apache/hadoop · error · UnsupportedOperationException

Unsupported path {} please check mount table

Error message

Unsupported path {} please check mount table

What it means

PathLocation.getDefaultLocation() returns the first remote destination of a resolved path; it throws UnsupportedOperationException when the destination list is empty or the first RemoteLocation's dest is null — i.e., the mount table record backing this path is malformed and carries no usable destination, so there is no default location to forward requests to.

Source

Thrown at hadoop-hdfs-project/hadoop-hdfs-rbf/src/main/java/org/apache/hadoop/hdfs/server/federation/resolver/PathLocation.java:224

  }

  /**
   * Get the order for the destinations.
   *
   * @return Order for the destinations.
   */
  public DestinationOrder getDestinationOrder() {
    return this.destOrder;
  }

  /**
   * Get the default or highest priority location.
   *
   * @return The default location.
   */
  public RemoteLocation getDefaultLocation() {
    if (destinations.isEmpty() || destinations.get(0).getDest() == null) {
      throw new UnsupportedOperationException(
          "Unsupported path " + sourcePath + " please check mount table");
    }
    return destinations.get(0);
  }
}

View on GitHub (pinned to 2add963021)

Solutions

1. Find the malformed entry: hdfs dfsrouteradmin -list and look for the mount with missing/empty destinations
2. Replace it: hdfs dfsrouteradmin -rm <path> followed by a clean hdfs dfsrouteradmin -add <path> -ns <ns> -dst <dst>
3. Refresh all routers' mount caches (hdfs dfsrouteradmin -refresh) after the fix
4. If records were hand-edited in the state store, restore from a known-good snapshot/backup

Example fix

# remove the malformed entry and re-add it correctly
hdfs dfsrouteradmin -rm /badmount
hdfs dfsrouteradmin -add /badmount -ns ns0 -dst /badmount
hdfs dfsrouteradmin -refresh

// Guard before using getDefaultLocation()
PathLocation loc = resolver.lookupLocation(path);
if (loc == null || loc.getDestinations().isEmpty()
    || loc.getDestinations().get(0).getDest() == null) {
  throw new IOException("No usable destination for " + path
      + "; fix the mount table entry");
}
RemoteLocation dst = loc.getDefaultLocation();

try {
  RemoteLocation dst = loc.getDefaultLocation();
} catch (UnsupportedOperationException e) {
  LOG.error("Malformed mount for {}: no default destination", path);
  // alert operators and skip this location rather than NPE later
}

When it happens

Trigger: A MountTable entry with zero destinations, or whose first RemoteLocation was built with a null dest (bad record inserted directly into the state store or by a buggy admin client), gets resolved into a PathLocation and getDefaultLocation() is called during request routing.

Common situations: Hand-edited or corrupted ZooKeeper/DB state store records; scripts calling the admin protobuf/JSON API with missing fields; partially written mount entries after a crashed admin operation.

Related errors

• Cannot find locations for {}, because the default nameservic
• Cannot find locations for {} in {}
• No mount point for %s
• Mount table " + mount + " doesn't exist
• Failed update mount table " + mount

AI-assisted analysis of apache/hadoop@2add963021 (2026-08-22). Data as JSON: /api/errors/fa0056615052b3ad. Report an issue: GitHub.