# chkbit

chkbit is a tool that ensures the safety of your files by checking if their *data integrity remains intact over time*, especially during transfers and backups. It helps detect issues like disk damage, filesystem errors, and malware interference.

Some filesystems (like Btrfs and ZFS, but not APFS or NTFS) already protect your files with checksums. However when you move files between locations, separate checks have the advantage of confirming that the data was not modified during transit. So you know the photo on your disk is the same as the copy in your cloud backup. This also protects you from overwriting good data with bad copies.


![gif of chkbit](https://raw.githubusercontent.com/wiki/laktak/chkbit/readme/chkbit.gif "chkbit")


- [How it works](#how-it-works)
- [Installation](#installation)
- [Usage](#usage)
- [Repair](#repair)
- [Ignore files](#ignore-files)
- [chkbit as a Go module](#chkbit-as-a-go-module)
- [FAQ](#faq)


## How it works

- **On your Disk**: chkbit starts by creating checksums for each folder on your main disk. It alerts you to potential problems such as damage on the disk, filesystem errors, and malware attacks that could alter your files.

- **On your Backup**: Regardless of your storage media, chkbit stores indexes in hidden files alongside your data during backups. When you run chkbit on your backup, it verifies that every byte was accurately transferred. If issues like [bitrot/data degradation](https://en.wikipedia.org/wiki/Data_degradation) occur, chkbit helps identify damaged files, alerting you to replace them with other backups.

- **For Data in the Cloud**: chkbit is useful for cloud-stored data, alerting you to any changes introduced by cloud providers like video re-encoding or image compression. It ensures your files remain unchanged in the cloud.

Remember to always maintain multiple backups for comprehensive data protection.


## Installation


### Binary releases

You can download the official chkbit binaries from the releases page and place it in your `PATH`.

- https://github.com/laktak/chkbit/releases

Prereleased versions can be found directly on the [GitHub Action](https://github.com/laktak/chkbit/actions). Click on the latest `ci` action and look for `prerelease-artifacts` at the bottom.

### Homebrew (macOS and Linux)

For macOS and Linux it can also be installed via [Homebrew](https://formulae.brew.sh/formula/chkbit):

```shell
brew install chkbit
```

### Build from Source

Building from the source requires Go.

- Either install it directly

```shell
go install github.com/laktak/chkbit/v5/cmd/chkbit@latest
```

- or clone and build

```shell
git clone https://github.com/laktak/chkbit
chkbit/scripts/build
# binary:
ls -l chkbit/chkbit
```


## Usage

Run `chkbit -u PATH` to create/update the chkbit index.

chkbit will

- create a `.chkbit` index in every subdirectory of the path it was given.
- update the index with blake3 (see --algo) hashes for every file.
- report damage for files that failed the integrity check since the last run (check the exit status).

Run `chkbit PATH` to verify only.

```
Usage: chkbit [<paths> ...] [flags]

Arguments:
  [<paths> ...]    directories to check

Flags:
  -h, --help                    Show context-sensitive help.
  -H, --tips                    Show tips.
  -c, --check                   check mode: chkbit will verify files in readonly
                                mode (default mode)
  -u, --update                  update mode: add and update indices
  -a, --add-only                add mode: only add new and modified files,
                                do not check existing (quicker)
  -i, --show-ignored-only       show-ignored mode: only show ignored files
  -m, --show-missing            show missing files/directories
  -d, --include-dot             include dot files
      --force                   force update of damaged items (advanced usage
                                only)
  -S, --skip-symlinks           do not follow symlinks
  -R, --no-recurse              do not recurse into subdirectories
  -D, --no-dir-in-index         do not track directories in the index
  -l, --log-file=STRING         write to a logfile if specified
      --log-verbose             verbose logging
      --algo="blake3"           hash algorithm: md5, sha512, blake3 (default:
                                blake3)
      --index-name=".chkbit"    filename where chkbit stores its hashes,
                                needs to start with '.' (default: .chkbit)
      --ignore-name=".chkbitignore"
                                filename that chkbit reads its ignore list from,
                                needs to start with '.' (default: .chkbitignore)
  -w, --workers=5               number of workers to use (default: 5)
      --plain                   show plain status instead of being fancy
  -q, --quiet                   quiet, don't show progress/information
  -v, --verbose                 verbose output
  -V, --version                 show version information
```

```
$ chkbit -H

.chkbitignore rules:
- each line should contain exactly one name
- you may use Unix shell-style wildcards
  - *       matches everything except /
  - ?       matches any single character except /
  - [seq]   matches any character/range in seq
  - [^seq]  matches any character/range not in seq
  - \\      escape to match the following character
- lines starting with '#' are skipped
- lines starting with '/' are only applied to the current directory

Status codes:
  DMG: error, data damage detected
  EIX: error, index damaged
  old: warning, file replaced by an older version
  new: new file
  upd: file updated
  ok : check ok
  del: file/directory removed
  ign: ignored (see .chkbitignore)
  EXC: exception/panic
```

