This file describes the configuration scheme such a frontend can use to
instruct the Acquire system to download those additional files.
-Note that you can't download files from other sources. It must be files
-in the same repository and below the Release file. The Release file must
-also contain hashes for the file itself as well as for the compressed
-file if wanted, otherwise a download isn't even tried!
-
-
# The Configuration Stanza
The Acquire system uses the same configuration settings to implement the
instructing the Acquire system to download the Packages files would look
like this (see also apt.conf(5) manpage for configuration file syntax):
- APT::Acquire::Targets::deb::Packages {
+ Acquire::IndexTargets::deb::Packages {
MetaKey "$(COMPONENT)/binary-$(ARCHITECTURE)/Packages";
ShortDescription "Packages";
Description "$(SITE) $(RELEASE)/$(COMPONENT) $(ARCHITECTURE) Packages";
};
All files which should be downloaded (nicknamed 'Targets') are mentioned
-below the APT::Acquire::Targets scope. 'deb' is here the type of the
+below the Acquire::IndexTargets scope. 'deb' is here the type of the
sources.list entry the file should be acquired for. The only other
supported value is hence 'deb-src'. Beware: You can't specify multiple
-types here and you can't download the same MetaKey form multiple types!
+types here and you can't download the same (evaluated) MetaKey from
+multiple types!
After the type you can pick any valid and unique string which preferable
refers to the file it downloads (In the example we picked 'Packages').
-This string is never shown or used.
+This string is used as identifier for the target class and accessible as
+'Created-By' e.g. in the "apt-get indextargets" output as detailed below.
All targets have three main properties you can define:
* MetaKey: The identifier of the file to be downloaded as used in the
* Optional: The default value is 'true' and should be kept at this
value. If enabled the acquire system will skip the download if the
file isn't mentioned in the Release file. Otherwise this is treated as
- a hard error and the update process fails.
+ a hard error and the update process fails. Note that failures while
+ downloading (e.g. 404 or hash verification errors) are failures,
+ regardless of this setting.
-Note that the acquire system will automatically choose to download
-a compressed file if it is available and uncompress it for you, just as
-it will also use pdiff patching if provided by the repository and
-enabled by the user. You only have to ensure that the Release file
-contains the information about the compressed files/pdiffs to make this
-happen. NO properties have to be set to enable this.
+The acquire system will automatically choose to download a compressed
+file if it is available and uncompress it for you, just as it will also
+use pdiff patching if provided by the repository and enabled by the
+user. You only have to ensure that the Release file contains the
+information about the compressed files/pdiffs to make this happen.
+NO properties have to be set to enable this.
# More examples
The stanzas for Translation-* files as well as for Sources files would
look like this:
-APT::Acquire::Targets {
+Acquire::IndexTargets {
deb::Translations {
MetaKey "$(COMPONENT)/i18n/Translation-$(LANGUAGE)";
ShortDescription "Translation-$(LANGUAGE)";
As seen in the examples, properties can contain placeholders filled in
by the acquire system. The following variables are known; note that
unknown variables have no default value nor are they touched: They are
-printed literally.
+printed as-is.
-* $(SITE): An identifier of the site we access, e.g.
- "http://example.org/".
+* $(SITE): An identifier of the site we access as seen in sources.list,
+ e.g. "http://example.org/debian" or "file:/path/to/a/repository". You
+ can't use this field in {,flat}MetaKey, it is for description proposes
+ only.
* $(RELEASE): This is usually an archive- or codename, e.g. "stable" or
"stretch". Note that flat-style repositories do not have a archive-
or codename per-se, so the value might very well be just "/" or so.
+ Again, as seen in the sources.list.
* $(COMPONENT): as given in the sources.list, e.g. "main", "non-free" or
"universe". Note that flat-style repositories again do not really
have a meaningful value here.
APT::Architectures (potentially modified by sources.list options),
e.g. "amd64", "i386" or "armel" for the 'deb' type. In type 'deb-src'
this variable has the value "source".
