Managing Log Output

Buildkite uses our open-source terminal Golang library to provide you with the best possible terminal rendering experience for your build logs, including ANSI terminal emulation to ensure spinners, progress bars, colors and emojis are rendered beautifully.

Collapsing output

You can group and collapse your build output by echoing --- [group name] in your build output.

echo "--- A section of the build"

You can group, collapse and de-emphasize your build output by echoing ~~~ [group name] in your build output.

echo "~~~ An unimportant section of the build"

If you want to have the group open by default, use +++ instead:

echo "+++ A section of the build"

If no group is explicitly expanded (+++), then the last collapsed regular group (---) gets expanded instead. If you really want all groups to be collapsed, add an empty expanded group (+++).

If you'd like to open the previously defined group, use ^^^ +++. This is useful if a command within a group fails, and you'd like to have the group already open when you view the log.

echo "--- Bundling"
bundle
if [[ $? -ne 0 ]]; then
  echo "^^^ +++"
  echo "Bundler failed, oh no!!"
fi

You can even include colors and emojis!

echo -e "--- Running \033[33mspecs\033[0m :cow::bell:"

Log output limits

If your build output exceeds 1MB then we'll only show the last 1MB of it in the rendered terminal output on your build page. In addition, your log file must not exceed 100MB else it may fail to upload.

If your log exceeds 1MB then we highly recommend reconfiguring your build tools to filter out unnecessary lines. Sometimes this isn't always possible, so you can use the below techniques to store and filter your log.

Storing the original log

One method for storing the original log is the Unix tee command. It allows you to store the output stream of a command to a file and passing it straight through unchanged to the next command.

#!/bin/bash

set -euo pipefail

your_build_command | tee build.log | <filter command>

When this script is run it will store the original output of your_build_command to the file build.log.

To store this file alongside your build, add the artifact_paths attribute to the command step running your script:

steps:
  - command: build.sh
    artifact_paths: "build.log"

When your build is finished the agent will upload build.log as a build artifact, which will be downloadable from the "Artifacts" tab on your build page.

Filtering with grep

Grep is a Unix tool to help you filter lines of text that match a pattern. For example, the following script only sends Buildkite the matching lines as your log output, whilst storing the original log for artifact uploading.

#!/bin/bash

set -euo pipefail

your_build_command | tee build.log | grep 'some pattern'

Truncating with tail

Tail is a Unix tool that returns the last portion of a file. This is useful if your log output is exceeding our hard limit of 100MB. For example, the following script only sends Buildkite the last 90MB as your output log, whilst storing the original log for artifact uploading.

#!/bin/bash

set -euo pipefail

your_build_command | tee build.log | tail -c90000000

Improving Xcode logs with xcpretty

xcpretty is an open-source tool that helps to reduce, format and color-code your Xcode build output. Once you've installed xcpretty you can pipe the output of xcodebuild into it:

#!/bin/bash

set -euo pipefail

xcodebuild <build options> | tee -a build.log | xcpretty -c

Make sure to set the -o pipefail option in your buildscript as above, otherwise the build failure status might not be passed through correctly.

Encryption and security

Buildkite has zero access to your source code in the pipelines and only receives and stores the log output of the builds and build artifacts in encrypted form.

Logs are AES-encrypted, and the build artifacts are encrypted in transit and at rest using AWS encryption (KMS or S3 SSE). As a result, the keys cannot be extracted on the Buildkite's side, and the AWS solutions provide mitigations against zero-day attacks and other security issues. Beyond this, the control over security measures within your infrastructure is up to you.

If you choose to host your build artifacts yourself, they end up in your private AWS bucket.

If you are a Buildkite customer on the Enterprise plan, you can also set up a private AWS S3 build log archive location and store the logs in your private bucket.

To further tighten the security in a Buildkite organization, you can use the API Access Audit to track the actions of the users who have API access tokens that can access your organization's data using the REST and GraphQL API.

Redacted environment variables

The Buildkite agent can redact the values of environment variables whose names match common patterns for passwords, and other secure information, before the build log is uploaded to Buildkite.

The default environment variable name patterns are *_PASSWORD, *_SECRET and *_TOKEN. You can replace the default patterns by setting redacted-vars on your agent.

For example, if you have environment variable MY_SECRET="topsecret"and you run a command that outputs This is topsecret info, the log output will actually be This is [REDACTED] info.

Private build log archive storage

By default, build logs are stored in encrypted form in Buildkite's Amazon S3 buckets, but you can also store the archived build logs in your private AWS S3 bucket.

To set up a private build log archive storage:

1. Create an Amazon S3 bucket in us-east-1 location (the only region that is currently supported).

2. Provide read and write access permission policy for the Buildkite's AWS account 032379705303.

   Here's an example policy that contains an Amazon S3 bucket configuration with Buildkite's account number in it. Replace my-bucket and my-prefix placeholders with your Amazon S3 bucket information:

   {
       "Version": "2012-10-17",
       "Statement": [
           {
               "Sid": "AllowBuildkiteToWriteObjectsInLogsPrefix",
               "Effect": "Allow",
               "Principal": {
                   "AWS": "arn:aws:iam::032379705303:root"
               },
               "Action": "s3:PutObject",
               "Resource": "arn:aws:s3:::my-bucket/my-prefix/*",
               "Condition": {
                   "StringEquals": {
                       "s3:x-amz-acl": "bucket-owner-full-control"
                   }
               }
           },
           {
               "Sid": "AllowBuildkiteToReadObjectsInLogsPrefix",
               "Effect": "Allow",
               "Principal": {
                   "AWS": "arn:aws:iam::032379705303:root"
               },
               "Action": "s3:GetObject",
               "Resource": "arn:aws:s3:::my-bucket/my-prefix/*"
           },
           {
               "Sid": "AllowBuildkiteToDeleteObjectsInLogsPrefix",
               "Effect": "Allow",
               "Principal": {
                   "AWS": "arn:aws:iam::032379705303:root"
               },
               "Action": "s3:DeleteObject",
               "Resource": "arn:aws:s3:::my-bucket/my-prefix/*"
           },
           {
               "Sid": "AllowBuildkiteToListBucketInLogsPrefix",
               "Effect": "Allow",
               "Principal": {
                   "AWS": "arn:aws:iam::032379705303:root"
               },
               "Action": "s3:ListBucket",
               "Resource": "arn:aws:s3:::my-bucket",
               "Condition": {
                   "StringLike": {
                       "s3:prefix": "my-prefix/*"
                   }
               }
           }
       ]
   }
   

3. Reach out to support@buildkite.com and provide the address of your Amazon S3 bucket. The Buildkite engineering team will continue the configuration to complete the setup.