How to View RAR Header Blocks with Unrar

This guide explains how to inspect and view specific header block details in a RAR archive using the command-line utility unrar. By leveraging built-in technical listing flags, you can extract low-level metadata such as archive headers, block flags, compression methods, host OS information, and checksums directly from your terminal without extracting the archive contents.

The Technical List Command

The standard unrar l command only displays basic file names and sizes. To view the internal header blocks and technical parameters of a RAR file, use the vt (Verbose Technical) or lt (List Technical) switch.

Run the following command:

unrar vt archive.rar

Alternatively, for a more concise technical listing:

unrar lt archive.rar

Filtering Specific Header Blocks

RAR archives contain distinct header blocks, including the Main Archive Header, File Headers, and optional Service Headers. Because unrar vt outputs technical information for every block in the archive, you can pipe the output to text-filtering tools like grep to locate specific block fields.

1. View the Main Archive Header

To inspect the overall archive flags (such as whether the archive is solid, locked, or multi-volume):

unrar vt archive.rar | grep -A 10 "Archive:"

2. View Specific File Block Headers

To view technical header data for a specific file within the archive, specify the filename at the end of the command:

unrar vt archive.rar target_file.txt

This isolates the individual file header block and displays:

  • Host OS: The operating system where the file was archived.
  • Attributes: File system permissions and flags.
  • Packing method: The specific compression algorithm version used.
  • Dictionary size: The sliding dictionary window size allocated for the block.
  • Checksum (CRC32 or BLAKE2): The integrity validation block.

3. View Block Header Checksums and Flags

To extract only the integrity checksums and header flags across all blocks:

unrar vt archive.rar | grep -E "(Flags|CRC32|BLAKE2|Host OS)"

Example Output

When running unrar vt archive.rar filename.ext, the output displays the parsed header structure:

Details: RAR 5.0

Attributes: -rw-r--r--
Host OS: Unix
Compression: -m3 -md=32M -mt=1
Flags: Data encrypted, Block continued
CRC32: 3B2A10C4

This output confirms the internal parameters stored within the file's binary header block, allowing you to debug corrupted archives or analyze archive configurations programmatically.