What causes "An error occurred while copying the file." in apache/flink?

Check the getCause() of this RuntimeException to see the original failure (e.g. FileNotFoundException, AccessControlException, IOException) and address that specific issue.

apache/flink · error · RuntimeException

An error occurred while copying the file.

Error message

An error occurred while copying the file.

What it means

Thrown by DistributedCache when fetching a registered cached file fails during the background copy from the distributed filesystem to local storage. The RuntimeException wraps the cause of an ExecutionException from a Future.get() call, meaning the asynchronous file-copy task threw an exception. Common root causes include network connectivity issues to HDFS/S3, permission denials, the file not existing at the registered path, or disk-full conditions on the local TaskManager.

Source

Thrown at flink-core/src/main/java/org/apache/flink/api/common/cache/DistributedCache.java:162

        if (name == null) {
            throw new NullPointerException("name must not be null");
        }

        Future<Path> future = cacheCopyTasks.get(name);
        if (future == null) {
            throw new IllegalArgumentException(
                    "File with name '"
                            + name
                            + "' is not available."
                            + " Did you forget to register the file?");
        }

        try {
            final Path path = future.get();
            URI tmp = path.makeQualified(path.getFileSystem()).toUri();
            return new File(tmp);
        } catch (ExecutionException e) {
            throw new RuntimeException("An error occurred while copying the file.", e.getCause());
        } catch (Exception e) {
            throw new RuntimeException(
                    "Error while getting the file registered under '"
                            + name
                            + "' from the distributed cache",
                    e);
        }
    }

    // ------------------------------------------------------------------------
    //  Utilities to read/write cache files from/to the configuration
    // ------------------------------------------------------------------------

    public static void writeFileInfoToConfig(
            String name, DistributedCacheEntry e, Configuration conf) {
        int num = conf.get(getIntConfigOption(CACHE_FILE_NUM), 0) + 1;
        conf.set(getIntConfigOption(CACHE_FILE_NUM), num);
        conf.setString(CACHE_FILE_NAME + num, name);

View on GitHub (pinned to 2f3c205e92)

Solutions

Check the getCause() of this RuntimeException to see the original failure (e.g. FileNotFoundException, AccessControlException, IOException) and address that specific issue.
Verify the file path registered with registerCachedFile() actually exists and is readable by the TaskManager's service account.
Ensure the TaskManager has sufficient free disk space and write permission on its configured temp directory (taskmanager.tmp.dirs / java.io.tmpdir).
If using HDFS/S3, confirm connectivity and credentials from the TaskManager node (not just the client).

Example fix

// before
File cached = getRuntimeContext().getDistributedCache().getFile("model");

// after — inspect the root cause before retrying
try {
    File cached = getRuntimeContext().getDistributedCache().getFile("model");
} catch (RuntimeException e) {
    Throwable root = e.getCause() != null ? e.getCause() : e;
    log.error("Distributed cache copy failed for 'model': {}", root.getMessage());
    throw e;
}

Defensive patterns

Strategy: try-catch

Validate before calling

// Before calling getFile, verify the file is registered
DistributedCache cache = getRuntimeContext().getDistributedCache();
// No public API to check registration; wrap in try-catch instead

Try / catch

try {
    File cachedFile = getRuntimeContext().getDistributedCache().getFile("myFile");
} catch (RuntimeException e) {
    Throwable cause = e.getCause() != null ? e.getCause() : e;
    log.error("Failed to fetch distributed cache file: {}", cause.getMessage(), cause);
    throw e;
}

Prevention

Verify cached file paths exist and are accessible from TaskManager nodes before deploying.
Use small files (< 100MB) for distributed cache to minimize copy failure window.
Monitor TaskManager disk space to ensure temp directories have capacity.
Test file accessibility from a TaskManager node using the same service account.

When it happens

Trigger: A user function calls RuntimeContext.getDistributedCache().getFile(name) for a file registered via DistributedCache.registerFileWithClasspathResolve() or ExecutionEnvironment.registerCachedFile(). The underlying future that copies the remote file to local temp storage fails, and ExecutionException is caught and re-thrown as this RuntimeException.

Common situations: The cached file path is wrong or was deleted after registration. The TaskManager lacks read permissions on HDFS/S3. Network partition between the TaskManager and the NameNode/object store. Local disk on the TaskManager is full or the temp directory is unwritable.

Related errors

AI-assisted analysis of apache/flink@2f3c205e92 (2026-08-14). Data as JSON: /api/errors/b421b65aee5a5616. Report an issue: GitHub.