chkbit is set to use only 5 workers by default so it will not slow your system to a crawl. You can specify a higher number to make it a lot faster if the IO throughput can also keep up.


## Repair

chkbit is designed to detect "damage". To repair your files you need to think ahead:

- backup regularly
- run chkbit *before* each backup
- run chkbit *after* a backup on the backup media (readonly)
- in case of any issues, *restore* from a checked backup medium.


## Ignore files

Add a `.chkbitignore` file containing the names of the files/directories you wish to ignore

- each line should contain exactly one name
- you may use Unix shell-style wildcards
  - `*` matches everything except `/`
  - `?`  matches any single character except `/`
  - `[seq]` matches any character/range in seq
  - `[^seq]` matches any character/range not in seq
  - `\\` escape to match the following character
- lines starting with `#` are skipped
- lines starting with `/` are only applied to the current directory
- you can use `path/sub/name` to ignore a file/directory in a sub path
- hidden files (starting with a `.`) are ignored by default unless you use the `-d` option


## chkbit as a Go module

chkbit is can also be used in other Go programs.

```
go get github.com/laktak/chkbit/v5
```

For more information see the documentation on [pkg.go.dev](https://pkg.go.dev/github.com/laktak/chkbit/v5).


## FAQ

### Should I run `chkbit` on my whole drive?

You would typically run it only on *content* that you keep for a long time (e.g. your pictures, music, videos).

### Why is chkbit placing the index in `.chkbit` files (vs a database)?

The advantage of the .chkbit files is that

- when you make a backup the index is also backed up, a central index would need to be backed up separately
- if the index is just a play file it can't be damaged as easily
- if it is damaged, only one directory is affected
- if you split up your files over backups, the relevant index is alwys included
- when updating an index, only the index in one directory is affected, reducing the risk of errors
- also useful, when you move a directory the index moves with it

The disadvantage is obviously that you get hidden `.chkbit` files in your content folders.

### How does chkbit work?

chkbit operates on files.

When run for the first time it records a hash of the file contents as well as the file modification time.

When you run it again it first checks the modification time,

- if the time changed (because you made an edit) it records a new hash.
- otherwise it will compare the current hash to the recorded value and report an error if they do not match.

### I wish to use a different hash algorithm

chkbit now uses blake3 by default. You can also specify `--algo sha512` or `--algo md5`.

Note that existing index files will use the hash that they were created with. If you wish to update all hashes you need to delete your existing indexes first. A conversion mode may be added later (PR welcome).

### How can I delete the index files?

List them with

```
find . -name .chkbit
```

and add `-delete` to delete.

### Can I test if chkbit is working correctly?

On Linux/macOS you can try:

Create test and set the modified time:
```
$ echo foo1 > test; touch -t 201501010000 test
$ chkbit -u .
new ./test

Processed 1 file.
- 0:00:00 elapsed
- 192.31 files/second
- 0.00 MB/second
- 1 directory was updated
- 1 file hash was added
- 0 file hashes were updated
```

`new` indicates a new file was added.

Now update test with a new modified:
```
$ echo foo2 > test; touch -t 201501010001 test # update test & modified
$ chkbit -u .
upd ./test

Processed 1 file.
- 0:00:00 elapsed
- 191.61 files/second
- 0.00 MB/second
- 1 directory was updated
- 0 file hashes were added
- 1 file hash was updated
```

`upd` indicates the file was updated.

Now update test with the same modified to simulate damage:
```
$ echo foo3 > test; touch -t 201501010001 test
$ chkbit -u .
DMG ./test

Processed 1 file.
- 0:00:00 elapsed
- 173.93 files/second
- 0.00 MB/second
chkbit detected damage in these files:
./test
error: detected 1 file with damage!
```

`DMG` indicates damage.