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dh_assistant - Man Page

tool for supporting debhelper tools and provide introspection


dh_assistant command [additional options]


dh_assistant is a debhelper program that provides introspection into the debhelper stack to assist third-party tools (e.g. linters) or third-party debhelper implementations not using the debhelper script API (e.g., because they are not written in Perl).


The dh_assistant supports the following commands:

active-compat-level (JSON)

Synopsis: dh_assistant active-compat-level

Outputs information about which compat level the package is using.

For packages without valid debhelper compatibility information (whether missing, ambiguous, not supported or simply invalid), this command operates on a "best effort" basis and may abort when error instead of providing data.

The returned JSON dictionary contains the following key-value pairs:


The compat level that debhelper will be using.  This is the same as DH_COMPAT when present or else declared-compat-level.  This can be null when no compat level can be detected.


The compat level that the package declared as its default compat level.  This can be null if the package does not declare any compat level at all.


Defines how the compat level was declared.  This is null (for the same reason as declared-compat-level) or one of:


The compatibility level was declared in the first line debian/compat file.

Build-Depends: debhelper-compat (= <C>)

The compatibility was declared in the debian/control via a build dependency on the debhelper-compat (= <C>) package in the Build-Depends field.  In the output, the C is replaced by the actual compatibility level.  A full example value would be:

   Build-Depends: debhelper-compat (= 13)

supported-compat-levels (JSON, CRFA)

Synopsis: dh_assistant supported-compat-levels

Outputs information about which compat levels, this build of debhelper knows about.

This command accepts no options or arguments.

which-build-system (JSON)

Synopsis: dh_assistant which-build-system [build step] [build system options]

Output information about which build system would be used for a particular build step.  The build step must be one of configure, build, test, install or clean and must be the first argument after which-build-system when provided.  If omitted, it defaults to configure as it is the most reliable step to use auto-detection on in a clean source directory.  Note that build steps do not always agree when using auto-detection - particularly if the configure step has not been run.

Additionally, the clean step can also provide "surprising" results for builds that rely on a separate build directory.  In such cases, debhelper will return the first build system that uses a separate build directory rather than the one build system that configure would detect. This is generally a cosmetic issue as both build systems are all basically a glorified rm -fr builddir and more precise detection is functionally irrelevant as far as debhelper is concerned.

The option accepts all debhelper build system arguments - i.e., options you can pass to all of the dh_auto_* commands plus (for the install step) the --destdir option.  These options affect the output and auto-detection in various ways.  Passing -S or --buildsystem overrides the auto-detection (as it does for dh_auto_*) but it still provides introspection into the chosen build system.

Things that are useful to know about the output:

  • The key build-system is the build system that would be used by debhelper for the given step (with the given options, debhelper compat level, environment variables and the given working directory).  When -S and --buildsystem are omitted, this is the result of debhelper's auto-detection logic.

    The value is valid as a parameter for the --buildsystem option.

    The special value none is used to denote that no build system would be used.  This value is not present in --list parameter for the dh_auto_* commands, but since debhelper/12.9 the value is accepted for the --buildsystem option.

    Note that auto-detection is subject to limitations in regards to third-party build systems. While debhelper does support auto-detecting some third-party build systems, they must be installed for the detection to work.  If they are not installed, the detection logic silently skips that build system (often resulting in build-system being none in the output).

  • The build-directory and buildpath values serve different but related purposes.  The build-directory generally mirrors the --builddirectory option where as buildpath is the output directory that debhelper will use.  Therefore the former will often be null when --builddirectory has not been passed while the latter will generally not be null (except when build-system is none).
  • The dest-directory (--destdir) is undefined for all build steps except the install build step (will be output as null or absent).  For the same reason, --destdir should only be passed for install build step.

    Note that if not specified, this value is currently null by default.

  • The parallel value is subject to DEB_BUILD_OPTIONS.  Notably, if that does not include the parallel keyword, then parallel field in the output will always be 1.
  • Most fields in the output can be null.  Particular if there is no build system is detected (or when --buildsystem=none).  Additionally, many of the fields can be null even if there is a build system if the build system does not use/set/define that variable.

detect-hook-targets (JSON)

Synopsis: dh_assistant detect-hook-targets

Detects possible override targets and hook targets that dh(1) might use (provided that the relevant command is in the sequence).

The detection is based on scanning the rules file for any target that might look like a hook target and can therefore list targets that are in fact not hook targets (or are but will never be triggered for other reasons).

The detection uses a similar logic for scanning the rules file and is therefore subject to makefile conditionals (i.e., the truth value of makefile conditionals can change whether a hook target is visible in the output of this command).  In theory, you would have to setup up the environment to look like it would during a build for getting the most accurate output.  Though, a lot of packages will not have conditional hook targets, so the "out of the box" behaviour will work well in most cases.

The output looks something like this:

       "commands-not-in-path": [
       "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"

In more details:


This attribute lists all the commands related to hook targets, which dh_assistant could not find in PATH.  These are usually caused by either the command not being installed on the system where dh_assistant is run or by the command not existing at all.

If you are using this command to verify an hook target is present, please double check that the command is spelled correctly.


List over hook targets found along with additional information about them.


Attribute that lists which command this hook target is related too.


The actual target name detected in the debian/rules file.


A boolean that determines whether dh(1) will optimize the hook out at runtime (see "Completely empty targets" in dh(1)). Note that empty override targets will still cause dh(1)  to skip the original command.


This attribute defines what package selection parameter should be passed to dh_* commands used in the hook target.  It can either be -a, -i or (if no parameter should be used) null.

This command accepts no options or arguments.


Synopsis: dh_assistant -ppkg [--on-behalf-of-cmd=dh_foo] path ...

Mark one or more paths as installed for a given package.  This is useful for telling dh_missing(1) that the paths have been installed manually.

The --on-behalf-of-cmd option can be used by third-party tools to have dh_assistant list them as the installer of the provided paths.  The convention is to use the basename of the tool itself as its name (e.g. dh_install).

Please keep in mind that:

  • No glob or substitution expansion is done by dh_assistant on the provided paths.  If you want to use globs, have the shell perform the expansion first.
  • Paths must be given as relative to the source root directory (e.g., debian/tmp/...)
  • You can provide a directory.  If you do, the directory and anything recursively below it will be considered as installed.  Note that it is fine to provide the directory even if paths inside of it has been excluded as long as the directory is fully "covered".
  • Do not worry about providing the same filename twice in different invocations to dh_assistant due to -arch / -indep overrides.  While it will be recorded multiple internally, dh_missing(1) will deduplicate when it parses the records.

Note this command only marks paths as installed. It does not actually install them - the caller should ensure that the paths are in fact handled (or installed).

Command Tags

Most commands have one or more of the following "tags" associated with them.  Their meaning is defined here.


The command provides JSON output. See "JSON Output" for details.


Mnemonic "Can be Run From Anywhere"

Most commands must be run inside a source package root directory (a directory containing debian/control) because debhelper will need the package metadata to lookup the information.  Any command with this tag are exempt from this requirement and is expected to work regardless of where they are run.

JSON Output

Most commands uses JSON format as output.  Consumers need to be aware that:

The output will be prettified when stdout is detected as a terminal.  If you need to pipe the output to a pager/file (etc.) and still want it prettified, please use an external JSON formatter. An example of this:

     dh_assistant supported-compat-levels | json_pp | less

See Also


This program is a part of debhelper.

Referenced By

debhelper(7), dh(1).

2024-01-24 13.11.6 Debhelper