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NAME | SYNOPSIS | DESCRIPTION | OVERRIDE AND HOOK TARGETS | OPTIONS | EXAMPLES | DEBHELPER PROVIDED DH ADDONS | INTERNALS | SEE ALSO | AUTHOR | COLOPHON |
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DH(1) Debhelper DH(1)
dh - debhelper command sequencer
dh sequence [--with addon[,addon ...]] [--list]
[debhelper options]
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.
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 command 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_after_dh_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 and does not depend on any other target. 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
As of debhelper 13.10, you can use dh_assistant(1) to see which
override and hook targets will be seen by dh. Here is an example
run of dh_assistant(1) along with its output:
$ dh_assistant detect-hook-targets
{
"commands-not-in-path": [
"dh_foo"
],
"hook-targets": [
{
"command": "dh_strip_nondeterminism",
"is-empty": true,
"package-section-param": null,
"target-name": "override_dh_strip_nondeterminism"
},
{
"command": "dh_foo",
"is-empty": false,
"package-section-param": "-a",
"target-name": "override_dh_foo-arch"
}
]
}
The commands-not-in-path is useful for spotting mistakes in the
hook target names. A non-empty value implies one of more hook
targets are related to a command that is either not installed or
no command with that name exists at all. It is generally worth
double checking these.
Additionally, the is-empty attribute for each hook target can be
used for seeing whether a hook target triggers the "Completely
empty targets" optimization.
If you are interested in the other attributes, please read the
dh_assistant(1) for the details.
Verifying targets are picked up by dh (when debhelper is older
than 13.10)
On older versions of debhelper, you have to use dh with --no-act.
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.
Caveats with hook targets and makefile conditionals
If you choose to wrap a hook target in makefile conditionals,
please be aware that dh computes all the hook targets a head of
time and caches the result for that run. Furthermore, the
conditionals will be invoked again when dh calls the hook target
later and will assume the answer did not change.
The parsing and caching often happens before dh knows whether it
will build arch:any (-a) or/and arch:all (-i) packages, which can
produce confusing results - especially when dh_listpackages(1) is
part of the conditional.
Most of the problems can be avoided by making the hook target
unconditional and then have the "body" be partially or completely
conditional. As an example:
# SIMPLE: It is well-defined what happens. The hook target
# is always considered. The "maybe run this" bit is
# conditional but dh_foo is definitely skipped.
#
# Note: The conditional is evaluated "twice" where its
# influences what happens. Once when dh check which hook
# targets exist and once when the override_dh_foo hook target
# is run. If *either* times return false, "maybe run this"
# is skipped.
override_dh_foo:
ifneq (...)
maybe run this
endif
# SIMPLE: This is also well-defined. The hook target is always
# run and dh_bar is skipped. The "maybe run this" bit is
# conditional as one might expect.
#
# Note: The conditional is still evaluated multiple times (in
# different process each time). However, only the evaluation
# that happens when the hook target is run influences what
# happens.
override_dh_bar:
: # Dummy command to force the target to always be run
ifneq (...)
maybe run this
endif
# COMPLICATED: This case can be non-trivial and have sharp edges.
# Use at your own peril if dh_listpackages in the conditional.
#
# Here, either dh_baz is run normally OR "maybe run this" is run
# instead.
#
# And it gets even more complicated to reason about if dh needs to
# recurse into debian/rules because you have an "explicit"
# standard target (e.g. a "build-arch:" target separate from "%:").
ifneq (...)
override_dh_baz:
maybe run this
endif
These recipes are also relevant for conditional dependency
targets, which are often seen in a variant of the following
example:
COND_TASKS =
ifneq (...)
COND_TASKS += maybe-run-this
endif
...
maybe-run-this:
...
# SIMPLE: It is well-defined what happens. Either the
# $(COND_TASKS) are skipped or run.
#
# Note: The conditional is evaluated "twice" where its
# influences what happens. Once when dh check which hook
# targets exist and once when the override_dh_foo hook target
# is run. If *either* times return false, $(COND_TASKS)
# is skipped.
override_dh_foo: $(COND_TASKS)
# SIMPLE: This is also well-defined. The hook target is always
# run and dh_bar is skipped. The $(COND_TASKS) bit is
# conditional as one might expect.
#
# Note: The conditional is still evaluated multiple times (in
# different process each time). However, only the evaluation
# that happens when the hook target is run influences what
# happens.
override_dh_bar: $(COND_TASKS)
: # Dummy command to force the target to always be run
# COMPLICATED: This case can be non-trivial and have sharp edges.
# Use at your own peril if dh_listpackages in the conditional.
#
ifneq (...)
override_dh_baz: $(COND_TASKS)
endif
When in doubt, pick the relevant SIMPLE case in the examples
above that match your need.
--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.
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
The primary purpose of dh addons is to provide easy integration
with third-party provided features for debhelper. However,
debhelper itself also provide a few sequences that can be useful
in some cases. These are documented in this list:
build-stamp
A special addon for controlling whether dh (in compat 10 or
later) will create stamp files to tell whether the build
target has been run successfully. See "INTERNALS" for more
details.
This addon is active by default but can disabled by using dh
$@ --without build-stamp
dwz (obsolete)
Adds dh_dwz(1) to the sequence in compat level 11 or below.
Obsolete in compat 12 or later.
elf-tools
This addon adds tools related to ELF files to the sequence
such as dh_strip(1) and dh_shlibdeps(1)
This addon is conditionally active by default for
architecture specific packages - that is, it is skipped for
arch:all packages. In the special case where you need these
tools to work on arch:all packages, you can use --with elf-
tools to activate it unconditionally.
installinitramfs (obsolete)
Adds dh_installinitramfs(1) to the sequence in compat level
11 or below. Obsolete in compat 12 or later.
root-sequence (internal)
This is reserved for internal usage.
single-binary
A special-purpose addon that makes debhelper run in "single
binary" mode.
When active, it will pass --destdir=debian/package/ to
dh_auto_install(1). This makes every file "installed" by the
upstream build system part of the (only) binary package by
default without having to use other helpers such as
dh_install(1).
The addon will refuse to activate when the source package
lists 2 or more binary packages in debian/control as a
precaution.
Before compat 15. this behaviour was the default when there
was only a single binary package listed in debian/control.
In compat 15 and later, this addon must explicitly be
activated for this feature to work.
The rationale for requiring this as an explicit choice is
that if it is implicit then debhelper will silently change
behaviour on adding a new binary package. This has caused
many RC bugs when maintainers renamed a binary and added
transitional packages with the intention of supporting
seamless upgrades. The result would often be two empty
binary packages that were uploaded to archive with users
frustrated as their "upgrade" removed their programs.
systemd (obsolete)
Adds dh_systemd_enable(1) and dh_systemd_start(1) to the
sequence in compat level 10 or below. Obsolete in compat 11
or later.
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.
debhelper(7)
This program is a part of debhelper.
Joey Hess <[email protected]>
This page is part of the debhelper (helper programs for
debian/rules) project. Information about the project can be
found at [unknown -- if you know, please contact man-
[email protected]] If you have a bug report for this manual page,
send it to [email protected]. This page was obtained from
the project's upstream Git repository
⟨https://salsa.debian.org/debian/debhelper.git⟩ on 2024-06-14.
(At that time, the date of the most recent commit that was found
in the repository was 2024-06-09.) If you discover any rendering
problems in this HTML version of the page, or you believe there
is a better or more up-to-date source for the page, or you have
corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
[email protected]
13.11.7 2023-09-12 DH(1)
Pages that refer to this page: dh_assistant(1), dh_auto_install(1), debhelper(7)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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