Design an ideal reproducibility testing tool

60-minute session on day 3

Exercise in README driven development: think what the user documentation could be for the perfect tool to answer the question “How can I know if a piece of software is reproducible?”

This tool is intended for developers who want to test whether their software is reproducible.

Let’s call it “reprotest”.

Typical usage

$ git clone
$ cd bar
$ reprotest ./

Exit status :

  • 0 if reproducible
  • 1 if not
  • 2 in case of problems

Provide useful information in both cases, links to reproducible documentation.


The default is to do all possible variations. The first thing tested will be the software in its current environment—with whichever tools the developer has in their normal environment. If it is shown to be reproducible there, it will attempt to try other environments similar to the systems which reported it unreproducible (e.g.

To control which variations are being tested:

$ reprotest --keep-same=buildpath

$ reprotest --variations=date
# fail with something like:
#     Sorry, date is not supported in direct mode
# (or do we want to use libfaketime?)

$ reprotest --variations=date --runner=virtualbox

$ reprotest --variations=date --runner=qemu --qemu-image=debian-sid.img

$ reprotest --variations=cpu,kernel,user,domain,date,filesystem make

(filesystem will use disorderfs)


To control which artifacts will be compared at the end of the build:

# do not consider *.o file as files that need to match
$ reprotest --ignore=*.o

# only do a diff of *.deb files to determine if the thing is reproducible or not
$ reprotest --accept=*.deb dpkg-buildpackage


To compare different commands:

$ reprotest --command='make' --command='make CFLAGS=-g' --command='make CFLAGS=-O3'

Project configuration file

If you have a .reprotest file in the current directory, you can run reprotest without any arguments to use the command and variations specified there:

$ reprotest

By default, it will re-use the current system to run the build. To test with another toolchain:

$ reprotest --use-system-root=/path/to/chroot make

To recreate another build:

$ reprotest --buildinfo=file.buildinfo --os=debian make

# try to guess which kind of buildinfo if --os is not specified
$ reprotest --buildinfo=file.buildinfo make

If Debian allows all variations except build path then you can assess software is good for Debian by:

$ reprotest --profile=debian

User configuration file


default-runner = qemu

default-image = ~/.reprotest/debian-sid.img


$ reprotest --text=reprotest.txt => run diffoscope on all created files?

$ reprotest --html=reprotest.html

$ reprotest --junit=reprotest.junit (for jenkins) <- parsable output

# create reprotest-differences/build1/ and create reprotest-differences/build2/
$ reprotest --save-differences=reprotest-differences/

# create reprotest-differences.build1.tar.gz reprotest-differences.build2.tar.gz
$ reprotest --save-difference-archives=reprotest-differences

# create a json file with index and details about the test
$ reprotest --json=reprotest.json --save-differences=reprotest-differences/

# pass options to diffoscope
$ reprotest --diffoscope-options="--ignore=coverage/ --ignore=*.log"

Options can be combined:

$ reprotest --html=reprotest.html --save-differences=reprotest-differences/

If no output option is specified, plain text will be printed to the standard output.

Other possibilities:

Run build twice, reproducing $DEFAULT set of information from build environment:

$ reprotest make

Run build once, reproducing $DEFAULT set of information from xxx.buildinfo:

$ reprotest --buildinfo=bash_amd64.buildinfo make

Run build once, reproducing fields buildpath, username from bash_amd64.buildinfo:

$ reprotest --reproduce=buildpath,username --buildinfo=bash_amd64.buildinfo make 

Check that *.buildinfo have the same result hash, find all the fields that have the same value across all files, reproduce those common fields, then run build once, and check if output has same hash:

$ reprotest –buildinfo=1.buildinfo –buildinfo=2.buildinfo –buildinfo=3.buildinfo make