reprotest

reprotest builds the same source code twice in different environments, and then checks the binaries produced by each build for differences. If any are found, then diffoscope(1) (or if unavailable then diff(1)) is used to display them in detail for later analysis.

See the COMMAND-LINE EXAMPLES section further below to get you started, as well as more detailed explanations of all the command-line options. The same information is also available in /usr/share/doc/reprotest/README.rst or similar.

Command-line examples

The easiest way to run reprotest is via our presets:

# Build the current directory in a null server (/tmp)
$ reprotest .
$ reprotest . -vv -- null -d # for very verbose output

# Build the given Debian source package in an schroot
# See https://wiki.debian.org/sbuild for instructions on setting that up.
$ reprotest reprotest_0.3.3.dsc -- schroot unstable-amd64-sbuild

Currently, we only support this for Debian packages, but are keen on adding more. If we don't have knowledge on how to build your file or directory, you can send a patch to us on adding this intelligence - see the reprotest.presets python module, and adapt the existing logic.

In the meantime, you can use other parts of the CLI to build arbitrary things. You'll need to give two mandatory arguments, the build command to run and the build artifact file/pattern to test after running the build. For example:

$ reprotest 'python3 setup.py bdist' 'dist/*.tar.gz'

This runs the command on ., the current working directory. To run it on a project located elsewhere:

$ reprotest -s ../path/to/other/project 'python3 setup.py bdist' 'dist/*.tar.gz'
$ reprotest -c 'python3 setup.py bdist' ../path/to/other/project 'dist/*.tar.gz'

These two invocations are equivalent; you can pick the most convenient one for your use-case. When using these from a shell:

• If the build command has spaces, you will need to quote them, e.g. reprotest "dpkg-buildpackage -b --no-sign" [..].
• If you want to use several build artifact patterns, or if you want to use shell wildcards as a pattern, you will also need to quote them, e.g. reprotest [..] "*.tar.gz *.tar.xz".
• If your build artifacts have spaces in their names, you will need to quote these twice, e.g. '"a file with spaces.gz"' for a single artifact or '"dir 1"/* "dir 2"/*' for multiple patterns.

To get more help for the CLI, including documentation on optional arguments and what they do, run:

$ reprotest --help

Running in a virtual server

You can also run the build inside what is called a "virtual server". This could be a container, a chroot, etc. You run them like this:

$ reprotest 'python3 setup.py bdist_wheel'   'dist/*.whl' -- qemu    /path/to/qemu.img
$ reprotest 'dpkg-buildpackage -b --no-sign' '../*.deb'   -- schroot unstable-amd64

There are different server types available. See --help for a list of them, which appears near the top, in the "virtual_server_args" part of the "positional arguments" section.

For each virtual server (e.g. "schroot"), you see which extra arguments it supports:

$ reprotest --help schroot

When running builds inside a virtual server, you will probably have to give extra commands, in order to set up your build dependencies inside the virtual server. For example, to take you through what the "Debian directory" preset would look like, if we ran it using the full CLI:

# "Debian directory" preset
$ reprotest . -- schroot unstable-amd64-sbuild
# This is exactly equivalent to this:
$ reprotest -c auto . -- schroot unstable-amd64-sbuild
# In the non-preset full CLI, this is roughly similar to:
$ reprotest \
    --testbed-init 'apt-get -y --no-install-recommends install \
                    disorderfs faketime locales-all sudo util-linux; \
                    test -c /dev/fuse || mknod -m 666 /dev/fuse c 10 229; \
                    test -f /etc/mtab || ln -s ../proc/self/mounts /etc/mtab' \
    --testbed-build-pre 'apt-get -y --no-install-recommends build-dep ./' \
    --build-command 'dpkg-buildpackage --no-sign -b' \
    . \
    '../*.deb' \
    -- \
    schroot unstable-amd64-sbuild

The --testbed-init argument is needed to set up basic tools, which reprotest needs in order to make the variations in the first place. This should be the same regardless of what package is being built, but might differ depending on what virtual_server is being used.

Next, we have --testbed-build-pre, then --build-command (or -c). For our Debian directory, we install build-dependencies using apt-get, then we run the actual build command itself using dpkg-buildpackage(1).

Then, we have the source_root and the artifact_pattern. For reproducibility, we're only interested in the binary packages.

Finally, we specify that this is to take place in the "schroot" virtual_server with arguments "unstable-amd64-sbuild".

Of course, all of this is a burden to remember, if you must run the same thing many times. So that is why adding new presets for new package types would be good.

