# update-alternatives

## NAME



           update-alternatives - maintain symbolic links determining default
           commands
    


## SYNOPSIS



           **update-alternatives**[_option_...] _command_
    


## DESCRIPTION



           **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



           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



           **--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



           **--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



           **0** The requested action was successfully performed.
    
           **2** Problems were encountered whilst parsing the command line or
               performing the action.
    


## ENVIRONMENT



           **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



           _/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



           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



           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



           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
    


* * *