This page documents the latest, unreleased version of Buildbot. For documentation for released versions, see

Global Configuration

The keys in this section affect the operations of the buildmaster globally.

Database Specification

Buildbot requires a connection to a database to maintain certain state information, such as tracking pending build requests. In the default configuration Buildbot uses a file-based SQLite database, stored in the state.sqlite file of the master's base directory. Override this configuration with the db_url parameter.

Buildbot accepts a database configuration in a dictionary named db. All keys are optional:

c['db'] = {
    'db_url' : 'sqlite:///state.sqlite',

The db_url key indicates the database engine to use. The format of this parameter is completely documented at, but is generally of the form:


These parameters can be specified directly in the configuration dictionary, as c['db_url'] and c['db_poll_interval'], although this method is deprecated.

The following sections give additional information for particular database backends:


For sqlite databases, since there is no host and port, relative paths are specified with sqlite:/// and absolute paths with sqlite:////. Examples:

c['db_url'] = "sqlite:///state.sqlite"

SQLite requires no special configuration.

If Buildbot produces "database is locked" exceptions, try adding serialize_access=1 to the DB URL as a workaround:

c['db_url'] = "sqlite:///state.sqlite?serialize_access=1"

and please file a bug at


c['db_url'] = "mysql://"

The max_idle argument for MySQL connections is unique to Buildbot, and should be set to something less than the wait_timeout configured for your server. This controls the SQLAlchemy pool_recycle parameter, which defaults to no timeout. Setting this parameter ensures that connections are closed and re-opened after the configured amount of idle time. If you see errors such as _mysql_exceptions.OperationalError: (2006, 'MySQL server has gone away'), this means your max_idle setting is probably too high. show global variables like 'wait_timeout'; will show what the currently configured wait_timeout is on your MySQL server.

Buildbot requires use_unique=True and charset=utf8, and will add them automatically, so they do not need to be specified in db_url.

MySQL defaults to the MyISAM storage engine, but this can be overridden with the storage_engine URL argument.

Note that, because of InnoDB's extremely short key length limitations, it cannot be used to run Buildbot. See for more information.


c['db_url'] = "postgresql://username@hostname/dbname"

PosgreSQL requires no special configuration.

MQ Specification

Buildbot uses a message-queueing system to handle communication within the master. Messages are used to indicate events within the master, and components that are interested in those events arrange to receive them.

The message queueing implementation is configured as a dictionary in the mq option. The type key describes the type of MQ implemetation to be used. Note that the implementation type cannot be changed in a reconfig.

The available implemenetation types are described in the following sections.


c['mq'] = {
    'type' : 'simple',
    'debug' : False,

This is the default MQ implementation. Similar to SQLite, it has no additional software dependencies, but does not support multi-master mode.

Note that this implementation also does not support message persistence across a restart of the master. For example, if a change is received, but the master shuts down before the schedulers can create build requests for it, then those schedulers will not be notified of the change when the master starts again.

The debug key, which defaults to False, can be used to enable logging of every message produced on this master.


c['mq'] = {
    'type' : 'wamp',
    'router_url': 'ws://url/to/crossbar'
    'realm': 'buildbot'
    'debug' : False,
    'debug_websockets' : False,
    'debug_lowlevel' : False,

This is a MQ implementation using wamp protocol. This implementation uses Python Autobahn wamp client library, and is fully asynchronous (no use of threads) To use this implementation, you need a wamp router like Crossbar. The implementation does not yet support wamp authentication yet. This MQ allows buildbot to run in multi-master mode.

Note that this implementation also does not support message persistence across a restart of the master. For example, if a change is received, but the master shuts down before the schedulers can create build requests for it, then those schedulers will not be notified of the change when the master starts again.

router_url key is mandatory, and should point to your router websocket url. Buildbot is only supporting wamp over websocket, which is a sub-protocol of http. SSL is supported using wss:// instead of ws://. You must use a router with very reliable connection to the master. If for some reason, the wamp connection is lost, then the master will stop, and should be restarted via a process manager.

realm key is optional and defaults to buildbot, and configures the wamp realm to use for your buildbot messages.

