the start.bat script exactly. Typos are common culprits.

4. Save changes: Save the start.bat file after making any necessary corrections.

4. Java Compatibility or Installation Issues

Minecraft servers, especially modded ones like FTB Infinity Evolved, require a compatible version of Java. An outdated or incompatible Java version, or a corrupted Java installation, can lead to the “unable to access jarfile” error.

Solution:

Ensure you have a compatible version of Java installed and that it’s correctly configured in your system’s PATH environment variable. For Minecraft 1.7.10 (FTB Infinity Evolved’s Minecraft version), Java 7 or Java 8 are generally recommended.

Steps to Check Java:

1. Check Java Version: Open command prompt and type java -version. This should display your installed Java version. Ensure it’s Java 7 or 8. If Java is not recognized, or you have an incompatible version:
2. Download and Install Java: Download a suitable Java version (Java 8 is a safe bet for older Minecraft versions) from the official Oracle website or a trusted Java distribution provider like AdoptOpenJDK (now Eclipse Temurin). Ensure you download the correct version for your operating system (Windows 64-bit or 32-bit).
3. Set JAVA_HOME Environment Variable (Optional but Recommended): Setting JAVA_HOME can help ensure the system and applications correctly locate Java.
   • Windows: Search for “Environment Variables” in the Start Menu, click “Edit the system environment variables”. In “System Properties,” click “Environment Variables.” Under “System variables,” click “New.” Set “Variable name” to JAVA_HOME and “Variable value” to your Java installation directory (e.g., C:Program FilesJavajdk1.8.0_XXX). Click “OK” on all windows to save.
4. Update PATH variable (If necessary): Ensure Java’s bin directory is in your system’s PATH environment variable. This allows you to run java commands from any directory. The Java installer often does this automatically, but you might need to verify. Edit the Path system variable and add ;%JAVA_HOME%bin; (or the specific path to your Java bin directory if you didn’t set JAVA_HOME).

5. File Permission Issues

In some cases, especially on Linux or macOS systems, file permission issues can prevent Java from accessing the server.jar file.

Solution:

Ensure that the user running the server has read and execute permissions for the server.jar file and the directory containing it.

Steps to Check/Modify Permissions (Linux/macOS):

1. Open Terminal: Navigate to your server directory in the terminal.
2. Check Permissions: Use the command ls -l to list files and permissions. Look at the permissions for forge-*-universal.jar and start.sh (if you’re using a shell script to start the server).
3. Modify Permissions (If needed): Use the chmod command to grant execute permissions. For example, chmod +x start.sh forge-*-universal.jar. You might also need to ensure the user running the server has read permissions on the parent directories.

Example Scenario and Log Analysis

The original user provided an installer.log which shows a successful download and installation process.

Installer Log Screenshot

The log indicates: “The server installed successfully, you should now be able to run the file forge-1.7.10-10.13.4.1614-1.7.10-universal.jar”. This suggests that the installation itself was not the problem.

Given this, the most likely culprits in this scenario are:

• Incorrect Working Directory: The user might be running start.bat from the wrong location.
• Typo in start.bat (less likely after installer): While less probable after a successful install, a manual edit could have introduced an error in the start.bat file referencing the JAR name.

Conclusion

The “Error: Unable to Access Jarfile server.jar” error, while seemingly cryptic, is usually resolved by systematically checking the common causes outlined above. By verifying your working directory, ensuring the server.jar (or Forge universal JAR) file exists and is correctly referenced in your startup script, confirming Java compatibility, and checking file permissions, you can effectively troubleshoot and fix this issue.

Remember to double-check each step and pay close attention to file names and directory paths. With careful troubleshooting, you’ll be back to enjoying your FTB Infinity Evolved server in no time. If you continue to experience issues, revisiting the FTB forums or community support channels can provide further assistance tailored to your specific setup.