From c78686e411e0a14cff51836fe6c35d7584171df3 Mon Sep 17 00:00:00 2001 From: Graham Christensen Date: Fri, 10 May 2019 16:39:31 -0400 Subject: build: run diff-hook under --check and document diff-hook --- doc/manual/advanced-topics/diff-hook.xml | 207 +++++++++++++++++++++++++++++++ 1 file changed, 207 insertions(+) create mode 100644 doc/manual/advanced-topics/diff-hook.xml (limited to 'doc/manual/advanced-topics/diff-hook.xml') diff --git a/doc/manual/advanced-topics/diff-hook.xml b/doc/manual/advanced-topics/diff-hook.xml new file mode 100644 index 000000000..d2613f6df --- /dev/null +++ b/doc/manual/advanced-topics/diff-hook.xml @@ -0,0 +1,207 @@ + + +Verifying Build Reproducibility with <option linkend="conf-diff-hook">diff-hook</option> + +Check build reproducibility by running builds multiple times +and comparing their results. + +Specify a program with Nix's to +compare build results when two builds produce different results. Note: +this hook is only executed if the results are not the same, this hook +is not used for determining if the results are the same. + +For purposes of demonstration, we'll use the following Nix file, +deterministic.nix for testing: + + +let + inherit (import <nixpkgs> {}) runCommand; +in { + stable = runCommand "stable" {} '' + touch $out + ''; + + unstable = runCommand "unstable" {} '' + echo $RANDOM > $out + ''; +} + + +Additionally, nix.conf contains: + + +diff-hook = /etc/nix/my-diff-hook +run-diff-hook = true + + +where /etc/nix/my-diff-hook is an executable +file containing: + + +#!/bin/sh +exec >&2 +echo "For derivation $3:" +/run/current-system/sw/bin/runuser -u nobody -- /run/current-system/sw/bin/diff -r "$1" "$2" + + + + The diff hook can be run as root. Take care to run as little + as possible as root, for this example we use runuser + to drop privileges. + + + + +
+ + Spot-Checking Build Determinism + + + + Verify a path which already exists in the Nix store by passing + to the build command. + + + If the build passes and is deterministic, Nix will exit with a + status code of 0: + + +$ nix-build ./deterministic.nix -A stable +these derivations will be built: + /nix/store/z98fasz2jqy9gs0xbvdj939p27jwda38-stable.drv +building '/nix/store/z98fasz2jqy9gs0xbvdj939p27jwda38-stable.drv'... +/nix/store/yyxlzw3vqaas7wfp04g0b1xg51f2czgq-stable + +$ nix-build ./deterministic.nix -A stable --check +checking outputs of '/nix/store/z98fasz2jqy9gs0xbvdj939p27jwda38-stable.drv'... +/nix/store/yyxlzw3vqaas7wfp04g0b1xg51f2czgq-stable + + + If the build is not deterministic, Nix will exit with a status + code of 1: + + +$ nix-build ./deterministic.nix -A unstable +these derivations will be built: + /nix/store/cgl13lbj1w368r5z8gywipl1ifli7dhk-unstable.drv +building '/nix/store/cgl13lbj1w368r5z8gywipl1ifli7dhk-unstable.drv'... +/nix/store/krpqk0l9ib0ibi1d2w52z293zw455cap-unstable + +$ nix-build ./deterministic.nix -A unstable --check +checking outputs of '/nix/store/cgl13lbj1w368r5z8gywipl1ifli7dhk-unstable.drv'... +error: derivation '/nix/store/cgl13lbj1w368r5z8gywipl1ifli7dhk-unstable.drv' may not be deterministic: output '/nix/store/krpqk0l9ib0ibi1d2w52z293zw455cap-unstable' differs + + +In the Nix daemon's log, we will now see: + +For derivation /nix/store/cgl13lbj1w368r5z8gywipl1ifli7dhk-unstable.drv: +1c1 +< 8108 +--- +> 30204 + + + + Using with + will cause Nix to keep the second build's output in a special, + .check path: + + +$ nix-build ./deterministic.nix -A unstable --check --keep-failed +checking outputs of '/nix/store/cgl13lbj1w368r5z8gywipl1ifli7dhk-unstable.drv'... +note: keeping build directory '/tmp/nix-build-unstable.drv-0' +error: derivation '/nix/store/cgl13lbj1w368r5z8gywipl1ifli7dhk-unstable.drv' may