Ubuntu Manpage: sources.list - List of configured APT data sources

NAME

       sources.list - List of configured APT data sources

DESCRIPTION

       The source list /etc/apt/sources.list and the files contained in /etc/apt/sources.list.d/
       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 apt-get update (or by an equivalent command
       from another APT front-end).

SOURCES.LIST.D

       The /etc/apt/sources.list.d 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 .list or .sources 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
       Dir::Ignore-Files-Silently configuration list - in which case it will be silently ignored.

ONE-LINE-STYLE FORMAT

       Files in this format have the extension .list. Each line specifying a source starts with a
       type (e.g.  deb-src) followed by options and arguments for this type. Individual entries
       cannot be continued onto a following line. Empty lines are ignored, and a # 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 ([]) 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 (,). An option name is separated
       from its value(s) by an equals sign (=). Multivalue options also have -= and += 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.

       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.

DEB822-STYLE FORMAT

Files in this format have the extension .sources. 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 debian/control file in a Debian source
package. Individual entries are separated by an empty line; additional empty lines are
ignored, and a # 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 re-enables it. Options have the same syntax as every other
field: A field name separated by a colon (:) and optionally spaces from its value(s). Note
especially that multiple values are separated by whitespaces (like spaces, tabs and
newlines), not by commas as in the one-line format. Multivalue fields like Architectures
also have Architectures-Add and Architectures-Remove to modify the default value rather
than replacing it.

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.

THE DEB AND DEB-SRC TYPES: GENERAL FORMAT

       The deb type references a typical two-level Debian archive, distribution/component. The
       distribution is generally a suite name like stable or testing or a codename like buster or
       bullseye while component is one of main, contrib or non-free. The deb-src type references
       a Debian distribution's source code in the same form as the deb type. A deb-src line is
       required to fetch source indexes.

       The format for two one-line-style entries using the deb and deb-src types is:

           deb [ option1=value1 option2=value2 ] uri suite [component1] [component2] [...]
           deb-src [ option1=value1 option2=value2 ] uri suite [component1] [component2] [...]

       Alternatively the equivalent entry in deb822 style looks like this:

                Types: deb deb-src
                URIs: uri
                Suites: suite
                Components: [component1] [component2] [...]
                option1: value1
                option2: value2

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

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

       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.

       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).

       As an example, the sources for your distribution could look like this in one-line-style
       format:

           deb http://us.archive.ubuntu.com/ubuntu focal main restricted
           deb http://security.ubuntu.com/ubuntu focal-security main restricted
           deb http://us.archive.ubuntu.com/ubuntu focal-updates main restricted

       or like this in deb822 style format:

           Types: deb
           URIs: http://us.archive.ubuntu.com/ubuntu
           Suites: focal focal-updates
           Components: main restricted

           Types: deb
           URIs: http://security.ubuntu.com/ubuntu
           Suites: focal-security
           Components: main restricted

THE DEB AND DEB-SRC TYPES: OPTIONS

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 field name 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.

• Architectures (arch) 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 APT::Architectures config option.

• Languages (lang) 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 Acquire::Languages config option.

• Targets (target) 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
Acquire::IndexTargets configuration scope (targets are specified by their name in the
Created-By field). Additionally, targets can be enabled or disabled by using the
Identifier field as an option with a boolean value instead of using this multivalue
option.

• PDiffs (pdiffs) 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 Acquire::IndexTargets scope, which itself defaults to the value of
configuration option Acquire::PDiffs which defaults to yes.

• By-Hash (by-hash) can have the value yes, no or force 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 yes or no value activates/disables the
use of this feature if this source indicates support for it, while force 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 Acquire::IndexTargets
scope, which itself defaults to the value of configuration option Acquire::By-Hash
which defaults to yes.

Furthermore, there are options which if set affect all 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.

• Allow-Insecure (allow-insecure), Allow-Weak (allow-weak) and
Allow-Downgrade-To-Insecure (allow-downgrade-to-insecure) are boolean values which all
default to no. If set to yes they circumvent parts of apt-secure(8) and should
therefore not be used lightly!

• Trusted (trusted) 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 yes
tells APT always to consider this source as trusted, even if it doesn't pass
authentication checks. It disables parts of apt-secure(8), and should therefore only
be used in a local and trusted context (if at all) as otherwise security is breached.
The value no 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.

