Provided by: apt_1.2.10ubuntu1_amd64 bug

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. 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. 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.

       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.

       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', 'jessie', 'stretch', '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
           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 buglink 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 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-Valid-Until
           Security related option defaulting to true, as giving a 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.

       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 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
           http::Proxy sets the default proxy to use for HTTP URIs. It is in the standard form of
           http://[[user][:pass]@]host[:port]/. Per host proxies can also be specified by using
           the form http::Proxy::<host> with the special keyword DIRECT meaning to use no
           proxies. If no one of the above settings is specified, http_proxy environment variable
           will be used.

           Three settings are provided for cache control with HTTP/1.1 compliant proxy caches.
           No-Cache tells the proxy not to use its cached response under any circumstances.
           Max-Age sets the allowed maximum age (in seconds) of an index file in the cache of the
           proxy.  No-Store specifies that the proxy should not store the requested archive files
           in its cache, which can be used to prevent the proxy from polluting its cache with
           (big) .deb files.

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

           The setting Acquire::http::Pipeline-Depth can be used to enable HTTP pipelining (RFC
           2616 section 8.1.2.2) which can be beneficial e.g. on high-latency connections. It
           specifies how many requests are sent in a pipeline. APT tries to detect and workaround
           misbehaving webservers and proxies at runtime, but if you know that yours does not
           conform to the HTTP/1.1 specification pipelining can be disabled by setting the value
           to 0. It is enabled by default with the value 10.

           Acquire::http::AllowRedirect controls whether APT will follow redirects, which is
           enabled by default.

           The used bandwidth can be limited with Acquire::http::Dl-Limit which accepts integer
           values in kilobytes per second. The default value is 0 which deactivates the limit and
           tries to use all available bandwidth. Note that this option implicitly disables
           downloading from multiple servers at the same time.

           Acquire::http::User-Agent can be used to set a different User-Agent for the http
           download method as some proxies allow access for clients only if the client uses a
           known identifier.

           Acquire::http::Proxy-Auto-Detect can be used to specify an external command to
           discover the http proxy to use. Apt expects the command to output the proxy on stdout
           in the style http://proxy:port/. This will override the generic Acquire::http::Proxy
           but not any specific host proxy configuration set via Acquire::http::Proxy::$HOST. See
           the squid-deb-proxy-client(1) package for an example implementation that uses avahi.
           This option takes precedence over the legacy option name ProxyAutoDetect.

       https
           The Cache-control, Timeout, AllowRedirect, Dl-Limit and proxy options work for HTTPS
           URIs in the same way as for the http method, and default to the same values if they
           are not explicitly set. The Pipeline-Depth option is not yet supported.

           CaInfo suboption specifies place of file that holds info about trusted certificates.
           <host>::CaInfo is the corresponding per-host option.  Verify-Peer boolean suboption
           determines whether or not the server's host certificate should be verified against
           trusted certificates.  <host>::Verify-Peer is the corresponding per-host option.
           Verify-Host boolean suboption determines whether or not the server's hostname should
           be verified.  <host>::Verify-Host is the corresponding per-host option.  SslCert
           determines what certificate to use for client authentication.  <host>::SslCert is the
           corresponding per-host option.  SslKey determines what private key to use for client
           authentication.  <host>::SslKey is the corresponding per-host option.  SslForceVersion
           overrides default SSL version to use. It can contain either of the strings 'TLSv1' or
           'SSLv3'.  <host>::SslForceVersion is the corresponding per-host option.

       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 /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.

       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 bzip2, lzma and gzip compressed files; with this setting more
           formats can be added on the fly or the used method can be changed. 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 - default 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 bzip2 and lzma. If lzma should be
           preferred over gzip and bzip2 the configure setting should look like this:

               Acquire::CompressionTypes::Order { "lzma"; "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, 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 mostly only
           useable 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.

       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 the update operation to load data files from a repository without a trusted
           signature. If enabled this option no data files will be loaded and the update
           operation fails with a error for this source. The default is false for backward
           compatibility. This will be changed in the future.

