APT.CONF(5)             (03 January 2016)             APT.CONF(5)

     NAME
          apt.conf - Configuration file for APT

     DESCRIPTION
          /etc/apt/apt.conf is the main configuration file shared by
          all the tools in the APT suite of tools, though it is by no
          means the only place options can be set. The suite also
          shares a common command line parser to provide a uniform
          environment.

          When an APT tool starts up it will read the configuration
          files in the following order:

           1. the file specified by the APT_CONFIG environment
              variable (if any)

           2. all files in Dir::Etc::Parts in alphanumeric ascending
              order which have either no or "conf" as filename
              extension and which only contain alphanumeric, hyphen
              (-), underscore (_) and period (.) characters. Otherwise
              APT will print a notice that it has ignored a file,
              unless that file matches a pattern in the
              Dir::Ignore-Files-Silently configuration list - in which
              case it will be silently ignored.

           3. the main configuration file specified by Dir::Etc::main

           4. all options set in the binary specific configuration
              subtree are moved into the root of the tree.

           5. the command line options are applied to override the
              configuration directives or to load even more
              configuration files.

     SYNTAX
          The configuration file is organized in a tree with options
          organized into functional groups. Option specification is
          given with a double colon notation; for instance
          APT::Get::Assume-Yes is an option within the APT tool group,
          for the Get tool. Options do not inherit from their parent
          groups.

          Syntactically the configuration language is modeled after
          what the ISC tools such as bind and dhcp use. Lines starting
          with // are treated as comments (ignored), as well as all
          text between /* and */, just like C/C++ comments. Lines
          starting with # are also treated as comments. Each line is
          of the form APT::Get::Assume-Yes "true";. The quotation
          marks and trailing semicolon are required. The value must be
          on one line, and there is no kind of string concatenation.

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          Values must not include backslashes or extra quotation
          marks. Option names are made up of alphanumeric characters
          and the characters "/-:._+". A new scope can be opened with
          curly braces, like this:

              APT {
                Get {
                  Assume-Yes "true";
                  Fix-Broken "true";
                };
              };

          with newlines placed to make it more readable. Lists can be
          created by opening a scope and including a single string
          enclosed in quotes followed by a semicolon. Multiple entries
          can be included, separated by a semicolon.

              DPkg::Pre-Install-Pkgs {"/usr/sbin/dpkg-preconfigure --apt";};

          In general the sample configuration file
          /usr/share/doc/apt/examples/configure-index.gz is a good
          guide for how it should look.

          Case is not significant in names of configuration items, so
          in the previous example you could use
          dpkg::pre-install-pkgs.

          Names for the configuration items are optional if a list is
          defined as can be seen in the DPkg::Pre-Install-Pkgs example
          above. If you don't specify a name a new entry will simply
          add a new option to the list. If you specify a name you can
          override the option in the same way as any other option by
          reassigning a new value to the option.

          Two special commands are defined: #include (which is
          deprecated and not supported by alternative implementations)
          and #clear.  #include will include the given file, unless
          the filename ends in a slash, in which case the whole
          directory is included.  #clear is used to erase a part of
          the configuration tree. The specified element and all its
          descendants are erased. (Note that these lines also need to
          end with a semicolon.)

          The #clear command is the only way to delete a list or a
          complete scope. Reopening a scope (or using the syntax
          described below with an appended ::) will not override
          previously written entries. Options can only be overridden
          by addressing a new value to them - lists and scopes can't
          be overridden, only cleared.

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          All of the APT tools take an -o option which allows an
          arbitrary configuration directive to be specified on the
          command line. The syntax is a full option name
          (APT::Get::Assume-Yes for instance) followed by an equals
          sign then the new value of the option. To append a new
          element to a list, add a trailing :: to the name of the
          list. (As you might suspect, the scope syntax can't be used
          on the command line.)

          Note that appending items to a list using :: only works for
          one item per line, and that you should not use it in
          combination with the scope syntax (which adds ::
          implicitly). Using both syntaxes together will trigger a bug
          which some users unfortunately depend on: an option with the
          unusual name "::" which acts like every other option with a
          name. This introduces many problems; for one thing, users
          who write multiple lines in this wrong syntax in the hope of
          appending to a list will achieve the opposite, as only the
          last assignment for this option "::" will be used. Future
          versions of APT will raise errors and stop working if they
          encounter this misuse, so please correct such statements now
          while APT doesn't explicitly complain about them.