+
+Note that while more variables might exist in the implementation, these
+are to be considered undefined and their usage strongly discouraged. If
+you have a need for other variables contact us.
+
+# Accessing files
+
+Do NOT hardcode specific file locations, names or compression types in
+your application! You will notice that the configuration options give
+you no choice over where the downloaded files will be stored. This is by
+design so multiple applications can download and use the same file
+rather than each and every one of them potentially downloads and uses
+its own copy somewhere on disk.
+
+"apt-get indextargets" can be used to get the location as well as other
+information about all files downloaded (aka: you will see Packages,
+Sources and Translation-* files here as well). Provide a line of the
+default output format as parameter to filter out all entries which do
+not have such a line. With --format, you can further more define your
+own output style. The variables are what you see in the output, just all
+uppercase and wrapped in $(), as in the configuration file.
+
+To get all the filenames of all Translation-en files you can e.g. call:
+ apt-get indextargets --format '$(FILENAME)' "Created-By: Translations" "Language: en"
+
+The line-based filtering and the formating is rather crude and feature-
+less by design, so it is recommend to use dedicated and more powerful
+tools like 'grep-dctrl'.
+
+Accessing this information via libapt is done by reading the
+sources.lists (pkgSourceList), iterating over the metaIndex objects this
+creates and calling GetIndexTargets() on them. See the sourcecode of
+"apt-get indextargets" for a complete example.
+
+Note that by default targets are not listed if they weren't downloaded.
+If you want to see all targets, you can use the --no-release-info, which
+also removes the Codename, Suite, Version, Origin, Label and Trusted
+fields from the output as these also display data which needs to be
+downloaded first and could hence be inaccurate [on the pro-side: This
+mode is faster as it doesn't require a valid binary cache to operate].
+The most notable difference perhaps is in the Filename field through: By
+default it indicates an existing file, potentially compressed (Hint:
+libapt users can use FileFd to open compressed files transparently). In
+the --no-release-info mode the indicated file doesn't need to exist and
+it will always refer to an uncompressed file, even if the index would be
+(or is) stored compressed.
+
+Remarks on fields only available in (default) --release-info mode:
+* Trusted: Denotes with a 'yes' or 'no' if the data in this file is
+ authenticated by a trustchain rooted in a trusted gpg key. You should
+ be careful with untrusted data and warn the user if you use it.
+* Codename, Suite, Version, Origin and Label are fields from the Release
+ file, are only present if they are present in the Release file and
+ contain the same data.
+
+Remarks on other available fields:
+* MetaKey, ShortDesc, Description, Site, Release: as defined
+ by the configuration and described further above.
+* Created-By: configuration entity responsible for this target
+* Target-Of: type of the sources.list entry
+* URI, Repo-URI: avoid using. Contains potentially username/password.
+ Prefer 'Site', especially for display.
+* Optional: Decodes the option of the same name from the configuration.
+ Note that it is using 'yes' and 'no' instead of 'true' and 'false'.
+* Language, Architecture, Component: as defined further above, but with
+ the catch that they might be missing if they don't effect the target
+ (aka: They weren't used while evaluating the MetaKey template).
+
+Again, additional fields might be visible in certain implementations,
+but you should avoid using them and instead talk to us about a portable
+implementation.
+
+# Multiple application requiring the same files
+
+It is highly encouraged that applications talk to each other and to us
+about which files they require. It is usually best to have a common
+package ship the configuration needed to get the files, but specific
+needs might require specific solutions. Again: talk to us.
+
+# Acquiring files not mentioned in the Release file
+
+You can't. This is by design as these files couldn't be verified to not
+be modified in transit, corrupted by the download process or simple if
+they are present at all on the server, which would require apt to probe
+for them. APT did this in the past for legacy reasons, we do not intend
+to go back to these dark times.
+
+This is also why you can't request files from a different server. It
+would have the additional problem that this server might not even be
+accessible (e.g. proxy settings) or that local sources (file:/, cdrom:/)
+start requesting online files…
+
+In other words: We would be opening Pandora's box.
projects / apt.git / blobdiff