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<H1>DH</H1>
Section: Debhelper (1)<BR>Updated: 2020-03-27<BR><A HREF="#index">Index</A>
<A HREF="/cgi-bin/man/man2html">Return to Main Contents</A><HR>
<A NAME="lbAB">&nbsp;</A>
<H2>NAME</H2>
dh - debhelper command sequencer
<A NAME="lbAC">&nbsp;</A>
<H2>SYNOPSIS</H2>
<B>dh</B> <I>sequence</I> [<B>--with</B> <I>addon</I>[<B>,</B><I>addon</I> ...]] [<B>--list</B>] [<I>debhelper options</I>]
<A NAME="lbAD">&nbsp;</A>
<H2>DESCRIPTION</H2>
<B>dh</B> runs a sequence of debhelper commands. The supported <I>sequence</I>s
correspond to the targets of a <I>debian/rules</I> file: <B>build-arch</B>,
<B>build-indep</B>, <B>build</B>, <B>clean</B>, <B>install-indep</B>, <B>install-arch</B>,
<B>install</B>, <B>binary-arch</B>, <B>binary-indep</B>, and <B>binary</B>.
<A NAME="lbAE">&nbsp;</A>
<H2>OVERRIDE AND HOOK TARGETS</H2>
A <I>debian/rules</I> file using <B>dh</B> 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.
<A NAME="lbAF">&nbsp;</A>
<H3>Injecting commands before or after a step</H3>
<I>Note</I>: This feature requires debhelper 12.8 or later plus the package must
use compatibility mode 10 or later.
<P>
To inject commands before <I>dh_command</I>, add a target named
<B>execute_before_</B><I>dh_command</I> to the rules files. Similarly, if you
want to inject commands after <I>dh_command</I>, add the target
<B>execute_after_</B><I>dh_command</I>. Both targets can be used for the same
<I>dh_command</I> and also even if the command is overridden (as described in
``Overriding a command'' below).
<P>
When these targets are defined, <B>dh</B> will call the targets respectively
before or after it would invoke <I>dh_command</I> (or its override target).
<A NAME="lbAG">&nbsp;</A>
<H3>Overriding a command</H3>
To override <I>dh_command</I>, add a target named <B>override_</B><I>dh_command</I> to
the rules file. When it would normally run <I>dh_command</I>, <B>dh</B> 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.
<A NAME="lbAH">&nbsp;</A>
<H3>Architecture dependent/independent override and hook targets</H3>
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 <B>override_</B><I>dh_command</I><B>-arch</B>
and <B>execute_after</B><I>dh_command</I><B>-indep</B>.
<P>
This feature is available since debhelper 8.9.7 (for override targets)
and 12.8 (for hook targets).
<A NAME="lbAI">&nbsp;</A>
<H3>Completely empty targets</H3>
As a special optimization, <B>dh</B> 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.
<P>
Note that the target has to be completely empty for this to work:
<P>
<PRE>
# 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)
</PRE>
<A NAME="lbAJ">&nbsp;</A>
<H3>Verifying targets are picked up by dh</H3>
If you want to confirm that <B>dh</B> has seen an override or a hook target, you
can use the following command as an example:
<P>
<PRE>
$ dh binary --no-act | grep dh_install | head -n5
dh_installdirs
dh_install
debian/rules execute_after_dh_install
dh_installdocs
dh_installchangelogs
</PRE>
<P>
The <B>debian/rules execute_after_dh_install</B> in the output, which signals
that <B>dh</B> registered a <B>execute_after_dh_install</B> target and would
run it directly after <B><A HREF="/cgi-bin/man/man2html?1+dh_install">dh_install</A></B>(1).
<P>
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.
<A NAME="lbAK">&nbsp;</A>
<H2>OPTIONS</H2>
<DL COMPACT>
<DT id="1"><B>--with</B> <I>addon</I>[<B>,</B><I>addon</I> ...]<DD>
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 <I></I><FONT SIZE="-1"><I>PROGRAMMING</I></FONT><I></I> file for documentation about
the sequence addon interface.
<P>
A <B>Build-Depends</B> relation on the package <B>dh-sequence-</B><I>addon</I>
implies a <B>--with</B> <I>addon</I>. This avoids the need for an explicit
<B>--with</B> in <I>debian/rules</I> that only duplicates what is already
declared via the build dependencies in <I>debian/control</I>. 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).
