Man Linux: Main Page and Category List


       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 no or "conf" as filename extension and which only contain
           alphanumeric, hyphen (-), underscore (_) and period (.) characters
           - otherwise they 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
       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/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.

           Default release to install packages from if more than one version
           available. Contains release name, codename or release version.
           Examples: 'stable', 'testing', 'unstable', 'lenny', 'squeeze',
           '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

           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
           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

           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. The default is "for ever" (0) if the Release file of the
           archive doesn't include a Valid-Until header. If it does then this
           date is the default. The date from the Release file or the date
           specified by the creation time of the Release file (Date header)
           plus the seconds specified with this options are used to check if
           the validation of a file has expired by using the earlier date of
           the two. Archive specific settings can be made 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
           precentage 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 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
           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

           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.
           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 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 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 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.

           While it is possible to add an empty compression type to the order
           list, but APT in its current version doesn't understand it
           correctly and will display many warnings about not downloaded files
           - these warnings are most of the time false negatives. Future
           versions will maybe include a way to really prefer uncompressed
           files to support the usage of 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

           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,

               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

           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 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
       over multiply 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

           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.

           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 useful.

           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:

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

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

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

       o    Debug::IdentCdrom disables the inclusion of statfs data in 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.

           Print information related to verifying cryptographic signatures
           using gpg.

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

           Describes the process of resolving build-dependencies in apt-

           Output each cryptographic hash that is generated by the apt

           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
           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

           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

           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

           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::*.


        1. APT bug page