     THE APT GROUP
          This group of options controls general APT behavior as well
          as holding the options for all of the tools.

          Architecture
              System Architecture; sets the architecture to use when
              fetching files and parsing package lists. The internal
              default is the architecture apt was compiled for.

          Architectures
              All Architectures the system supports. For instance,
              CPUs implementing the amd64 (also called x86-64)
              instruction set are also able to execute binaries
              compiled for the i386 (x86) instruction set. This list
              is used when fetching files and parsing package lists.
              The initial default is always the system's native
              architecture (APT::Architecture), and foreign
              architectures are added to the default list when they
              are registered via dpkg --add-architecture.

          Compressor
              This scope defines which compression formats are
              supported, how compression and decompression can be
              performed if support for this format isn't built into
              apt directly and a cost-value indicating how costly it
              is to compress something in this format. As an example
              the following configuration stanza would allow apt to
              download and uncompress as well as create and store
              files with the low-cost .reversed file extension which

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              it will pass to the command rev without additional
              commandline parameters for compression and
              uncompression:

                  APT::Compressor::rev {
                       Name "rev";
                       Extension ".reversed";
                       Binary "rev";
                       CompressArg {};
                       UncompressArg {};
                       Cost "10";
                  };

          Build-Profiles
              List of all build profiles enabled for build-dependency
              resolution, without the "profile." namespace prefix. By
              default this list is empty. The DEB_BUILD_PROFILES as
              used by dpkg-buildpackage(1) overrides the list
              notation.

          Default-Release
              Default release to install packages from if more than
              one version is available. Contains release name,
              codename or release version. Examples: 'stable',
              'testing', 'unstable', 'bullseye', 'bookworm', '4.0',
              '5.0*'. See also apt_preferences(5).

          Ignore-Hold
              Ignore held packages; this global option causes the
              problem resolver to ignore held packages in its decision
              making.

          Clean-Installed
              Defaults to on. When turned on the autoclean feature
              will remove any packages which can no longer be
              downloaded from the cache. If turned off then packages
              that are locally installed are also excluded from
              cleaning - but note that APT provides no direct means to
              reinstall them.

          Immediate-Configure
              Defaults to on, which will cause APT to install
              essential and important packages as soon as possible in
              an install/upgrade operation, in order to limit the
              effect of a failing dpkg(1) call. If this option is
              disabled, APT treats an important package in the same
              way as an extra package: between the unpacking of the
              package A and its configuration there can be many other
              unpack or configuration calls for other unrelated
              packages B, C etc. If these cause the dpkg(1) call to
              fail (e.g. because package B's maintainer scripts
              generate an error), this results in a system state in

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              which package A is unpacked but unconfigured - so any
              package depending on A is now no longer guaranteed to
              work, as its dependency on A is no longer satisfied.

              The immediate configuration marker is also applied in
              the potentially problematic case of circular
              dependencies, since a dependency with the immediate flag
              is equivalent to a Pre-Dependency. In theory this allows
              APT to recognise a situation in which it is unable to
              perform immediate configuration, abort, and suggest to
              the user that the option should be temporarily
              deactivated in order to allow the operation to proceed.
              Note the use of the word "theory" here; in the real
              world this problem has rarely been encountered, in
              non-stable distribution versions, and was caused by
              wrong dependencies of the package in question or by a
              system in an already broken state; so you should not
              blindly disable this option, as the scenario mentioned
              above is not the only problem it can help to prevent in
              the first place.

              Before a big operation like dist-upgrade is run with
              this option disabled you should try to explicitly
              install the package APT is unable to configure
              immediately; but please make sure you also report your
              problem to your distribution and to the APT team with
              the bug link below, so they can work on improving or
              correcting the upgrade process.

          Force-LoopBreak
              Never enable this option unless you really know what you
              are doing. It permits APT to temporarily remove an
              essential package to break a Conflicts/Conflicts or
              Conflicts/Pre-Depends loop between two essential
              packages.  Such a loop should never exist and is a grave
              bug. This option will work if the essential packages are
              not tar, gzip, libc, dpkg, dash or anything that those
              packages depend on.

