--- layout: documentation title: User Manual ---
To run Bazel, go to
your base workspace directory
or any of its subdirectories and type bazel
.
% bazel help [Bazel release bazel-<version>] Usage: bazel <command> <options> ... Available commands: analyze-profile Analyzes build profile data. build Builds the specified targets. canonicalize-flags Canonicalize Bazel flags. clean Removes output files and optionally stops the server. help Prints help for commands, or the index. info Displays runtime info about the bazel server. fetch Fetches all external dependencies of a target. mobile-install Installs apps on mobile devices. query Executes a dependency graph query. run Runs the specified target. shutdown Stops the Bazel server. test Builds and runs the specified test targets. version Prints version information for Bazel. Getting more help: bazel help <command> Prints help and options for <command>. bazel help startup_options Options for the JVM hosting Bazel. bazel help target-syntax Explains the syntax for specifying targets. bazel help info-keys Displays a list of keys used by the info command.
The bazel
tool performs many functions, called
commands; users of CVS and Subversion will be familiar
with this "Swiss army knife" arrangement. The most commonly used one is of
course bazel build
. You can browse the online help
messages using bazel help
.
The Bazel system is implemented as a long-lived server process.
This allows it to perform many optimizations not possible with a
batch-oriented implementation, such as caching of BUILD files,
dependency graphs, and other metadata from one build to the
next. This improves the speed of incremental builds, and allows
different commands, such as build
and query
to share the same cache of loaded packages,
making queries very fast.
When you run bazel
, you're running the client. The
client finds the server based on the path of the base workspace directory
and your userid, so if you build in multiple workspaces, you'll have
multiple Bazel server processes. Multiple users on the same
workstation can build concurrently in the same workspace. If the
client cannot find a running server instance, it starts a new one.
The server process will stop after a period of inactivity (3 hours,
by default).
For the most part, the fact that there is a server running is invisible to the user, but sometimes it helps to bear this in mind. For example, if you're running scripts that perform a lot of automated builds in different directories, it's important to ensure that you don't accumulate a lot of idle servers; you can do this by explicitly shutting them down when you're finished with them, or by specifying a short timeout period.
The name of a Bazel server process appears in the output of ps
x
or ps -e f
as
bazel(dirname)
, where dirname is the
basename of the directory enclosing the root your workspace directory.
For example:
% ps -e f 16143 ? Sl 3:00 bazel(src-jrluser2) -server -Djava.library.path=...
This makes it easier to find out which server process belongs to a
given workspace. (Beware that with certain other options
to ps
, Bazel server processes may be named just
java
.) Bazel servers can be stopped using
the shutdown command.
You can also run Bazel in batch mode using the --batch
startup flag. This will immediately shut down the process after the
command (build, test, etc.) has finished and not keep a server process
around.
When running bazel
, the client first checks that the
server is the appropriate version; if not, the server is stopped and
a new one started. This ensures that the use of a long-running
server process doesn't interfere with proper versioning.
.bazelrc
, the Bazel configuration file,
the --bazelrc=file
option, and the
--config=value
option
Bazel accepts many options. Typically, some of these are varied
frequently (e.g. --subcommands
) while others stay the
same across several builds (e.g. --package_path
).
To avoid having to specify these constant options every time you do
a build or run some other Bazel command, Bazel allows you to
specify options in a configuration file.
Bazel looks for an optional configuration file in the location
specified by the --bazelrc=file
option. If
this option is not specified then, by default, Bazel looks for the
file called .bazelrc
in one of two directories: first,
in your base workspace directory, then in your home directory. If
it finds a file in the first (workspace-specific) location, it will
not look at the second (global) location.
The --bazelrc=file
option must
appear before the command name (e.g. build
).
The option --bazelrc=/dev/null
effectively disables the
use of a configuration file. We strongly recommend that you use
this option when performing release builds, or automated tests that
invoke Bazel.
Aside from the configuration file described above, Bazel also looks
for a master configuration file next to the binary, in the workspace
at tools/bazel.rc
or system-wide at
/etc/bazel.bazelrc
. These files are here to support
installation-wide options or options shared between users.
Like all UNIX "rc" files, the .bazelrc
file is a text
file with a line-based grammar. Lines starting #
are
considered comments and are ignored, as are blank lines. Each line
contains a sequence of words, which are tokenized according to the
same rules as the Bourne shell.
The first word on each line is the name of a Bazel command, such
as build
or query
. The remaining words
are the default options that apply to that command.
More than one line may be used for a command; the options are combined
as if they had appeared on a single line.
(Users of CVS, another tool with a "Swiss army knife" command-line
interface, will find the syntax familiar to that of .cvsrc
.)
Startup options may be specified in the
.bazelrc
file using the command startup
.
These options are described in the interactive help
at bazel help startup_options
.
Options specified in the command line always take precedence over those from a configuration file. In configuration files, lines for a more specific command take precedence over lines for a less specific command (e.g. the 'test' command inherits all the options from the 'build' command, so a 'test --foo=bar' line takes precedence over a 'build --foo=baz' line, regardless of which configuration files these two lines are in) and lines equally specific for which command they apply have precedence based on the configuration file they are in, with the user-specific configuration file taking precedence over the master one.
Options may include words other than flags, such as the names of build targets, etc; these are always prepended to the explicit argument list provided on the command-line, if any.
Common command options may be specified in the
.bazelrc
file using the command common
.
In addition, commands may have :name
suffixes. These
options are ignored by default, but can be pulled in through the
--config=name
option, either on the command line or in
a .bazelrc
file. The intention is that these bundle command line
options that are commonly used together, for example
--config=memcheck
.
Note that some config sections are defined in the master bazelrc file. To avoid conflicts, user-defined sections should start with the '_' (underscore) character.
The command named import
is special: if Bazel encounters such
a line in a .bazelrc
file, it parses the contents of the file
referenced by the import statement, too. Options specified in an imported file
take precedence over ones specified before the import statement, options
specified after the import statement take precedence over the ones in the
imported file, and options in files imported later take precedence over files
imported earlier.
Here's an example ~/.bazelrc
file:
# Bob's Bazel option defaults startup --batch --host_jvm_args=-XX:-UseParallelGC import /home/bobs_project/bazelrc build --show_timestamps --keep_going --jobs 600 build --color=yes query --keep_going build:memcheck --strip=never --test_timeout=3600
build
command
The most important function of Bazel is, of course, building code. Type
bazel build
followed by the name of the
target you wish to build. Here's a typical
session:
% bazel build //foo ____Loading package: foo ____Loading package: bar ____Loading package: baz ____Loading complete. Analyzing... ____Building 1 target... ____[0 / 3] Executing Genrule //bar:helper_rule ____[1 / 3] Executing Genrule //baz:another_helper_rule ____[2 / 3] Building foo/foo.bin Target //foo:foo up-to-date: bazel-bin/foo/foo.bin bazel-bin/foo/foo ____Elapsed time: 9.905s
Bazel prints the progress messages as it loads all the packages in the transitive closure of dependencies of the requested target, then analyzes them for correctness and to create the build actions, finally executing the compilers and other tools of the build.
Bazel prints progress messages during the execution phase of the build, showing the current build step (compiler, linker, etc.) that is being started, and the number of completed over total number of build actions. As the build starts the number of total actions will often increase as Bazel discovers the entire action graph, but the number will usually stabilize within a few seconds.
At the end of the build Bazel
prints which targets were requested, whether or not they were
successfully built, and if so, where the output files can be found.
Scripts that run builds can reliably parse this output; see --show_result
for more
details.
Typing the same command again:
% bazel build //foo ____Loading... ____Found 1 target... ____Building complete. Target //foo:foo up-to-date: bazel-bin/foo/foo.bin bazel-bin/foo/foo ____Elapsed time: 0.280s
we see a "null" build: in this case, there are no packages to re-load, since nothing has changed, and no build steps to execute. (If something had changed in "foo" or some of its dependencies, resulting in the reexecution of some build actions, we would call it an "incremental" build, not a "null" build.)
Before you can start a build, you will need a Bazel workspace. This is simply a directory tree that contains all the source files needed to build your application. Bazel allows you to perform a build from a completely read-only volume.
--package_path
Bazel finds its packages by searching the package path. This is a colon separated ordered list of bazel directories, each being the root of a partial source tree.
To specify a custom package path using the
--package_path
option:
% bazel build --package_path %workspace%:/some/other/root
Package path elements may be specified in three formats:
/
, the path is absolute.
%workspace%
, the path is taken relative
to the nearest enclosing bazel directory./home/bob/clients/bob_client/bazel/foo
, then the
string %workspace%
in the package-path is expanded
to /home/bob/clients/bob_client/bazel
.
.
,
and then cd into the directory
/home/bob/clients/bob_client/bazel/foo
, packages
will be resolved from the
/home/bob/clients/bob_client/bazel/foo
directory.
If you use a non-default package path, we recommend that you specify it in your Bazel configuration file for convenience.
Bazel doesn't require any packages to be in the current directory, so you can do a build from an empty bazel workspace if all the necessary packages can be found somewhere else on the package path.
Example: Building from an empty client
% mkdir -p foo/bazel % cd foo/bazel % bazel build --package_path /some/other/path //foo
Bazel allows a number of ways to specify the targets to be built. Collectively, these are known as target patterns. The on-line help displays a summary of supported patterns:
% bazel help target-syntax Target pattern syntax ===================== The BUILD file label syntax is used to specify a single target. Target patterns generalize this syntax to sets of targets, and also support working-directory-relative forms, recursion, subtraction and filtering. Examples: Specifying a single target: //foo/bar:wiz The single target '//foo/bar:wiz'. foo/bar/wiz Equivalent to: '//foo/bar/wiz:wiz' if foo/bar/wiz is a package, '//foo/bar:wiz' if foo/bar is a package, '//foo:bar/wiz' otherwise. //foo/bar Equivalent to '//foo/bar:bar'. Specifying all rules in a package: //foo/bar:all Matches all rules in package 'foo/bar'. Specifying all rules recursively beneath a package: //foo/...:all Matches all rules in all packages beneath directory 'foo'. //foo/... (ditto) By default, directory symlinks are followed when performing this recursive traversal, except those that point to under the output base (for example, the convenience symlinks that are created in the root directory of the workspace) But we understand that your workspace may intentionally contain directories with unusual symlink structures that you don't want consumed. As such, if a directory has a file named 'DONT_FOLLOW_SYMLINKS_WHEN_TRAVERSING_THIS_DIRECTORY_VIA_A_RECURSIVE_TARGET_PATTERN' then symlinks in that directory won't be followed when evaluating recursive target patterns. Working-directory relative forms: (assume cwd = 'workspace/foo') Target patterns which do not begin with '//' are taken relative to the working directory. Patterns which begin with '//' are always absolute. ...:all Equivalent to '//foo/...:all'. ... (ditto) bar/...:all Equivalent to '//foo/bar/...:all'. bar/... (ditto) bar:wiz Equivalent to '//foo/bar:wiz'. :foo Equivalent to '//foo:foo'. bar Equivalent to '//foo/bar:bar'. foo/bar Equivalent to '//foo/foo/bar:bar'. bar:all Equivalent to '//foo/bar:all'. :all Equivalent to '//foo:all'. Summary of target wildcards: :all, Match all rules in the specified packages. :*, :all-targets Match all targets (rules and files) in the specified packages, including ones not built by default, such as _deploy.jar files. Subtractive patterns: Target patterns may be preceded by '-', meaning they should be subtracted from the set of targets accumulated by preceding patterns. (Note that this means order matters.) For example: % bazel build -- foo/... -foo/contrib/... builds everything in 'foo', except 'contrib'. In case a target not under 'contrib' depends on something under 'contrib' though, in order to build the former bazel has to build the latter too. As usual, the '--' is required to prevent '-f' from being interpreted as an option.
