# Brck -- a simple bit rot checker

Brck is a simple bit rot checker for legacy file systems.
It records and compares the modification times and cryptographic hash sums of regular files.
When a file's hash changed but it's modification time did not, then Brck reports the file as corrupted so you have a chance to restore the file from backup.
You do have backups, right? 😉

Brck's original source code is hosted on [git.skreutz.com](https://git.skreutz.com/brck.git/).

## Installation

Brck is available on [crates.io](https://crates.io/crates/brck).
You can install it using Rust's package manager [Cargo](https://doc.rust-lang.org/cargo/).

    $ cargo install brck

Alternatively you can run (or install) the experimental Nix flake.

    $ nix run git+https://git.skreutz.com/brck.git -- --help

## Usage

Without any options, Brck will record all regular files in current working directory recursively and write those records to a gzipped `.brck` file.

    $ brck

When you run the same command again, Brck will compare the recorded files against the current file system and report any corrupted files.

    $ brck
    corrupted: ./test_file
    Error: Found 1 denied difference

You can optionally deny all changes to existing files:

    $ brck -d changed,removed,corrupted

Brck is quiet by default.
Increase the verbosity using `-v` or request a summary using `-s`.
Alternatively, enable the JSON output using `-J` and perform your own post-processing, e.g., using [jq](https://jqlang.github.io/jq/):

    $ brck -vvJ | jq -sr 'group_by(.type)[] | [.[0].type, length] | @tsv' 2>/dev/null
    added   4
    corrupted       1
    unchanged       1219

See the built-in help for all supported options:

    $ brck --help

## Features

* Parallel sequential processing: Brck processes files in parallel, yet outputs and records files in-order

* One-pass: Brck reads your files only once

* Constant memory: Brck's memory footprint is independent of the number of processed files

* Relative paths: Brck records relative paths such that you can move the containing directory around

* Quiet by default: Without any options, Brck prints denied differences to standard output, and errors to standard error; nothing else

* Human readable or machine readable, newline-delimited JSON output, at your option

* Graceful shutdown on the first interrupt signal, forceful immediate shutdown on the second

* [Pledged](https://man.openbsd.org/pledge) and [unveiled](https://man.openbsd.org/unveil) on OpenBSD

## Limitations

* Brck doesn't follow symlinks.

* Brck doesn't track hardlinks. Performance will be suboptimal in the presence of large hardlinked files because Brck hashes each copy individually.

* Brck doesn't track reflinks. Modern copy-on-write file systems are out of scope because they should check file content integrity themselves, like OpenZFS and Btrfs do.

* Brck may leak file meta data because its `.brck` file may have different permissions than the listed files.

* Brck doesn't respect platform-specific temporary directories such as `TMPDIR` on UNIX. Instead, it creates its temporary files in the current working directory, next to the `.brck` file. This way, Brck can update the files atomically on POSIX-conform systems.

* Brck may fail to remove its temporary files, e.g., when the process gets killed.

## Maintenance

Brck is semi-actively maintained.
I intend to fix bugs, and keep it working.

Releases adhere to [Semantic Versioning](https://semver.org/spec/v2.0.0.html), see the [changelog](CHANGELOG.md).

The minimum supported Rust version (MSRV) is the latest stable release.

The Nix flake is experimental.

## Contribution

Contributions are welcome! Please [contact](https://www.skreutz.com/contact/) me via email.

## License

This work is dual-licensed under [MIT](LICENSE-MIT) or [Apache License, Version 2.0](LICENSE-APACHE-2.0).

## See also

* Definition of *bit rot* in the [Jargon File](http://www.catb.org/jargon/html/B/bit-rot.html) ([archive](https://web.archive.org/web/20240312124910/http://www.catb.org/jargon/html/B/bit-rot.html))

* A similar Python program named [Bitrot](https://github.com/ambv/bitrot/)

* A similar Rust program named [Legdur](https://git.cyplo.dev/cyplo/legdur) ([crates.io](https://crates.io/crates/legdur))

* A blog post on [Things UNIX can do atomically](https://web.archive.org/web/20160304224616/http://rcrowley.org/2010/01/06/things-unix-can-do-atomically)