update-alternatives(1) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | TERMINOLOGY | COMMANDS | OPTIONS | EXIT STATUS | ENVIRONMENT | FILES | QUERY FORMAT | DIAGNOSTICS | EXAMPLES | SEE ALSO | COLOPHON

update-alternatives(1)         dpkg suite         update-alternatives(1)

NAME         top

       update-alternatives - maintain symbolic links determining default
       commands

SYNOPSIS         top

       update-alternatives [option...] command

DESCRIPTION         top

       update-alternatives creates, removes, maintains and displays
       information about the symbolic links comprising the alternatives
       system.

       It is possible for several programs fulfilling the same or
       similar functions to be installed on a single system at the same
       time.  For example, many systems have several text editors
       installed at once.  This gives choice to the users of a system,
       allowing each to use a different editor, if desired, but makes it
       difficult for a program to make a good choice for an editor to
       invoke if the user has not specified a particular preference.

       The alternatives system aims to solve this problem.  A generic
       name in the filesystem is shared by all files providing
       interchangeable functionality.  The alternatives system and the
       system administrator together determine which actual file is
       referenced by this generic name.  For example, if the text
       editors ed(1) and nvi(1) are both installed on the system, the
       alternatives system will cause the generic name /usr/bin/editor
       to refer to /usr/bin/nvi by default. The system administrator can
       override this and cause it to refer to /usr/bin/ed instead, and
       the alternatives system will not alter this setting until
       explicitly requested to do so.

       The generic name is not a direct symbolic link to the selected
       alternative.  Instead, it is a symbolic link to a name in the
       alternatives directory, which in turn is a symbolic link to the
       actual file referenced.  This is done so that the system
       administrator's changes can be confined within the /usr/local/etc
       directory: the FHS (q.v.) gives reasons why this is a Good Thing.

       When each package providing a file with a particular
       functionality is installed, changed or removed, update-
       alternatives is called to update information about that file in
       the alternatives system.  update-alternatives is usually called
       from the following Debian package maintainer scripts, postinst
       (configure) to install the alternative and from prerm and postrm
       (remove) to remove the alternative.  Note: in most (if not all)
       cases no other maintainer script actions should call update-
       alternatives, in particular neither of upgrade nor disappear, as
       any other such action can lose the manual state of an
       alternative, or make the alternative temporarily flip-flop, or
       completely switch when several of them have the same priority.

       It is often useful for a number of alternatives to be
       synchronized, so that they are changed as a group; for example,
       when several versions of the vi(1) editor are installed, the
       manual page referenced by /usr/share/man/man1/vi.1 should
       correspond to the executable referenced by /usr/bin/vi.  update-
       alternatives handles this by means of master and slave links;
       when the master is changed, any associated slaves are changed
       too.  A master link and its associated slaves make up a link
       group.

       Each link group is, at any given time, in one of two modes:
       automatic or manual.  When a group is in automatic mode, the
       alternatives system will automatically decide, as packages are
       installed and removed, whether and how to update the links.  In
       manual mode, the alternatives system will retain the choice of
       the administrator and avoid changing the links (except when
       something is broken).

       Link groups are in automatic mode when they are first introduced
       to the system.  If the system administrator makes changes to the
       system's automatic settings, this will be noticed the next time
       update-alternatives is run on the changed link's group, and the
       group will automatically be switched to manual mode.

       Each alternative has a priority associated with it.  When a link
       group is in automatic mode, the alternatives pointed to by
       members of the group will be those which have the highest
       priority.

       When using the --config option, update-alternatives will list all
       of the choices for the link group of which given name is the
       master alternative name.  The current choice is marked with a
       ‘*’.  You will then be prompted for your choice regarding this
       link group.  Depending on the choice made, the link group might
       no longer be in auto mode. You will need to use the --auto option
       in order to return to the automatic mode (or you can rerun
       --config and select the entry marked as automatic).

       If you want to configure non-interactively you can use the --set
       option instead (see below).

       Different packages providing the same file need to do so
       cooperatively.  In other words, the usage of update-alternatives
       is mandatory for all involved packages in such case. It is not
       possible to override some file in a package that does not employ
       the update-alternatives mechanism.

TERMINOLOGY         top

       Since the activities of update-alternatives are quite involved,
       some specific terms will help to explain its operation.

       generic name (or alternative link)
           A name, like /usr/bin/editor, which refers, via the
           alternatives system, to one of a number of files of similar
           function.

       alternative name
           The name of a symbolic link in the alternatives directory.

       alternative (or alternative path)
           The name of a specific file in the filesystem, which may be
           made accessible via a generic name using the alternatives
           system.

       alternatives directory
           A directory, by default /usr/local/etc/alternatives,
           containing the symlinks.

       administrative directory
           A directory, by default /usr/local/var/lib/dpkg/alternatives,
           containing update-alternatives' state information.

       link group
           A set of related symlinks, intended to be updated as a group.

       master link
           The alternative link in a link group which determines how the
           other links in the group are configured.

       slave link
           An alternative link in a link group which is controlled by
           the setting of the master link.

       automatic mode
           When a link group is in automatic mode, the alternatives
           system ensures that the links in the group point to the
           highest priority alternative appropriate for the group.

       manual mode
           When a link group is in manual mode, the alternatives system
           will not make any changes to the system administrator's
           settings.