Whereas labels are used to specify individual targets, e.g. for declaring dependencies in BUILD files, Bazel's target patterns are a syntax for specifying multiple targets: they are a generalization of the label syntax for sets of targets, using wildcards. In the simplest case, any valid label is also a valid target pattern, identifying a set of exactly one target.
foo/...
is a wildcard over packages,
indicating all packages recursively beneath
directory foo
(for all roots of the package
path). :all
is a wildcard
over targets, matching all rules within a package. These two may be
combined, as in foo/...:all
, and when both wildcards
are used, this may be abbreviated to foo/...
.
In addition, :*
(or :all-targets
) is a
wildcard that matches every target in the matched packages,
including files that aren't normally built by any rule, such
as _deploy.jar
files associated
with java_binary
rules.
This implies that :*
denotes a superset
of :all
; while potentially confusing, this syntax does
allow the familiar :all
wildcard to be used for
typical builds, where building targets like the _deploy.jar
is not desired.
In addition, Bazel allows a slash to be used instead of the colon
required by the label syntax; this is often convenient when using
Bash filename expansion. For example, foo/bar/wiz
is
equivalent to //foo/bar:wiz
(if there is a
package foo/bar
) or to //foo:bar/wiz
(if
there is a package foo
).
Many Bazel commands accept a list of target patterns as arguments,
and they all honor the prefix negation operator `-
'.
This can be used to subtract a set of targets from the set specified
by the preceding arguments. (Note that this means order matters.)
For example,
bazel build foo/... bar/...
means "build all
targets beneath foo
and all targets
beneath bar
", whereas
bazel build -- foo/... -foo/bar/...
means "build all targets beneath foo
except
those beneath foo/bar
".
(The --
argument is required to prevent the subsequent
arguments starting with -
from being interpreted as
additional options.)
It's important to point out though that subtracting targets this way will not
guarantee that they are not built, since they may be dependencies of targets
that weren't subtracted. For example, if there were a target
//foo:all-apis
that among others depended on
//foo/bar:api
, then the latter would be built as part of
building the former.
Targets with tags=["manual"]
will not be included in wildcard target patterns (...,
:*, :all, etc). You should specify such test targets with explicit target patterns on the command
line if you want Bazel to build/test them.
By default, Bazel will download and symlink external dependencies during the
build. However, this can be undesirable, either because you'd like to know
when new external dependendencies are added or because you'd like to
"prefetch" dependencies (say, before a flight where you'll be offline). If you
would like to prevent new dependencies from being added during builds, you
can specify the --fetch=false
flag. Note that this flag only
applies to repository rules that do not point to a directory in the local
file system. Changes, for example, to local_repository
,
new_local_repository
and Android SDK and NDK repository rules
will always take effect regardless of the value --fetch
.
If you disallow fetching during builds and Bazel finds new external dependencies, your build will fail.
You can manually fetch dependencies by running bazel fetch
. If
you disallow during-build fetching, you'll need to run bazel
fetch
:
fetch
takes a list of targets to fetch dependencies for. For
example, this would fetch dependencies needed to build //foo:bar
and //bar:baz
:
$ bazel fetch //foo:bar //bar:baz
To fetch all external dependencies for a workspace, run:
$ bazel fetch //...
You do not need to run bazel fetch at all if you have all of the tools you are
using (from library jars to the JDK itself) under your workspace root.
However, if you're using anything outside of the workspace directory then you
will need to run bazel fetch
before running
bazel build
.
All the inputs that specify the behavior and result of a given build can be divided into two distinct categories. The first kind is the intrinsic information stored in the BUILD files of your project: the build rule, the values of its attributes, and the complete set of its transitive dependencies. The second kind is the external or environmental data, supplied by the user or by the build tool: the choice of target architecture, compilation and linking options, and other toolchain configuration options. We refer to a complete set of environmental data as a configuration.
In any given build, there may be more than one configuration.
Consider a cross-compile, in which you build
a //foo:bin
executable for a 64-bit architecture,
but your workstation is a 32-bit machine. Clearly, the build
will require building //foo:bin
using a toolchain
capable of creating 64-bit executables, but the build system must
also build various tools used during the build itself—for example
tools that are built from source, then subsequently used in, say, a
genrule—and these must be built to run on your workstation.
Thus we can identify two configurations: the host
configuration, which is used for building tools that run during
the build, and the target configuration (or request
configuration, but we say "target configuration" more often even
though that word already has many meanings), which is
used for building the binary you ultimately requested.
Typically, there are many libraries that are prerequisites of both
the requested build target (//foo:bin
) and one or more of
the host tools, for example some base libraries. Such libraries must be built
twice, once for the host configuration, and once for the target
configuration.
Bazel takes care of ensuring that both variants are built, and that
the derived files are kept separate to avoid interference; usually
such targets can be built concurrently, since they are independent
of each other. If you see progress messages indicating that a given
target is being built twice, this is most likely the explanation.
Bazel uses one of two ways to select the host configuration, based
on the --distinct_host_configuration
option. This
boolean option is somewhat subtle, and the setting may improve (or
worsen) the speed of your builds.
--distinct_host_configuration=false
When this option is false, the host and request configurations are identical: all tools required during the build will be built in exactly the same way as target programs. This setting means that no libraries need to be built twice during a single build, so it keeps builds short. However, it does mean that any change to your request configuration also affects your host configuration, causing all the tools to be rebuilt, and then anything that depends on the tool output to be rebuilt too. Thus, for example, simply changing a linker option between builds might cause all tools to be re-linked, and then all actions using them reexecuted, and so on, resulting in a very large rebuild. Also, please note: if your host architecture is not capable of running your target binaries, your build will not work.
If you frequently make changes to your request configuration, such
as alternating between -c opt
and -c dbg
builds, or between simple- and cross-compilation, we do not
recommend this option, as you will typically rebuild the majority of
your codebase each time you switch.
--distinct_host_configuration=true
(default)If this option is true, then instead of using the same configuration for the host and request, a completely distinct host configuration is used. The host configuration is derived from the target configuration as follows:
--crosstool_top
) as specified in the request
configuration, unless --host_crosstool_top
is
specified.
--host_cpu
for
--cpu
(default: k8
).
--compiler
,
--thin_archives
,
--use_ijars
,
--java_toolchain
,
If --host_crosstool_top
is used, then the value of
--host_cpu
is used to look up a
default_toolchain
in the Crosstool
(ignoring --compiler
) for the host configuration.
-c opt
).
--copt=-g0
).
--strip=always
).
--embed_*
options).
There are many reasons why it might be preferable to select a distinct host configuration from the request configuration. Some are too esoteric to mention here, but two of them are worth pointing out.
Firstly, by using stripped, optimized binaries, you reduce the time spent linking and executing the tools, the disk space occupied by the tools, and the network I/O time in distributed builds.
Secondly, by decoupling the host and request configurations in all builds, you avoid very expensive rebuilds that would result from minor changes to the request configuration (such as changing a linker options does), as described earlier.
That said, for certain builds, this option may be a hindrance. In particular, builds in which changes of configuration are infrequent (especially certain Java builds), and builds where the amount of code that must be built in both host and target configurations is large, may not benefit.
One of the primary goals of the Bazel project is to ensure correct incremental rebuilds. Previous build tools, especially those based on Make, make several unsound assumptions in their implementation of incremental builds.
Firstly, that timestamps of files increase monotonically. While this is the typical case, it is very easy to fall afoul of this assumption; syncing to an earlier revision of a file causes that file's modification time to decrease; Make-based systems will not rebuild.
More generally, while Make detects changes to files, it does
not detect changes to commands. If you alter the options passed to
the compiler in a given build step, Make will not re-run the
compiler, and it is necessary to manually discard the invalid
outputs of the previous build using make clean
.
Also, Make is not robust against the unsuccessful termination of one of its subprocesses after that subprocess has started writing to its output file. While the current execution of Make will fail, the subsequent invocation of Make will blindly assume that the truncated output file is valid (because it is newer than its inputs), and it will not be rebuilt. Similarly, if the Make process is killed, a similar situation can occur.
Bazel avoids these assumptions, and others. Bazel maintains a database of all work previously done, and will only omit a build step if it finds that the set of input files (and their timestamps) to that build step, and the compilation command for that build step, exactly match one in the database, and, that the set of output files (and their timestamps) for the database entry exactly match the timestamps of the files on disk. Any change to the input files or output files, or to the command itself, will cause re-execution of the build step.
The benefit to users of correct incremental builds is: less time
wasted due to confusion. (Also, less time spent waiting for
rebuilds caused by use of make clean
, whether necessary
or pre-emptive.)
Formally, we define the state of a build as consistent when all the expected output files exist, and their contents are correct, as specified by the steps or rules required to create them. When you edit a source file, the state of the build is said to be inconsistent, and remains inconsistent until you next run the build tool to successful completion. We describe this situation as unstable inconsistency, because it is only temporary, and consistency is restored by running the build tool.
There is another kind of inconsistency that is pernicious: stable
inconsistency. If the build reaches a stable inconsistent
state, then repeated successful invocation of the build tool does
not restore consistency: the build has gotten "stuck", and the
outputs remain incorrect. Stable inconsistent states are the main
reason why users of Make (and other build tools) type make
clean
. Discovering that the build tool has failed in this
manner (and then recovering from it) can be time consuming and very
frustrating.
Conceptually, the simplest way to achieve a consistent build is to throw away all the previous build outputs and start again: make every build a clean build. This approach is obviously too time-consuming to be practical (except perhaps for release engineers), and therefore to be useful, the build tool must be able to perform incremental builds without compromising consistency.
Correct incremental dependency analysis is hard, and as described above, many other build tools do a poor job of avoiding stable inconsistent states during incremental builds. In contrast, Bazel offers the following guarantee: after a successful invocation of the build tool during which you made no edits, the build will be in a consistent state. (If you edit your source files during a build, Bazel makes no guarantee about the consistency of the result of the current build. But it does guarantee that the results of the next build will restore consistency.)
As with all guarantees, there comes some fine print: there are some known ways of getting into a stable inconsistent state with Bazel. We won't guarantee to investigate such problems arising from deliberate attempts to find bugs in the incremental dependency analysis, but we will investigate and do our best to fix all stable inconsistent states arising from normal or "reasonable" use of the build tool.
If you ever detect a stable inconsistent state with Bazel, please report a bug.
Bazel uses sandboxes to guarantee that actions run hermetically1 and correctly.
Bazel runs Spawns (loosely speaking: actions) in sandboxes that only contain the minimal
set of files the tool requires to do its job. Currently sandboxing works on Linux 3.12 or newer
with the CONFIG_USER_NS
option enabled.
Bazel will print a warning if your system does not support sandboxing to alert you to the fact
that builds are not guaranteed to be hermetic and might affect the host system in unknown ways.
To disable this warning you can pass the --ignore_unsupported_sandboxing
flag to
Bazel.
On some platforms such as Google Container
Engine cluster nodes or Debian, user namespaces are deactivated by default due to security
concerns. This can be checked by looking at the file
/proc/sys/kernel/unprivileged_userns_clone
: if it exists and contains a 0, then
user namespaces can be activated with sudo sysctl kernel.unprivileged_userns_clone=1
.
In some cases, the Bazel sandbox fails to execute rules because of the system setup. The symptom
is generally a failure that output a message similar to
namespace-sandbox.c:633: execvp(argv[0], argv): No such file or directory
. In that
case, try to deactivate the sandbox for genrules with --genrule_strategy=standalone
and for other rules with --spawn_strategy=standalone
. Also please report a bug on our
issue tracker and mention which Linux distribution you're using so that we can investigate and
provide a fix in a subsequent release.
1: Hermeticity means that the action only uses its declared input files and no other files in the filesystem, and it only produces its declared output files.
clean
command
Bazel has a clean
command, analogous to that of Make.
