Ubuntu Manpage: dh - debhelper command sequencer

NAME

       dh - debhelper command sequencer

SYNOPSIS

       dh sequence [--with addon[,addon ...]] [--list] [debhelper options]

DESCRIPTION

       dh runs a sequence of debhelper commands. The supported sequences correspond to the
       targets of a debian/rules file: build-arch, build-indep, build, clean, install-indep,
       install-arch, install, binary-arch, binary-indep, and binary.

OVERRIDE AND HOOK TARGETS

A debian/rules file using dh can override the command that is run at any step in a
sequence, by defining an override target. It is also possible to inject a commands before
or after any step without affecting the step itself.

Injecting commands before or after a step
Note: This feature requires debhelper 12.8 or later plus the package must use
compatibility mode 10 or later.

To inject commands before dh_command, add a target named execute_before_dh_command to the
rules files. Similarly, if you want to inject commands after dh_command, add the target
execute_after_dh_command. Both targets can be used for the same dh_command and also even
if the command is overridden (as described in "Overriding a command" below).

When these targets are defined, dh will call the targets respectively before or after it
would invoke dh_command (or its override target).

Overriding a command
To override dh_command, add a target named override_dh_command to the rules file. When it
would normally run dh_command, dh will instead call that target. The override target can
then run the command with additional options, or run entirely different commands instead.
See examples below.

Architecture dependent/independent override and hook targets
The override and hook targets can also be defined to run only when building architecture
dependent or architecture independent packages. Use targets with names like
override_dh_command-arch and execute_afterdh_command-indep.

This feature is available since debhelper 8.9.7 (for override targets) and 12.8 (for hook
targets).

Completely empty targets
As a special optimization, dh will skip a target if it is completely empty. This is
mostly useful for override targets, where the command will simply be skipped without the
overhead of invoking a dummy target.

Note that the target has to be completely empty for this to work:

# Skip dh_bar - the good and optimized way
# Some rationale for skipping dh_bar goes here
override_dh_bar:

# Skip dh_foo - the slow way
override_dh_foo:
# Some rationale for skipping dh_foo goes here
# (these comments causes a dummy target to be run)

Verifying targets are picked up by dh
If you want to confirm that dh has seen an override or a hook target, you can use the
following command as an example:

$ dh binary --no-act | grep dh_install | head -n5
dh_installdirs
dh_install
debian/rules execute_after_dh_install
dh_installdocs
dh_installchangelogs

The debian/rules execute_after_dh_install in the output, which signals that dh registered
a execute_after_dh_install target and would run it directly after dh_install(1).

Note that "Completely empty targets" will be omitted in the listing above. This makes it
a bit harder to spot as you are looking for the omission of a command name. But
otherwise, the principle remains the same.

OPTIONS

--with addon[,addon ...]
Add the debhelper commands specified by the given addon to appropriate places in the
sequence of commands that is run. This option can be repeated more than once, or
multiple addons can be listed, separated by commas. This is used when there is a
third-party package that provides debhelper commands. See the PROGRAMMING file for
documentation about the sequence addon interface.

A Build-Depends relation on the package dh-sequence-addon implies a --with addon. This
avoids the need for an explicit --with in debian/rules that only duplicates what is
already declared via the build dependencies in debian/control. The relation can
(since 12.5) be made optional via e.g. build-profiles. This enables you to easily
disable an addon that is only useful with certain profiles (e.g. to facilitate
bootstrapping).

Since debhelper 12.5, addons can also be activated in indep-only mode (via Build-
Depends-Indep) or arch-only mode (via Build-Depends-Arch). Such addons are only active
in the particular sequence (e.g. binary-indep) which simplifies dependency management
for cross-builds.

Please note that addons activated via Build-Depends-Indep or Build-Depends-Arch are
subject to additional limitations to ensure the result is deterministic even when the
addon is unavailable (e.g. during clean). This implies that some addons are
incompatible with these restrictions and can only be used via Build-Depends (or
manually via debian/rules). Currently, such addons can only add commands to
sequences.

--without addon
The inverse of --with, disables using the given addon. This option can be repeated
more than once, or multiple addons to disable can be listed, separated by commas.

--list, -l
List all available addons.

When called only with this option, dh can be called from any directory (i.e. it does
not need access to files from a source package).

--no-act
Prints commands that would run for a given sequence, but does not run them.

Note that dh normally skips running commands that it knows will do nothing. With
--no-act, the full list of commands in a sequence is printed.

Other options passed to dh are passed on to each command it runs. This can be used to set
an option like -v or -X or -N, as well as for more specialised options.

EXAMPLES

       To see what commands are included in a sequence, without actually doing anything:

               dh binary-arch --no-act

       This is a very simple rules file, for packages where the default sequences of commands
       work with no additional options.

               #!/usr/bin/make -f
               %:
                       dh $@

       Often you'll want to pass an option to a specific debhelper command. The easy way to do
       with is by adding an override target for that command.

