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           apt.conf is the main configuration file for the APT suite of tools, but
           by far not the only place changes to options can be made. All tools
           therefore share the configuration files and also use 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 if the file doesn't match a pattern in the
               Dir::Ignore-Files-Silently configuration list - in this case it
               will be silently ignored.
            3. the main configuration file specified by Dir::Etc::main
            4. the command line options are applied to override the configuration
               directives or to load even more configuration files.


           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 trailing semicolon and the quotes are required. The value must be
           on one line, and there is no kind of string concatenation. It must not
           include inside quotes. The behavior of the backslash "\" and escaped
           characters inside a value is undefined and it should not be used. An
           option name may include alphanumerical characters and the "/-:._+"
           characters. A new scope can be opened with curly braces, like:
               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
           Names for the configuration items are optional if a list is defined as
           it can be see 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 as every other option by
           reassigning a new value to the option.
           Two specials are allowed, #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, then 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 the ::-style described below will not
           override previously written entries. Only options can be overridden by
           addressing a new value to it - lists and scopes can't be overridden,
           only cleared.
           All of the APT tools take a -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. Lists can be appended
           too by adding a trailing :: to the list name. (As you might suspect:
           The scope syntax can't be used on the command line.)
           Note that you can use :: only for appending one item per line to a list
           and that you should not use it in combination with the scope syntax.
           (The scope syntax implicit insert ::) Using both syntaxes together will
           trigger a bug which some users unfortunately relay on: An option with
           the unusual name "::" which acts like every other option with a name.
           These introduces many problems including that a user who writes
           multiple lines in this wrong syntax in the hope to append to a list
           will gain the opposite as only the last assignment for this option "::"
           will be used. Upcoming APT versions will raise errors and will stop
           working if they encounter this misuse, so please correct such
           statements now as long as APT doesn't complain explicit about them.


           This group of options controls general APT behavior as well as holding
           the options for all of the tools.
               System Architecture; sets the architecture to use when fetching
               files and parsing package lists. The internal default is the
               architecture apt was compiled for.
               All Architectures the system supports. Processors implementing the
               amd64 are e.g. also able to execute binaries compiled for i386;
               This list is use when fetching files and parsing package lists. The
               internal default is always the native architecture
               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.
               Defaults to on which will cause APT to install essential and
               important packages as fast as possible in the install/upgrade
               operation. This is done to limit the effect of a failing dpkg(1)
               call: If this option is disabled APT does treat an important
               package in the same way as an extra package: Between the unpacking
               of the important package A and his configuration can then be many
               other unpack or configuration calls, e.g. for package B which has
               no relation to A, but causes the dpkg call to fail (e.g. because
               maintainer script of package B generates an error) which results in
               a system state in which package A is unpacked but unconfigured -
               each package depending on A is now no longer guaranteed to work as
               their dependency on A is not longer satisfied. The immediate
               configuration marker is also applied to all dependencies which can
               generate a problem if the dependencies e.g. form a circle as a
               dependency with the immediate flag is comparable with a
               Pre-Dependency. So in theory it is possible that APT encounters a
               situation in which it is unable to perform immediate configuration,
               errors out and refers to this option so the user can deactivate the
               immediate configuration temporarily to be able to perform an
               install/upgrade again. Note the use of the word "theory" here as
               this problem was only encountered by now in real world a few times
               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 mentioned scenario above is not the only problem immediate
               configuration can help to prevent in the first place. Before a big
               operation like dist-upgrade is run with this option disabled it
               should be tried to explicitly install the package APT is unable to
               configure immediately, but please make sure to report your problem
               also to your distribution and to the APT team with the buglink
               below so they can work on improving or correcting the upgrade
               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-Depend 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, bash or anything that those packages depend
           Cache-Start, Cache-Grow and 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
               Defines which package(s) are considered essential build
               The Get subsection controls the apt-get(8) tool, please see its
               documentation for more information about the options here.
               The Cache subsection controls the apt-cache(8) tool, please see its
               documentation for more information about the options here.
               The CDROM subsection controls the apt-cdrom(8) tool, please see its
               documentation for more information about the options here.