It deletes the output directories for all build configurations performed
by this Bazel instance, or the entire working tree created by this
Bazel instance, and resets internal caches. If executed without any
command-line options, then the output directory for all configurations
will be cleaned.
Recall that each Bazel instance is associated with a single workspace, thus the
clean
command will delete all outputs from all builds you've done
with that Bazel instance in that workspace.
To completely remove the entire working tree created by a Bazel
instance, you can specify the --expunge
option. When
executed with --expunge
, the clean command simply
removes the entire output base tree which, in addition to the build
output, contains all temp files created by Bazel. It also
stops the Bazel server after the clean, equivalent to the shutdown
command. For example, to
clean up all disk and memory traces of a Bazel instance, you could
specify:
% bazel clean --expunge
Alternatively, you can expunge in the background by using
--expunge_async
. It is safe to invoke a Bazel command
in the same client while the asynchronous expunge continues to run.
Note, however, that this may introduce IO contention.
The clean
command is provided primarily as a means of
reclaiming disk space for workspaces that are no longer needed.
However, we recognize that Bazel's incremental rebuilds might not be
perfect; clean
may be used to recover a consistent
state when problems arise.
Bazel's design is such that these problems are fixable; we consider
such bugs a high priority, and will do our best fix them. If you
ever find an incorrect incremental build, please file a bug report.
We encourage developers to get out of the habit of
using clean
and into that of reporting bugs in the
tools.
In Bazel, a build occurs in three distinct phases; as a user, understanding the difference between them provides insight into the options which control a build (see below).
The first is loading during which all the necessary BUILD files for the initial targets, and their transitive closure of dependencies, are loaded, parsed, evaluated and cached.
For the first build after a Bazel server is started, the loading phase typically takes many seconds as many BUILD files are loaded from the file system. In subsequent builds, especially if no BUILD files have changed, loading occurs very quickly.
Errors reported during this phase include: package not found, target not found, lexical and grammatical errors in a BUILD file, and evaluation errors.
The second phase, analysis, involves the semantic analysis and validation of each build rule, the construction of a build dependency graph, and the determination of exactly what work is to be done in each step of the build.
Like loading, analysis also takes several seconds when computed in its entirety. However, Bazel caches the dependency graph from one build to the next and only reanalyzes what it has to, which can make incremental builds extremely fast in the case where the packages haven't changed since the previous build.
Errors reported at this stage include: inappropriate dependencies, invalid inputs to a rule, and all rule-specific error messages.
The loading and analysis phases are fast because Bazel avoids unnecessary file I/O at this stage, reading only BUILD files in order to determine the work to be done. This is by design, and makes Bazel a good foundation for analysis tools, such as Bazel's query command, which is implemented atop the loading phase.
The third and final phase of the build is execution. This phase ensures that the outputs of each step in the build are consistent with its inputs, re-running compilation/linking/etc. tools as necessary. This step is where the build spends the majority of its time, ranging from a few seconds to over an hour for a large build. Errors reported during this phase include: missing source files, errors in a tool executed by some build action, or failure of a tool to produce the expected set of outputs.
The following sections describe the options available during a
build. When --long
is used on a help command, the on-line
help messages provide summary information about the meaning, type and
default value for each option.
Most options can only be specified once. When specified multiple times, the last instance wins. Options that can be specified multiple times are identified in the on-line help with the text 'may be used multiple times'.
See also the --show_package_location
option.
--package_path
This option specifies the set of directories that are searched to find the BUILD file for a given package.
--deleted_packages
This option specifies a comma-separated list of packages which Bazel should consider deleted, and not attempt to load from any directory on the package path. This can be used to simulate the deletion of packages without actually deleting them.
These options control Bazel's error-checking and/or warnings.
--check_constraint constraint
This option takes an argument that specifies which constraint should be checked.
Bazel performs special checks on each rule that is annotated with the given constraint.
The supported constraints and their checks are as follows:
public
: Verify that all java_libraries marked with
constraints = ['public']
only depend on java_libraries
that are marked as constraints = ['public']
too. If bazel
finds a dependency that does not conform to this rule, bazel will issue
an error.
--[no]check_visibility
If this option is set to false, visibility checks are demoted to warnings. The default value of this option is true, so that by default, visibility checking is done.
--experimental_action_listener=label
The experimental_action_listener
option instructs Bazel to use
details from the action_listener
rule specified by label to
insert extra_actions
into the build graph.
--experimental_extra_action_filter=regex
The experimental_extra_action_filter
option instructs Bazel to
filter the set of targets to schedule extra_actions
for.
This flag is only applicable in combination with the
--experimental_action_listener
flag.
By default all extra_actions
in the transitive closure of the
requested targets-to-build get scheduled for execution.
--experimental_extra_action_filter
will restrict scheduling to
extra_actions
of which the owner's label matches the specified
regular expression.
The following example will limit scheduling of extra_actions
to only apply to actions of which the owner's label contains '/bar/':
% bazel build --experimental_action_listener=//test:al //foo/... \ --experimental_extra_action_filter=.*/bar/.*
--output_filter regex
The --output_filter
option will only show build and compilation
warnings for targets that match the regular expression. If a target does not
match the given regular expression and its execution succeeds, its standard
output and standard error are thrown away. This option is intended to be used
to help focus efforts on fixing warnings in packages under development. Here
are some typical values for this option:
--output_filter= |
Show all output. |
--output_filter='^//(first/project|second/project):' |
Show the output for the specified packages. |
--output_filter='^//((?!(first/bad_project|second/bad_project):).)*$' |
Don't show output for the specified packages. |
--output_filter=DONT_MATCH_ANYTHING |
Don't show output. |
--[no]analysis_warnings_as_errors
When this option is enabled, visible analysis warnings (as specified by the output filter) are treated as errors, effectively preventing the build phase from starting. This feature can be used to enable strict builds that do not allow new warnings to creep into a project.
These options control which options Bazel will pass to other tools.
--copt gcc-option
This option takes an argument which is to be passed to gcc. The argument will be passed to gcc whenever gcc is invoked for preprocessing, compiling, and/or assembling C, C++, or assembler code. It will not be passed when linking.
This option can be used multiple times. For example:
% bazel build --copt="-g0" --copt="-fpic" //foo
will compile the foo
library without debug tables, generating
position-independent code.
Note that changing --copt
settings will force a recompilation
of all affected object files. Also note that copts values listed in specific
cc_library or cc_binary build rules will be placed on the gcc command line
after these options.
Warning: C++-specific options (such as -fno-implicit-templates
)
should be specified in --cxxopt
, not in
--copt
. Likewise, C-specific options (such as -Wstrict-prototypes)
should be specified in --conlyopt
, not in copt
.
Similarly, gcc options that only have an
effect at link time (such as -l
) should be specified in
--linkopt
, not in --copt
.
--host_copt gcc-option
This option takes an argument which is to be passed to gcc for source files
that are compiled in the host configuration. This is analogous to
the --copt
option, but applies only to the
host configuration.
--conlyopt gcc-option
This option takes an argument which is to be passed to gcc when compiling C source files.
This is similar to --copt
, but only applies to C compilation,
not to C++ compilation or linking. So you can pass C-specific options
(such as -Wno-pointer-sign
) using --conlyopt
.
Note that copts parameters listed in specific cc_library or cc_binary build rules will be placed on the gcc command line after these options.
--cxxopt gcc-option
This option takes an argument which is to be passed to gcc when compiling C++ source files.
This is similar to --copt
, but only applies to C++ compilation,
not to C compilation or linking. So you can pass C++-specific options
(such as -fpermissive
or -fno-implicit-templates
) using --cxxopt
.
For example:
% bazel build --cxxopt="-fpermissive" --cxxopt="-Wno-error" //foo/cruddy_code
Note that copts parameters listed in specific cc_library or cc_binary build rules will be placed on the gcc command line after these options.
--linkopt linker-option
This option takes an argument which is to be passed to gcc when linking.
This is similar to --copt
, but only applies to linking,
not to compilation. So you can pass gcc options that only make sense
at link time (such as -lssp
or -Wl,--wrap,abort
)
using --linkopt
. For example:
% bazel build --copt="-fmudflap" --linkopt="-lmudflap" //foo/buggy_code
Build rules can also specify link options in their attributes. This option's settings always take precedence. Also see cc_library.linkopts.
--strip (always|never|sometimes)
This option determines whether Bazel will strip debugging information from
all binaries and shared libraries, by invoking the linker with the -Wl,--strip-debug
option.
--strip=always
means always strip debugging information.
--strip=never
means never strip debugging information.
The default value of --strip=sometimes
means strip iff the --compilation_mode
is fastbuild
.
% bazel build --strip=always //foo:bar
will compile the target while stripping debugging information from all generated binaries.
Note that if you want debugging information, it's not enough to disable stripping; you also need to make
sure that the debugging information was generated by the compiler, which you can do by using either
-c dbg
or --copt -g
.
Note also that Bazel's --strip
option corresponds with ld's --strip-debug
option:
it only strips debugging information. If for some reason you want to strip all symbols,
not just debug symbols, you would need to use ld's --strip-all
option,
which you can do by passing --linkopt=-Wl,--strip-all
to Bazel.
--stripopt strip-option
An additional option to pass to the strip
command when generating
a *.stripped
binary. The default is -S -p
. This option can be used
multiple times.
Note that --stripopt
does not apply to the stripping of the main
binary with --strip=(always|sometimes)
.
--fdo_instrument profile-output-dir
The --fdo_instrument
option enables the generation of
FDO (feedback directed optimization) profile output when the
built C/C++ binary is executed. For GCC, the argument provided is used as a
directory prefix for a per-object file directory tree of .gcda files
containing profile information for each .o file.
Once the profile data tree has been generated, the profile tree
should be zipped up, and provided to the
--fdo_optimize=profile-zip
Bazel option to enable the FDO optimized compilation.
For the LLVM compiler the argument instead is the path to the raw LLVM profile
output file to generate, e.g.
--fdo_instrument=/path/to/profile.profraw
.
The options --fdo_instrument
and --fdo_optimize
cannot be used at the same time.
--fdo_optimize profile-zip
The --fdo_optimize
option enables the use of the
per-object file profile information to perform FDO (feedback
directed optimization) optimizations when compiling. For GCC, the argument
provided is the zip file containing the previously-generated file tree
of .gcda files containing profile information for each .o file.
Alternatively, the argument provided can point to an auto profile identified by the extension .afdo.
Note that this option also accepts labels that resolve to source files. You
may need to add an exports_files
directive to the corresponding package to
make the file visible to Bazel.
For the LLVM compiler the argument provided should point to the indexed LLVM profile output file prepared by the llvm-profdata tool, and should have a .profdata extension.
The options --fdo_instrument
and
--fdo_optimize
cannot be used at the same time.
--lipo (off|binary)
The --lipo=binary
option enables
LIPO
(Lightweight Inter-Procedural Optimization). LIPO is an extended C/C++ optimization technique
that optimizes code across different object files. It involves compiling each C/C++ source
file differently for every binary. This is in contrast to normal compilation where compilation
outputs are reused. This means that LIPO is more expensive than normal compilation.
This option only has an effect when FDO is also enabled (see the
--fdo_instrument and
--fdo_options).
Currently LIPO is only supported when building a single cc_binary
rule.
Setting --lipo=binary
implicitly sets
--dynamic_mode=off
.
--lipo_context
context-binary
Specifies the label of a cc_binary
rule that was used to generate
the profile information for LIPO that was given to
the --fdo_optimize
option.
Specifying the context is mandatory when --lipo=binary
is set.
Using this option implicitly also sets
--linkopt=-Wl,--warn-unresolved-symbols
.