               #!/usr/bin/make -f
               %:
                       dh $@

               override_dh_strip:
                       dh_strip -Xfoo

               override_dh_auto_configure:
                       dh_auto_configure -- --with-foo --disable-bar

       Sometimes the automated dh_auto_configure(1) and dh_auto_build(1) can't guess what to do
       for a strange package. Here's how to avoid running either and instead run your own
       commands.

               #!/usr/bin/make -f
               %:
                       dh $@

               override_dh_auto_configure:
                       ./mondoconfig

               override_dh_auto_build:
                       make universe-explode-in-delight

       Another common case is wanting to do something manually before or after a particular
       debhelper command is run.

               #!/usr/bin/make -f
               %:
                       dh $@

               # Example assumes debhelper/12.8 and compat 10+
               execute_after_dh_fixperms:
                       chmod 4755 debian/foo/usr/bin/foo

       If you are on an older debhelper or compatibility level, the above example would have to
       be written as.

               #!/usr/bin/make -f
               %:
                       dh $@

               # Older debhelper versions or using compat 9 or lower.
               override_dh_fixperms:
                       dh_fixperms
                       chmod 4755 debian/foo/usr/bin/foo

       Python tools are not run by dh by default, due to the continual change in that area. Here
       is how to use dh_python2.

               #!/usr/bin/make -f
               %:
                       dh $@ --with python2

       Here is how to force use of Perl's Module::Build build system, which can be necessary if
       debhelper wrongly detects that the package uses MakeMaker.

               #!/usr/bin/make -f
               %:
                       dh $@ --buildsystem=perl_build

       Here is an example of overriding where the dh_auto_* commands find the package's source,
       for a package where the source is located in a subdirectory.

               #!/usr/bin/make -f
               %:
                       dh $@ --sourcedirectory=src

       And here is an example of how to tell the dh_auto_* commands to build in a subdirectory,
       which will be removed on clean.

               #!/usr/bin/make -f
               %:
                       dh $@ --builddirectory=build

       If your package can be built in parallel, please either use compat 10 or pass --parallel
       to dh. Then dpkg-buildpackage -j will work.

               #!/usr/bin/make -f
               %:
                       dh $@ --parallel

       If your package cannot be built reliably while using multiple threads, please pass
       --no-parallel to dh (or the relevant dh_auto_* command):

               #!/usr/bin/make -f
               %:
                       dh $@ --no-parallel

       Here is a way to prevent dh from running several commands that you don't want it to run,
       by defining empty override targets for each command.

               #!/usr/bin/make -f
               %:
                       dh $@

               # Commands not to run:
               override_dh_auto_test override_dh_compress override_dh_fixperms:

       A long build process for a separate documentation package can be separated out using
       architecture independent overrides.  These will be skipped when running build-arch and
       binary-arch sequences.

               #!/usr/bin/make -f
               %:
                       dh $@

               override_dh_auto_build-indep:
                       $(MAKE) -C docs

               # No tests needed for docs
               override_dh_auto_test-indep:

               override_dh_auto_install-indep:
                       $(MAKE) -C docs install

       Adding to the example above, suppose you need to chmod a file, but only when building the
       architecture dependent package, as it's not present when building only documentation.

               # Example assumes debhelper/12.8 and compat 10+
               execute_after_dh_fixperms-arch:
                       chmod 4755 debian/foo/usr/bin/foo

INTERNALS

If you're curious about dh's internals, here's how it works under the hood.

In compat 10 (or later), dh creates a stamp file debian/debhelper-build-stamp after the
build step(s) are complete to avoid re-running them. It is possible to avoid the stamp
file by passing --without=build-stamp to dh. This makes "no clean" builds behave more
like what some people expect at the expense of possibly running the build and test twice
(the second time as root or under fakeroot(1)).

Inside an override target, dh_* commands will create a log file
debian/package.debhelper.log to keep track of which packages the command(s) have been run
for. These log files are then removed once the override target is complete.

In compat 9 or earlier, each debhelper command will record when it's successfully run in
debian/package.debhelper.log. (Which dh_clean deletes.) So dh can tell which commands have
already been run, for which packages, and skip running those commands again.

Each time dh is run (in compat 9 or earlier), it examines the log, and finds the last
logged command that is in the specified sequence. It then continues with the next command
in the sequence.

A sequence can also run dependent targets in debian/rules. For example, the "binary"
sequence runs the "install" target.

dh uses the DH_INTERNAL_OPTIONS environment variable to pass information through to
debhelper commands that are run inside override targets. The contents (and indeed,
existence) of this environment variable, as the name might suggest, is subject to change
at any time.

Commands in the build-indep, install-indep and binary-indep sequences are passed the -i
option to ensure they only work on architecture independent packages, and commands in the
build-arch, install-arch and binary-arch sequences are passed the -a option to ensure they
only work on architecture dependent packages.

AUTHOR

       Joey Hess <joeyh@debian.org>