<P>
Since debhelper 12.5, addons can also be activated in <B>indep</B>-only
mode (via <B>Build-Depends-Indep</B>) or <B>arch</B>-only mode (via
<B>Build-Depends-Arch</B>). Such addons are only active in the particular
sequence (e.g. <B>binary-indep</B>) which simplifies dependency
management for cross-builds.
<P>
Please note that addons activated via <B>Build-Depends-Indep</B> or
<B>Build-Depends-Arch</B> 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
<B>Build-Depends</B> (or manually via <I>debian/rules</I>). Currently,
such addons can only add commands to sequences.
<DT id="2"><B>--without</B> <I>addon</I><DD>
The inverse of <B>--with</B>, disables using the given addon. This option
can be repeated more than once, or multiple addons to disable can be
listed, separated by commas.
<DT id="3"><B>--list</B>, <B>-l</B><DD>
List all available addons.
<P>
When called only with this option, <B>dh</B> can be called from any
directory (i.e. it does not need access to files from a source
package).
<DT id="4"><B>--no-act</B><DD>
Prints commands that would run for a given sequence, but does not run them.
<P>
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.
</DL>
<P>
Other options passed to <B>dh</B> are passed on to each command it runs. This
can be used to set an option like <B>-v</B> or <B>-X</B> or <B>-N</B>, as well as for more
specialised options.
<A NAME="lbAL">&nbsp;</A>
<H2>EXAMPLES</H2>
To see what commands are included in a sequence, without actually doing
anything:
<P>
<PRE>
dh binary-arch --no-act
</PRE>
<P>
This is a very simple rules file, for packages where the default sequences of
commands work with no additional options.
<P>
<PRE>
#!/usr/bin/make -f
%:
dh $@
</PRE>
<P>
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.
<P>
<PRE>
#!/usr/bin/make -f
%:
dh $@
override_dh_strip:
dh_strip -Xfoo
override_dh_auto_configure:
dh_auto_configure -- --with-foo --disable-bar
</PRE>
<P>
Sometimes the automated <B><A HREF="/cgi-bin/man/man2html?1+dh_auto_configure">dh_auto_configure</A></B>(1) and <B><A HREF="/cgi-bin/man/man2html?1+dh_auto_build">dh_auto_build</A></B>(1)
can't guess what to do for a strange package. Here's how to avoid running
either and instead run your own commands.
<P>
<PRE>
#!/usr/bin/make -f
%:
dh $@
override_dh_auto_configure:
./mondoconfig
override_dh_auto_build:
make universe-explode-in-delight
</PRE>
<P>
Another common case is wanting to do something manually before or
after a particular debhelper command is run.
<P>
<PRE>
#!/usr/bin/make -f
%:
dh $@
# Example assumes debhelper/12.8 and compat 10+
execute_after_dh_fixperms:
chmod 4755 debian/foo/usr/bin/foo
</PRE>
<P>
If you are on an older debhelper or compatibility level, the above
example would have to be written as.
<P>
<PRE>
#!/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
</PRE>
<P>
Python tools are not run by dh by default, due to the continual change
in that area. Here is how to use <B>dh_python2</B>.
<P>
<PRE>
#!/usr/bin/make -f
%:
dh $@ --with python2
</PRE>
<P>
Here is how to force use of Perl's <B>Module::Build</B> build system,
which can be necessary if debhelper wrongly detects that the package
uses MakeMaker.
<P>
<PRE>
#!/usr/bin/make -f
%:
dh $@ --buildsystem=perl_build
</PRE>
<P>
Here is an example of overriding where the <B>dh_auto_</B><I>*</I> commands find
the package's source, for a package where the source is located in a
subdirectory.
<P>
<PRE>
#!/usr/bin/make -f
%:
dh $@ --sourcedirectory=src
</PRE>
<P>
And here is an example of how to tell the <B>dh_auto_</B><I>*</I> commands to build
in a subdirectory, which will be removed on <B>clean</B>.
<P>
<PRE>
#!/usr/bin/make -f
%:
dh $@ --builddirectory=build
</PRE>
<P>
If your package can be built in parallel, please either use compat 10 or
pass <B>--parallel</B> to dh. Then <B>dpkg-buildpackage -j</B> will work.
