apt-transport-mirror(1)



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 stretch 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 stretch 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 1.6.4                      09 December 2017          APT-TRANSPORT-MIRR(1)

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