not be deterministic: output '/nix/store/krpqk0l9ib0ibi1d2w52z293zw455cap-unstable' differs from '/nix/store/krpqk0l9ib0ibi1d2w52z293zw455cap-unstable.check' + + + In particular, notice the + /nix/store/krpqk0l9ib0ibi1d2w52z293zw455cap-unstable.check + output. Nix has copied the build results to that directory where you + can examine it. + + + <literal>.check</literal> paths are not registered store paths + + Check paths are not protected against garbage collection, + and this path will be deleted on the next garbage collection. + + The path is guaranteed to be alive for the duration of + 's execution, but may be deleted + any time after. + + If the comparison is performed as part of automated tooling, + please use the diff-hook or author your tooling to handle the case + where the build was not deterministic and also a check path does + not exist. + + + + is only usable if the derivation has + been built on the system already. If the derivation has not been + built Nix will fail with the error: + +error: some outputs of '/nix/store/hzi1h60z2qf0nb85iwnpvrai3j2w7rr6-unstable.drv' are not valid, so checking is not possible + + + Run the build without , and then try with + again. + +
+ +
+ + Automatic and Optionally Enforced Determinism Verification + + + + Automatically verify every build at build time by executing the + build multiple times. + + + + Setting and + in your + nix.conf permits the automated verification + of every build Nix performs. + + + + The following configuration will run each build three times, and + will require the build to be deterministic: + + +enforce-determinism = true +repeat = 2 + + + + + Setting to false as in + the following configuration will run the build multiple times, + execute the build hook, but will allow the build to succeed even + if it does not build reproducibly: + + +enforce-determinism = false +repeat = 1 + + + + + An example output of this configuration: + +$ nix-build ./test.nix -A unstable +these derivations will be built: + /nix/store/ch6llwpr2h8c3jmnf3f2ghkhx59aa97f-unstable.drv +building '/nix/store/ch6llwpr2h8c3jmnf3f2ghkhx59aa97f-unstable.drv' (round 1/2)... +building '/nix/store/ch6llwpr2h8c3jmnf3f2ghkhx59aa97f-unstable.drv' (round 2/2)... +output '/nix/store/6xg356v9gl03hpbbg8gws77n19qanh02-unstable' of '/nix/store/ch6llwpr2h8c3jmnf3f2ghkhx59aa97f-unstable.drv' differs from '/nix/store/6xg356v9gl03hpbbg8gws77n19qanh02-unstable.check' from previous round +/nix/store/6xg356v9gl03hpbbg8gws77n19qanh02-unstable + + +
+ -- cgit v1.2.3 From 6df61db0600ca73ccd51e3e5bec5312a04e99da1 Mon Sep 17 00:00:00 2001 From: Graham Christensen Date: Fri, 10 May 2019 20:59:39 -0400 Subject: diff hook: execute as the build user, and pass the temp dir --- doc/manual/advanced-topics/diff-hook.xml | 12 +++++------- 1 file changed, 5 insertions(+), 7 deletions(-) (limited to 'doc/manual/advanced-topics/diff-hook.xml') diff --git a/doc/manual/advanced-topics/diff-hook.xml b/doc/manual/advanced-topics/diff-hook.xml index d2613f6df..fb4bf819f 100644 --- a/doc/manual/advanced-topics/diff-hook.xml +++ b/doc/manual/advanced-topics/diff-hook.xml @@ -46,17 +46,15 @@ file containing: #!/bin/sh exec >&2 echo "For derivation $3:" -/run/current-system/sw/bin/runuser -u nobody -- /run/current-system/sw/bin/diff -r "$1" "$2" +/run/current-system/sw/bin/diff -r "$1" "$2" - - The diff hook can be run as root. Take care to run as little - as possible as root, for this example we use runuser - to drop privileges. - - +The diff hook is executed by the same user and group who ran the +build. However, the diff hook does not have write access to the store +path just built. +
Spot-Checking Build Determinism -- cgit v1.2.3