treat an empty dependency field just like it doesn't exist

[apt.git] / doc / sources.list.5.xml

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<!ENTITY % aptent SYSTEM "apt.ent"> %aptent;
<!ENTITY % aptverbatiment SYSTEM "apt-verbatim.ent"> %aptverbatiment;
<!ENTITY % aptvendor SYSTEM "apt-vendor.ent"> %aptvendor;
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<refentry>

 <refentryinfo>
   &apt-author.jgunthorpe;
   &apt-author.team;
   &apt-email;
   &apt-product;
   <!-- The last update date -->
   <date>2015-11-26T00:00:00Z</date>
 </refentryinfo>
 
 <refmeta>
   <refentrytitle>sources.list</refentrytitle>
   <manvolnum>5</manvolnum>
   <refmiscinfo class="manual">APT</refmiscinfo>
 </refmeta>
 
 <!-- Man page title -->
 <refnamediv>
    <refname>sources.list</refname>
    <refpurpose>List of configured APT data sources</refpurpose>
 </refnamediv>
 
 <refsect1><title>Description</title>
   <para>
      The source list <filename>/etc/apt/sources.list</filename> and the
      files contained in <filename>/etc/apt/sources.list.d/</filename> are
      designed to support any number of active sources and a variety of source
      media. The files list one source per line (one-line style) or contain multiline
      stanzas defining one or more sources per stanza (deb822 style), with the
      most preferred source listed first (in case a single version is
      available from more than one source). The information available from the
      configured sources is acquired by <command>apt-get update</command> (or
      by an equivalent command from another APT front-end).
   </para>
 </refsect1>
 
 <refsect1><title>sources.list.d</title>
    <para>The <filename>/etc/apt/sources.list.d</filename> directory provides
       a way to add sources.list entries in separate files.
       Two different file formats are allowed as described in the next two sections.
       Filenames need to have either the extension <filename>.list</filename> or
       <filename>.sources</filename> depending on the contained format.
       The filenames may only contain letters (a-z and A-Z),
       digits (0-9), underscore (_), hyphen (-) and period (.) characters.
       Otherwise APT will print a notice that it has ignored a file, unless that
       file matches a pattern in the <literal>Dir::Ignore-Files-Silently</literal>
       configuration list - in which case it will be silently ignored.</para>
 </refsect1>

 <refsect1><title>One-Line-Style Format</title>
    <para>
       Files in this format have the extension <filename>.list</filename>.
       Each line specifying a source starts with a type (e.g. <literal>deb-src</literal>)
       followed by options and arguments for this type.

       Individual entries cannot be continued onto a following line. Empty lines
       are ignored, and a <literal>#</literal> character anywhere on a line marks
       the remainder of that line as a comment. Consequently an entry can be
       disabled by commenting out the entire line.

       If options should be provided they are separated by spaces and all of
       them together are enclosed by square brackets (<literal>[]</literal>)
       included in the line after the type separated from it with a space.
       If an option allows multiple values these are separated from each other
       with a comma (<literal>,</literal>). An option name is separated from its
       value(s) by an equals sign (<literal>=</literal>). Multivalue options also
       have <literal>-=</literal> and <literal>+=</literal> as separators, which
       instead of replacing the default with the given value(s) modify the default
       value(s) to remove or include the given values.
   </para><para>
       This is the traditional format and supported by all apt versions.
       Note that not all options as described below are supported by all apt versions.
       Note also that some older applications parsing this format on their own might not
       expect to encounter options as they were uncommon before the introduction of
       multi-architecture support.
    </para>
 </refsect1>

 <refsect1><title>deb822-Style Format</title>
    <para>
       Files in this format have the extension <filename>.sources</filename>.
       The format is similar in syntax to other files used by Debian and its
       derivatives, such as the metadata files that apt will download from the configured
       sources or the <filename>debian/control</filename> file in a Debian source package.

       Individual entries are separated by an empty line; additional empty
       lines are ignored, and a <literal>#</literal> character at the start of
       the line marks the entire line as a comment. An entry can hence be
       disabled by commenting out each line belonging to the stanza, but it is
       usually easier to add the field "Enabled: no" to the stanza to disable
       the entry. Removing the field or setting it to yes reenables it.