           The Acquire group of options controls the download of packages and the
           URI handlers.
               Security related option defaulting to true as an expiring
               validation for a Release file prevents longtime replay attacks and
               can e.g. also help users to identify no longer updated mirrors -
               but the feature depends on the correctness of the time 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 volitional the following Max-ValidTime option can be used.
               Seconds the Release file should be considered valid after it was
               created (indicated by the Date header). 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
               "for ever". Archive specific settings can be made by appending the
               label of the archive to the option name.
               Minimum of seconds the Release file should be considered valid
               after it was created (indicated by the Date header). Use this if
               you need to use a seldomly updated (local) mirror of a more regular
               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.
               Try to download deltas called PDiffs for Packages or Sources files
               instead of downloading whole ones. True by default.
               Two sub-options to limit the use of PDiffs are also available: With
               failed files the given number of times.
               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 URIs; http::Proxy is the default http proxy to use. 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 to not use its
               cached response under any circumstances, Max-Age is sent only for
               index files and tells the cache to refresh its object if it is
               older than the given number of seconds. Debian updates its index
               files daily so the default is 1 day.  No-Store specifies that the
               cache should never store this request, it is only set for archive
               files. This may be useful to prevent polluting a proxy cache with
               very large .deb files. Note: Squid 2.0.2 does not support any of
               these options.
               The option timeout sets the timeout timer used by the method, this
               applies to all things including connection timeout and data
               One setting is provided to control the pipeline depth in cases
               where the remote server is not RFC conforming or buggy (such as
               Squid 2.0.2).  Acquire::http::Pipeline-Depth can be a value from 0
               to 5 indicating how many outstanding requests APT should send. A
               value of zero MUST be specified if the remote host does not
               properly linger on TCP connections - otherwise data corruption will
               occur. Hosts which require this are in violation of RFC 2068.
               The used bandwidth can be limited with Acquire::http::Dl-Limit
               which accepts integer values in kilobyte. The default value is 0
               which deactivates the limit and tries uses as much as possible of
               the bandwidth (Note that this option implicit deactivates the
               download 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.
               HTTPS URIs. Cache-control, Timeout, AllowRedirect, Dl-Limit and
               proxy options are the same as for http method and will also default
               to the options from the http method if they are not explicitly set
               'TLSv1' or 'SSLv3' string.  <host>::SslForceVersion is
               corresponding per-host option.
               FTP URIs; ftp::Proxy is the default ftp proxy to use. 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 a 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 available are
               $(PROXY_USER) $(PROXY_PASS) $(SITE_USER) $(SITE_PASS) $(SITE) and
               $(SITE_PORT) Each is taken from it's respective URI component.
               The option timeout sets the timeout timer used by the method, this
               applies to all things including connection timeout and data
               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,
               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 a 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
               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 URIs; the only setting for CDROM URIs is the mount point,
               cdrom::Mount which must be the mount point for the CDROM 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 (such as an SMB mount and old mount packages). The syntax is
               to put
                   /cdrom/::Mount "foo";
               within the cdrom block. It is important to have the trailing slash.
                   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 simple add the preferred type at first - not already
               added default types will be added at run time 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 explicit to the list as it will be
               added automatic.
               Note that at run time the Dir::Bin::Methodname will be checked: If
               this setting exists 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
               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.
               The Languages subsection controls which Translation files are
               downloaded and in which order APT tries to display the
               use the setting Acquire::Languages=none. "none" is another special
               meaning code which will stop the search for a fitting Translation
               file. This can be used by the system administrator to let APT know
               that it should download also this files without actually use them
               if the environment doesn't specify this languages. So the following
               example configuration will result in the order "en, de" in an
               english and in "de, en" in a german localization. Note that "fr" is
               downloaded, but not used if APT is not used in a french
               localization, in such an environment the order would be "fr, de,
                   Acquire::Languages { "environment"; "de"; "en"; "none"; "fr"; };


           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 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 their names to be blank. This
           will slow down startup but save disk space. It is probably preferred 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
           in Dir:: 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.
           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
               The contents of this variable is passed to apt-get(8) as command
               line options when it is run for the install phase.
               The contents of this variable is passed to apt-get(8) as command
               line options when it is run for the update phase.
               If true the [U]pdate operation in dselect(1) will always prompt to
               continue. The default is to prompt only on error.