          Cache-Start, Cache-Grow, Cache-Limit
              APT uses since version 0.7.26 a resizable memory mapped
              cache file to store the available information.
              Cache-Start acts as a hint of the size the cache will
              grow to, and is therefore the amount of memory APT will
              request at startup. The default value is 20971520 bytes
              (~20 MB). Note that this amount of space needs to be
              available for APT; otherwise it will likely fail
              ungracefully, so for memory restricted devices this
              value should be lowered while on systems with a lot of
              configured sources it should be increased.  Cache-Grow
              defines in bytes with the default of 1048576 (~1 MB) how
              much the cache size will be increased in the event the

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              space defined by Cache-Start is not enough. This value
              will be applied again and again until either the cache
              is big enough to store all information or the size of
              the cache reaches the Cache-Limit. The default of
              Cache-Limit is 0 which stands for no limit. If
              Cache-Grow is set to 0 the automatic growth of the cache
              is disabled.

          Build-Essential
              Defines which packages are considered essential build
              dependencies.

          Get
              The Get subsection controls the apt-get(8) tool; please
              see its documentation for more information about the
              options here.

          Cache
              The Cache subsection controls the apt-cache(8) tool;
              please see its documentation for more information about
              the options here.

          CDROM
              The CDROM subsection controls the apt-cdrom(8) tool;
              please see its documentation for more information about
              the options here.

     THE ACQUIRE GROUP
          The Acquire group of options controls the download of
          packages as well as the various "acquire methods"
          responsible for the download itself (see also
          sources.list(5)).

          Check-Date
              Security related option defaulting to true, enabling
              time-related checks. Disabling it means that the
              machine's time cannot be trusted, and APT will hence
              disable all time-related checks, such as
              Check-Valid-Until and verifying that the Date field of a
              release file is not in the future.

          Max-FutureTime
              Maximum time (in seconds) before its creation (as
              indicated by the Date header) that the Release file
              should be considered valid. The default value is 10.
              Archive specific settings can be made by appending the
              label of the archive to the option name. Preferably, the
              same can be achieved for specific sources.list(5)
              entries by using the Date-Max-Future option there.

          Check-Valid-Until
              Security related option defaulting to true, as giving a

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              Release file's validation an expiration date prevents
              replay attacks over a long timescale, and can also for
              example help users to identify mirrors that are no
              longer updated - but the feature depends on the
              correctness of the clock on the user system. Archive
              maintainers are encouraged to create Release files with
              the Valid-Until header, but if they don't or a stricter
              value is desired the Max-ValidTime option below can be
              used. The Check-Valid-Until option of sources.list(5)
              entries should be preferred to disable the check
              selectively instead of using this global override.

          Max-ValidTime
              Maximum time (in seconds) after its creation (as
              indicated by the Date header) that the Release file
              should be considered valid. If the Release file itself
              includes a Valid-Until header the earlier date of the
              two is used as the expiration date. The default value is
              0 which stands for "valid forever". Archive specific
              settings can be made by appending the label of the
              archive to the option name. Preferably, the same can be
              achieved for specific sources.list(5) entries by using
              the Valid-Until-Max option there.

          Min-ValidTime
              Minimum time (in seconds) after its creation (as
              indicated by the Date header) that the Release file
              should be considered valid. Use this if you need to use
              a seldom updated (local) mirror of a more frequently
              updated archive with a Valid-Until header instead of
              completely disabling the expiration date checking.
              Archive specific settings can and should be used by
              appending the label of the archive to the option name.
              Preferably, the same can be achieved for specific
              sources.list(5) entries by using the Valid-Until-Min
              option there.

          AllowTLS
              Allow use of the internal TLS support in the http
              method. If set to false, this completely disables
              support for TLS in apt's own methods (excluding the
              curl-based https method). No TLS-related functions will
              be called anymore.

          PDiffs
              Try to download deltas called PDiffs for indexes (like
              Packages files) instead of downloading whole ones. True
              by default. Preferably, this can be set for specific
              sources.list(5) entries or index files by using the
              PDiffs option there.

              Two sub-options to limit the use of PDiffs are also

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              available: FileLimit can be used to specify a maximum
              number of PDiff files should be downloaded to update a
              file.  SizeLimit on the other hand is the maximum
              percentage of the size of all patches compared to the
              size of the targeted file. If one of these limits is
              exceeded the complete file is downloaded instead of the
              patches.

          By-Hash
              Try to download indexes via an URI constructed from a
              hashsum of the expected file rather than downloaded via
              a well-known stable filename. True by default, but
              automatically disabled if the source indicates no
              support for it. Usage can be forced with the special
              value "force". Preferably, this can be set for specific
              sources.list(5) entries or index files by using the
              By-Hash option there.