The debug key, which defaults to False, can be used to enable logging of every message produced on this master. debug_websocket and debug_lowlevel, enable more debug logs in autobahn.

Multi-master mode

Normally buildbot operates using a single master process that uses the configured database to save state.

It is possible to configure buildbot to have multiple master processes that share state in the same database. This has been well tested using a MySQL database. There are several benefits of Multi-master mode:

  • You can have large numbers of build slaves handling the same queue of build requests. A single master can only handle so many slaves (the number is based on a number of factors including type of builds, number of builds, and master and slave IO and CPU capacity--there is no fixed formula). By adding another master which shares the queue of build requests, you can attach more slaves to this additional master, and increase your build throughput.
  • You can shut one master down to do maintenance, and other masters will continue to do builds.

State that is shared in the database includes:

  • List of changes
  • Scheduler names and internal state
  • Build requests, including the builder name

Because of this shared state, you are strongly encouraged to:

  • Ensure that each named scheduler runs on only one master. If the same scheduler runs on multiple masters, it will trigger duplicate builds and may produce other undesirable behaviors.
  • Ensure builder names are unique for a given build factory implementation. You can have the same builder name configured on many masters, but if the build factories differ, you will get different results depending on which master claims the build.

One suggested configuration is to have one buildbot master configured with just the scheduler and change sources; and then other masters configured with just the builders.

To enable multi-master mode in this configuration, you will need to set the multiMaster option so that buildbot doesn't warn about missing schedulers or builders.

# Enable multiMaster mode; disables warnings about unknown builders and
# schedulers
c['multiMaster'] = True
# Check for new build requests every 60 seconds
c['db'] = {
    'db_url' : 'mysql://...',

Site Definitions

Three basic settings describe the buildmaster in status reports:

c['title'] = "Buildbot"
c['titleURL'] = ""

title is a short string that will appear at the top of this buildbot installation's home page (linked to the titleURL).

titleURL is a URL string that must end with a slash (/). HTML status displays will show title as a link to titleURL. This URL is often used to provide a link from buildbot HTML pages to your project's home page.

The buildbotURL string should point to the location where the buildbot's internal web server is visible. This URL must end with a slash (/).

When status notices are sent to users (e.g., by email or over IRC), buildbotURL will be used to create a URL to the specific build or problem that they are being notified about.

Log Handling

c['logCompressionLimit'] = 16384
c['logCompressionMethod'] = 'gz'
c['logMaxSize'] = 1024*1024 # 1M
c['logMaxTailSize'] = 32768
c['logEncoding'] = 'utf-8'

The logCompressionLimit enables compression of build logs on disk for logs that are bigger than the given size, or disables that completely if set to False. The default value is 4096, which should be a reasonable default on most file systems. This setting has no impact on status plugins, and merely affects the required disk space on the master for build logs.

The logCompressionMethod controls what type of compression is used for build logs. The default is 'gz', and the other valid option are 'raw' (no compression), 'gz' or 'lz4' (required lz4 package).

Please find below some stats extracted from 50x "Pyflakes" runs (results may differ according to log type).

Space saving details
compression raw log size compressed log size space saving compression speed
bz2 2.981 MB 0.603 MB 79.77% 3.433 MB/s
gz 2.981 MB 0.568 MB 80.95% 6.604 MB/s
lz4 2.981 MB 0.844 MB 71.68% 77.668 MB/s

The logMaxSize parameter sets an upper limit (in bytes) to how large logs from an individual build step can be. The default value is None, meaning no upper limit to the log size. Any output exceeding logMaxSize will be truncated, and a message to this effect will be added to the log's HEADER channel.

If logMaxSize is set, and the output from a step exceeds the maximum, the logMaxTailSize parameter controls how much of the end of the build log will be kept. The effect of setting this parameter is that the log will contain the first logMaxSize bytes and the last logMaxTailSize bytes of output. Don't set this value too high, as the the tail of the log is kept in memory.

The logEncoding parameter specifies the character encoding to use to decode bytestrings provided as logs. It defaults to utf-8, which should work in most cases, but can be overridden if necessary. In extreme cases, a callable can be specified for this parameter. It will be called with byte strings, and should return the corresponding Unicode string.

