# sum

_Peios / Using Peios / Peiosutils / Hashing and encoding_

> Compute a small, legacy block checksum of a file.

`sum` computes a small, old-style checksum of a file and reports it along with the file's size in blocks.

```
sum [options] [file...]
```

```
$ sum archive.tar
12345 84 archive.tar
```

The output is the checksum, the block count, and the file name. With no file, `sum` reads standard input.

## Which algorithm

`sum` predates the modern hashes and offers two historical algorithms:

| Option | Algorithm |
|---|---|
| `-r` | The BSD checksum, counted in 1 KiB blocks. This is the default. |
| `-s`, `--sysv` | The System V checksum, counted in 512-byte blocks. |

## When to use it

`sum` exists for compatibility — for reading checksums produced by old tools, and for scripts that still expect its output. Its checksum is short and weak: it catches some accidental corruption, but it is easily fooled and gives no protection against tampering.

For anything new, do not use `sum`. Use a [checksum command](/peios/using-peios/peiosutils/hashing-and-encoding/checksum-commands.md) such as `sha256sum`, or [`cksum`](/peios/using-peios/peiosutils/hashing-and-encoding/cksum.md) — both of which `cksum` can still produce, via `cksum -a bsd` and `cksum -a sysv`, if you need the legacy values.

## Exit status

| Code | Meaning |
|---|---|
| `0` | The checksum was computed. |
| `1` | A file could not be read. |

Related content:

- [cksum](/peios/using-peios/peiosutils/hashing-and-encoding/cksum.md)
- [Checksum commands](/peios/using-peios/peiosutils/hashing-and-encoding/checksum-commands.md)
- [Hashing and encoding](/peios/using-peios/peiosutils/hashing-and-encoding/overview.md)