          Queue-Mode
              Queuing mode; Queue-Mode can be one of host or access
              which determines how APT parallelizes outgoing
              connections.  host means that one connection per target
              host will be opened, access means that one connection
              per URI type will be opened.

          Retries
              Number of retries to perform. If this is non-zero APT
              will retry failed files the given number of times.

          Source-Symlinks
              Use symlinks for source archives. If set to true then
              source archives will be symlinked when possible instead
              of copying. True is the default.

          http https
              The options in these scopes configure APT's acquire
              transports for the protocols HTTP and HTTPS and are
              documented in the apt-transport-http(1) and apt-
              transport-https(1) manpages respectively.

          ftp
              ftp::Proxy sets the default proxy to use for FTP URIs.
              It is in the standard form of
              ftp://[[user][:pass]@]host[:port]/. Per host proxies can
              also be specified by using the form ftp::Proxy::<host>
              with the special keyword DIRECT meaning to use no
              proxies. If no one of the above settings is specified,
              ftp_proxy environment variable will be used. To use an
              FTP proxy you will have to set the ftp::ProxyLogin
              script in the configuration file. This entry specifies
              the commands to send to tell the proxy server what to
              connect to. Please see

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              /usr/share/doc/apt/examples/configure-index.gz for an
              example of how to do this. The substitution variables
              representing the corresponding URI component are
              $(PROXY_USER), $(PROXY_PASS), $(SITE_USER),
              $(SITE_PASS), $(SITE) and $(SITE_PORT).

              The option timeout sets the timeout timer used by the
              method; this value applies to the connection as well as
              the data timeout.

              Several settings are provided to control passive mode.
              Generally it is safe to leave passive mode on; it works
              in nearly every environment. However, some situations
              require that passive mode be disabled and port mode FTP
              used instead. This can be done globally or for
              connections that go through a proxy or for a specific
              host (see the sample config file for examples).

              It is possible to proxy FTP over HTTP by setting the
              ftp_proxy environment variable to an HTTP URL - see the
              discussion of the http method above for syntax. You
              cannot set this in the configuration file and it is not
              recommended to use FTP over HTTP due to its low
              efficiency.

              The setting ForceExtended controls the use of RFC2428
              EPSV and EPRT commands. The default is false, which
              means these commands are only used if the control
              connection is IPv6. Setting this to true forces their
              use even on IPv4 connections. Note that most FTP servers
              do not support RFC2428.

          cdrom
              For URIs using the cdrom method, the only configurable
              option is the mount point, cdrom::Mount, which must be
              the mount point for the CD-ROM (or DVD, or whatever)
              drive as specified in /etc/fstab. It is possible to
              provide alternate mount and unmount commands if your
              mount point cannot be listed in the fstab. The syntax is
              to put

                  /cdrom/::Mount "foo";

              within the cdrom block. It is important to have the
              trailing slash. Unmount commands can be specified using
              UMount.

          gpgv
              For GPGV URIs the only configurable option is
              gpgv::Options, which passes additional parameters to
              gpgv.

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          CompressionTypes
              List of compression types which are understood by the
              acquire methods. Files like Packages can be available in
              various compression formats. By default the acquire
              methods can decompress and recompress many common
              formats like xz and gzip; with this scope the supported
              formats can be queried, modified as well as support for
              more formats added (see also APT::Compressor). The
              syntax for this is:

                  Acquire::CompressionTypes::FileExtension "Methodname";

              Also, the Order subgroup can be used to define in which
              order the acquire system will try to download the
              compressed files. The acquire system will try the first
              and proceed with the next compression type in this list
              on error, so to prefer one over the other type simply
              add the preferred type first - types not already added
              will be implicitly appended to the end of the list, so
              e.g.

                  Acquire::CompressionTypes::Order:: "gz";

              can be used to prefer gzip compressed files over all
              other compression formats. If xz should be preferred
              over gzip and bzip2 the configure setting should look
              like this:

                  Acquire::CompressionTypes::Order { "xz"; "gz"; };

              It is not needed to add bz2 to the list explicitly as it
              will be added automatically.

