cshatag-rs

A Rust port of cshatag - a tool to detect silent data corruption.

What it does

cshatag stores the SHA-256 hash and modification time of each file as extended attributes (user.shatag.sha256 and user.shatag.ts). When run again, it compares the stored values against the current file state to detect corruption.

The key detection is silent data corruption: when a file's mtime is unchanged but its content hash has changed, indicating the file was modified without touching the timestamp (e.g., bit rot on disk).

File Statuses

Status	Meaning
<new>	File has never been tagged (both xattrs missing)
<ok>	File is unchanged (hash and mtime match)
<timechange>	mtime changed but hash is the same (e.g., touch)
<outdated>	Both mtime and hash changed (normal edit)
<corrupt>	Silent data corruption - mtime unchanged but hash differs

Build

git clone <repo-url>
cd cshatag-rs
cargo build --release

The binary will be at target/release/cshatag.

Usage

cshatag [OPTIONS] <FILE>...

Options

Flag	Description
-q	Quiet: don't print <ok> files
-qq	Very quiet: only print <corrupt> files and errors (implies -q)
-r, --recursive	Recursively descend into directories (skips symlinks)
--remove	Remove previously stored extended attributes
--dry-run	Read-only mode: no changes written
--fix	Force-update the stored hash on corrupt files
-h, --help	Print help
-V, --version	Print version

Examples

Check all files recursively, suppress <ok> output:

cshatag -q -r /path/to/files

Check all files, only show errors and corrupt files:

cshatag -qq -r /path/to/files

Remove cshatag's extended attributes from all files:

cshatag -r --remove /path/to/files

Dry run (no changes):

cshatag --dry-run -r /path/to/files

Exit Codes

Code	Meaning
0	Success
2	One or more files could not be opened
3	One or more files is not a regular file
4	Extended attributes could not be written
5	At least one corrupt file detected
6	Multiple error types occurred

Extended Attributes

cshatag uses two extended attributes on each file:

• user.shatag.sha256 - SHA-256 hash as 64-character hex string
• user.shatag.ts - Modification time as SSSSSSSSSS.NNNNNNNNN (seconds.nanoseconds)

The filesystem must be mounted with user_xattr enabled.

Compatibility

cshatag-rs is format-compatible with the original cshatag and shatag. Files tagged by one tool can be read by the other.

Timestamp Precision

• Linux: 100ns resolution (matches SMB protocol limits)
• macOS: 1s resolution (matches macOS SMB client limits)

License

MIT