Here is a more complex example. It tells reprotest to store the build products into ./artifacts to analyse later; and also tweaks the "Debian dsc" preset so that it uses our experimental toolchain:

$ reprotest --store-dir=artifacts \
    --auto-preset-expr '_.prepend.testbed_init("apt-get install -y wget; \
        echo deb http://reproducible.alioth.debian.org/debian/ ./ >> /etc/apt/sources.list; \
        wget -q -O- https://reproducible.alioth.debian.org/reproducible.asc | apt-key add -; \
        apt-get update; apt-get upgrade -y; ")' \
    ./bash_4.4-4.0~reproducible1.dsc \
    -- \
    schroot unstable-amd64-sbuild

Alternatively, you can clone your unstable-amd64-sbuild chroot, add our repo to the cloned chroot, then use this chroot in place of "unstable-amd64-sbuild". That would allow you to omit the long --auto-preset-expr flag above.

Config File

You can also give options to reprotest via a config file. This is a time-saving measure similar to auto presets; the difference is that these are more suited for local builds that are suited to your personal purposes. (You may use both presets and config files in the same build.)

The config file takes exactly the same options as the command-line interface, but with the additional restriction that the section name must match the ones given in the --help output. Whitespace is allowed if and only if the same command-line option allows whitespace. Finally, it is not possible to give positional arguments via this mechanism.

Reprotest by default does not load any config file. You can tell it to load one with the --config-file or -f command line options. If you give it a directory such as ., it will load .reprotestrc within that directory.

A sample config file is below:

[basics]
verbosity = 1
variations =
  environment
  build_path
  user_group.available+=builduser:builduser
  fileordering
  home
  kernel
  locales
  exec_path
  time
  timezone
  umask
store_dir =
  /home/foo/build/reprotest-artifacts

[diff]
diffoscope_arg =
  --debug

Analysing diff output

Normally when diffoscope compares directories, it also compares the metadata of files in those directories - file permissions, owners, and so on.

However depending on the circumstance, this filesystem-level metadata may or may not be intended to be distributed to other systems. For example: (1) for most distros' package builders, we don't care about the metadata of the output package files; only the file contents will be distributed to other systems. On the other hand, (2) when running something like make install, we do care about the metadata, because this is what will be recreated on another system.

In developing reprotest, our experience has been that case (1) is more common and so we pass --exclude-directory-metadata by default to diffoscope. If you find that you are using reprotest for case (2) then you should pass --diffoscope-args=--no-exclude-directory-metadata to reprotest, to tell diffoscope to not ignore the metadata since it will be distributed and should therefore be reproducible. Otherwise, you may get a false-positive result.

Variations

The --vary and --variations flags in their simple forms, are a comma-separated list of variation names that indicate which variations to apply. The full list of names is given in the --help text for --variations.

In full detail, the flags are a comma-separated list of actions, as follows:

+$variation (or $variation with no explicit operator)

-$variation

Enable or disable a variation

@$variation

Enable a variation, resetting its parameters (see below) to default values.

$variation.$param=$value

$variation.$param+=$value

$variation.$param-=$value

Set/add/remove $value as/to/from the current value of the $param parameter of the $variation.

$variation.$param++

$variation.$param--

Increment/decrement the value of the $param parameter of the $variation.

Most variations do not have parameters, and for them only the + and - operators are relevant. The variations that accept parameters are:

domain_host.use_sudo

An integer, whether to use sudo(1) together with unshare(1) to change the system hostname and domainname. 0 means don't use sudo; any non-zero value means to use sudo. Default is 0, however this is not recommended and make may your build fail, see "Varying the domain and host names" for details.

environment.variables

A semicolon-separated ordered set, specifying environment variables that reprotest should try to vary. Default is "REPROTEST_CAPTURE_ENVIRONMENT". Supports regex-based syntax e.g.

• PID=\d{1,6}
• HOME=(/\w{3,12}){1,4}
• (GO|PYTHON|)PATH=(/\w{3,12}){1,4}(:(/\w{3,12}){1,4}){0,4}

Special cases:

• $VARNAME= (empty RHS) to tell reprotest to delete the variable
• $VARNAME=.{0} to tell reprotest to actually set an empty value
• \x2c and \x3b to match or generate , and ; respectively.

user_group.available

A semicolon-separated ordered set, specifying the available user+group combinations that reprotest can sudo(1) to. Default is empty, in which case the variation is a no-op, and you'll see a warning about this. Each user+group should be given in the form $user:$group where either component can be omitted, or else if there is no colon then it is interpreted as only a $user, with no $group variation.

time.faketimes

A semicolon-separated ordered set, specifying possible faketime(1) time descriptors to use. Default is empty, in which case we randomly choose a time: either now (if the latest file-modtime in source_root is older than about half-a-year) or more than half-a-year in the future.