              Note that the Dir::Bin::Methodname will be checked at
              run time. If this option has been set and support for
              this format isn't directly built into apt, the method
              will only be used if this file exists; e.g. for the
              bzip2 method (the inbuilt) setting is:

                  Dir::Bin::bzip2 "/bin/bzip2";

              Note also that list entries specified on the command
              line will be added at the end of the list specified in
              the configuration files, but before the default entries.
              To prefer a type in this case over the ones specified in
              the configuration files you can set the option direct -
              not in list style. This will not override the defined
              list; it will only prefix the list with this type.

              The special type uncompressed can be used to give
              uncompressed files a preference, but note that most
              archives don't provide uncompressed files so this is

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              mostly only usable for local mirrors.

          GzipIndexes
              When downloading gzip compressed indexes (Packages,
              Sources, or Translations), keep them gzip compressed
              locally instead of unpacking them. This saves quite a
              lot of disk space at the expense of more CPU
              requirements when building the local package caches.
              False by default.

          Languages
              The Languages subsection controls which Translation
              files are downloaded and in which order APT tries to
              display the description-translations. APT will try to
              display the first available description in the language
              which is listed first. Languages can be defined with
              their short or long language codes. Note that not all
              archives provide Translation files for every language -
              the long language codes are especially rare.

              The default list includes "environment" and "en".
              "environment" has a special meaning here: it will be
              replaced at runtime with the language codes extracted
              from the LC_MESSAGES environment variable. It will also
              ensure that these codes are not included twice in the
              list. If LC_MESSAGES is set to "C" only the
              Translation-en file (if available) will be used. To
              force APT to use no Translation file use the setting
              Acquire::Languages=none. "none" is another special
              meaning code which will stop the search for a suitable
              Translation file. This tells APT to download these
              translations too, without actually using them unless the
              environment specifies the languages. So the following
              example configuration will result in the order "en, de"
              in an English locale or "de, en" in a German one. Note
              that "fr" is downloaded, but not used unless APT is used
              in a French locale (where the order would be "fr, de,
              en").

                  Acquire::Languages { "environment"; "de"; "en"; "none"; "fr"; };

              Note: To prevent problems resulting from APT being
              executed in different environments (e.g. by different
              users or by other programs) all Translation files which
              are found in /var/lib/apt/lists/ will be added to the
              end of the list (after an implicit "none").

          ForceIPv4
              When downloading, force to use only the IPv4 protocol.

          ForceIPv6
              When downloading, force to use only the IPv6 protocol.

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          MaxReleaseFileSize
              The maximum file size of Release/Release.gpg/InRelease
              files. The default is 10MB.

          EnableSrvRecords
              This option controls if apt will use the DNS SRV server
              record as specified in RFC 2782 to select an alternative
              server to connect to. The default is "true".

          AllowInsecureRepositories
              Allow update operations to load data files from
              repositories without sufficient security information.
              The default value is "false". Concept, implications as
              well as alternatives are detailed in apt-secure(8).

          AllowWeakRepositories
              Allow update operations to load data files from
              repositories which provide security information, but
              these are deemed no longer cryptographically strong
              enough. The default value is "false". Concept,
              implications as well as alternatives are detailed in
              apt-secure(8).

          AllowDowngradeToInsecureRepositories
              Allow that a repository that was previously gpg signed
              to become unsigned during an update operation. When
              there is no valid signature for a previously trusted
              repository apt will refuse the update. This option can
              be used to override this protection. You almost
              certainly never want to enable this. The default is
              false. Concept, implications as well as alternatives are
              detailed in apt-secure(8).

          Changelogs::URI scope
              Acquiring changelogs can only be done if an URI is known
              from where to get them. Preferable the Release file
              indicates this in a 'Changelogs' field. If this isn't
              available the Label/Origin field of the Release file is
              used to check if a
              Acquire::Changelogs::URI::Label::LABEL or
              Acquire::Changelogs::URI::Origin::ORIGIN option exists
              and if so this value is taken. The value in the Release
              file can be overridden with
              Acquire::Changelogs::URI::Override::Label::LABEL or
              Acquire::Changelogs::URI::Override::Origin::ORIGIN. The
              value should be a normal URI to a text file, except that
              package specific data is replaced with the placeholder
              @CHANGEPATH@. The value for it is: 1. if the package is
              from a component (e.g.  main) this is the first part
              otherwise it is omitted, 2. the first letter of source
              package name, except if the source package name starts
              with 'lib' in which case it will be the first four

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              letters. 3. The complete source package name. 4. the
              complete name again and 5. the source version. The first
              (if present), second, third and fourth part are
              separated by a slash ('/') and between the fourth and
              fifth part is an underscore ('_'). The special value
              'no' is available for this option indicating that this
              source can't be used to acquire changelog files from.
              Another source will be tried if available in this case.