COMMANDS         top

       --install link name path priority [--slave link name path]...
           Add a group of alternatives to the system.  link is the
           generic name for the master link, name is the name of its
           symlink in the alternatives directory, and path is the
           alternative being introduced for the master link.  The
           arguments after --slave are the generic name, symlink name in
           the alternatives directory and the alternative path for a
           slave link.  Zero or more --slave options, each followed by
           three arguments, may be specified. Note that the master
           alternative must exist or the call will fail. However if a
           slave alternative doesn't exist, the corresponding slave
           alternative link will simply not be installed (a warning will
           still be displayed). If some real file is installed where an
           alternative link has to be installed, it is kept unless
           --force is used.

           If the alternative name specified exists already in the
           alternatives system's records, the information supplied will
           be added as a new set of alternatives for the group.
           Otherwise, a new group, set to automatic mode, will be added
           with this information.  If the group is in automatic mode,
           and the newly added alternatives' priority is higher than any
           other installed alternatives for this group, the symlinks
           will be updated to point to the newly added alternatives.

       --set name path
           Set the program path as alternative for name.  This is
           equivalent to --config but is non-interactive and thus
           scriptable.

       --remove name path
           Remove an alternative and all of its associated slave links.
           name is a name in the alternatives directory, and path is an
           absolute filename to which name could be linked. If name is
           indeed linked to path, name will be updated to point to
           another appropriate alternative (and the group is put back in
           automatic mode), or removed if there is no such alternative
           left.  Associated slave links will be updated or removed,
           correspondingly.  If the link is not currently pointing to
           path, no links are changed; only the information about the
           alternative is removed.

       --remove-all name
           Remove all alternatives and all of their associated slave
           links.  name is a name in the alternatives directory.

       --all
           Call --config on all alternatives. It can be usefully
           combined with --skip-auto to review and configure all
           alternatives which are not configured in automatic mode.
           Broken alternatives are also displayed.  Thus a simple way to
           fix all broken alternatives is to call yes '' | update-
           alternatives --force --all.

       --auto name
           Switch the link group behind the alternative for name to
           automatic mode.  In the process, the master symlink and its
           slaves are updated to point to the highest priority installed
           alternatives.

       --display name
           Display information about the link group.  Information
           displayed includes the group's mode (auto or manual), the
           master and slave links, which alternative the master link
           currently points to, what other alternatives are available
           (and their corresponding slave alternatives), and the highest
           priority alternative currently installed.

       --get-selections
           List all master alternative names (those controlling a link
           group) and their status (since version 1.15.0).  Each line
           contains up to 3 fields (separated by one or more spaces).
           The first field is the alternative name, the second one is
           the status (either auto or manual), and the last one contains
           the current choice in the alternative (beware: it's a
           filename and thus might contain spaces).

       --set-selections
           Read configuration of alternatives on standard input in the
           format generated by --get-selections and reconfigure them
           accordingly (since version 1.15.0).

       --query name
           Display information about the link group like --display does,
           but in a machine parseable way (since version 1.15.0, see
           section "QUERY FORMAT" below).

       --list name
           Display all targets of the link group.

       --config name
           Show available alternatives for a link group and allow the
           user to interactively select which one to use. The link group
           is updated.

       --help
           Show the usage message and exit.

       --version
           Show the version and exit.

OPTIONS         top

       --altdir directory
           Specifies the alternatives directory, when this is to be
           different from the default.  Defaults to
           «/usr/local/etc/alternatives».

       --admindir directory
           Specifies the administrative directory, when this is to be
           different from the default.  Defaults to
           «/usr/local/var/lib/dpkg/alternatives» if DPKG_ADMINDIR has
           not been set.

       --instdir directory
           Specifies the installation directory where alternatives links
           will be created (since version 1.20.1).  Defaults to «/» if
           DPKG_ROOT has not been set.

       --root directory
           Specifies the root directory (since version 1.20.1).  This
           also sets the alternatives, installation and administrative
           directories to match.  Defaults to «/» if DPKG_ROOT has not
           been set.

       --log file
           Specifies the log file (since version 1.15.0), when this is
           to be different from the default
           (/usr/local/var/log/alternatives.log).

       --force
           Allow replacing or dropping any real file that is installed
           where an alternative link has to be installed or removed.

       --skip-auto
           Skip configuration prompt for alternatives which are properly
           configured in automatic mode. This option is only relevant
           with --config or --all.

       --quiet
           Do not generate any comments unless errors occur.

       --verbose
           Generate more comments about what is being done.

       --debug
           Generate even more comments, helpful for debugging, about
           what is being done (since version 1.19.3).

