chkbit/README.md

# chkbit

chkbit is a lightweight **bitrot detection tool**.

bitrot (a bit flipping in your data) can occur

- at a low level on the storage media through decay (hdd/sdd)
- at a high level in the OS or firmware through bugs

chkbit is independent of the file system and can help you detect bitrot on you primary system, on backups and in the cloud.

This is the successor to [chkbit/node](https://github.com/laktak/chkbit-py). It will use and upgrade the index files created by the node version.

## Installation

```
pip install --user chkbit
```

Or in its own environment:

```
pipx install 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 md5 hashes for every file.
- report bitrot for files that rotted since the last run (check the exit status).

Run `chkbit PATH` to verify only.

```
usage: chkbit.py [-h] [-u] [-f] [-q] [-v] PATH [PATH ...]

Checks files for bitrot. See https://github.com/laktak/chkbit-py

positional arguments:
  PATH

optional arguments:
  -h, --help     show this help message and exit
  -u, --update   update indices (without this chkbit will only verify files)
  -f, --force    force update of damaged items
  -q, --quiet    quiet, don't show progress/information
  -v, --verbose  verbose output

Status codes:
  ROT: error, bitrot detected
  EIX: error, index damaged
  old: warning, file replaced by an older version
  add: add to index
  upd: file updated
  ok : check ok
  skp: skipped (see .chkbitignore)
  EXC: internal exception
```

## Repair

chkbit cannot repair bitrot, its job is simply to detect it.

You should

- backup regularly.
- run chkbit *before* each backup.
- check for bitrot on the backup media.
- in case of bitrot *restore* from a checked backup.

## Ignore files

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

- each line should contain exactly one name
- lines starting with `#` are skipped

## 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 move a directory the index moves with it
- when you make a backup the index is also backed up

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 md5 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 md5 hash.
- otherwise it will compare the current md5 to the recorded value and report an error if they do not match.

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

On Linux/OS X you can try:

Create test and set the modified time:
```
$ echo foo1 > test; touch -t 201501010000 test
$ chkbit -u .
add ./test
Processed 1 file(s).
Indices were updated.
```
`add` indicates the 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(s).
Indices were updated.
```

`upd` indicates the file was updated.

Now update test with the same modified to simulate bitrot:
```
$ echo foo3 > test; touch -t 201501010001 test
$ chkbit -u .
ROT ./test
Processed 0 file(s).
chkbit detected bitrot in these files:
./test
error: detected 1 file(s) with bitrot!
```

`ROT` indicates bitrot.