       Options have the same syntax as every other field: A fieldname separated by
       a colon (<literal>:</literal>) and optionally spaces from its value(s).
       Note especially that multiple values are separated by spaces, not by
       commas as in the one-line format. Multivalue fields like <literal>Architectures</literal>
       also have <literal>Architectures-Add</literal> and <literal>Architectures-Remove</literal>
       to modify the default value rather than replacing it.
   </para><para>
       This is a new format supported by apt itself since version 1.1. Previous
       versions ignore such files with a notice message as described earlier.
       It is intended to make this format gradually the default format,
       deprecating the previously described one-line-style format, as it is
       easier to create, extend and modify for humans and machines alike
       especially if a lot of sources and/or options are involved.

       Developers who are working with and/or parsing apt sources are highly
       encouraged to add support for this format and to contact the APT team
       to coordinate and share this work. Users can freely adopt this format
       already, but may encounter problems with software not supporting
       the format yet.
    </para>
 </refsect1>

 <refsect1><title>The deb and deb-src Types: General Format</title>
   <para>The <literal>deb</literal> type references a typical two-level Debian
   archive, <filename>distribution/component</filename>. The
   <literal>distribution</literal> is generally a suite name like
   <literal>stable</literal> or <literal>testing</literal> or a codename like
   <literal>&debian-stable-codename;</literal> or <literal>&debian-testing-codename;</literal>
   while component is one of <literal>main</literal>, <literal>contrib</literal> or
   <literal>non-free</literal>. The
   <literal>deb-src</literal> type references a Debian distribution's source
   code in the same form as the <literal>deb</literal> type.
   A <literal>deb-src</literal> line is required to fetch source indexes.</para>

   <para>The format for two one-line-style entries using the
   <literal>deb</literal> and <literal>deb-src</literal> types is:</para>

   <literallayout>deb [ option1=value1 option2=value2 ] uri suite [component1] [component2] [...]
deb-src [ option1=value1 option2=value2 ] uri suite [component1] [component2] [...]</literallayout>

   <para>Alternatively the equivalent entry in deb822 style looks like this:
   <literallayout>
     Types: deb deb-src
     URIs: uri
     Suites: suite
     Components: [component1] [component2] [...]
     option1: value1
     option2: value2
   </literallayout>
   </para>

   <para>The URI for the <literal>deb</literal> type must specify the base of the
   Debian distribution, from which APT will find the information it needs.
   <literal>suite</literal> can specify an exact path, in which case the
   components must be omitted and <literal>suite</literal> must end with
   a slash (<literal>/</literal>). This is useful for the case when only a
   particular sub-directory of the archive denoted by the URI is of interest.
   If <literal>suite</literal> does not specify an exact path, at least
   one <literal>component</literal> must be present.</para>

   <para><literal>suite</literal> may also contain a variable,
   <literal>$(ARCH)</literal>
   which expands to the Debian architecture (such as <literal>amd64</literal> or
   <literal>armel</literal>) used on the system. This permits architecture-independent
   <filename>sources.list</filename> files to be used. In general this is only
   of interest when specifying an exact path; <literal>APT</literal> will
   automatically generate a URI with the current architecture otherwise.</para>

   <para>Especially in the one-line-style format since only one distribution
      can be specified per line it may be necessary to have multiple lines for
      the same URI, if a subset of all available distributions or components at
      that location is desired.  APT will sort the URI list after it has
      generated a complete set internally, and will collapse multiple
      references to the same Internet host, for instance, into a single
      connection, so that it does not inefficiently establish a
      connection, close it, do something else, and then re-establish a
      connection to that same host. APT also parallelizes connections to
      different hosts to more effectively deal with sites with low
      bandwidth.</para>

   <para>It is important to list sources in order of preference, with the most
   preferred source listed first. Typically this will result in sorting
   by speed from fastest to slowest (CD-ROM followed by hosts on a local
   network, followed by distant Internet hosts, for example).</para>

   <para>As an example, the sources for your distribution could look like this
      in one-line-style format:
      <literallayout>&sourceslist-list-format;</literallayout> or like this in
      deb822 style format:
      <literallayout>&sourceslist-sources-format;</literallayout></para>
 </refsect1>

 <refsect1><title>The deb and deb-src types: Options</title>
    <para>Each source entry can have options specified to modify which source
       is accessed and how data is acquired from it. Format, syntax and names
       of the options vary between the one-line-style and deb822-style formats
       as described, but they both have the same options available. For simplicity
       we list the deb822 fieldname and provide the one-line name in brackets.
       Remember that besides setting multivalue options explicitly, there is also
       the option to modify them based on the default, but we aren't listing those
       names explicitly here. Unsupported options are silently ignored by all
       APT versions.