This setting can be overridden for a single build step with the logEncoding step parameter. It can also be overridden for a single log file by passing the logEncoding parameter to addLog.

Data Lifetime


c['changeHorizon'] = 200
c['buildHorizon'] = 100
c['eventHorizon'] = 50
c['logHorizon'] = 40
c['buildCacheSize'] = 15

Buildbot stores historical information on disk in the form of "Pickle" files and compressed logfiles. In a large installation, these can quickly consume disk space, yet in many cases developers never consult this historical information.

The changeHorizon key determines how many changes the master will keep a record of. One place these changes are displayed is on the waterfall page. This parameter defaults to 0, which means keep all changes indefinitely.

The buildHorizon specifies the minimum number of builds for each builder which should be kept on disk. The eventHorizon specifies the minimum number of events to keep--events mostly describe connections and disconnections of slaves, and are seldom helpful to developers. The logHorizon gives the minimum number of builds for which logs should be maintained; this parameter must be less than or equal to buildHorizon. Builds older than logHorizon but not older than buildHorizon will maintain their overall status and the status of each step, but the logfiles will be deleted.


c['caches'] = {
    'Changes' : 100,     # formerly c['changeCacheSize']
    'Builds' : 500,      # formerly c['buildCacheSize']
    'chdicts' : 100,
    'BuildRequests' : 10,
    'SourceStamps' : 20,
    'ssdicts' : 20,
    'objectids' : 10,
    'usdicts' : 100,

The caches configuration key contains the configuration for Buildbot's in-memory caches. These caches keep frequently-used objects in memory to avoid unnecessary trips to the database or to pickle files. Caches are divided by object type, and each has a configurable maximum size.

The default size for each cache is 1, except where noted below. A value of 1 allows Buildbot to make a number of optimizations without consuming much memory. Larger, busier installations will likely want to increase these values.

The available caches are:


the number of change objects to cache in memory. This should be larger than the number of changes that typically arrive in the span of a few minutes, otherwise your schedulers will be reloading changes from the database every time they run. For distributed version control systems, like Git or Hg, several thousand changes may arrive at once, so setting this parameter to something like 10000 isn't unreasonable.

This parameter is the same as the deprecated global parameter changeCacheSize. Its default value is 10.


The buildCacheSize parameter gives the number of builds for each builder which are cached in memory. This number should be larger than the number of builds required for commonly-used status displays (the waterfall or grid views), so that those displays do not miss the cache on a refresh.

This parameter is the same as the deprecated global parameter buildCacheSize. Its default value is 15.

The number of rows from the changes table to cache in memory. This value should be similar to the value for Changes.
The number of BuildRequest objects kept in memory. This number should be higher than the typical number of outstanding build requests. If the master ordinarily finds jobs for BuildRequests immediately, you may set a lower value.
the number of SourceStamp objects kept in memory. This number should generally be similar to the number BuildRequesets.
The number of rows from the sourcestamps table to cache in memory. This value should be similar to the value for SourceStamps.
The number of object IDs - a means to correlate an object in the Buildbot configuration with an identity in the database--to cache. In this version, object IDs are not looked up often during runtime, so a relatively low value such as 10 is fine.

The number of rows from the users table to cache in memory. Note that for a given user there will be a row for each attribute that user has.

c['buildCacheSize'] = 15

Merging Build Requests

c['collapseRequests'] = True

This is a global default value for builders' collapseRequests parameter, and controls the merging of build requests.

This parameter can be overridden on a per-builder basis. See Collapsing Build Requests for the allowed values for this parameter.

Prioritizing Builders

def prioritizeBuilders(buildmaster, builders):
c['prioritizeBuilders'] = prioritizeBuilders

By default, buildbot will attempt to start builds on builders in order, beginning with the builder with the oldest pending request. Customize this behavior with the prioritizeBuilders configuration key, which takes a callable. See Builder Priority Functions for details on this callable.

This parameter controls the order that the build master can start builds, and is useful in situations where there is resource contention between builders, e.g., for a test database. It does not affect the order in which a builder processes the build requests in its queue. For that purpose, see Prioritizing Builds.