--[no]output_symbol_counts
If enabled, each gold-invoked link of a C++ executable binary will also output
a symbol counts file (via the --print-symbol-counts
gold
option) that logs the number of symbols from each .o input that were used in
the binary. This can be used to track unnecessary link dependencies. The
symbol counts file is written to the binary's output path with the name
[targetname].sc
.
This option is disabled by default.
--jvmopt jvm-option
This option allows option arguments to be passed to the Java VM. It can be used with one big argument, or multiple times with individual arguments. For example:
% bazel build --jvmopt="-server -Xms256m" java/com/example/common/foo:all
will use the server VM for launching all Java binaries and set the startup heap size for the VM to 256 MB.
--javacopt javac-option
This option allows option arguments to be passed to javac. It can be used with one big argument, or multiple times with individual arguments. For example:
% bazel build --javacopt="-g:source,lines" //myprojects:prog
will rebuild a java_binary with the javac default debug info (instead of the bazel default).
The option is passed to javac after the Bazel built-in default options for javac and before the per-rule options. The last specification of any option to javac wins. The default options for javac are:
-source 8 -target 8 -encoding UTF-8
Note that changing --javacopt
settings will force a recompilation
of all affected classes. Also note that javacopts parameters listed in
specific java_library or java_binary build rules will be placed on the javac
command line after these options.
-extra_checks[:(off|on)]
This javac option enables extra correctness checks. Any problems found will
be presented as errors.
Either -extra_checks
or -extra_checks:on
may be used
to force the checks to be turned on. -extra_checks:off
completely
disables the analysis.
When this option is not specified, the default behavior is used.
--strict_java_deps
(default|strict|off|warn|error)
This option controls whether javac checks for missing direct dependencies. Java targets must explicitly declare all directly used targets as dependencies. This flag instructs javac to determine the jars actually used for type checking each java file, and warn/error if they are not the output of a direct dependency of the current target.
off
means checking is disabled.
warn
means javac will generate standard java warnings of
type [strict]
for each missing direct dependency.
default
, strict
and error
all
mean javac will generate errors instead of warnings, causing the current
target to fail to build if any missing direct dependencies are found.
This is also the default behavior when the flag is unspecified.
--javawarn (all|cast|deprecation|empty|unchecked|fallthrough|path|rawtypes|serial|finally|overrides)
This option is used to enable Java warnings across an entire build. It takes an argument which is a javac warning to be enabled, overriding any other Java options that disable the given warning. The arguments to this option are appended to the "-Xlint:" flag to javac, and must be exactly one of the listed warnings.
For example:
% bazel build --javawarn="deprecation" --javawarn="unchecked" //java/...
Note that changing --javawarn
settings will force a recompilation
of all affected classes.
These options affect the build commands and/or the output file contents.
--compilation_mode (fastbuild|opt|dbg)
(-c)
This option takes an argument of fastbuild
, dbg
or opt
, and affects various C/C++ code-generation
options, such as the level of optimization and the completeness of
debug tables. Bazel uses a different output directory for each
different compilation mode, so you can switch between modes without
needing to do a full rebuild every time.
fastbuild
means build as fast as possible:
generate minimal debugging information (-gmlt
-Wl,-S
), and don't optimize. This is the
default. Note: -DNDEBUG
will not be set.
dbg
means build with debugging enabled (-g
),
so that you can use gdb (or another debugger).
opt
means build with optimization enabled and
with assert()
calls disabled (-O2 -DNDEBUG
).
Debugging information will not be generated in opt
mode
unless you also pass --copt -g
.
--cpu cpu
This option specifies the target CPU architecture to be used for the compilation of binaries during the build.
Note that a particular combination of crosstool version, compiler version, libc version, and target CPU is allowed only if it has been specified in the currently used CROSSTOOL file.
--host_cpu cpu
This option specifies the name of the CPU architecture that should be used to build host tools.
--experimental_skip_static_outputs
The --experimental_skip_static_outputs
option causes all
statically-linked C++ binaries to not be output in any meaningful
way.
If you set this flag, you must also
set --distinct_host_configuration
.
It is also inherently incompatible with running tests — don't use it for
that. This option is experimental and may go away at any time.
--per_file_copt
[+-]regex[,[+-]regex]...@option[,option]...
When present, any C++ file with a label or an execution path matching one of the inclusion regex
expressions and not matching any of the exclusion expressions will be built
with the given options. The label matching uses the canonical form of the label
(i.e //package
:label_name
).
The execution path is the relative path to your workspace directory including the base name
(including extension) of the C++ file. It also includes any platform dependent prefixes.
Note, that if only one of the label or the execution path matches the options will be used.
Notes:
To match the generated files (e.g. genrule outputs)
Bazel can only use the execution path. In this case the regexp shouldn't start with '//'
since that doesn't match any execution paths. Package names can be used like this:
--per_file_copt=base/.*\.pb\.cc@-g0
. This will match every
.pb.cc
file under a directory called base
.
This option can be used multiple times.
The option is applied regardless of the compilation mode used. I.e. it is possible
to compile with --compilation_mode=opt
and selectively compile some
files with stronger optimization turned on, or with optimization disabled.
Caveat: If some files are selectively compiled with debug symbols the symbols
might be stripped during linking. This can be prevented by setting
--strip=never
.
Syntax: [+-]regex[,[+-]regex]...@option[,option]...
Where
regex
stands for a regular expression that can be prefixed with
a +
to identify include patterns and with -
to identify
exclude patterns. option
stands for an arbitrary option that is passed
to the C++ compiler. If an option contains a ,
it has to be quoted like so
\,
. Options can also contain @
, since only the first
@
is used to separate regular expressions from options.
Example:
--per_file_copt=//foo:.*\.cc,-//foo:file\.cc@-O0,-fprofile-arcs
adds the -O0
and the -fprofile-arcs
options to the command
line of the C++ compiler for all .cc
files in //foo/
except
file.cc
.
--dynamic_mode mode
Determines whether C++ binaries will be linked dynamically, interacting with the linkstatic attribute on build rules.
Modes:
auto
: Translates to a platform-dependent mode;
default
for linux and off
for cygwin.default
: Allows bazel to choose whether to link dynamically.
See linkstatic for more
information.fully
: Links all targets dynamically. This will speed up
linking time, and reduce the size of the resulting binaries.
off
: Links all targets in
mostly static mode.
If -static
is set in linkopts, targets will change to fully
static.--fission (yes|no|[dbg][,opt][,fastbuild])
Enables Fission, which writes C++ debug information to dedicated .dwo files instead of .o files, where it would otherwise go. This substantially reduces the input size to links and can reduce link times.
When set to [dbg][,opt][,fastbuild]
(example:
--fission=dbg,fastbuild
), Fission is enabled
only for the specified set of compilation modes. This is useful for bazelrc
settings. When set to yes
, Fission is enabled
universally. When set to no
, Fission is disabled
universally. Default is dbg
.
--force_ignore_dash_static
If this flag is set, any -static
options in linkopts of
cc_*
rules BUILD files are ignored. This is only intended as a
workaround for C++ hardening builds.
--[no]force_pic
If enabled, all C++ compilations produce position-independent code ("-fPIC"), links prefer PIC pre-built libraries over non-PIC libraries, and links produce position-independent executables ("-pie"). Default is disabled.
Note that dynamically linked binaries (i.e. --dynamic_mode fully
)
generate PIC code regardless of this flag's setting. So this flag is for cases
where users want PIC code explicitly generated for static links.
--custom_malloc malloc-library-target
When specified, always use the given malloc implementation, overriding all
malloc="target"
attributes, including in those targets that use the
default (by not specifying any malloc
).
--crosstool_top label
This option specifies the location of the crosstool compiler suite
to be used for all C++ compilation during a build. Bazel will look in that
location for a CROSSTOOL file and uses that to automatically determine
settings for
--compiler
.
--host_crosstool_top label
If not specified, bazel uses the value of --crosstool_top
to compile
code in the host configuration, i.e., tools run during the build. The main purpose of this flag
is to enable cross-compilation.
--compiler version
This option specifies the C/C++ compiler version (e.g. gcc-4.1.0
)
to be used for the compilation of binaries during the build. If you want to
build with a custom crosstool, you should use a CROSSTOOL file instead of
specifying this flag.
Note that only certain combinations of crosstool version, compiler version, libc version, and target CPU are allowed.
--glibc version
This option specifies the version of glibc that the target should be linked against. If you want to build with a custom crosstool, you should use a CROSSTOOL file instead of specifying this flag. In that case, Bazel will use the CROSSTOOL file and the following options where appropriate:
Note that only certain combinations of crosstool version, compiler version, glibc version, and target CPU are allowed.
--java_toolchain label
This option specifies the label of the java_toolchain used to compile Java source files.
--javabase (path|label)
This options set the label or the path of the base Java installation to use
for running JavaBuilder, SingleJar, and is also used for bazel run and inside
Java binaries built by java_binary
rules. The various
"Make" variables for
Java (JAVABASE
, JAVA
, JAVAC
and
JAR
) are derived from this option.
This does not select the Java compiler that is used to compile Java
source files. The compiler can be selected by settings the
--java_toolchain
option.
These options affect how Bazel will execute the build. They should not have any significant effect on the output files generated by the build. Typically their main effect is on the speed on the build.
--spawn_strategy strategy
This option controls where and how commands are executed.
standalone
causes commands to be executed as local subprocesses.
sandboxed
causes commands to be executed inside a sandbox on the local machine.
This requires that all input files, data dependencies and tools are listed as direct
dependencies in the srcs
, data
and tools
attributes.
This is the default on systems that support sandboxed execution.
--genrule_strategy strategy
This option controls where and how genrules are executed.
standalone
causes genrules to run as local subprocesses.
sandboxed
causes genrules to run inside a sandbox on the local machine.
This requires that all input files are listed as direct dependencies in
the srcs
attribute, and the program(s) executed are listed
in the tools
attribute.
This is the default for Bazel on systems that support sandboxed execution.
--local_genrule_timeout_seconds seconds
Sets a timeout value for local genrules with the given number of seconds.
--jobs n
(-j)This option, which takes an integer argument, specifies a limit on the number of jobs that should be executed concurrently during the execution phase of the build. The default is 200.
Note that the number of concurrent jobs that Bazel will run
is determined not only by the --jobs
setting, but also
by Bazel's scheduler, which tries to avoid running concurrent jobs
that will use up more resources (RAM or CPU) than are available,
based on some (very crude) estimates of the resource consumption
of each job. The behavior of the scheduler can be controlled by
the --ram_utilization_factor
option.
--progress_report_interval n
Bazel periodically prints a progress report on jobs that are not
finished yet (e.g. long running tests). This option sets the
reporting frequency, progress will be printed every n
seconds.
The default is 0, that means an incremental algorithm: the first report will be printed after 10 seconds, then 30 seconds and after that progress is reported once every minute.
--ram_utilization_factor
percentageThis option, which takes an integer argument, specifies what percentage of the system's RAM Bazel should try to use for its subprocesses. This option affects how many processes Bazel will try to run in parallel. The default value is 67. If you run several Bazel builds in parallel, using a lower value for this option may avoid thrashing and thus improve overall throughput. Using a value higher than the default is NOT recommended. Note that Bazel's estimates are very coarse, so the actual RAM usage may be much higher or much lower than specified. Note also that this option does not affect the amount of memory that the Bazel server itself will use.
--local_resources
availableRAM,availableCPU,availableIOThis option, which takes three comma-separated floating point arguments, specifies the amount of local resources that Bazel can take into consideration when scheduling build and test activities. Option expects amount of available RAM (in MB), number of CPU cores (with 1.0 representing single full core) and workstation I/O capability (with 1.0 representing average workstation). By default Bazel will estimate amount of RAM and number of CPU cores directly from system configuration and will assume 1.0 I/O resource.
If this option is used, Bazel will ignore --ram_utilization_factor.