       <itemizedlist>
	  <listitem><para><option>Architectures</option>
		(<option>arch</option>) is a multivalue option defining for
		which architectures information should be downloaded. If this
		option isn't set the default is all architectures as defined by
		the <option>APT::Architectures</option> config option.
	  </para></listitem>

	  <listitem><para><option>Languages</option>
		(<option>lang</option>) is a multivalue option defining for
		which languages information such as translated package
		descriptions should be downloaded.  If this option isn't set
		the default is all languages as defined by the
		<option>Acquire::Languages</option> config option.
	  </para></listitem>

	  <listitem><para><option>Targets</option>
		(<option>target</option>) is a multivalue option defining
		which download targets apt will try to acquire from this
		source. If not specified, the default set is defined by the
		<option>Acquire::IndexTargets</option> configuration scope.
		Additionally, specific targets can be enabled or disabled by
		using the identifier as field name instead of using this
		multivalue option.
	  </para></listitem>

	  <listitem><para><option>PDiffs</option> (<option>pdiffs</option>)
		is a yes/no value which controls if APT should try to use PDiffs
		to update old indexes instead of downloading the new indexes
		entirely. The value of this option is ignored if the repository
		doesn't announce the availability of PDiffs.  Defaults to the
		value of the option with the same name for a specific index file
		defined in the <option>Acquire::IndexTargets</option> scope,
		which itself defaults to the value of configuration option
		<option>Acquire::PDiffs</option> which defaults to
		<literal>yes</literal>.
	  </para></listitem>

	  <listitem><para><option>By-Hash</option> (<option>by-hash</option>)
		can have the value <literal>yes</literal>, <literal>no</literal>
		or <literal>force</literal> and controls if APT should try to
		acquire indexes via a URI constructed from a hashsum of the
		expected file instead of using the well-known stable filename
		of the index. Using this can avoid hashsum mismatches, but
		requires a supporting mirror. A <literal>yes</literal> or
		<literal>no</literal> value activates/disables the use of this
		feature if this source indicates support for it, while
		<literal>force</literal> will enable the feature regardless of
		what the source indicates. Defaults to the value of the option
		of the same name for a specific index file defined in the
		<option>Acquire::IndexTargets</option> scope, which itself
		defaults to the value of configuration option
		<option>Acquire::By-Hash</option> which defaults to
		<literal>yes</literal>.
	  </para></listitem>

       </itemizedlist>

       Furthermore, there are options which if set affect
       <emphasis>all</emphasis> sources with the same URI and Suite, so they
       have to be set on all such entries and can not be varied between
       different components. APT will try to detect and error out on such
       anomalies.

       <itemizedlist>
	  <listitem><para><option>Trusted</option> (<option>trusted</option>)
		is a tri-state value which defaults to APT deciding if a source
		is considered trusted or if warnings should be raised before e.g.
		packages are installed from this source. This option can be used
		to override that decision. The value <literal>yes</literal> tells APT
		always to consider this source as trusted, even if it doesn't pass
		authentication checks. It disables parts of &apt-secure;, and should
		therefore only be used in a local and trusted context (if at all) as
		otherwise security is breached. The value <literal>no</literal> does
		the opposite, causing the source to be handled as untrusted even if
		the authentication checks passed successfully. The default value can't
		be set explicitly.
	  </para></listitem>

	  <listitem><para><option>Signed-By</option> (<option>signed-by</option>)
		is either an absolute path to a keyring file (has to be
		accessible and readable for the <literal>_apt</literal> user,
		so ensure everyone has read-permissions on the file) or a
		fingerprint of a key either in the
		<filename>trusted.gpg</filename> keyring or in one of the
		keyrings in the <filename>trusted.gpg.d/</filename> directory
		(see <command>apt-key fingerprint</command>). If the option is
		set, only the key(s) in this keyring or only the key with this
		fingerprint is used for the &apt-secure; verification of this
		repository. Otherwise all keys in the trusted keyrings are
		considered valid signers for this repository.
	  </para></listitem>

