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Recreating a Snapshot or Buildspec

This document describes how a developer can get their chromiumos repo into the state described by a snapshot or buildspec.

What are snapshots and buildspecs?

Snapshots and buildspecs are both special manifests in which every project is pinned to an explicit git revision. They allow exact recreations of the state of a builder, but only if you know how to do the recreation. This document describes the steps needed to do that recreation.

The difference is where they come from. Snapshots are created periodically by annealing. Buildspecs are the definition of a particular ChromeOS version, and are created when a new version is made.

NOTE: Googlers can read more about snapshots and buildspecs at go/chromeos-manifests#buildspecs.

Often, a build breakage or failing test can be traced to a particular ChromeOS snapshot or version. For instance, "This test passed in snapshot 54673 but started failing in snapshot 54674."

If you cannot determine the root cause, you may need to recreate the successful build (snapshot 54673 in this example) and then apply individual changes to the successful build until the problem appears.

Recreating a snapshot buildspec

Ensure you have no local modifications

Ensure there are no branches checked out:

$ repo branch

The output should not have any branches with a "*" in the first column. If there are, go into each directory and run

$ git checkout cros/main

(or cros-internal/main for internal repos)

Check for changes that haven't been added to git:

$ repo diff

Make sure the output is empty.

Depending on exactly what you need to accomplish, you may also wish to make sure you are not cros workoning anything:

$ cros workon --board=${BOARD} list
# for each package listed:
$ cros workon --board=${BOARD} stop ${PACKAGE}

(This is especially important if you are trying to recreate a bug in build-packages' dependency calculations; cros workon start ensures a package will always be emerged even if its dependencies didn't change.)

Next, you will need to know if you looking for a snapshot or a buildspec.

If you want a snapshot

Find the snapshot you are looking for

Snapshots are found by going to the snapshot branch: for public and for internal. Each commit has the snapshot number at the top of the commit message.

Find the commit hash for that commit. (Hint: hit the [log] link to bring up a list of all the snapshots in that branch.)

For example, for public snapshot 54673, you would look at and see the commit hash was 9619dc893f4dfdc27a936c79cd1f891ebef65d75.

Switch repo to the snapshot

From the root chromiumos directory (normally ~/chromiumos), run

$ repo init -u -b <commit hash>

for a public snapshot/buildspec or

$ repo init -u  -b <commit hash>

for a private snapshot/buildspec.

Regardless of which variant of repo init you used, immediately run

$ repo sync -j <number>

After this completes, all the git logs in all the git repos should show that the latest commit is tagged "m/<manifest commit hash>"; for instance, after going to public snapshot 54673 (with a manifest commit hash of 9619dc893f4dfdc27a936c79cd1f891ebef65d75), git log in src/platform2 will show:

commit 4bce3873f6a8bc88df4182ae642442b4e39a51f4 (HEAD, m/9619dc893f4dfdc27a936c79cd1f891ebef65d75)
Author: Betul Soysal <>
Date:   Wed Aug 16 01:22:50 2023 +0000

If you want a buildspec

Find the buildspec you are looking for

To re-initialize the repo to a buildspec, you will need the "gsutil URI" (a URI starting with gs://) that leads to the buildspec XML file.

For everyone

If you already know the milestone and version, you should be able to just construct the URI manually as

For example, version 15550.0.0 was in milestone 117, so the gsutil URI for the public buildspec is gs://chromiumos-manifest-versions/buildspecs/117/15550.0.0.xml.

If you are building a release buildspec, pass --no-usepkg to cros build-packages to build from source.

For Googlers

If you want to browse the list of all the available buildspecs, Googlers can refer to http://go/chromeos-manifests#buildspec-storage for the location of the internal websites that list them. Find the XML file corresponding to the version you want to recreate then click on the ⋮ (three vertical dots) menu on the righthand side and select "Copy gsutil URI".

Alternatively, you can use the gsutil tool with the above URIs.

For Non-Googlers

It is only possible to browse the buildspecs for the public manifest using the tool that comes with depot_tools; there is no browser-based access.

If you are external to Google and you need to browse the list of buildspecs, start with

$ ls gs://chromiumos-manifest-versions

and work your way downwards until you find the XML file you want.

Switch repo to the buildspec

From the root chromiumos directory (normally ~/chromiumos), run

$ repo init --standalone-manifest <gsutil URI>

For example, for 15550.0.0 in the public manifest, this would look like

$ repo init --standalone-manifest gs://chromiumos-manifest-versions/buildspecs/117/15550.0.0.xml

Then run

$ repo sync -j <number>

Getting back to normal

Once you are done with your investigations, run

$ repo init -u -b HEAD

if you are external or

$ repo init -u -b HEAD

if you are a Googler. Once that completes, run

$ repo sync -j <number>

git log in one of the git repositories should now show the latest commit tagged with "m/main" and "cros/main".

Remember to cros workon any projects you stopped working on above.