Setting the PB Port for Slaves

c['protocols'] = {"pb": {"port": 10000}}

The buildmaster will listen on a TCP port of your choosing for connections from buildslaves. It can also use this port for connections from remote Change Sources, status clients, and debug tools. This port should be visible to the outside world, and you'll need to tell your buildslave admins about your choice.

It does not matter which port you pick, as long it is externally visible; however, you should probably use something larger than 1024, since most operating systems don't allow non-root processes to bind to low-numbered ports. If your buildmaster is behind a firewall or a NAT box of some sort, you may have to configure your firewall to permit inbound connections to this port.

c['protocols']['pb']['port'] is a strports specification string, defined in the twisted.application.strports module (try pydoc twisted.application.strports to get documentation on the format).

This means that you can have the buildmaster listen on a localhost-only port by doing:

c['protocols'] = {"pb": {"port": "tcp:10000:interface="}}

This might be useful if you only run buildslaves on the same machine, and they are all configured to contact the buildmaster at localhost:10000.


In Buildbot versions <=0.8.8 you might see slavePortnum option. This option contains same value as c['protocols']['pb']['port'] but not recomended to use.

Defining Global Properties

The properties configuration key defines a dictionary of properties that will be available to all builds started by the buildmaster:

c['properties'] = {
    'Widget-version' : '1.2',
    'release-stage' : 'alpha'


If you set manhole to an instance of one of the classes in buildbot.manhole, you can telnet or ssh into the buildmaster and get an interactive Python shell, which may be useful for debugging buildbot internals. It is probably only useful for buildbot developers. It exposes full access to the buildmaster's account (including the ability to modify and delete files), so it should not be enabled with a weak or easily guessable password.

There are three separate Manhole classes. Two of them use SSH, one uses unencrypted telnet. Two of them use a username+password combination to grant access, one of them uses an SSH-style authorized_keys file which contains a list of ssh public keys.


Using any Manhole requires that pycrypto and pyasn1 be installed. These are not part of the normal Buildbot dependencies.

You construct this with the name of a file that contains one SSH public key per line, just like ~/.ssh/authorized_keys. If you provide a non-absolute filename, it will be interpreted relative to the buildmaster's base directory.
This one accepts SSH connections but asks for a username and password when authenticating. It accepts only one such pair.
This accepts regular unencrypted telnet connections, and asks for a username/password pair before providing access. Because this username/password is transmitted in the clear, and because Manhole access to the buildmaster is equivalent to granting full shell privileges to both the buildmaster and all the buildslaves (and to all accounts which then run code produced by the buildslaves), it is highly recommended that you use one of the SSH manholes instead.
# some examples:
from buildbot.plugins import util
c['manhole'] = util.AuthorizedKeysManhole(1234, "authorized_keys")
c['manhole'] = util.PasswordManhole(1234, "alice", "mysecretpassword")
c['manhole'] = util.TelnetManhole(1234, "bob", "snoop_my_password_please")

The Manhole instance can be configured to listen on a specific port. You may wish to have this listening port bind to the loopback interface (sometimes known as lo0, localhost, or to restrict access to clients which are running on the same host.

from buildbot.plugins import util
c['manhole'] = util.PasswordManhole("tcp:9999:interface=","admin","passwd")

To have the Manhole listen on all interfaces, use "tcp:9999" or simply 9999. This port specification uses twisted.application.strports, so you can make it listen on SSL or even UNIX-domain sockets if you want.

Note that using any Manhole requires that the TwistedConch package be installed.

The buildmaster's SSH server will use a different host key than the normal sshd running on a typical unix host. This will cause the ssh client to complain about a host key mismatch, because it does not realize there are two separate servers running on the same host. To avoid this, use a clause like the following in your .ssh/config file:

Host remotehost-buildbot
HostName remotehost
HostKeyAlias remotehost-buildbot
Port 9999
# use 'user' if you use PasswordManhole and your name is not 'admin'.
# if you use AuthorizedKeysManhole, this probably doesn't matter.
User admin

Using Manhole

After you have connected to a manhole instance, you will find yourself at a Python prompt. You have access to two objects: master (the BuildMaster) and status (the master's Status object). Most interesting objects on the master can be reached from these two objects.