--[no]build_runfile_links
This option, which is currently enabled by default, specifies
whether the runfiles symlinks for tests and
cc_binary
targets should be built in the output directory.
Using --nobuild_runfile_links
can be useful
to validate if all targets compile without incurring the overhead
for building the runfiles trees.
Within Bazel's output tree, the
runfiles symlink tree is typically rooted as a sibling of the corresponding
binary or test.
When tests (or applications) are executed, their
run-time data dependencies are gathered together in one place, and
may be accessed by the test using paths of the form
$TEST_SRCDIR/workspace/packagename/filename
.
The "runfiles" tree ensures that tests have access to all the files
upon which they have a declared dependence, and nothing more. By
default, the runfiles tree is implemented by constructing a set of
symbolic links to the required files. As the set of links grows, so
does the cost of this operation, and for some large builds it can
contribute significantly to overall build time, particularly because
each individual test (or application) requires its own runfiles tree.
The --build_runfile_links
flag controls the
construction of the tree of symbolic links (for C++ applications and
tests only). The reasons only C++ non-test rules are affected are numerous
and subtle: C++ builds are more likely to be slower due to runfiles;
no C++ host tools (tools that run during the build) need their runfiles,
so this option can be used by the host configuration; and other rules
(notably Python) need their runfiles for other purposes besides test
execution.
--[no]discard_analysis_cache
When this option is enabled, Bazel will discard the analysis cache right before execution starts, thus freeing up additional memory (around 10%) for the execution phase. The drawback is that further incremental builds will be slower.
--[no]keep_going
(-k)As in GNU Make, the execution phase of a build stops when the first error is encountered. Sometimes it is useful to try to build as much as possible even in the face of errors. This option enables that behavior, and when it is specified, the build will attempt to build every target whose prerequisites were successfully built, but will ignore errors.
While this option is usually associated with the execution phase of
a build, it also effects the analysis phase: if several targets are
specified in a build command, but only some of them can be
successfully analyzed, the build will stop with an error
unless --keep_going
is specified, in which case the
build will proceed to the execution phase, but only for the targets
that were successfully analyzed.
--[no]thin_archives
This option enables use of thin archives, an optimization which avoids duplicating the content of object files when they are placed in archive libraries; the archive library references the object file by name, and the linker follows this reference as needed. This may give a speedup for C++ builds, especially when building a single large executable from clean.
This option is enabled by default;
use --nothin_archives
to disable.
--[no]use_ijars
This option changes the way java_library
targets are
compiled by Bazel. Instead of using the output of a
java_library
for compiling dependent
java_library
targets, Bazel will create interface jars
that contain only the signatures of non-private members (public,
protected, and default (package) access methods and fields) and use
the interface jars to compile the dependent targets. This makes it
possible to avoid recompilation when changes are only made to
method bodies or private members of a class.
Note that using --use_ijars
might give you a different
error message when you are accidentally referring to a non visible
member of another class: Instead of getting an error that the member
is not visible you will get an error that the member does not exist.
Note that changing the --use_ijars
setting will force
a recompilation of all affected classes.
--[no]interface_shared_objects
This option enables interface shared objects, which makes binaries and other shared libraries depend on the interface of a shared object, rather than its implementation. When only the implementation changes, Bazel can avoid rebuilding targets that depend on the changed shared library unnecessarily.
These options determine what to build or test.
--[no]build
This option causes the execution phase of the build to occur; it is on by default. When it is switched off, the execution phase is skipped, and only the first two phases, loading and analysis, occur.
This option can be useful for validating BUILD files and detecting errors in the inputs, without actually building anything.
--[no]build_tests_only
If specified, Bazel will build only what is necessary to run the *_test
and test_suite rules that were not filtered due to their
size,
timeout,
tag, or
language.
If specified, Bazel will ignore other targets specified on the command line.
By default, this option is disabled and Bazel will build everything
requested, including *_test and test_suite rules that are filtered out from
testing. This is useful because running
bazel test --build_tests_only foo/...
may not detect all build
breakages in the foo
tree.
--[no]check_up_to_date
This option causes Bazel not to perform a build, but merely check whether all specified targets are up-to-date. If so, the build completes successfully, as usual. However, if any files are out of date, instead of being built, an error is reported and the build fails. This option may be useful to determine whether a build has been performed more recently than a source edit (e.g. for pre-submit checks) without incurring the cost of a build.
See also --check_tests_up_to_date
.
--[no]compile_one_dependency
Compile a single dependency of the argument files. This is useful for syntax checking source files in IDEs, for example, by rebuilding a single target that depends on the source file to detect errors as early as possible in the edit/build/test cycle. This argument affects the way all non-flag arguments are interpreted: for each source filename, one rule that depends on it will be built. For C++ and Java sources, rules in the same language space are preferentially chosen. For multiple rules with the same preference, the one that appears first in the BUILD file is chosen. An explicitly named target pattern which does not reference a source file results in an error.
--save_temps
The --save_temps
option causes temporary outputs from gcc to be saved.
These include .s files (assembler code), .i (preprocessed C) and .ii
(preprocessed C++) files. These outputs are often useful for debugging. Temps will only be
generated for the set of targets specified on the command line.
Note that our implementation of --save_temps
does not use gcc's
-save-temps
flag. Instead, we do two passes, one with -S
and one with -E
. A consequence of this is that if your build fails,
Bazel may not yet have produced the ".i" or ".ii" and ".s" files.
If you're trying to use --save_temps
to debug a failed compilation,
you may need to also use --keep_going
so that Bazel will still try to
produce the preprocessed files after the compilation fails.
The --save_temps
flag currently works only for cc_* rules.
To ensure that Bazel prints the location of the additional output files, check that
your --show_result n
setting is high enough.
--test_size_filters size[,size]*
If specified, Bazel will test (or build if --build_tests_only
is also specified) only test targets with the given size. Test size filter
is specified as comma delimited list of allowed test size values (small,
medium, large or enormous), optionally preceded with '-' sign used to denote
excluded test sizes. For example,
% bazel test --test_size_filters=small,medium //foo:alland
% bazel test --test_size_filters=-large,-enormous //foo:all
will test only small and medium tests inside //foo.
By default, test size filtering is not applied.
--test_timeout_filters timeout[,timeout]*
If specified, Bazel will test (or build if --build_tests_only
is also specified) only test targets with the given timeout. Test timeout filter
is specified as comma delimited list of allowed test timeout values (short,
moderate, long or eternal), optionally preceded with '-' sign used to denote
excluded test timeouts. See --test_size_filters
for example syntax.
By default, test timeout filtering is not applied.
--test_tag_filters tag[,tag]*
If specified, Bazel will test (or build if --build_tests_only
is also specified) only test targets that have at least one required tag
(if any of them are specified) and does not have any excluded tags. Test tag
filter is specified as comma delimited list of tag keywords, optionally
preceded with '-' sign used to denote excluded tags. Required tags may also
have a preceding '+' sign.
For example,
% bazel test --test_tag_filters=performance,stress,-flaky //myproject:all
will test targets that are tagged with either performance
or
stress
tag but are not tagged with the flaky
tag.
By default, test tag filtering is not applied. Note that you can also filter
on test's size
and local
tags in
this manner.
--test_lang_filters lang[,lang]*
Specifies a comma-separated list of test languages for languages with an official *_test
rule the
(see build encyclopedia for a full list of these). Each
language can be optionally preceded with '-' to specify excluded
languages. The name used for each language should be the same as
the language prefix in the *_test
rule, for example,
cc
, java
or sh
.
If specified, Bazel will test (or build if --build_tests_only
is also specified) only test targets of the specified language(s).
For example,
% bazel test --test_lang_filters=cc,java foo/...
will test only the C/C++ and Java tests (defined using
cc_test
and java_test
rules, respectively)
in foo/...
, while
% bazel test --test_lang_filters=-sh,-java foo/...
will run all of the tests in foo/...
except for the
sh_test
and java_test
tests.
By default, test language filtering is not applied.
--test_filter=filter-expression
Specifies a filter that the test runner may use to pick a subset of tests for running. All targets specified in the invocation are built, but depending on the expression only some of them may be executed; in some cases, only certain test methods are run.
The particular interpretation of filter-expression is up to
the test framework responsible for running the test. It may be a glob,
substring, or regexp. --test_filter
is a convenience
over passing different --test_arg
filter arguments,
but not all frameworks support it.
--explain logfile
This option, which requires a filename argument, causes the
dependency checker in bazel build
's execution phase to
explain, for each build step, either why it is being executed, or
that it is up-to-date. The explanation is written
to logfile.
If you are encountering unexpected rebuilds, this option can help to
understand the reason. Add it to your .bazelrc
so that
logging occurs for all subsequent builds, and then inspect the log
when you see an execution step executed unexpectedly. This option
may carry a small performance penalty, so you might want to remove
it when it is no longer needed.
--verbose_explanations
This option increases the verbosity of the explanations generated when the --explain option is enabled.
In particular, if verbose explanations are enabled, and an output file is rebuilt because the command used to build it has changed, then the output in the explanation file will include the full details of the new command (at least for most commands).
Using this option may significantly increase the length of the
generated explanation file and the performance penalty of using
--explain
.
If --explain
is not enabled, then
--verbose_explanations
has no effect.
--profile file
This option, which takes a filename argument, causes Bazel to write
profiling data into a file. The data then can be analyzed or parsed using the
bazel analyze-profile
command. The Build profile can be useful in
understanding where Bazel's build
command is spending its time.
--[no]show_loading_progress
This option causes Bazel to output package-loading progress messages. If it is disabled, the messages won't be shown.
--[no]show_progress
This option causes progress messages to be displayed; it is on by default. When disabled, progress messages are suppressed.
--show_progress_rate_limit
n
This option causes bazel to display only
one progress message per n
seconds, where n is a real number.
If n
is -1, all progress messages will be displayed. The default value for
this option is 0.03, meaning bazel will limit the progress messages to one per every
0.03 seconds.
--show_result n
This option controls the printing of result information at the end
of a bazel build
command. By default, if a single
build target was specified, Bazel prints a message stating whether
or not the target was successfully brought up-to-date, and if so,
the list of output files that the target created. If multiple
targets were specified, result information is not displayed.
While the result information may be useful for builds of a single
target or a few targets, for large builds (e.g. an entire top-level
project tree), this information can be overwhelming and distracting;
this option allows it to be controlled. --show_result
takes an integer argument, which is the maximum number of targets
for which full result information should be printed. By default,
the value is 1. Above this threshold, no result information is
shown for individual targets. Thus zero causes the result
information to be suppressed always, and a very large value causes
the result to be printed always.
Users may wish to choose a value in-between if they regularly
alternate between building a small group of targets (for example,
during the compile-edit-test cycle) and a large group of targets
(for example, when establishing a new workspace or running
regression tests). In the former case, the result information is
very useful whereas in the latter case it is less so. As with all
options, this can be specified implicitly via
the .bazelrc
file.
The files are printed so as to make it easy to copy and paste the filename to the shell, to run built executables. The "up-to-date" or "failed" messages for each target can be easily parsed by scripts which drive a build.
--subcommands
(-s
)This option causes Bazel's execution phase to print the full command line for each command prior to executing it.
>>>>> # //examples/cpp:hello-world [action 'Linking examples/cpp/hello-world'] (cd /home/jrluser/.cache/bazel/_bazel_jrluser/4c084335afceb392cfbe7c31afee3a9f/bazel && \ exec env - \ /usr/bin/gcc -o bazel-out/local_linux-fastbuild/bin/examples/cpp/hello-world -B/usr/bin/ -Wl,-z,relro,-z,now -no-canonical-prefixes -pass-exit-codes '-Wl,--build-id=md5' '-Wl,--hash-style=gnu' -Wl,-S<EMAIL_ADDRESS>Where possible, commands are printed in a Bourne shell compatible syntax,
so that they can be easily copied and pasted to a shell command prompt.
