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 Debian
       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.

       Debian's 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 postinst (configure) or prerm (remove and
       deconfigure) scripts in Debian packages.

       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 man
       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.

       --admindir directory
              Specifies the administrative directory, when this is to be
              different from the default.

       --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_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 blocks where n is the number of alternatives available
       in the queried link group. The first block 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 blocks describe the available alternatives in the
       queried link group:

       Alternative: path-of-this-alternative
              Path to this block'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 manpage.

       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
       ⟨https://salsa.debian.org/dpkg-team/dpkg.git⟩ on 2021-06-20.  (At
       that time, the date of the most recent commit that was found in
       the repository was 2021-06-17.)  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

1.19.6-2-g6e42d5               2019-03-25         update-alternatives(1)

Pages that refer to this page: dh_installalternatives(1)