• Signed-By (signed-by) is an option to require a repository to pass apt-secure(8)
verification with a certain set of keys rather than all trusted keys apt has
configured. It is specified as a list of absolute paths to keyring files (have to be
accessible and readable for the _apt system user, so ensure everyone has
read-permissions on the file) and fingerprints of keys to select from these keyrings.
If no keyring files are specified the default is the trusted.gpg keyring and all
keyrings in the trusted.gpg.d/ directory (see apt-key fingerprint). If no fingerprint
is specified all keys in the keyrings are selected. A fingerprint will accept also all
signatures by a subkey of this key, if this isn't desired an exclamation mark (!) can
be appended to the fingerprint to disable this behaviour. The option defaults to the
value of the option with the same name if set in the previously acquired Release file
of this repository (only fingerprints can be specified there through). Otherwise all
keys in the trusted keyrings are considered valid signers for this repository.

• Check-Valid-Until (check-valid-until) 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 no. Defaults to the value of configuration option
Acquire::Check-Valid-Until which itself defaults to yes.

• Valid-Until-Min (valid-until-min) and Valid-Until-Max (valid-until-max) 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
Acquire::Min-ValidTime and Acquire::Max-ValidTime which are both unset by default.

• Check-Date (check-date) is a yes/no value which controls if APT should consider the
machine's time correct and hence perform time related checks, such as verifying that a
Release file is not from the future. Disabling it also disables the Check-Valid-Until
option mentioned above.

• Date-Max-Future (date-max-future) controls how far from the future a repository may
be. Default to the value of the configuration option Acquire::Max-FutureTime which is
10 seconds by default.

• InRelease-Path (inrelease-path) determines the path to the InRelease file, relative to
the normal position of an InRelease file. By default, this option is unset and APT
will try to fetch an InRelease or, if that fails, a Release file and its associated
Release.gpg file. By setting this option, the specified path will be tried instead of
the InRelease file, and the fallback to Release files will be disabled.

• Snapshot (snapshot) allows selecting an earlier version of the archive from the
snapshot service. Supported values are:

• enable to allow selecting a snapshot with the --snapshot option, or

• a snapshot ID to select a specific snapshot.

Snapshot IDs are usually timestamps in the form of YYYYMMDDTHHMMSSZ, such as
20220102T030405Z which is the January 2nd, 2022 at 03:04:05 UTC, servers may however
support additional types of IDs, and APT does not perform any checks so far.

URI SPECIFICATION

The currently recognized URI types are:

http (apt-transport-http(1))
The http scheme specifies an HTTP server for an archive and is the most commonly used
method. The URI can directly include login information if the archive requires it, but
the use of apt_auth.conf(5) should be preferred. The method also supports SOCKS5 and
HTTP(S) proxies either configured via apt-specific configuration or specified by the
environment variable http_proxy in the format (assuming an HTTP proxy requiring
authentication) http://user:pass@server:port/. The authentication details for proxies
can also be supplied via apt_auth.conf(5).

Note that these forms of authentication are insecure as the whole communication with
the remote server (or proxy) is not encrypted so a sufficiently capable attacker can
observe and record login as well as all other interactions. The attacker can not
modify the communication through as APT's data security model is independent of the
chosen transport method. See apt-secure(8) for details.

https (apt-transport-https(1))
The https scheme specifies an HTTPS server for an archive and is very similar in use
and available options to the http scheme. The main difference is that the
communication between apt and server (or proxy) is encrypted. Note that the encryption
does not prevent an attacker from knowing which server (or proxy) apt is communicating
with and deeper analysis can potentially still reveal which data was downloaded. If
this is a concern the Tor-based schemes mentioned further below might be a suitable
alternative.

mirror, mirror+scheme (apt-transport-mirror(1))
The mirror scheme specifies the location of a mirrorlist. By default the scheme used
for the location is http, but any other scheme can be used via mirror+scheme. The
mirrorlist itself can contain many different URIs for mirrors the APT client can
transparently pick, choose and fallback between intended to help both with
distributing the load over the available mirrors and ensuring that clients can acquire
data even if some configured mirrors are not available.

file
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.

cdrom
The cdrom scheme allows APT to use a local CD-ROM, DVD or USB drive with media
swapping. Use the apt-cdrom(8) program to create cdrom entries in the source list.

ftp
The ftp scheme specifies an FTP server for an archive. Use of FTP is on the decline in
favour of http and https and many archives either never offered or are retiring FTP
access. If you still need this method many configuration options for it are available
in the Acquire::ftp scope and detailed in apt.conf(5).