(The surrounding parentheses are provided to protect your shell from the
cd
and exec
calls; be sure to copy them!)
However some commands are implemented internally within Bazel, such as
creating symlink trees. For these there's no command line to display.
See also --verbose_failures, below.
--verbose_failures
This option causes Bazel's execution phase to print the full command line for commands that failed. This can be invaluable for debugging a failing build.
Failing commands are printed in a Bourne shell compatible syntax, suitable for copying and pasting to a shell prompt.
--[no]stamp
This option controls whether stamping is enabled for
rule types that support it. For most of the supported rule types stamping is
enabled by default (e.g. cc_binary
).
By default, stamping is disabled for all tests. Specifying
--stamp
does not force affected targets to be rebuilt,
if their dependencies have not changed.
Stamping can be enabled or disabled explicitly in BUILD using
the stamp
attribute of certain rule types, please refer to
the build encyclopedia for details. For
rules that are neither explicitly or implicitly configured as stamp =
0
or stamp = 1
, the --[no]stamp
option
selects whether stamping is enabled. Bazel never stamps binaries that are
built for the host configuration, regardless of the stamp attribute.
--symlink_prefix string
Changes the prefix of the generated convenience symlinks. The
default value for the symlink prefix is bazel-
which
will create the symlinks bazel-bin
, bazel-testlogs
, and
bazel-genfiles
.
If the symbolic links cannot be created for any reason, a warning is issued but the build is still considered a success. In particular, this allows you to build in a read-only directory or one that you have no permission to write into. Any paths printed in informational messages at the conclusion of a build will only use the symlink-relative short form if the symlinks point to the expected location; in other words, you can rely on the correctness of those paths, even if you cannot rely on the symlinks being created.
Some common values of this option:
Suppress symlink creation:
--symlink_prefix=/
will cause Bazel to not
create or update any symlinks, including the bazel-out
and
bazel-<workspace>
symlinks. Use this option to suppress symlink creation entirely.
Reduce clutter:
--symlink_prefix=.bazel/
will cause Bazel to create
symlinks called bin
(etc) inside a hidden directory .bazel
.
--platform_suffix string
Adds a suffix to the configuration short name, which is used to determine the output directory. Setting this option to different values puts the files into different directories, for example to improve cache hit rates for builds that otherwise clobber each others output files, or to keep the output files around for comparisons.
--default_visibility=(private|public)
Temporary flag for testing bazel default visibility changes. Not intended for general use but documented for completeness' sake.
Bazel is used both by software engineers during the development cycle, and by release engineers when preparing binaries for deployment to production. This section provides a list of tips for release engineers using Bazel.
When using Bazel for release builds, the same issues arise as for other scripts that perform a build, so you should read the scripting section of this manual. In particular, the following options are strongly recommended:
These options (q.v.) are also important:
--package_path
--symlink_prefix
:
for managing builds for multiple configurations,
it may be convenient to distinguish each build
with a distinct identifier, e.g. "64bit" vs. "32bit". This option
differentiates the bazel-bin
(etc.) symlinks.
To build and run tests with bazel, type bazel test
followed by
the name of the test targets.
By default, this command performs simultaneous build and test
activity, building all specified targets (including any non-test
targets specified on the command line) and testing
*_test
and test_suite
targets as soon as
their prerequisites are built, meaning that test execution is
interleaved with building. Doing so usually results in significant
speed gains.
bazel test
--cache_test_results=(yes|no|auto)
(-t
)If this option is set to 'auto' (the default) then Bazel will only rerun a test if any of the following conditions applies:
external
--runs_per_test
If 'no', all tests will be executed unconditionally.
If 'yes', the caching behavior will be the same as auto
except that it may cache test failures and test runs with
--runs_per_test
.
Note that test results are always saved in Bazel's output tree,
regardless of whether this option is enabled, so
you needn't have used --cache_test_results
on the
prior run(s) of bazel test
in order to get cache hits.
The option only affects whether Bazel will use previously
saved results, not whether it will save results of the current run.
Users who have enabled this option by default in
their .bazelrc
file may find the
abbreviations -t
(on) or -t-
(off)
convenient for overriding the default on a particular run.
--check_tests_up_to_date
This option tells Bazel not to run the tests, but to merely check and report the cached test results. If there are any tests which have not been previously built and run, or whose tests results are out-of-date (e.g. because the source code or the build options have changed), then Bazel will report an error message ("test result is not up-to-date"), will record the test's status as "NO STATUS" (in red, if color output is enabled), and will return a non-zero exit code.
This option also implies
--check_up_to_date
behavior.
This option may be useful for pre-submit checks.
--test_verbose_timeout_warnings
This option tells Bazel to explicitly warn the user if a test's timeout is significantly longer then the test's actual execution time. While a test's timeout should be set such that it is not flaky, a test that has a highly over-generous timeout can hide real problems that crop up unexpectedly.
For instance, a test that normally executes in a minute or two should not have a timeout of ETERNAL or LONG as these are much, much too generous. This option is useful to help users decide on a good timeout value or sanity check existing timeout values.
Note that each test shard is allotted the timeout of the entire
XX_test
target. Using this option does not affect a test's timeout
value, merely warns if Bazel thinks the timeout could be restricted further.
--[no]test_keep_going
By default, all tests are run to completion. If this flag is disabled,
however, the build is aborted on any non-passing test. Subsequent build steps
and test invocations are not run, and in-flight invocations are canceled.
Do not specify both --notest_keep_going
and
--keep_going
.
--flaky_test_attempts attempts
This option specifies the maximum number of times a test should be attempted
if it fails for any reason. A test that initially fails but eventually
succeeds is reported as FLAKY
on the test summary. It is,
however, considered to be passed when it comes to identifying Bazel exit code
or total number of passed tests. Tests that fail all allowed attempts are
considered to be failed.
By default (when this option is not specified, or when it is set to
"default"), only a single attempt is allowed for regular tests, and
3 for test rules with the flaky
attribute set. You can specify
an integer value to override the maximum limit of test attempts. Bazel allows
a maximum of 10 test attempts in order to prevent abuse of the system.
--runs_per_test [regex@]number
This option specifies the number of times each test should be executed. All test executions are treated as separate tests (e.g. fallback functionality will apply to each of them independently).
The status of a target with failing runs depends on the value of the
--runs_per_test_detects_flakes
flag:
If a single number is specified, all tests will run that many times. Alternatively, a regular expression may be specified using the syntax regex@number. This constrains the effect of --runs_per_test to targets which match the regex (e.g. "--runs_per_test=^//pizza:.*@4" runs all tests under //pizza/ 4 times). This form of --runs_per_test may be specified more than once.
--[no]runs_per_test_detects_flakes
If this option is specified (by default it is not), Bazel will detect flaky test shards through --runs_per_test. If one or more runs for a single shard fail and one or more runs for the same shard pass, the target will be considered flaky with the flag. If unspecified, the target will report a failing status.
--test_summary output_style
Specifies how the test result summary should be displayed.
short
prints the results of each test along with the name of
the file containing the test output if the test failed. This is the default
value.
terse
like short
, but even shorter: only print
information about tests which did not pass.
detailed
prints each individual test case that failed, not
only each test. The names of test output files are omitted.
none
does not print test summary.
--test_output output_style
Specifies how test output should be displayed:
summary
shows a summary of whether each test passed or
failed. Also shows the output log file name for failed tests. The summary
will be printed at the end of the build (during the build, one would see
just simple progress messages when tests start, pass or fail).
This is the default behavior.
errors
sends combined stdout/stderr output from failed tests
only into the stdout immediately after test is completed, ensuring that
test output from simultaneous tests is not interleaved with each other.
Prints a summary at the build as per summary output above.
all
is similar to errors
but prints output for
all tests, including those which passed.
streamed
streams stdout/stderr output from each test in
real-time.
--java_debug
This option causes the Java virtual machine of a java test to wait for a connection from a JDWP-compliant debugger before starting the test. This option implies --test_output=streamed.
--[no]verbose_test_summary
By default this option is enabled, causing test times and other additional
information (such as test attempts) to be printed to the test summary. If
--noverbose_test_summary
is specified, test summary will
include only test name, test status and cached test indicator and will
be formatted to stay within 80 characters when possible.
--test_tmpdir path
Specifies temporary directory for tests executed locally. Each test will be
executed in a separate subdirectory inside this directory. The directory will
be cleaned at the beginning of the each bazel test
command.
By default, bazel will place this directory under Bazel output base directory.
Note that this is a directory for running tests, not storing test results
(those are always stored under the bazel-out
directory).
--test_timeout
seconds
OR
--test_timeout
seconds,seconds,seconds,seconds
Overrides the timeout value for all tests by using specified number of seconds as a new timeout value. If only one value is provided, then it will be used for all test timeout categories.
Alternatively, four comma-separated values may be provided, specifying individual timeouts for short, moderate, long and eternal tests (in that order). In either form, zero or a negative value for any of the test sizes will be substituted by the default timeout for the given timeout categories as defined by the page Writing Tests. By default, Bazel will use these timeouts for all tests by inferring the timeout limit from the test's size whether the size is implicitly or explicitly set.
Tests which explicitly state their timeout category as distinct from their size will receive the same value as if that timeout had been implicitly set by the size tag. So a test of size 'small' which declares a 'long' timeout will have the same effective timeout that a 'large' tests has with no explicit timeout.
--test_arg arg
Passes command-line options/flags/arguments to the test (not to the test runner). This
option can be used multiple times to pass several arguments, e.g.
--test_arg=--logtostderr --test_arg=--v=3
.
--test_env variable=value
OR
--test_env variable
Specifies additional variables that must be injected into the test
environment for each test. If value is not specified it will be
inherited from the shell environment used to start the bazel test
command.
The environment can be accessed from within a test by using
System.getenv("var")
(Java),
getenv("var")
(C or C++),
--run_under=command-prefix
This specifies a prefix that the test runner will insert in front of the test command before running it. The command-prefix is split into words using Bourne shell tokenization rules, and then the list of words is prepended to the command that will be executed.
If the first word is a fully qualified label (i.e. starts with
//
) it is built. Then the label is substituted by the
corresponding executable location that is prepended to the command
that will be executed along with the other words.
Some caveats apply:
--run_under
command (the first word in command-prefix).
stdin
is not connected, so --run_under
can't be used for interactive commands.
Examples:
--run_under=/usr/bin/valgrind --run_under=/usr/bin/strace --run_under='/usr/bin/strace -c' --run_under='/usr/bin/valgrind --quiet --num-callers=20'
As documented under Output selection options, you can filter tests by size, timeout, tag, or language. A convenience general name filter can forward particular filter args to the test runner.
bazel test
The syntax and the remaining options are exactly like bazel build.
The bazel run
command is similar to bazel build
, except
it is used to build and run a single target. Here is a typical session:
% bazel run -- java/myapp:myapp --arg1 --arg2 Welcome to Bazel INFO: Loading package: java/myapp INFO: Loading package: foo/bar INFO: Loading complete. Analyzing... INFO: Found 1 target... ... Target //java/myapp:myapp up-to-date: bazel-bin/java/myapp:myapp INFO: Elapsed time: 0.638s, Critical Path: 0.34s INFO: Running command line: bazel-bin/java/myapp:myapp --arg1 --arg2 Hello there $EXEC_ROOT/java/myapp/myapp --arg1 --arg2
Bazel closes stdin, so you can't use bazel run
if you want to start an interactive program or pipe data to it.
Note the use of the --
. This is needed so that Bazel
does not interpret --arg1
and --arg2
as
Bazel options, but rather as part of the command line for running the binary.