To aid in navigation, the show method is defined. It displays the non-method attributes of an object.

A manhole session might look like:

>>> show(master)
data attributes of <buildbot.master.BuildMaster instance at 0x7f7a4ab7df38>
                       basedir : '/home/dustin/code/buildbot/t/buildbot/'...
                     botmaster : <type 'instance'>
                buildCacheSize : None
                  buildHorizon : None
                   buildbotURL : http://localhost:8010/
               changeCacheSize : None
                    change_svc : <type 'instance'>
                configFileName : master.cfg
                            db : <class 'buildbot.db.connector.DBConnector'>
                        db_url : sqlite:///state.sqlite
>>> show(['win32'])
data attributes of <Builder ''builder'' at 48963528>
>>> win32 = _
>>> win32.category = 'w32'

Metrics Options

c['metrics'] = dict(log_interval=10, periodic_interval=10)

metrics can be a dictionary that configures various aspects of the metrics subsystem. If metrics is None, then metrics collection, logging and reporting will be disabled.

log_interval determines how often metrics should be logged to twistd.log. It defaults to 60s. If set to 0 or None, then logging of metrics will be disabled. This value can be changed via a reconfig.

periodic_interval determines how often various non-event based metrics are collected, such as memory usage, uncollectable garbage, reactor delay. This defaults to 10s. If set to 0 or None, then periodic collection of this data is disabled. This value can also be changed via a reconfig.

Read more about metrics in the Metrics section in the developer documentation.

Statistics Service

The Statistics Service (or stats service) is a new service being introduced in Buildbot Nine. This service supports for collecting arbitrary data from within a running Buildbot instance and export it do a number of storage backends. Currently, only InfluxDB is supported as a storage backend. Also, InfluxDB (or any other storage backend) is not a mandatory dependency. Buildbot can run without it although StatsService will be of no use in such a case. At present, StatsService can only keep track of build properties and build times (start, end, duration).

Example usage:

captures = [stats.CaptureProperty('runtests', 'tree-size-KiB'),
c['services'] = []
        stats.InfluxStorageService('localhost', 8086, 'root', 'root', 'test', captures)
    ], name="StatsService"))

The services configuration value should be initialized as a list and a StatsService instance should be appended to it as shown in the example above.

Statistics Service

class StatsService:

This is the main class for statistics service. It is initialized in the master configuration as show in the example above. It takes two arguments:

  • storage_backends: A list of storage backends (see Storage Backends). In the example above, stats.InfluxStorageService is an instance of a storage backend. Each storage backend is an instances of subclasses of statsStorageBase.
  • name: The name of this service.

yieldMetricsValue: This method can be used to send arbitrary data for storage. (See Using StatsService.yieldMetricsValue for more.)

Capture Classes

class CaptureProperty:

Instance of this class declares which properties must be captured and sent to the Storage Backends. It takes the following arguments:

  • builder_name: The name of builder in which the property is recorded.
  • property_name: The name of property needed to be recorded as a statistic.
  • callback=None: (Optional) A custom callback function for this class. This callback function should take in two arguments - build_properties (dict) and property_name (str) and return a string that will be sent for storage in the storage backends.

class CaptureBuildStartTime:

Instance of this class declares which builders start times are to be captured and sent to Storage Backends. It takes the following arguments:

  • builder_name: The name of builder whose times are to be recorded.
  • callback=None: (Optional) A custom callback function for this class. This callback function should take in a Python datetime object and return a string that will be sent for storage in the storage backends.

class CaptureBuildEndTime:

Exactly like CaptureBuildStartTime except it declares the builders whose end time is to be recorded. The arguments are same as CaptureBuildStartTime.

class CaptureBuildDuration:

Instance of this class declares the builders whose build durations are to be recorded. It takes the following arguments:

  • builder_name: The name of builder whose times are to be recorded.
  • report_in='seconds': Can be one of three: 'seconds', 'minutes', or 'hours'. This is the units in which the build time will be reported.
  • callback=None: (Optional) A custom callback function for this class. This callback function should take in two Python datetime objects - a start_time and an end_time and return a string that will be sent for storage in the storage backends.

