Can Unrar Automatically Rebuild Missing Volumes?

This article examines whether the unrar command-line utility can automatically rebuild missing archive volumes prior to extraction. It explains the requirements for file reconstruction, how the RAR format handles missing data through recovery volumes, and the exact steps needed to restore and extract split archives.

The short answer is no: unrar cannot automatically rebuild missing archive volumes during a standard extraction command, nor can it generate missing data out of nothing. If a volume (such as .part02.rar) is missing, running unrar x will simply fail once the missing segment is reached.

However, missing volumes can be rebuilt if the archive creator provided Recovery Volumes (.rev files).

How Volume Reconstruction Works

RAR archives do not contain redundancy by default. To protect against lost parts, creators generate .rev files. Each .rev file can replace any single missing archive volume. For example, if two parts are missing, you need at least two .rev files to reconstruct them.

Limitations of the unrar Command

The standard unrar utility is a lightweight, extraction-only tool. In most operating systems (especially Linux and macOS):

  1. Extraction Does Not Auto-Repair: Running unrar e or unrar x on the main archive will not automatically search for and apply .rev files to replace missing parts.
  2. Rebuild Command Requirements: In older or minimal versions of unrar, the recovery volume reconstruction feature is omitted. Rebuilding typically requires the full rar command-line package or the WinRAR GUI.

How to Rebuild Missing Volumes

If you have the necessary .rev files in the same directory as your remaining .rar files, you can rebuild the missing volumes using the following methods:

Using Command-Line Tools

If using the full rar utility:

rar rc archive.part01.rev

In modern versions that support it, you can also target any .rev file directly:

unrar rc archive.part01.rev

The program will scan the directory, identify which numbered volumes are missing, use the mathematical parity in the .rev files to recreate the exact missing .rar segments, and save them to the disk.

Using WinRAR (GUI)

If you are on Windows, simply double-clicking any .rev file in the folder will cause WinRAR to automatically verify the archive, rebuild the missing volumes, and allow you to proceed with extraction.

What to Do If No .rev Files Exist

If the archive does not include .rev files, rebuilding is mathematically impossible. In this scenario, your only options are:

  • Re-downloading or re-requesting the specific missing volume.
  • Using the -kb (Keep Broken Files) switch in unrar (unrar x -kb archive.part01.rar), which forces the utility to extract whatever data is available from the remaining volumes, though the resulting files may be incomplete or corrupted.