(The program being run simply says hello and prints out its args.)
bazel run
--run_under=command-prefix
This has the same effect as the --run_under
option for
bazel test
(see above),
except that it applies to the command being run by bazel
run
rather than to the tests being run by bazel test
and cannot run under label.
bazel run
can also execute test binaries, which has the effect of
running the test, but without the setup documented on the page
Writing Tests, so that the test runs
in an environment closer to the current shell environment. Note that none of the
--test_* arguments have an effect when running a test in this manner.
Bazel includes a query language for asking questions about the dependency graph used during the build. The query tool is an invaluable aid to many software engineering tasks.
The query language is based on the idea of algebraic operations over graphs; it is documented in detail in Bazel Query Reference. Please refer to that document for reference, for examples, and for query-specific command-line options.
The query tool accepts several command-line
option. --output
selects the output format.
--[no]keep_going
(disabled by default) causes the query
tool to continue to make progress upon errors; this behavior may be
disabled if an incomplete result is not acceptable in case of errors.
The --[no]host_deps
option,
enabled by default, causes dependencies on "host
configuration" targets to be included in the dependency graph over
which the query operates.
The --[no]implicit_deps
option, enabled by default, causes
implicit dependencies to be included in the dependency graph over which the query operates. An
implicit dependency is one that is not explicitly specified in the BUILD file
but added by bazel.
Example: "Show the locations of the definitions (in BUILD files) of all genrules required to build all the tests in the PEBL tree."
bazel query --output location 'kind(genrule, deps(kind(".*_test rule", foo/bar/pebl/...)))'
help
command
The help
command provides on-line help. By default, it
shows a summary of available commands and help topics, as shown in
the Bazel overview section above.
Specifying an argument displays detailed help for a particular
topic. Most topics are Bazel commands, e.g. build
or query
, but there are some additional help topics
that do not correspond to commands.
--[no]long
(-l
)
By default, bazel help [topic]
prints only a
summary of the relevant options for a topic. If
the --long
option is specified, the type, default value
and full description of each option is also printed.
shutdown
command
Bazel server processes (see Client/server
implementation) may be stopped by using the shutdown
command. This command causes the Bazel server to exit as soon as it
becomes idle (i.e. after the completion of any builds or other
commands that are currently in progress).
Bazel servers stop themselves after an idle timeout, so this command
is rarely necessary; however, it can be useful in scripts when it is
known that no further builds will occur in a given workspace.
shutdown
accepts one
option, --iff_heap_size_greater_than n
, which
requires an integer argument (in MB). If specified, this makes the shutdown
conditional on the amount of memory already consumed. This is
useful for scripts that initiate a lot of builds, as any memory
leaks in the Bazel server could cause it to crash spuriously on
occasion; performing a conditional restart preempts this condition.
info
command
The info
command prints various values associated with
the Bazel server instance, or with a specific build configuration.
(These may be used by scripts that drive a build.)
The info
command also permits a single (optional)
argument, which is the name of one of the keys in the list below.
In this case, bazel info key
will print only
the value for that one key. (This is especially convenient when
scripting Bazel, as it avoids the need to pipe the result
through sed -ne /key:/s/key://p
:
release
: the release label for this Bazel
instance, or "development version" if this is not a released
binary.
workspace
the absolute path to the base workspace
directory.
install_base
: the absolute path to the installation
directory used by this Bazel instance for the current user. Bazel
installs its internally required executables below this directory.
output_base
: the absolute path to the base output
directory used by this Bazel instance for the current user and
workspace combination. Bazel puts all of its scratch and build
output below this directory.
execution_root
: the absolute path to the execution
root directory under output_base. This directory is the root for all files
accessible to commands executed during the build, and is the working
directory for those commands. If the workspace directory is writable, a
symlink named
bazel-<workspace>
is placed there pointing to this directory.
output_path
: the absolute path to the output
directory beneath the execution root used for all files actually
generated as a result of build commands. If the workspace directory is
writable, a symlink named bazel-out
is placed there pointing
to this directory.
server_pid
: the process ID of the Bazel server
process. command_log
: the absolute path to the command log file;
this contains the interleaved stdout and stderr streams of the most recent
Bazel command. Note that running bazel info
will overwrite the
contents of this file, since it then becomes the most recent Bazel command.
However, the location of the command log file will not change unless you
change the setting of the --output_base
or
--output_user_root
options.
used-heap-size
,
committed-size
,
max-heap-size
: reports various JVM heap size
parameters. Respectively: memory currently used, memory currently
guaranteed to be available to the JVM from the system, maximum
possible allocation.
gc-count
, gc-time
: The cumulative count of
garbage collections since the start of this Bazel server and the time spent
to perform them. Note that these values are not reset at the start of every
build.
package_path
: A colon-separated list of paths which would be
searched for packages by bazel. Has the same format as the
--package_path
build command line argument.
Example: the process ID of the Bazel server.
% bazel info server_pid 1285
These data may be affected by the configuration options passed
to bazel info
, for
example --cpu
, --compilation_mode
,
etc. The info
command accepts all
the options that control dependency
analysis, since some of these determine the location of the
output directory of a build, the choice of compiler, etc.
bazel-bin
, bazel-testlogs
,
bazel-genfiles
: reports the absolute path to
the bazel-*
directories in which programs generated by the
build are located. This is usually, though not always, the same as
the bazel-*
symlinks created in the base workspace directory after a
successful build. However, if the workspace directory is read-only,
no bazel-*
symlinks can be created. Scripts that use
the value reported by bazel info
, instead of assuming the
existence of the symlink, will be more robust.
--show_make_env
flag is
specified, all variables in the current configuration's "Make" environment
are also displayed (e.g. CC
, GLIBC_VERSION
, etc).
These are the variables accessed using the $(CC)
or varref("CC")
syntax inside BUILD files.
Example: the C++ compiler for the current configuration.
This is the $(CC)
variable in the "Make" environment,
so the --show_make_env
flag is needed.
% bazel info --show_make_env -c opt BINMODE -opt
Example: the bazel-bin
output directory for the current
configuration. This is guaranteed to be correct even in cases where
the bazel-bin
symlink cannot be created for some reason
(e.g. you are building from a read-only directory).
version
commandThe version command prints version details about the built Bazel binary, including the changelist at which it was built and the date. These are particularly useful in determining if you have the latest Bazel, or if you are reporting bugs. Some of the interesting values are:
changelist
: the changelist at which this version of
Bazel was released.
label
: the release label for this Bazel
instance, or "development version" if this is not a released
binary. Very useful when reporting bugs.
mobile-install
command
The mobile-install
command installs apps to mobile devices.
Currently only Android devices running ART are supported.
Note that this command does not install the same thing that
bazel build
produces: Bazel tweaks the app so that it can be
built, installed and re-installed quickly. This should, however, be mostly
transparent to the app.
The following options are supported:
--incremental
If set, Bazel tries to install the app incrementally, that is, only those
parts that have changed since the last build. This cannot update resources
referenced from AndroidManifest.xml
, native code or Java
resources (i.e. ones referenced by Class.getResource()
). If these
things change, this option must be omitted. Contrary to the spirit of Bazel
and due to limitations of the Android platform, it is the
responsibility of the user to know when this command is good enough and
when a full install is needed. We are working to come up with a better
solution.
--adb
Indicates the adb
binary to be used. When unspecified, the binary
in the repository is used.
--adb_arg
Extra arguments to adb
. These come before the subcommand in the
command line and are typically used to specify which device to install to.
Example:
% bazel mobile-install --adb_arg=-s --adb_arg=deadbeefwill invoke
adb
as
adb -s deadbeef install ...
analyze-profile
command
The analyze-profile
command analyzes data previously gathered
during the build using --profile
option. It provides several
options to either perform analysis of the build execution or export data in
the specified format.
The following options are supported:
--dump=text
displays all gathered data in a
human-readable format--dump=raw
displays all gathered data in a
script-friendly format--html
generates an HTML file visualizing the
actions and rules executed in the build, as well as summary statistics for the build
--html_details
adds more fine-grained
information on actions and rules to the HTML visualizationSee the section on Troubleshooting performance by profiling for format details and usage help.
canonicalize-flags
command
The canonicalize-flags
command, which takes a list of options for
a Bazel command and returns a list of options that has the same effect. The
new list of options is canonical, i.e., two lists of options with the same
effect are canonicalized to the same new list.
The --for_command
option can be used to select between different
commands. At this time, only build
and test
are
supported. Options that the given command does not support cause an error.
Note that a small number of options cannot be reordered, because Bazel cannot ensure that the effect is identical.
The options described in this section affect the startup of the Java virtual machine used by Bazel server process, and they apply to all subsequent commands handled by that server. If there is an already running Bazel server and the startup options do not match, it will be restarted.
All of the options described in this section must be specified using the
--key=value
or --key value
syntax. Also, these options must appear before the name of the Bazel
command.
--output_base=dir
This option requires a path argument, which must specify a writable directory. Bazel will use this location to write all its output. The output base is also the key by which the client locates the Bazel server. By changing the output base, you change the server which will handle the command.
By default, the output base is derived from the user's login name,
and the name of the workspace directory (actually, its MD5 digest),
so a typical value looks like:
/var/tmp/google/_bazel_jrluser/d41d8cd98f00b204e9800998ecf8427e
.
Note that the client uses the output base to find the Bazel server
instance, so if you specify a different output base in a Bazel
command, a different server will be found (or started) to handle the
request. It's possible to perform two concurrent builds in the same
workspace directory by varying the output base.
For example:
% bazel --output_base /tmp/1 build //foo & bazel --output_base /tmp/2 build //bar
In this command, the two Bazel commands run concurrently (because of
the shell &
operator), each using a different Bazel
server instance (because of the different output bases).
In contrast, if the default output base was used in both commands,
then both requests would be sent to the same server, which would
handle them sequentially: building //foo
first, followed
by an incremental build of //bar
.
We recommend you do not use NFS locations for the output base, as the higher access latency of NFS will cause noticeably slower builds.
--output_user_root=dir
By default, the output_base
value is chosen to as to
avoid conflicts between multiple users building in the same workspace directory.
In some situations, though, it is desirable to build from a directory
shared between multiple users; release engineers often do this. In
those cases it may be useful to deliberately override the default so
as to ensure "conflicts" (i.e., sharing) between multiple users.
Use the --output_user_root
option to achieve this: the
output base is placed in a subdirectory of the output user root,
with a unique name based on the workspace, so the result of using an
output user root that is not a function of $USER
is
sharing. Of course, it is important to ensure (via umask and group
membership) that all the cooperating users can read/write each
others files.
If the --output_base
option is specified, it overrides
using --output_user_root
to calculate the output base.
The install base location is also calculated based on
--output_user_root
, plus the MD5 identity of the Bazel embedded
binaries.
You can also use the --output_user_root
option to choose an
alternate base location for all of Bazel's output (install base and output
base) if there is a better location in your filesystem layout.
--host_jvm_args=string
Specifies a startup option to be passed to the Java virtual machine in which Bazel itself runs. This can be used to set the stack size, for example:
% bazel --host_jvm_args="-Xss256K" build //foo
This option can be used multiple times with individual arguments. Note that setting this flag should rarely be needed. You can also pass a space-separated list of strings, each of which will be interpreted as a separate JVM argument, but this feature will soon be deprecated.
That this does not affect any JVMs used by
subprocesses of Bazel: applications, tests, tools, etc. To pass
JVM options to executable Java programs, whether run by bazel
run
or on the command-line, you should use
the --jvm_flags
argument which
all java_binary
and java_test
programs
support. Alternatively for tests, use bazel
test --test_arg=--jvm_flags=foo ...
.
--host_jvm_debug
This option causes the Java virtual machine to wait for a connection from a JDWP-compliant debugger before calling the main method of Bazel itself. This is primarily intended for use by Bazel developers.
(Please note that this does not affect any JVMs used by subprocesses of Bazel: applications, tests, tools, etc.)