Note that the clock continues to run during the build. It is possible for faketime(1) to freeze it, but we don't yet support that yet; it has a higher chance of causing your build to fail or misbehave.

The difference between --vary and --variations is that the former appends onto previous values but the latter resets them. Furthermore, the last value set for --variations is treated as the zeroth --vary argument. For example:

reprotest --vary=-user_group

means to vary +all (the default value for --variations) and -user_group (the given value for --vary), whereas:

reprotest --variations=-all,locales --variations=home,time --vary=timezone --vary=-time

means to vary home, time (the last given value for --variations), timezone, and -time (the given multiple values for --vary), i.e. home and timezone.

Notes on variations

reprotest tries hard to perform variations without assuming it has full root access to the system. It also assumes other software may be running on the same system, so it does not perform system-level modifications that would affect other processes. Due to these assumptions, some variations are implemented using hacks at various levels of dirtiness, which are documented below.

We will hopefully lift these assumptions for certain virtual_server contexts, in future. That would likely allow for smoother operation in those contexts. The assumptions will remain for the "null" (default) virtual_server however.

Number of CPUs

The control build uses only 1 CPU in order to try to reduce nondeterminism that might exist due to multithreading or multiprocessing. If you are sure your build is not affected by this (and good builds ought not to be), you can give --min-cpus=99999 to use all available cores for both builds.

Domain or host

Doing this without sudo may result in your build failing.

Failure is likely if your build must do system-related things - as opposed to only processing bits and bytes. This is because it runs in a separate namespace where your non-privileged user looks like it is "root", but this prevents the filesystem from recognising files owned by the real "root" user, amongst other things. This is a limitation of unshare(1) and it is not possible work around this in reprotest without heavy effort.

Therefore, it is recommended to run this variation with use_sudo=1. To avoid password prompts, see the section "Avoid sudo(1) password prompts" below.

When running inside a virtual-server:

The non-sudo method fails with "Operation not permitted", even if you edited /proc/sys/kernel/unprivileged_userns_clone. The cause is currently unknown.

The sudo method works only if you take measures to avoid sudo password prompts, since containers don't have a method to input this.

User or group

If you also vary fileordering at the same time (this is the case by default), each user you use needs to be in the "fuse" group. Do that by running usermod -aG fuse $OTHERUSER as root.

To avoid sudo(1) password prompts, see the section "Avoid sudo(1) password prompts" below.

Time

The "time" variation uses faketime(1) which sometimes causes weird and hard-to-diagnose problems. In the past, this has included:

• builds taking an infinite amount of time; though this should be fixed in recent versions of reprotest.
• builds with implausibly huge differences caused by ./configure scripts producing different results with and without faketime. This still affects bash and probably certain other packages using autotools.
• builds accessing the network failing due to certificate expiration errors and/or other time-related security errors. (Transparent builds of FOSS should not access the network in the first place, but it's outside of reprotest's scope to audit or prevent this.)

If you see a difference that you really think should not be there, try passing --variations=-time to reprotest, and/or check our results on https://tests.reproducible-builds.org/ which use a different (more reliable) mechanism to vary the system time.

Avoid sudo(1) password prompts

There is currently no good way to do this. The following is an EXPERIMENTAL solution and is brittle and unclean. You will have to decide for yourself if it's worth it for your use-case:

$ reprotest --print-sudoers \
    --variations=user_group.available+=guest-builder,domain_host.use_sudo=1 \
    | sudo EDITOR=tee visudo -f /etc/sudoers.d/local-reprotest

Make sure you set the variations you actually want to use. Obviously, don't pick privileged users for this purpose, such as root.

(Simplifying the output using wildcards, would open up passwordless access to chown anything on your system, because wildcards here match whitespace. I don't know what the sudo authors were thinking.)

No, this is not nice at all - suggestions and patches welcome.

If you want to use this in a virtual server such as a chroot, you'll need to copy (or mount or otherwise map) the resulting sudoers file into your chroot.

For example, for an schroot, you should (1) login to the source schroot and create an empty file /etc/sudoers.d/local-reprotest (this is important) and then (2) add the line:

/etc/sudoers.d/local-reprotest /etc/sudoers.d/local-reprotest none bind 0 0

to your schroot's fstab.