class CaptureData:

A capture class for capturing arbitrary data that is not stored as build-data. Needs to be used in conjunction with yieldMetricsValue (See Using StatsService.yieldMetricsValue). Takes the following arguments:

  • data_name: The name of data to be captured. Same as in yieldMetricsValue.
  • builder_name: The name of builder whose times are to be recorded.
  • callback=None: The callback function for this class. This callback receives the data sent to yieldMetricsValue as post_data (See Using StatsService.yieldMetricsValue). It must return a string that is to be sent to the storage backends for storage.

Using StatsService.yieldMetricsValue

Advanced users can modify BuildSteps to use StatsService.yieldMetricsValue which will send arbitrary data for storage to the StatsService. It takes the following arguments:

  • data_name: The name of the data being sent or storage.
  • post_data: A dictionary of key value pair that is sent for storage. The keys will act as columns in a database and the value is stored under that column.
  • buildid: The integer build id of the current build. Obtainable in all BuildSteps.

Along with using yieldMetricsValue, the user will also need to use the CaptureData capture class.

Storage Backends

Storage backends are responsible for storing any statistics data sent to them. A storage backend will generally be some sort of a database-server running on a machine. (Note: This machine may be different from the one running BuildMaster)

Currently, only InfluxDB is supported as a storage backend.

class InfluxStorageService:

This class is a Buildbot client to the InfluxDB storage backend. InfluxDB is a distributed, time series database that employs a key-value pair storage system.

It requires the following arguments:

  • url: The URL where the service is running.
  • port: The port on which the service is listening.
  • user: Username of a InfluxDB user.
  • password: Password for user.
  • db: The name of database to be used.
  • captures: A list of objects of Capture Classes. This tells which statistics are to be stored in this storage backend.
  • name=None: (Optional) The name of this storage backend.

Users Options

from buildbot.plugins import util
c['user_managers'] = []

user_managers contains a list of ways to manually manage User Objects within Buildbot (see User Objects). Currently implemented is a commandline tool buildbot user, described at length in user. In the future, a web client will also be able to manage User Objects and their attributes.

As shown above, to enable the buildbot user tool, you must initialize a CommandlineUserManager instance in your master.cfg. CommandlineUserManager instances require the following arguments:

This is the username that will be registered on the PB connection and need to be used when calling buildbot user.
This is the passwd that will be registered on the PB connection and need to be used when calling buildbot user.
The PB connection port must be different than c['protocols']['pb']['port'] and be specified when calling buildbot user

Input Validation

import re
c['validation'] = {
    'branch' : re.compile(r'^[\w.+/~-]*$'),
    'revision' : re.compile(r'^[ \w\.\-\/]*$'),
    'property_name' : re.compile(r'^[\w\.\-\/\~:]*$'),
    'property_value' : re.compile(r'^[\w\.\-\/\~:]*$'),

This option configures the validation applied to user inputs of various types. This validation is important since these values are often included in command-line arguments executed on slaves. Allowing arbitrary input from untrusted users may raise security concerns.

The keys describe the type of input validated; the values are compiled regular expressions against which the input will be matched. The defaults for each type of input are those given in the example, above.

Codebase Generator

all_repositories = {
    r'https://hg/hg/mailsuite/mailclient': 'mailexe',
    r'https://hg/hg/mailsuite/mapilib': 'mapilib',
    r'https://hg/hg/mailsuite/imaplib': 'imaplib',
    r'': 'mailexe',
    r'': 'mapilib',
    r'': 'imaplib',

def codebaseGenerator(chdict):
    return all_repositories[chdict['repository']]

c['codebaseGenerator'] = codebaseGenerator

For any incoming change, the codebase is set to ''. This codebase value is sufficient if all changes come from the same repository (or clones). If changes come from different repositories, extra processing will be needed to determine the codebase for the incoming change. This codebase will then be a logical name for the combination of repository and or branch etc.

The codebaseGenerator accepts a change dictionary as produced by the buildbot.db.changes.ChangesConnectorComponent, with a changeid equal to None.