apache/hadoop · error · IOException

Har: truncate not allowed

Error message

Har: truncate not allowed

What it means

IOException thrown by HarFileSystem.truncate() because the HAR (Hadoop Archive) filesystem is read-only and does not support truncating files. Hadoop Archives (.har) are immutable collections of files created via 'hadoop archive'; operations that modify file contents (truncate, append, rename, setReplication, delete) are intentionally unimplemented. Fix: do not call truncate on paths inside a .har archive; instead unpack the archive (hadoop fs -cp har:///... localfs), truncate the extracted file on a writable filesystem, and re-create the archive if needed. This is an expected failure for programs that generically invoke FileSystem.truncate without checking whether the target filesystem supports modification.

Solutions

1. Truncate the source file on the underlying HDFS and re-create the archive
2. If the whole archive is disposable, delete the .har directory via the underlying filesystem
3. Skip truncate calls for read-only filesystems by checking the scheme first

Example fix

// before
fs.truncate(new Path("har://hdfs-nn:8020/a/data.har/blob.bin"), 1024);

// after
hdfs.truncate(new Path("hdfs://nn:8020/a/data/blob.bin"), 1024);
// then rebuild the archive from the truncated tree

if ("har".equals(p.toUri().getScheme())) {
  throw new UnsupportedOperationException("truncate is not supported on har; rebuild the archive instead");
}

When it happens

Trigger: fs.truncate(harPath, newLength) on any har:// path — tools that shrink files or reclaim space, or generic file-management code that truncates instead of delete+recreate.

Common situations: Space-reclamation jobs sweeping all filesystems; ported code that relied on truncate semantics (e.g., HBase-style truncation) and now points at archived data.

Related errors

• Har: append not allowed.
• Har: completeLocalOutput not allowed
• Har: copyfromlocalfile not allowed
• Har: create not allowed.
• Har: delete not allowed

AI-assisted analysis of apache/hadoop@2add963021 (2026-08-22). Data as JSON: /api/errors/8fa0345593471e22. Report an issue: GitHub.

Appendix: source

Thrown at hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/fs/HarFileSystem.java:769

    throw new IOException("Har: setReplication not allowed");
  }

  @Override
  public boolean rename(Path src, Path dst) throws IOException {
    throw new IOException("Har: rename not allowed");
  }

  @Override
  public FSDataOutputStream append(Path f) throws IOException {
    throw new IOException("Har: append not allowed");
  }

  /**
   * Not implemented.
   */
  @Override
  public boolean truncate(Path f, long newLength) throws IOException {
    throw new IOException("Har: truncate not allowed");
  }

  /**
   * Not implemented.
   */
  @Override
  public boolean delete(Path f, boolean recursive) throws IOException { 
    throw new IOException("Har: delete not allowed");
  }

  /**
   * liststatus returns the children of a directory 
   * after looking up the index files.
   */
  @Override
  public FileStatus[] listStatus(Path f) throws IOException {
    //need to see if the file is an index in file
    //get the filestatus of the archive directory

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