           Several configuration directives control how APT invokes dpkg(1). These
           are in the DPkg section.
               This is a list of options to pass to dpkg. 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.
               This is a list of shell commands to run before invoking dpkg. 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 to the commands on standard input the filenames of all
               .deb files it is going to install, one per line.
               Version 2 of this protocol dumps more information, including the
               protocol version, the APT configuration space and the packages,
               files and versions being changed. Version 2 is enabled by setting
               DPkg::Tools::options::cmd::Version to 2.  cmd is a command given to
               APT chdirs to this directory before invoking dpkg, the default is
               These options are passed to dpkg-buildpackage(1) when compiling
               packages, the default is to disable signing and produce all
       dpkg trigger usage (and related options)
           APT can call dpkg in a way so it can make aggressive use of triggers
           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 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";
               Add the no triggers flag to all dpkg calls (except the
               ConfigurePending call). See dpkg(1) if you are interested in what
               this actually means. In short: dpkg 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 - now apt will add these flag also to the unpack and remove
               Valid values are "all", "smart" and "no". "all" is the default
               value and causes APT to configure all packages explicit. The
               "smart" way is it to configure only packages which need to be
               configured before another package can be unpacked (Pre-Depends) and
               let the rest configure by dpkg with a call generated by the next
               option. "no" on the other hand will not configure anything and
               totally rely on dpkg for configuration (which will at the moment
               fail if a Pre-Depends is encountered). Setting this option to
               another than the all value will implicitly activate also the next
               option per default as otherwise the system could end in an
               unconfigured status which could be unbootable!
               If this option is set apt will call dpkg --configure --pending to
               let dpkg handle all required configurations and triggers. This
               option is activated automatic per default if the previous option is
               not set to all, but deactivating 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.
               Useful for smart configuration as a package which has pending
               triggers is not considered as installed and dpkg treats them as
               unpacked currently which is a dealbreaker for Pre-Dependencies (see
               debbugs #526774). Note that this will process all triggers, not
               only the triggers needed to configure this package.
               high score but the immediate flag is relatively low (a package
               which has a Pre-Depends is higher rated). These option and the
               others in the same group can be used to change the scoring. The
               following example shows the settings with there default values.
                   OrderList::Score {
                        Delete 500;
                        Essential 200;
                        Immediate 10;
                        PreDepends 50;


           APT::Periodic and APT::Archives groups of options configure behavior of
           apt periodic updates, which is done by /etc/cron.daily/apt script. See
           header of this script for the brief documentation of these 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 CDROM
           A full list of debugging options to apt follows.
               Print information related to accessing cdrom:// sources.
               Print information related to downloading packages using FTP.
               Print information related to downloading packages using HTTP.
               Print information related to downloading packages using HTTPS.
               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.
               Disable all file locking. For instance, this will allow two
               instances of "apt-get update" to run at the same time.
               Log when items are added to or removed from the global download
               Output status messages and errors related to verifying checksums
               and cryptographic signatures of downloaded files.
               Output information about downloading and applying package index
               list diffs, and errors relating to package index list diffs.
               Output information related to patching apt package lists when
               downloading index diffs instead of full indices.
               Log all interactions with the sub-processes that actually perform
               Log events related to the automatically-installed status of
               packages and to the removal of unused packages.
               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.
               Generate debug messages describing which package is 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 space 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
               descriptor and any errors encountered while parsing it.
               Generate a trace of the algorithm that decides the order in which
               apt should pass packages to dpkg(1).
               Output status messages tracing the steps performed when invoking
               Output the priority of each package list on startup.
               Trace the execution of the dependency resolver (this applies only
               to what happens when a complex dependency problem is encountered).
               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
               Print information about the vendors read from


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


               APT configuration file. Configuration Item: Dir::Etc::Main.
               APT configuration file fragments. Configuration Item:


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


           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.


           Jason Gunthorpe
           APT team
           Daniel Burrows <>
               Initial documentation of Debug::*.

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