     BINARY SPECIFIC CONFIGURATION
          Especially with the introduction of the apt binary it can be
          useful to set certain options only for a specific binary as
          even options which look like they would effect only a
          certain binary like APT::Get::Show-Versions effect apt-get
          as well as apt.

          Setting an option for a specific binary only can be achieved
          by setting the option inside the Binary::specific-binary
          scope. Setting the option APT::Get::Show-Versions for the
          apt only can e.g. by done by setting
          Binary::apt::APT::Get::Show-Versions instead.

          Note that as seen in the DESCRIPTION section further above
          you can't set binary-specific options on the commandline
          itself nor in configuration files loaded via the
          commandline.

     DIRECTORIES
          The Dir::State section has directories that pertain to local
          state information.  lists is the directory to place
          downloaded package lists in and status is the name of the
          dpkg(1) status file.  preferences is the name of the APT
          preferences file.  Dir::State contains the default directory
          to prefix on all sub-items if they do not start with / or
          ./.

          Dir::Cache contains locations pertaining to local cache
          information, such as the two package caches srcpkgcache and
          pkgcache as well as the location to place downloaded
          archives, Dir::Cache::archives. Generation of caches can be
          turned off by setting pkgcache or srcpkgcache to "". This
          will slow down startup but save disk space. It is probably
          preferable to turn off the pkgcache rather than the
          srcpkgcache. Like Dir::State the default directory is
          contained in Dir::Cache

          Dir::Etc contains the location of configuration files,
          sourcelist gives the location of the sourcelist and main is
          the default configuration file (setting has no effect,
          unless it is done from the config file specified by
          APT_CONFIG).

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          The Dir::Parts setting reads in all the config fragments in
          lexical order from the directory specified. After this is
          done then the main config file is loaded.

          Binary programs are pointed to by Dir::Bin.
          Dir::Bin::Methods specifies the location of the method
          handlers and gzip, bzip2, lzma, dpkg, apt-get dpkg-source
          dpkg-buildpackage and apt-cache specify the location of the
          respective programs.

          The configuration item RootDir has a special meaning. If
          set, all paths will be relative to RootDir, even paths that
          are specified absolutely. So, for instance, if RootDir is
          set to /tmp/staging and Dir::State::status is set to
          /var/lib/dpkg/status, then the status file will be looked up
          in /tmp/staging/var/lib/dpkg/status. If you want to prefix
          only relative paths, set Dir instead.

          The Ignore-Files-Silently list can be used to specify which
          files APT should silently ignore while parsing the files in
          the fragment directories. Per default a file which ends with
          .disabled, ~, .bak or .dpkg-[a-z]+ is silently ignored. As
          seen in the last default value these patterns can use
          regular expression syntax.

     APT IN DSELECT
          When APT is used as a dselect(1) method several
          configuration directives control the default behavior. These
          are in the DSelect section.

          Clean
              Cache Clean mode; this value may be one of always,
              prompt, auto, pre-auto and never.  always and prompt
              will remove all packages from the cache after upgrading,
              prompt (the default) does so conditionally.  auto
              removes only those packages which are no longer
              downloadable (replaced with a new version for instance).
              pre-auto performs this action before downloading new
              packages.

          options
              The contents of this variable are passed to apt-get(8)
              as command line options when it is run for the install
              phase.

          Updateoptions
              The contents of this variable are passed to apt-get(8)
              as command line options when it is run for the update
              phase.

          PromptAfterUpdate
              If true the [U]pdate operation in dselect(1) will always

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              prompt to continue. The default is to prompt only on
              error.

     HOW APT CALLS DPKG(1)
          Several configuration directives control how APT invokes
          dpkg(1). These are in the DPkg section.

          options
              This is a list of options to pass to dpkg(1). The
              options must be specified using the list notation and
              each list item is passed as a single argument to
              dpkg(1).

          Path
              This is a string that defines the PATH environment
              variable used when running dpkg. It may be set to any
              valid value of that environment variable; or the empty
              string, in which case the variable is not changed.

          Pre-Invoke, Post-Invoke
              This is a list of shell commands to run before/after
              invoking dpkg(1). Like options this must be specified in
              list notation. The commands are invoked in order using
              /bin/sh; should any fail APT will abort.

