apache/hadoop · error · UnsupportedOperationException

No DFS available in child file systems.

Error message

No DFS available in child file systems.

What it means

ViewDistributedFileSystem.modifyCacheDirective(info) fans the call out to all child filesystems. If none is a DistributedFileSystem it throws UnsupportedOperationException("No DFS available in child file systems."); if some children are DFS but their calls fail, failures are aggregated into MultipleIOException.

Source

Thrown at hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/ViewDistributedFileSystem.java:1260

    // No path available in CacheDirectiveInfo, Let's shoot to all child fs.
    List<IOException> failedExceptions = new ArrayList<>();
    boolean isDFSExistsInChilds = false;

    for (FileSystem fs : getChildFileSystems()) {
      if (!(fs instanceof DistributedFileSystem)) {
        continue;
      }
      isDFSExistsInChilds = true;
      DistributedFileSystem dfs = (DistributedFileSystem) fs;
      try {
        dfs.modifyCacheDirective(info);
      } catch (IOException ioe) {
        failedExceptions.add(ioe);
      }
    }
    if (!isDFSExistsInChilds) {
      throw new UnsupportedOperationException(
          "No DFS available in child file systems.");
    }
    if (failedExceptions.size() > 0) {
      throw MultipleIOException.createIOException(failedExceptions);
    }
  }

  @Override
  public void modifyCacheDirective(CacheDirectiveInfo info,
      EnumSet<CacheFlag> flags) throws IOException {
    if (this.vfs == null) {
      super.modifyCacheDirective(info, flags);
      return;
    }
    if (info.getPath() != null) {
      ViewFileSystemOverloadScheme.MountPathInfo<FileSystem> mountPathInfo =
          this.vfs.getMountPathInfo(info.getPath(), getConf());
      checkDFS(mountPathInfo.getTargetFs(), "modifyCacheDirective");

View on GitHub (pinned to 2add963021)

Solutions

1. Invoke modifyCacheDirective on the concrete DistributedFileSystem of the target cluster
2. Ensure at least one HDFS mount exists if the view-level cache API must work
3. Catch UnsupportedOperationException to detect a DFS-less view configuration early

DistributedFileSystem dfs = findChildDfs(vfs);
if (dfs == null) {
  throw new UnsupportedOperationException(
      "no HDFS child; call modifyCacheDirective on the target cluster");
}
dfs.modifyCacheDirective(info);

static boolean hasDfsChild(FileSystem fs) {
  return fs instanceof DistributedFileSystem
      || (fs instanceof ViewDistributedFileSystem
          && ((ViewDistributedFileSystem) fs).getChildFileSystems().stream()
              .anyMatch(c -> c instanceof DistributedFileSystem));
}

try {
  vfs.modifyCacheDirective(info);
} catch (UnsupportedOperationException e) {
  if ("No DFS available in child file systems.".equals(e.getMessage())) {
    dfs.modifyCacheDirective(info); // route to concrete cluster
  } else {
    throw e;
  }
}

When it happens

Trigger: Calling modifyCacheDirective on a ViewHDFS instance whose mounts are all non-HDFS (object stores or local filesystem), so getChildFileSystems() yields no DistributedFileSystem.

Common situations: Centralized caching scripts run against a viewfs URI with no HDFS mounts; mixed mount tables where admins expect cache APIs to work on a non-DFS default.

Related errors

• No DFS found in child fs. This API can't be supported in non
• createSymlink is not supported in ViewHDFS
• No more elements
• Not able to initialize fs in getDefaultBlockSize for path <
• Not able to initialize fs in getDefaultReplication for path

AI-assisted analysis of apache/hadoop@2add963021 (2026-08-22). Data as JSON: /api/errors/99021bd82ab24c6e. Report an issue: GitHub.