Provided by: apt_0.8.16~exp12ubuntu10_amd64 bug


       apt.conf - Configuration file for APT


       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

        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 followed by a semicolon. Multiple entries can
       be included, each separated by a semicolon.

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

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

       The names of the configuration items are not case-sensitive. 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 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
           (APT::Architecture) and all foreign architectures it can retrieve by calling dpkg

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

           Ignore Held packages; This global option causes the problem resolver to ignore held
           packages in its decision making.

           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 process.

           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 on.

       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 to which size the Cache will grow
           and is therefore the amount of memory APT will request at startup. The default value
           is 20971520 bytes (~20 MB). Note that these amount of space need to be available for
           APT otherwise it will likely fail ungracefully, so for memory restricted devices these
           value should be lowered while on systems with a lot of configured sources this might
           be increased.  Cache-Grow defines in byte 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. These 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 grow of the cache is disabled.

           Defines which package(s) are considered essential build dependencies.

           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 FileLimit can be
           specified how many PDiff files are downloaded at most to patch 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.

           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.

           Number of retries to perform. If this is non-zero APT will retry 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

           The option timeout sets the timeout timer used by the method, this applies to all
           things including connection timeout and data timeout.

           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 for https.  Pipeline-Depth option is not supported yet.

           CaInfo suboption specifies place of file that holds info about trusted certificates.
           <host>::CaInfo is corresponding per-host option.  Verify-Peer boolean suboption
           determines whether verify server's host certificate against trusted certificates or
           not.  <host>::Verify-Peer is corresponding per-host option.  Verify-Host boolean
           suboption determines whether verify server's hostname or not.  <host>::Verify-Host is
           corresponding per-host option.  SslCert determines what certificate to use for client
           authentication.  <host>::SslCert is corresponding per-host option.  SslKey determines
           what private key to use for client authentication.  <host>::SslKey is corresponding
           per-host option.  SslForceVersion overrides default SSL version to use. Can contain
           '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 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, 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 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 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. Unmount commands
           can be specified using UMount.

           GPGV URIs; the only option for GPGV URIs is the option to pass additional parameters
           to gpgv.  gpgv::Options Additional options passed to gpgv.

           List of compression types which are understood by the acquire methods. Files like
           Packages can be available in various compression formats. Per 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

               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 mirrors.

           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 Description-Translations. APT will try to display the
           first available Description in the Language which is listed at first. Languages can be
           defined with their short or long Languagecodes. Note that not all archives provide
           Translation files for every Language - especially the long Languagecodes are rare, so
           please inform you which ones are available before you set here impossible values.

           The default list includes "environment" and "en". "environment" has a special meaning
           here: It will be replaced at runtime with the languagecodes 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 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, en".

               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 these patterns can use regular expression syntax.


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

           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.

           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

           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 Pre-Install-Pkgs.

           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 binaries.

   dpkg trigger usage (and related options)
       APT can call dpkg in a way so it can make aggressive use of triggers over multiple calls
       of dpkg. Without further options dpkg will use triggers only in between his own run.
       Activating these options can therefore decrease the time needed to perform the install /
       upgrade. Note that it is intended to activate these options per default in the future, but
       as it changes the way APT calling dpkg drastically it needs a lot more testing.  These
       options are therefore currently experimental and should not be used in productive
       environments.  Also it breaks the progress reporting so all frontends will currently stay
       around half (or more) of the time in the 100% state while it actually configures all

       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 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 calls.

           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

           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.

           As the configuration can be deferred to be done at the end by dpkg it can be tried to
           order the unpack series only by critical needs, e.g. by Pre-Depends. Default is true
           and therefore the "old" method of ordering in various steps by everything. While both
           method were present in earlier APT versions the OrderCritical method was unused, so
           this method is very experimental and needs further improvements before becoming really

           Essential packages (and there dependencies) should be configured immediately after
           unpacking. It will be a good idea to do this quite early in the upgrade process as
           these these configure calls require currently also DPkg::TriggersPending which will
           run quite a few triggers (which maybe not needed). Essentials get per default a 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

       ·    Debug::IdentCdrom disables the inclusion of statfs data in CDROM IDs.

       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.

           Print information related to verifying cryptographic signatures using gpg.

           Output information about the process of accessing collections of packages stored on

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

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

           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 queue.

           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 downloads.

           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 omitted if there is none or if it is the same version as the installed.
           section is the name of the section the package appears in.

           Dump the default configuration to standard error on startup.

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

           Output all the data received from dpkg(1) on the status file 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 dpkg(1).

           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

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


       /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: Dir::Etc::Parts.


       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::*.


        1. APT bug page