Please note that an FTP proxy can be specified by using the ftp_proxy environment
variable. It is possible to specify an HTTP proxy (HTTP proxy servers often understand
FTP URLs) using this environment variable and only this environment variable. Proxies
using HTTP specified in the configuration file will be ignored.

copy
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.

rsh, ssh
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
find and dd commands are used to perform the file transfers from the remote host.

adding more recognizable URI types
APT can be extended with more methods shipped in other optional packages, which should
follow the naming scheme apt-transport-method. For instance, the APT team also
maintains the package apt-transport-tor, which provides access methods for HTTP and
HTTPS URIs routed via the Tor network.

EXAMPLES

       Uses the archive stored locally (or NFS mounted) at /home/apt/debian for stable/main,
       stable/contrib, and stable/non-free.

           deb file:/home/apt/debian stable main contrib non-free

           Types: deb
           URIs: file:/home/apt/debian
           Suites: stable
           Components: main contrib non-free

       As above, except this uses the unstable (development) distribution.

           deb file:/home/apt/debian unstable main contrib non-free

           Types: deb
           URIs: file:/home/apt/debian
           Suites: unstable
           Components: main contrib non-free

       Sources specification for the above.

           deb-src file:/home/apt/debian unstable main contrib non-free

           Types: deb-src
           URIs: file:/home/apt/debian
           Suites: unstable
           Components: main contrib non-free

       The first line gets package information for the architectures in APT::Architectures while
       the second always retrieves amd64 and armel.

           deb http://deb.debian.org/debian buster main
           deb [ arch=amd64,armel ] http://deb.debian.org/debian buster main

           Types: deb
           URIs: http://deb.debian.org/debian
           Suites: buster
           Components: main

           Types: deb
           URIs: http://deb.debian.org/debian
           Suites: buster
           Components: main
           Architectures: amd64 armel

       Uses HTTP to access the archive at archive.debian.org, and uses only the hamm/main area.

           deb http://archive.debian.org/debian-archive hamm main

           Types: deb
           URIs: http://archive.debian.org/debian-archive
           Suites: hamm
           Components: main

       Uses FTP to access the archive at ftp.debian.org, under the debian directory, and uses
       only the buster/contrib area.

           deb ftp://ftp.debian.org/debian buster contrib

           Types: deb
           URIs: ftp://ftp.debian.org/debian
           Suites: buster
           Components: contrib

       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 sources.list a single FTP session will be used for both resource lines.

           deb ftp://ftp.debian.org/debian unstable contrib

           Types: deb
           URIs: ftp://ftp.debian.org/debian
           Suites: unstable
           Components: contrib

       Uses HTTP to access the archive at ftp.tlh.debian.org, under the universe directory, and
       uses only files found under unstable/binary-i386 on i386 machines, unstable/binary-amd64
       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]

           deb http://ftp.tlh.debian.org/universe unstable/binary-$(ARCH)/

           Types: deb
           URIs: http://ftp.tlh.debian.org/universe
           Suites: unstable/binary-$(ARCH)/

       Uses HTTP to get binary packages as well as sources from the stable, testing and unstable
       suites and the components main and contrib.

           deb http://deb.debian.org/debian stable main contrib
           deb-src http://deb.debian.org/debian stable main contrib
           deb http://deb.debian.org/debian testing main contrib
           deb-src http://deb.debian.org/debian testing main contrib
           deb http://deb.debian.org/debian unstable main contrib
           deb-src http://deb.debian.org/debian unstable main contrib

           Types: deb deb-src
           URIs: http://deb.debian.org/debian
           Suites: stable testing unstable
           Components: main contrib

BUGS

       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.

AUTHORS

       Jason Gunthorpe

       APT team

NOTES

        1. APT bug page
           http://bugs.debian.org/src:apt