apache/hadoop · error · IOException

Mount table {mountTableName} has already been configured wit

Error message

Mount table {mountTableName} has already been configured with a link fallback. Multiple fallback links for the same mount table is not allowed.

What it means

Error "Mount table {mountTableName} has already been configured with a link fallback. Multiple fallback links for the same mount table is not allowed." thrown in apache/hadoop.

Source

Thrown at hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/fs/viewfs/InodeTree.java:736

    } // End of for loop.

    if (isMergeSlashConfigured) {
      Preconditions.checkNotNull(mergeSlashTarget);
      root = new INodeLink<T>(mountTableName, ugi,
          initAndGetTargetFs(), mergeSlashTarget);
      mountPoints.add(new MountPoint<T>("/", (INodeLink<T>) root));
      rootFallbackLink = null;
    } else {
      root = new INodeDir<T>("/", UserGroupInformation.getCurrentUser());
      getRootDir().setInternalDirFs(getTargetFileSystem(getRootDir()));
      getRootDir().setRoot(true);
      INodeLink<T> fallbackLink = null;

      for (LinkEntry le : getLinkEntries(linkEntries)) {
        switch (le.getLinkType()) {
        case SINGLE_FALLBACK:
          if (fallbackLink != null) {
            throw new IOException("Mount table " + mountTableName
                + " has already been configured with a link fallback. "
                + "Multiple fallback links for the same mount table is "
                + "not allowed.");
          }
          fallbackLink = new INodeLink<T>(mountTableName, ugi,
              initAndGetTargetFs(), le.getTarget());
          continue;
        case REGEX:
          addRegexMountEntry(le);
          continue;
        default:
          createLink(le.getSrc(), le.getTarget(), le.getLinkType(),
              le.getSettings(), le.getUgi(), le.getConfig());
        }
      }
      rootFallbackLink = fallbackLink;
      getRootDir().addFallbackLink(rootFallbackLink);
    }

View on GitHub (pinned to 2add963021)

Solutions

1. Configure only one linkFallback entry per mount table.
2. Remove the duplicate fallback link entries from the configuration.

When it happens

Trigger: Thrown during ViewFs mount table initialization when more than one linkFallback entry is configured for the same mount table.

Common situations: See trigger scenarios.

AI-assisted analysis of apache/hadoop@2add963021 (2026-08-22). Data as JSON: /api/errors/98bf6c42808b51e0. Report an issue: GitHub.