docs: add avoid unreproducible information documentation

  - deterministic-build-systems

  - volatile-inputs

  - stable-inputs

  - stripping-unreproducible-information

  - value-initialization

  - version-information

  - timestamps

---

title: Stripping of unreproducible information

layout: docs

permalink: /docs/stripping-unreproducible-information/

---

In addition to [handling timestamps]({{ "/docs/timestamps" | relative_url }}),

another crucial aspect of achieving reproducible builds is the removal of

"useless" and unreproducible information from the build artifacts.

This information often includes metadata, such as file ownership or access times,

which can vary depending on the build environment or the specific conditions

under which the build occurs. If left unaddressed, these variations can lead

to inconsistencies in the final output, making the build non-reproducible.

## Metadata are best avoided

Metadata like file ownership, permissions, or even unimportant data stored by

some formats can introduce variability.

For instance, many build tools or file formats capture the user ID or group ID

of the person running the build, which can lead to different outputs even when

the build process is otherwise identical. Stripping or standardizing this

metadata is essential to ensure that the build outputs are consistent regardless

of the environment.

## Using strip-nondeterminism

To tackle this issue, the

[strip-nondeterminism]({{ "/tools#strip-nondeterminism" | relative_url }})

tool was created. It automatically removes or normalizes non-deterministic

information in various types of files, such as archives, PDFs, and JAR files.

It can clamp timestamps, strip unnecessary metadata, and perform other

normalizations that ensure the build outputs remain identical across different

environments.

This tool is particularly useful when it’s not feasible to modify the build

process itself to eliminate the source of non-determinism. By incorporating

[strip-nondeterminism]({{ "/tools#strip-nondeterminism" | relative_url }})

into your build pipeline, you can address many reproducibility issues at a

post-processing stage, further ensuring that your builds are truly reproducible.

By diligently stripping away unreproducible information and using tools like

[strip-nondeterminism]({{ "/tools#strip-nondeterminism" | relative_url }}),

you can significantly improve the reproducibility of your

builds, ensuring that the same source code will always produce identical results,

regardless of where or when it is built.