          Pre-Install-Pkgs
              This is a list of shell commands to run before invoking
              dpkg(1). Like options this must be specified in list
              notation. The commands are invoked in order using
              /bin/sh; should any fail APT will abort. APT will pass
              the filenames of all .deb files it is going to install
              to the commands, one per line on the requested file
              descriptor, defaulting to standard input.

              Version 2 of this protocol sends more information
              through the requested file descriptor: a line with the
              text VERSION 2, the APT configuration space, and a list
              of package actions with filename and version
              information.

              Each configuration directive line has the form
              key=value. Special characters (equal signs, newlines,
              nonprintable characters, quotation marks, and percent
              signs in key and newlines, nonprintable characters, and
              percent signs in value) are %-encoded. Lists are
              represented by multiple key::=value lines with the same
              key. The configuration section ends with a blank line.

              Package action lines consist of five fields in Version
              2: package name (without architecture qualification even
              if foreign), old version, direction of version change (<
              for upgrades, > for downgrades, = for no change), new

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              version, action. The version fields are "-" for no
              version at all (for example when installing a package
              for the first time; no version is treated as earlier
              than any real version, so that is an upgrade, indicated
              as - < 1.23.4). The action field is "**CONFIGURE**" if
              the package is being configured, "**REMOVE**" if it is
              being removed, or the filename of a .deb file if it is
              being unpacked.

              In Version 3 after each version field follows the
              architecture of this version, which is "-" if there is
              no version, and a field showing the MultiArch type
              "same", "foreign", "allowed" or "none". Note that "none"
              is an incorrect typename which is just kept to remain
              compatible, it should be read as "no" and users are
              encouraged to support both.

              The version of the protocol to be used for the command
              cmd can be chosen by setting
              DPkg::Tools::options::cmd::Version accordingly, the
              default being version 1. If APT isn't supporting the
              requested version it will send the information in the
              highest version it has support for instead.

              The file descriptor to be used to send the information
              can be requested with DPkg::Tools::options::cmd::InfoFD
              which defaults to 0 for standard input and is available
              since version 0.9.11. Support for the option can be
              detected by looking for the environment variable
              APT_HOOK_INFO_FD which contains the number of the used
              file descriptor as a confirmation.

          Run-Directory
              APT chdirs to this directory before invoking dpkg(1),
              the default is /.

          Build-options
              These options are passed to dpkg-buildpackage(1) when
              compiling packages; the default is to disable signing
              and produce all binaries.

          DPkg::ConfigurePending
              If this option is set APT will call dpkg --configure
              --pending to let dpkg(1) handle all required
              configurations and triggers. This option is activated by
              default, but deactivating it could be useful if you want
              to run APT multiple times in a row - e.g. in an
              installer. In this scenario you could deactivate this
              option in all but the last run.

     PERIODIC AND ARCHIVES OPTIONS
          APT::Periodic and APT::Archives groups of options configure

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          behavior of apt periodic updates, which is done by the
          /usr/lib/apt/apt.systemd.daily script. See the top of this
          script for the brief documentation of these options.

     DEBUG OPTIONS
          Enabling options in the Debug:: section will cause debugging
          information to be sent to the standard error stream of the
          program utilizing the apt libraries, or enable special
          program modes that are primarily useful for debugging the
          behavior of apt. Most of these options are not interesting
          to a normal user, but a few may be:

          +o   Debug::pkgProblemResolver enables output about the
              decisions made by dist-upgrade, upgrade, install,
              remove, purge.

          +o   Debug::NoLocking disables all file locking. This can be
              used to run some operations (for instance, apt-get -s
              install) as a non-root user.

          +o   Debug::pkgDPkgPM prints out the actual command line each
              time that apt invokes dpkg(1).

          +o   Debug::IdentCdrom disables the inclusion of statfs data
              in CD-ROM IDs.

          A full list of debugging options to apt follows.

          Debug::Acquire::cdrom
              Print information related to accessing cdrom:// sources.

          Debug::Acquire::ftp
              Print information related to downloading packages using
              FTP.

          Debug::Acquire::http
              Print information related to downloading packages using
              HTTP.

          Debug::Acquire::https
              Print information related to downloading packages using
              HTTPS.

          Debug::Acquire::gpgv
              Print information related to verifying cryptographic
              signatures using gpg.