--batch
This switch will cause bazel to be run in batch mode, instead of the standard client/server mode described above. Doing so provides more predictable semantics with respect to signal handling, job control, and environment variable inheritance, and is necessary for running bazel in a chroot jail.
Batch mode retains proper queueing semantics within the same output_base. That is, simultaneous invocations will be processed in order, without overlap. If a batch mode bazel is run on a client with a running server, it first kills the server before processing the command.
Bazel will run slower in batch mode, compared to client/server mode. Among other things, the build file cache is memory-resident, so it is not preserved between sequential batch invocations. Therefore, using batch mode often makes more sense in cases where performance is less critical, such as continuous builds.
--max_idle_secs n
This option specifies how long, in seconds, the Bazel server process should wait after the last client request, before it exits. The default value is 10800 (3 hours).
This option may be used by scripts that invoke Bazel to ensure that
they do not leave Bazel server processes on a user's machine when they
would not be running otherwise.
For example, a presubmit script might wish to
invoke bazel query
to ensure that a user's pending
change does not introduce unwanted dependencies. However, if the
user has not done a recent build in that workspace, it would be
undesirable for the presubmit script to start a Bazel server just
for it to remain idle for the rest of the day.
By specifying a small value of --max_idle_secs
in the
query request, the script can ensure that if it caused a new
server to start, that server will exit promptly, but if instead
there was already a server running, that server will continue to run
until it has been idle for the usual time. Of course, the existing
server's idle timer will be reset.
--[no]block_for_lock
If enabled, Bazel will wait for other Bazel commands holding the server lock to complete before progressing. If disabled, Bazel will exit in error if it cannot immediately acquire the lock and proceed. Developers might use this in presubmit checks to avoid long waits caused by another Bazel command in the same client.
--io_nice_level n
Sets a level from 0-7 for best-effort IO scheduling. 0 is highest priority, 7 is lowest. The anticipatory scheduler may only honor up to priority 4. Negative values are ignored.
--batch_cpu_scheduling
Use batch
CPU scheduling for Bazel. This policy is useful for
workloads that are non-interactive, but do not want to lower their nice value.
See 'man 2 sched_setscheduler'. This policy may provide for better system
interactivity at the expense of Bazel throughput.
--[no]announce_rc
Controls whether Bazel announces command options read from the bazelrc file when starting up. (Startup options are unconditionally announced.)
--color (yes|no|auto)
This option determines whether Bazel will use colors to highlight its output on the screen.
If this option is set to yes
, color output is enabled.
If this option is set to auto
, Bazel will use color output only if
the output is being sent to a terminal and the TERM environment variable
is set to a value other than dumb
, emacs
, or xterm-mono
.
If this option is set to no
, color output is disabled,
regardless of whether the output is going to a terminal and regardless
of the setting of the TERM environment variable.
--config name
Selects additional config section from the rc files; for the current
command
, it also pulls in the options from
command:name
if such a section exists. Note that it is currently
only possible to provide these options on the command line, not in the rc
files. Can be specified multiple times to add flags from several
config sections.
--curses (yes|no|auto)
This option determines whether Bazel will use cursor controls
in its screen output. This results in less scrolling data, and a more
compact, easy-to-read stream of output from Bazel. This works well with
--color
.
If this option is set to yes
, use of cursor controls is enabled.
If this option is set to no
, use of cursor controls is disabled.
If this option is set to auto
, use of cursor controls will be
enabled under the same conditions as for --color=auto
.
--[no]show_timestamps
If specified, a timestamp is added to each message generated by Bazel specifying the time at which the message was displayed.
Bazel can be called from scripts in order to perform a build, run tests or query the dependency graph. Bazel has been designed to enable effective scripting, but this section lists some details to bear in mind to make your scripts more robust.
The --output_base
option controls where the Bazel process should
write the outputs of a build to, as well as various working files used
internally by Bazel, one of which is a lock that guards against
concurrent mutation of the output base by multiple Bazel processes.
Choosing the correct output base directory for your script depends
on several factors. If you need to put the build outputs in a
specific location, this will dictate the output base you need to
use. If you are making a "read only" call to Bazel
(e.g. bazel query
), the locking factors will be more important.
In particular, if you need to run multiple instances of your script
concurrently, you will need to give each one a different (or random) output
base.
If you use the default output base value, you will be contending for the same lock used by the user's interactive Bazel commands. If the user issues long-running commands such as builds, your script will have to wait for those commands to complete before it can continue.
By default, Bazel uses a long-running server process as an optimization; this
behavior can be disabled using the --batch
option. There's no hard and
fast rule about whether or not your script should use a server, but
in general, the trade-off is between performance and reliability.
The server mode makes a sequence of builds, especially incremental
builds, faster, but its behavior is more complex and prone to
failure. We recommend in most cases that you use batch mode unless
the performance advantage is critical.
If you do use the server, don't forget to call shutdown
when you're finished with it, or, specify
--max_idle_secs=5
so that idle servers shut themselves
down promptly.
Bazel attempts to differentiate failures due to the source code under consideration from external errors that prevent Bazel from executing properly. Bazel execution can result in following exit codes:
Exit Codes common to all commands:0
- Success2
- Command Line Problem, Bad or Illegal flags or command
combination, or Bad Environment Variables. Your command line must be
modified.8
- Build Interrupted but we terminated with an orderly shutdown.32
- External Environment Failure not on this machine.33
- OOM failure. You need to modify your command line.34
- Reserved for Google-internal use.35
- Reserved for Google-internal use.36
- Local Environmental Issue, suspected permanent.37
- Unhandled Exception / Internal Bazel Error.38
- Reserved for Google-internal use.40-44
- Reserved for errors in Bazel's command line launcher,
bazel.cc
that are not command line
related. Typically these are related to bazel server
being unable to launch itself.bazel build
, bazel test
.
1
- Build failed.3
- Build OK, but some tests failed or timed out.4
- Build successful but no tests were found even though
testing was requested.bazel run
:
1
- Build failed.6
- Run command failure. The executed subprocess returned a
non-zero exit code. The actual subprocess exit code is
given in stderr.bazel query
:
3
- Partial success, but the query encountered 1 or more
errors in the input BUILD file set and therefore the
results of the operation are not 100% reliable.
This is likely due to a --keep_going
option
on the command line.7
- Command failure.
Future Bazel versions may add additional exit codes, replacing generic failure
exit code 1
with a different non-zero value with a particular
meaning. However, all non-zero exit values will always constitute an error.
By default, Bazel will read the .bazelrc
file from the base workspace
directory or the user's home directory. Whether or not this is
desirable is a choice for your script; if your script needs to be
perfectly hermetic (e.g. when doing release builds), you should
disable reading the .bazelrc file by using the option
--bazelrc=/dev/null
. If you want to perform a build
using the user's preferred settings, the default behavior is better.
The Bazel output is also available in a command log file which you can find with the following command:
% bazel info command_log
The command log file contains the interleaved stdout and stderr streams
of the most recent Bazel command. Note that running bazel info
will overwrite the contents of this file, since it then becomes the most
recent Bazel command. However, the location of the command log file will
not change unless you change the setting of the --output_base
or --output_user_root
options.
The Bazel output is quite easy to parse for many purposes. Two
options that may be helpful for your script are
--noshow_progress
which suppresses progress messages,
and --show_result n
, which controls whether
or not "build up-to-date" messages are printed; these messages may
be parsed to discover which targets were successfully built, and the
location of the output files they created. Be sure to specify a
very large value of n if you rely on these messages.
The first step in analyzing the performance of your build is to profile your build with the
--profile
option.
The file generated by the --profile
command is a binary file. Once you have generated this binary profile, you can analyze it using
Bazel's analyze-profile
command. By default, it will
print out summary analysis information for each of the specified profile datafiles. This includes
cumulative statistics for different task types for each build phase and an analysis of the
critical execution path.
The first section of the default output describes an overview of the time spent on the different build phases:
=== PHASE SUMMARY INFORMATION === Total launch phase time 6.00 ms 0.01% Total init phase time 864 ms 1.11% Total loading phase time 21.841 s 28.05% Total analysis phase time 5.444 s 6.99% Total preparation phase time 155 ms 0.20% Total execution phase time 49.473 s 63.54% Total finish phase time 83.9 ms 0.11% Total run time 77.866 s 100.00%
The following sections show the execution time of different tasks happening during a particular phase:
=== INIT PHASE INFORMATION === Total init phase time 864 ms Total time (across all threads) spent on: Type Total Count Average VFS_STAT 2.72% 1 23.5 ms VFS_READLINK 32.19% 1 278 ms === LOADING PHASE INFORMATION === Total loading phase time 21.841 s Total time (across all threads) spent on: Type Total Count Average SPAWN 3.26% 154 475 ms VFS_STAT 10.81% 65416 3.71 ms [...] SKYLARK_BUILTIN_FN 13.12% 45138 6.52 ms === ANALYSIS PHASE INFORMATION === Total analysis phase time 5.444 s Total time (across all threads) spent on: Type Total Count Average SKYFRAME_EVAL 9.35% 1 4.782 s SKYFUNCTION 89.36% 43332 1.06 ms === EXECUTION PHASE INFORMATION === Total preparation time 155 ms Total execution phase time 49.473 s Total time finalizing build 83.9 ms Action dependency map creation 0.00 ms Actual execution time 49.473 s Total time (across all threads) spent on: Type Total Count Average ACTION 2.25% 12229 10.2 ms [...] SKYFUNCTION 1.87% 236131 0.44 ms
The last section shows the critical path:
Critical path (32.078 s): Id Time Percentage Description 1109746 5.171 s 16.12% Building [...] 1109745 164 ms 0.51% Extracting interface [...] 1109744 4.615 s 14.39% Building [...] [...] 1109639 2.202 s 6.86% Executing genrule [...] 1109637 2.00 ms 0.01% Symlinking [...] 1109636 163 ms 0.51% Executing genrule [...] 4.00 ms 0.01% [3 middleman actions]
You can use the following options to display more detailed information:
--dump=text
This option prints all recorded tasks in the order they occurred. Nested tasks are indented relative to the parent. For each task, output includes the following information:
[task type] [task description] Thread: [thread id] Id: [task id] Parent: [parent task id or 0 for top-level tasks] Start time: [time elapsed from the profiling session start] Duration: [task duration] [aggregated statistic for nested tasks, including count and total duration for each nested task]
--dump=raw
This option is most useful for automated analysis with scripts. It outputs each task record on a single line using '|' delimiter between fields. Fields are printed in the following order:
1|1|0|0|0||PHASE|Launch Bazel 1|2|0|6000000|0||PHASE|Initialize command 1|3|0|168963053|278111411||VFS_READLINK|/[...] 1|4|0|571055781|23495512||VFS_STAT|/[...] 1|5|0|869955040|0||PHASE|Load packages [...]
--html
This option writes a file called <profile-file>.html
in the directory of the
profile file. Open it in your browser to see the visualization of the actions in your build.
Note that the file can be quite large and may push the capabilities of your browser –
please wait for the file to load.
In most cases, the HTML output from --html
is easier to
read than the --dump
output.
It includes a Gantt chart that displays time on the horizontal axis and
threads of execution along the vertical axis. If you click on the Statistics link in the top
right corner of the page, you will jump to a section that lists summary analysis information
from your build.
--html_details
Additionally passing this option will render a more detailed execution chart and additional tables on the performance of built-in and user-defined Skylark functions. Beware that this increases the file size and the load on the browser considerably.
If Bazel appears to be hung, you can hit ctrl + \ or send
Bazel a SIGQUIT
signal (kill -3 $(bazel info server_pid)
) to get a
thread dump in the file $(bazel info output_base)/server/jvm.out
.
Since you may not be able to run bazel info
if bazel is hung, the
output_base
directory is usually the parent of the bazel-<workspace>
symlink in your workspace directory.