	  <listitem><para><option>Check-Valid-Until</option> (<option>check-valid-until</option>)
		is a yes/no value which controls if APT should try to detect
		replay attacks. A repository creator can declare a time until
		which the data provided in the repository should be considered valid,
		and if this time is reached, but no new data is provided, the data
		is considered expired and an error is raised.  Besides
		increasing security, as a malicious attacker can't send old data
		forever to prevent a user from upgrading to a new version,
		this also helps users identify mirrors which are no longer
		updated. However, some repositories such as historic archives
		are not updated any more by design, so this check can be
		disabled by setting this option to <literal>no</literal>.
		Defaults to the value of configuration option
		<option>Acquire::Check-Valid-Until</option> which itself
		defaults to <literal>yes</literal>.
	  </para></listitem>

	  <listitem><para><option>Valid-Until-Min</option>
		(<option>valid-until-min</option>) and
		<option>Valid-Until-Max</option>
		(<option>valid-until-max</option>) can be used to raise or
		lower the time period in seconds in which the data from this
		repository is considered valid. -Max can be especially useful
		if the repository provides no Valid-Until field on its Release
		file to set your own value, while -Min can be used to increase
		the valid time on seldom updated (local) mirrors of a more
		frequently updated but less accessible archive (which is in the
		sources.list as well) instead of disabling the check entirely.
		Default to the value of the configuration options
		<option>Acquire::Min-ValidTime</option> and
		<option>Acquire::Max-ValidTime</option> which are both unset by
		default.
	  </para></listitem>

       </itemizedlist>

    </para>
 </refsect1>

 <refsect1><title>URI Specification</title>

    <para>The currently recognized URI types are:
   <variablelist>
    <varlistentry><term><command>file</command></term>
    <listitem><para>
    The file scheme allows an arbitrary directory in the file system to be
    considered an archive. This is useful for NFS mounts and local mirrors or
    archives.</para></listitem>
    </varlistentry>
    
    <varlistentry><term><command>cdrom</command></term>
    <listitem><para>
    The cdrom scheme allows APT to use a local CD-ROM drive with media
    swapping. Use the &apt-cdrom; program to create cdrom entries in the
    source list.</para></listitem>
    </varlistentry>

    <varlistentry><term><command>http</command></term>
    <listitem><para>
    The http scheme specifies an HTTP server for the archive. If an environment
    variable <envar>http_proxy</envar> is set with the format 
    http://server:port/, the proxy server specified in
    <envar>http_proxy</envar> will be used. Users of authenticated
    HTTP/1.1 proxies may use a string of the format
    http://user:pass@server:port/.
    Note that this is an insecure method of authentication.</para></listitem>
    </varlistentry>

    <varlistentry><term><command>ftp</command></term>
    <listitem><para>
    The ftp scheme specifies an FTP server for the archive. APT's FTP behavior
    is highly configurable; for more information see the
    &apt-conf; manual page. Please note that an FTP proxy can be specified
    by using the <envar>ftp_proxy</envar> environment variable. It is possible
    to specify an HTTP proxy (HTTP proxy servers often understand FTP URLs)
    using this environment variable and <emphasis>only</emphasis> this
    environment variable. Proxies using HTTP specified in
    the configuration file will be ignored.</para></listitem>
    </varlistentry>

    <varlistentry><term><command>copy</command></term>
    <listitem><para>
    The copy scheme is identical to the file scheme except that packages are
    copied into the cache directory instead of used directly at their location.
    This is useful for people using removable media to copy files around with APT.</para></listitem>
    </varlistentry>
    
    <varlistentry><term><command>rsh</command></term><term><command>ssh</command></term>
    <listitem><para>
    The rsh/ssh method invokes RSH/SSH to connect to a remote host and
    access the files as a given user. Prior configuration of rhosts or RSA keys
    is recommended. The standard <command>find</command> and <command>dd</command>
    commands are used to perform the file transfers from the remote host.
    </para></listitem>
    </varlistentry>

    <varlistentry><term>adding more recognizable URI types</term>
    <listitem><para>
    APT can be extended with more methods shipped in other optional packages, which should
    follow the naming scheme <package>apt-transport-<replaceable>method</replaceable></package>.
    For instance, the APT team also maintains the package <package>apt-transport-https</package>,
    which provides access methods for HTTPS URIs with features similar to the http method.
    Methods for using e.g. debtorrent are also available - see &apt-transport-debtorrent;.
    </para></listitem>
    </varlistentry>
  </variablelist>
 </para>
 </refsect1>