       AllowDowngradeToInsecureRepositories
           Allow that a repository that was previously gpg signed to become unsigned durign a
           update operation. When there is no valid signature of a perviously 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. Note that apt will
           still consider packages from this source untrusted and warn about them if you try to
           install them.

       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 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).

       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 end
       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 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).

       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 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 trigger usage (and related options)
       APT can call dpkg(1) in such a way as to let it make aggressive use of triggers over
       multiple calls of dpkg(1). Without further options dpkg(1) will use triggers once each
       time it runs. Activating these options can therefore decrease the time needed to perform
       the install or upgrade. Note that it is intended to activate these options per default in
       the future, but as it drastically changes the way APT calls dpkg(1) it needs a lot more
       testing.  These options are therefore currently experimental and should not be used in
       production environments.  It also breaks progress reporting such that all front-ends will
       currently stay around half (or more) of the time in the 100% state while it actually
       configures all packages.

       Note that it is not guaranteed that APT will support these options or that these options
       will not cause (big) trouble in the future. If you have understand the current risks and
       problems with these options, but are brave enough to help testing them, create a new
       configuration file and test a combination of options. Please report any bugs, problems and
       improvements you encounter and make sure to note which options you have used in your
       reports. Asking dpkg(1) for help could also be useful for debugging proposes, see e.g.
       dpkg --audit. A defensive option combination would be

           DPkg::NoTriggers "true";
           PackageManager::Configure "smart";
           DPkg::ConfigurePending "true";
           DPkg::TriggersPending "true";

       DPkg::NoTriggers
           Add the no triggers flag to all dpkg(1) calls (except the ConfigurePending call). See
           dpkg(1) if you are interested in what this actually means. In short: dpkg(1) will not
           run the triggers when this flag is present unless it is explicitly called to do so in
           an extra call. Note that this option exists (undocumented) also in older APT versions
           with a slightly different meaning: Previously these option only append --no-triggers
           to the configure calls to dpkg(1) - now APT will also add this flag to the unpack and
           remove calls.

       PackageManager::Configure
           Valid values are "all", "smart" and "no". The default value is "all", which causes APT
           to configure all packages. The "smart" way is to configure only packages which need to
           be configured before another package can be unpacked (Pre-Depends), and let the rest
           be configured by dpkg(1) with a call generated by the ConfigurePending option (see
           below). On the other hand, "no" will not configure anything, and totally relies on
           dpkg(1) for configuration (which at the moment will fail if a Pre-Depends is
           encountered). Setting this option to any value other than all will implicitly also
           activate the next option by default, as otherwise the system could end in an
           unconfigured and potentially unbootable state.

       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 automatically per
           default if the previous option is not set to all, but deactivating it could be useful
           if you want to run APT multiple times in a row - e.g. in an installer. In these
           sceneries you could deactivate this option in all but the last run.

       DPkg::TriggersPending
           Useful for the smart configuration as a package which has pending triggers is not
           considered as installed, and dpkg(1) treats them as unpacked currently which is a
           showstopper for Pre-Dependencies (see debbugs #526774). Note that this will process
           all triggers, not only the triggers needed to configure this package.

       OrderList::Score::Immediate
           Essential packages (and their dependencies) should be configured immediately after
           unpacking. It is a good idea to do this quite early in the upgrade process as these
           configure calls also currently require DPkg::TriggersPending which will run quite a
           few triggers (which may not be needed). Essentials get per default a high score but
           the immediate flag is relatively low (a package which has a Pre-Depends is rated
           higher). These option and the others in the same group can be used to change the
           scoring. The following example shows the settings with their default values.

               OrderList::Score {
                    Delete 500;
                    Essential 200;
                    Immediate 10;
                    PreDepends 50;
               };

PERIODIC AND ARCHIVES OPTIONS

       APT::Periodic and APT::Archives groups of options configure behavior of apt periodic
       updates, which is done by the /etc/cron.daily/apt 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:

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

       ·   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.

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

       ·   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
           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 “apt-get
           update” 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
           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
           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

       APT bug page[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