<P>
<PRE>
#!/usr/bin/make -f
%:
dh $@ --parallel
</PRE>
<P>
If your package cannot be built reliably while using multiple threads,
please pass <B>--no-parallel</B> to dh (or the relevant <B>dh_auto_</B><I>*</I>
command):
<P>
<PRE>
#!/usr/bin/make -f
%:
dh $@ --no-parallel
</PRE>
<P>
Here is a way to prevent <B>dh</B> from running several commands that you don't
want it to run, by defining empty override targets for each command.
<P>
<PRE>
#!/usr/bin/make -f
%:
dh $@
# Commands not to run:
override_dh_auto_test override_dh_compress override_dh_fixperms:
</PRE>
<P>
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.
<P>
<PRE>
#!/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
</PRE>
<P>
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.
<P>
<PRE>
# Example assumes debhelper/12.8 and compat 10+
execute_after_dh_fixperms-arch:
chmod 4755 debian/foo/usr/bin/foo
</PRE>
<A NAME="lbAM">&nbsp;</A>
<H2>INTERNALS</H2>
If you're curious about <B>dh</B>'s internals, here's how it works under the hood.
<P>
In compat 10 (or later), <B>dh</B> creates a stamp file
<I>debian/debhelper-build-stamp</I> after the build step(s) are complete
to avoid re-running them. It is possible to avoid the stamp file by
passing <B>--without=build-stamp</B> to <B>dh</B>. 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 <B><A HREF="/cgi-bin/man/man2html?1+fakeroot">fakeroot</A></B>(1)).
<P>
Inside an override target, <B>dh_*</B> commands will create a log file
<I>debian/package.debhelper.log</I> 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.
<P>
In compat 9 or earlier, each debhelper command will record
when it's successfully run in <I>debian/package.debhelper.log</I>. (Which
<B>dh_clean</B> deletes.) So <B>dh</B> can tell which commands have already
been run, for which packages, and skip running those commands again.
<P>
Each time <B>dh</B> 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.
<P>
A sequence can also run dependent targets in debian/rules. For
example, the ``binary'' sequence runs the ``install'' target.
<P>
<B>dh</B> uses the <B></B><FONT SIZE="-1"><B>DH_INTERNAL_OPTIONS</B></FONT><B></B> 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.
<P>
Commands in the <B>build-indep</B>, <B>install-indep</B> and <B>binary-indep</B>
sequences are passed the <B>-i</B> option to ensure they only work on
architecture independent packages, and commands in the <B>build-arch</B>,
<B>install-arch</B> and <B>binary-arch</B> sequences are passed the <B>-a</B>
option to ensure they only work on architecture dependent packages.
<A NAME="lbAN">&nbsp;</A>
<H2>SEE ALSO</H2>
<B><A HREF="/cgi-bin/man/man2html?7+debhelper">debhelper</A></B>(7)
<P>
This program is a part of debhelper.
<A NAME="lbAO">&nbsp;</A>
<H2>AUTHOR</H2>
Joey Hess &lt;<A HREF="mailto:joeyh@debian.org">joeyh@debian.org</A>&gt;
<P>
<HR>
<A NAME="index">&nbsp;</A><H2>Index</H2>
<DL>
<DT id="5"><A HREF="#lbAB">NAME</A><DD>
<DT id="6"><A HREF="#lbAC">SYNOPSIS</A><DD>
<DT id="7"><A HREF="#lbAD">DESCRIPTION</A><DD>
<DT id="8"><A HREF="#lbAE">OVERRIDE AND HOOK TARGETS</A><DD>
<DL>
<DT id="9"><A HREF="#lbAF">Injecting commands before or after a step</A><DD>
<DT id="10"><A HREF="#lbAG">Overriding a command</A><DD>
<DT id="11"><A HREF="#lbAH">Architecture dependent/independent override and hook targets</A><DD>
<DT id="12"><A HREF="#lbAI">Completely empty targets</A><DD>
<DT id="13"><A HREF="#lbAJ">Verifying targets are picked up by dh</A><DD>
</DL>
<DT id="14"><A HREF="#lbAK">OPTIONS</A><DD>
<DT id="15"><A HREF="#lbAL">EXAMPLES</A><DD>
<DT id="16"><A HREF="#lbAM">INTERNALS</A><DD>
<DT id="17"><A HREF="#lbAN">SEE ALSO</A><DD>
<DT id="18"><A HREF="#lbAO">AUTHOR</A><DD>
</DL>
<HR>
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