          Debug::aptcdrom
              Output information about the process of accessing
              collections of packages stored on CD-ROMs.

          Debug::BuildDeps

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              Describes the process of resolving build-dependencies in
              apt-get(8).

          Debug::Hashes
              Output each cryptographic hash that is generated by the
              apt libraries.

          Debug::IdentCDROM
              Do not include information from statfs, namely the
              number of used and free blocks on the CD-ROM filesystem,
              when generating an ID for a CD-ROM.

          Debug::NoLocking
              Disable all file locking. For instance, this will allow
              two instances of lqapt-get updaterq to run at the same
              time.

          Debug::pkgAcquire
              Log when items are added to or removed from the global
              download queue.

          Debug::pkgAcquire::Auth
              Output status messages and errors related to verifying
              checksums and cryptographic signatures of downloaded
              files.

          Debug::pkgAcquire::Diffs
              Output information about downloading and applying
              package index list diffs, and errors relating to package
              index list diffs.

          Debug::pkgAcquire::RRed
              Output information related to patching apt package lists
              when downloading index diffs instead of full indices.

          Debug::pkgAcquire::Worker
              Log all interactions with the sub-processes that
              actually perform downloads.

          Debug::pkgAutoRemove
              Log events related to the automatically-installed status
              of packages and to the removal of unused packages.

          Debug::pkgDepCache::AutoInstall
              Generate debug messages describing which packages are
              being automatically installed to resolve dependencies.
              This corresponds to the initial auto-install pass
              performed in, e.g., apt-get install, and not to the full
              apt dependency resolver; see Debug::pkgProblemResolver
              for that.

          Debug::pkgDepCache::Marker

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              Generate debug messages describing which packages are
              marked as keep/install/remove while the ProblemResolver
              does his work. Each addition or deletion may trigger
              additional actions; they are shown indented two
              additional spaces under the original entry. The format
              for each line is MarkKeep, MarkDelete or MarkInstall
              followed by package-name <a.b.c -> d.e.f | x.y.z>
              (section) where a.b.c is the current version of the
              package, d.e.f is the version considered for
              installation and x.y.z is a newer version, but not
              considered for installation (because of a low pin
              score). The later two can be omitted if there is none or
              if it is the same as the installed version.  section is
              the name of the section the package appears in.

          Debug::pkgDPkgPM
              When invoking dpkg(1), output the precise command line
              with which it is being invoked, with arguments separated
              by a single space character.

          Debug::pkgDPkgProgressReporting
              Output all the data received from dpkg(1) on the status
              file descriptor and any errors encountered while parsing
              it.

          Debug::pkgOrderList
              Generate a trace of the algorithm that decides the order
              in which apt should pass packages to dpkg(1).

          Debug::pkgPackageManager
              Output status messages tracing the steps performed when
              invoking dpkg(1).

          Debug::pkgPolicy
              Output the priority of each package list on startup.

          Debug::pkgProblemResolver
              Trace the execution of the dependency resolver (this
              applies only to what happens when a complex dependency
              problem is encountered).

          Debug::pkgProblemResolver::ShowScores
              Display a list of all installed packages with their
              calculated score used by the pkgProblemResolver. The
              description of the package is the same as described in
              Debug::pkgDepCache::Marker

          Debug::sourceList
              Print information about the vendors read from
              /etc/apt/vendors.list.

          Debug::RunScripts

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              Display the external commands that are called by apt
              hooks. This includes e.g. the config options
              DPkg::{Pre,Post}-Invoke or
              APT::Update::{Pre,Post}-Invoke.

     EXAMPLES
          /usr/share/doc/apt/examples/configure-index.gz is a
          configuration file showing example values for all possible
          options.

     FILES
          /etc/apt/apt.conf
              APT configuration file. Configuration Item:
              Dir::Etc::Main.

          /etc/apt/apt.conf.d/
              APT configuration file fragments. Configuration Item:
              Dir::Etc::Parts.

     SEE ALSO
          apt-cache(8), apt-config(8), apt_preferences(5).

     BUGS
          m[blue]APT bug pagem[][1]. If you wish to report a bug in
          APT, please see /usr/share/doc/debian/bug-reporting.txt or
          the reportbug(1) command.

     AUTHORS
          Jason Gunthorpe

          APT team

          Daniel Burrows <dburrows@debian.org>
              Initial documentation of Debug::*.

     NOTES
           1. APT bug page
              http://bugs.debian.org/src:apt

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