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APT-TRANSPORT-MIRR(1) APT APT-TRANSPORT-MIRR(1)
NAME
apt-transport-mirror - APT transport for more automated mirror selection
DESCRIPTION
This APT transport isn't implementing a protocol to access local or remote repositories on
its own, but acquires a mirrorlist and redirects all requests to the mirror(s) picked from
this list, accessing them via other transports like apt-transport-http(1). The basic
functionality has been available since apt 0.7.24, but was undocumented until apt 1.6
which contained a complete rework of the transport and its supported features. Note that a
transport is never called directly by a user but used by APT tools based on user
configuration.
If the acquisition of a file via a mirror fails, the method ensures that another possible
mirror from the list is automatically tried until either the file is retrieved or no
mirror is left in the list, transparently handling server downtimes and similar problems.
The security implications of the transport depend on the security considerations
associated with the transport used to acquire the mirrorlist and the transports involved
in accessing the chosen mirror(s) by the transport.
OPTIONS
This transport has no configuration options at present. The mirror selection is based
entirely on the mirrors offered in the mirrorlist and the files APT needs to acquire.
Mirrorlist format
A mirrorlist contains one or more lines each specifying a URI for a mirror. Empty lines
and those starting with a hash character (#) are ignored. A URI always starts with a URI
scheme which defines the transport used for this mirror. If for example the URI starts
with http:, the responsible transport is apt-transport-http(1) which might have specific
requirements for the format of the remaining part of the URI.
Metadata about a mirror can be given on the same line, separated from the URI by a tab.
Multiple items of metadata can themselves be separated by either tabs or spaces. (This is
an advanced feature only available with apt >= 1.6. Earlier apt versions will fail to
parse mirrorlists using this feature.)
Since apt 1.6 the use of compressed mirrorlists is also supported. Note that the filename
of the mirrorlist must specify the compression algorithm used; there is no auto-detection
based on file contents.
Mirror selection by metadata
As specified in the format, a mirror can have additional metadata attached to prevent a
mirror from being selected for acquiring a file not matching this metadata. This way the
mirrorlist can e.g. contain partial mirrors serving only certain architectures and APT
will automatically choose a different mirror for files requiring an unlisted architecture.
Supported are limits for the architecture (arch), codename of the release (codename),
component of the repository the file is in (component), language the file applies to
(lang), suite name of the release (suite) and type of the file (type).
Fallback order for mirrors
If no priority is given for a mirror via the metadata key priority, the order in which
mirrors are contacted is random. If a certain set of mirrors should be tried first before
any of another set is tried, a priority can be explicitly set. The mirrors with the lowest
number are tried first. Mirrors which have no explicit priority set default to the highest
possible number and are therefore tried last. The choice between mirrors with the same
priority is again random.
Allowed transports in a mirrorlist
The availability and choice of transports in a mirrorlist is limited by how the APT client
is accessing the mirrorlist. If a local transport like file or copy is used, the
mirrorlist can also include local sources, while a mirrorlist accessed via http can not.
Additionally, a mirrorlist can not contain a mirrorlist or other wrapping transports (like
apt-transport-tor). See the documentation of these transports on how to use them with the
mirror method.
Note that apt versions before 1.6 do not support any other transport than http.
EXAMPLES
Basic example
A basic mirrorlist example supported by all apt versions with a mirror method (>= 0.7.24)
in which the client will pick any of the three mirrors:
http://ftp.de.debian.org/debian/
http://ftp.us.debian.org/debian/
http://deb.debian.org/debian/
Assuming a file with this content is stored as /etc/apt/mirrorlist.txt on your machine it
can be used like this in sources.list(5) (since apt 1.6):
deb mirror+file:/etc/apt/mirrorlist.txt bullseye main
All versions of the mirror method support a mirrorlist accessible via HTTP, so assuming it
is available at http://apt.example.org/mirror.lst the sources.list entry from above could
instead be written as:
deb mirror://apt.example.org/mirror.lst bullseye main
Note that since apt 1.6 the use of mirror+http should be preferred over mirror for
uniformity. The functionality is the same.
Example with metadata-enhanced mirror selection
As explained in the format definition apt versions before 1.6 do not support this and will
fail parsing the mirrorlist. The example mirrorlist is intentionally complicated to show
some aspects of the selection. The following setup is assumed: The first mirror is a local
mirror accessible via the file method, but potentially incomplete. The second mirror has a
great connection, but is a partial mirror insofar as it only contains files related to the
architectures amd64 and all. The remaining mirrors are average mirrors which should be
contacted only if the earlier ones didn't work.
file:/srv/local/debian/mirror/ priority:1 type:index
http://partial.example.org/mirror/ priority:2 arch:amd64 arch:all type:deb
http://ftp.us.debian.org/debian/ type:deb
http://ftp.de.debian.org/debian/ type:deb
https://deb.debian.org/debian/
In this setup with this mirrorlist the first mirror will be used to download all index
files assuming the mirrorlist itself is accessed via a local transport like file. If it
isn't, if the mirror is otherwise inaccessible or if it does not contain the requested
file another mirror will be used to acquire the file, chosen depending on the type of the
file: An index file will be served by the last mirror in the list, while a package of
architecture amd64 is served by the second and those of e.g. architecture i386 by one of
the last three.
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.
AUTHOR
APT team
NOTES
1. APT bug page
http://bugs.debian.org/src:apt
APT 2.4.13 09 December 2017 APT-TRANSPORT-MIRR(1)
Generated by $Id: phpMan.php,v 4.55 2007/09/05 04:42:51 chedong Exp $ Author: Che Dong
On Apache
Under GNU General Public License
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