EXIT STATUS         top

       0   The requested action was successfully performed.

       2   Problems were encountered whilst parsing the command line or
           performing the action.

ENVIRONMENT         top

       DPKG_ROOT
           If set and the --instdir or --root options have not been
           specified, it will be used as the filesystem root directory.

       DPKG_ADMINDIR
           If set and the --admindir option has not been specified, it
           will be used as the base administrative directory.

FILES         top

       /usr/local/etc/alternatives/
           The default alternatives directory.  Can be overridden by the
           --altdir option.

       /usr/local/var/lib/dpkg/alternatives/
           The default administration directory.  Can be overridden by
           the --admindir option.

QUERY FORMAT         top

       The --query format is using an RFC822-like flat format. It's made
       of n + 1 stanzas where n is the number of alternatives available
       in the queried link group. The first stanza contains the
       following fields:

       Name: name
           The alternative name in the alternative directory.

       Link: link
           The generic name of the alternative.

       Slaves: list-of-slaves
           When this field is present, the next lines hold all slave
           links associated to the master link of the alternative. There
           is one slave per line. Each line contains one space, the
           generic name of the slave alternative, another space, and the
           path to the slave link.

       Status: status
           The status of the alternative (auto or manual).

       Best: best-choice
           The path of the best alternative for this link group. Not
           present if there is no alternatives available.

       Value: currently-selected-alternative
           The path of the currently selected alternative. It can also
           take the magic value none. It is used if the link doesn't
           exist.

       The other stanzas describe the available alternatives in the
       queried link group:

       Alternative: path-of-this-alternative
           Path to this stanza's alternative.

       Priority: priority-value
           Value of the priority of this alternative.

       Slaves: list-of-slaves
           When this field is present, the next lines hold all slave
           alternatives associated to the master link of the
           alternative. There is one slave per line. Each line contains
           one space, the generic name of the slave alternative, another
           space, and the path to the slave alternative.

   Example
        $ update-alternatives --query editor
        Name: editor
        Link: /usr/bin/editor
        Slaves:
         editor.1.gz /usr/share/man/man1/editor.1.gz
         editor.fr.1.gz /usr/share/man/fr/man1/editor.1.gz
         editor.it.1.gz /usr/share/man/it/man1/editor.1.gz
         editor.pl.1.gz /usr/share/man/pl/man1/editor.1.gz
         editor.ru.1.gz /usr/share/man/ru/man1/editor.1.gz
        Status: auto
        Best: /usr/bin/vim.basic
        Value: /usr/bin/vim.basic

        Alternative: /bin/ed
        Priority: -100
        Slaves:
         editor.1.gz /usr/share/man/man1/ed.1.gz

        Alternative: /usr/bin/vim.basic
        Priority: 50
        Slaves:
         editor.1.gz /usr/share/man/man1/vim.1.gz
         editor.fr.1.gz /usr/share/man/fr/man1/vim.1.gz
         editor.it.1.gz /usr/share/man/it/man1/vim.1.gz
         editor.pl.1.gz /usr/share/man/pl/man1/vim.1.gz
         editor.ru.1.gz /usr/share/man/ru/man1/vim.1.gz

DIAGNOSTICS         top

       With --verbose update-alternatives chatters incessantly about its
       activities on its standard output channel.  If problems occur,
       update-alternatives outputs error messages on its standard error
       channel and returns an exit status of 2.  These diagnostics
       should be self-explanatory; if you do not find them so, please
       report this as a bug.

EXAMPLES         top

       There are several packages which provide a text editor compatible
       with vi, for example nvi and vim. Which one is used is controlled
       by the link group vi, which includes links for the program itself
       and the associated manual page.

       To display the available packages which provide vi and the
       current setting for it, use the --display action:

        update-alternatives --display vi

       To choose a particular vi implementation, use this command as
       root and then select a number from the list:

        update-alternatives --config vi

       To go back to having the vi implementation chosen automatically,
       do this as root:

        update-alternatives --auto vi

SEE ALSO         top

       ln(1), FHS (the Filesystem Hierarchy Standard).

COLOPHON         top

       This page is part of the dpkg (Debian Package Manager) project.
       Information about the project can be found at 
       ⟨https://wiki.debian.org/Teams/Dpkg/⟩.  If you have a bug report
       for this manual page, see
       ⟨http://bugs.debian.org/cgi-bin/pkgreport.cgi?src=dpkg⟩.  This
       page was obtained from the project's upstream Git repository ⟨git
       clone https://git.dpkg.org/git/dpkg/dpkg.git⟩ on 2023-12-22.  (At
       that time, the date of the most recent commit that was found in
       the repository was 2023-12-18.)  If you discover any rendering
       problems in this HTML version of the page, or you believe there
       is a better or more up-to-date source for the page, or you have
       corrections or improvements to the information in this COLOPHON
       (which is not part of the original manual page), send a mail to
       man-pages@man7.org

1.22.1-2-gddb42                2023-10-30         update-alternatives(1)

Pages that refer to this page: dh_installalternatives(1)