 <refsect1><title>Examples</title>
   <para>Uses the archive stored locally (or NFS mounted) at /home/apt/debian
   for stable/main, stable/contrib, and stable/non-free.</para>
   <literallayout>deb file:/home/apt/debian stable main contrib non-free</literallayout>
   <literallayout>Types: deb
URIs: file:/home/apt/debian
Suites: stable
Components: main contrib non-free</literallayout>

   <para>As above, except this uses the unstable (development) distribution.</para>
   <literallayout>deb file:/home/apt/debian unstable main contrib non-free</literallayout>
   <literallayout>Types: deb
URIs: file:/home/apt/debian
Suites: unstable
Components: main contrib non-free</literallayout>

   <para>Sources specification for the above.</para>
   <literallayout>deb-src file:/home/apt/debian unstable main contrib non-free</literallayout>
   <literallayout>Types: deb-src
URIs: file:/home/apt/debian
Suites: unstable
Components: main contrib non-free</literallayout>

   <para>The first line gets package information for the architectures in <literal>APT::Architectures</literal>
   while the second always retrieves <literal>amd64</literal> and <literal>armel</literal>.</para>
   <literallayout>deb http://httpredir.debian.org/debian &debian-stable-codename; main
deb [ arch=amd64,armel ] http://httpredir.debian.org/debian &debian-stable-codename; main</literallayout>
   <literallayout>Types: deb
URIs: http://httpredir.debian.org/debian
Suites: &debian-stable-codename;
Components: main

Types: deb
URIs: http://httpredir.debian.org/debian
Suites: &debian-stable-codename;
Components: main
Architectures: amd64 armel
</literallayout>

   <para>Uses HTTP to access the archive at archive.debian.org, and uses only
   the hamm/main area.</para>
   <literallayout>deb http://archive.debian.org/debian-archive hamm main</literallayout>
   <literallayout>Types: deb
URIs: http://archive.debian.org/debian-archive
Suites: hamm
Components: main</literallayout>

   <para>Uses FTP to access the archive at ftp.debian.org, under the debian
   directory, and uses only the &debian-stable-codename;/contrib area.</para>
   <literallayout>deb ftp://ftp.debian.org/debian &debian-stable-codename; contrib</literallayout>
   <literallayout>Types: deb
URIs: ftp://ftp.debian.org/debian
Suites: &debian-stable-codename;
Components: contrib</literallayout>

   <para>Uses FTP to access the archive at ftp.debian.org, under the debian
   directory, and uses only the unstable/contrib area. If this line appears as
   well as the one in the previous example in <filename>sources.list</filename>
   a single FTP session will be used for both resource lines.</para>
   <literallayout>deb ftp://ftp.debian.org/debian unstable contrib</literallayout>
   <literallayout>Types: deb
URIs: ftp://ftp.debian.org/debian
Suites: unstable
Components: contrib</literallayout>

   <para>Uses HTTP to access the archive at ftp.tlh.debian.org, under the
   universe directory, and uses only files found under
   <filename>unstable/binary-i386</filename> on i386 machines,
   <filename>unstable/binary-amd64</filename> on amd64, and so
   forth for other supported architectures. [Note this example only
   illustrates how to use the substitution variable; official debian
   archives are not structured like this]
   <literallayout>deb http://ftp.tlh.debian.org/universe unstable/binary-$(ARCH)/</literallayout>
   <literallayout>Types: deb
URIs: http://ftp.tlh.debian.org/universe
Suites: unstable/binary-$(ARCH)/</literallayout>
   </para>

   <para>Uses HTTP to get binary packages as well as sources from the stable, testing and unstable
      suites and the components main and contrib.</para>
   <literallayout>deb http://httpredir.debian.org/debian stable main contrib
deb-src http://httpredir.debian.org/debian stable main contrib
deb http://httpredir.debian.org/debian testing main contrib
deb-src http://httpredir.debian.org/debian testing main contrib
deb http://httpredir.debian.org/debian unstable main contrib
deb-src http://httpredir.debian.org/debian unstable main contrib</literallayout>
   <literallayout>Types: deb deb-src
URIs: http://httpredir.debian.org/debian
Suites: stable testing unstable
Components: main contrib
</literallayout>

 </refsect1>

 <refsect1><title>See Also</title>
   <para>&apt-get;, &apt-conf;
   </para>
 </refsect1>

 &manbugs;

</refentry>