HMCL-dev/HMCL · error · IOException

Unknown operating system:

Error message

Unknown operating system:

What it means

JavaInfo.fromReleaseFile() parses a JDK's release file and maps the OS_NAME property through OperatingSystem.parseOSName(). If the resulting OS is UNKNOWN (unrecognized os name or missing OS_NAME), it throws IOException("Unknown operating system: <osName>") because HMCL cannot pick a platform for this Java installation.

Solutions

  1. Check the release file next to the java executable and set OS_NAME to a standard value (Linux/Windows/Mac OS X)
  2. Use a full official JDK/JRE distribution that ships a proper release file
  3. Update HMCL, since newer versions may recognize more OS names
  4. Catch the IOException during Java scan and skip that installation
Defensive patterns

Strategy: try-catch

Validate before calling

Properties rel = new Properties();
rel.load(Files.newInputStream(javaHome.resolve("release")));
String osName = rel.getProperty("OS_NAME");
if (osName == null || OperatingSystem.parseOSName(osName) == OperatingSystem.UNKNOWN) {
    skipThisJavaInstallation();
}

Try / catch

try {
    JavaInfo info = JavaInfo.fromReleaseFile(javaHome);
} catch (IOException e) {
    markJavaInvalid(javaHome, e.getMessage()); // skip entry
}

Prevention

When it happens

Trigger: Scanning a Java installation whose release file has an OS_NAME that OperatingSystem.parseOSName does not recognize (typo, exotic distro string, or an empty/absent OS_NAME property, in which case osName is null).

Common situations: Manually built or patched JDK with a missing/modified release file; JREs (like old Java 8) that omit OS_NAME from the release file; custom lightweight runtimes (jlink images) without a release file; non-standard vendor distributions.

Understand the failure class

Background: "unsupported platform" / "not supported on this platform" errors: what they mean and how to fix them — this error's family across 47 libraries.

Related errors

AI-assisted analysis of HMCL-dev/HMCL@24702dc5a0 (2026-09-10). Data as JSON: /api/errors/351f13b35630d5b5. Report an issue: GitHub.

Appendix: source

Thrown at HMCLCore/src/main/java/org/jackhuang/hmcl/java/JavaInfo.java:77

            return -1;
        }
    }

    public static JavaInfo fromReleaseFile(BufferedReader reader) throws IOException {
        Map<String, String> properties = KeyValuePairUtils.loadProperties(reader);
        String osName = properties.get("OS_NAME");
        String osArch = properties.get("OS_ARCH");
        String vendor = properties.get("IMPLEMENTOR");

        OperatingSystem os = "".equals(osName) && "OpenJDK BSD Porting Team".equals(vendor)
                ? OperatingSystem.FREEBSD
                : OperatingSystem.parseOSName(osName);

        Architecture arch = Architecture.parseArchName(osArch);
        String javaVersion = properties.get("JAVA_VERSION");

        if (os == OperatingSystem.UNKNOWN)
            throw new IOException("Unknown operating system: " + osName);

        if (arch == Architecture.UNKNOWN)
            throw new IOException("Unknown architecture: " + osArch);

        if (javaVersion == null)
            throw new IOException("Missing Java version");

        return new JavaInfo(Platform.getPlatform(os, arch), javaVersion, vendor);
    }

    public static <F, E extends ArchiveEntry> JavaInfo fromArchive(ArchiveFileTree<F, E> tree) throws IOException {
        if (tree.getRoot().getSubDirs().size() != 1 || !tree.getRoot().getFiles().isEmpty())
            throw new IOException();

        ArchiveFileTree.Dir<E> jdkRoot = tree.getRoot().getSubDirs().values().iterator().next();
        E releaseEntry = jdkRoot.getFiles().get("release");
        if (releaseEntry == null)
            throw new IOException("Missing release file");

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