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NAME    [Toc]    [Back]

       update-alternatives  - maintain symbolic links determining default commands

SYNOPSIS    [Toc]    [Back]

       update-alternatives  [options]  --install  link	name   path   priority
       [--slave link name path]...

       update-alternatives [options] --remove name path

       update-alternatives [options] --auto name

       update-alternatives [options] --display name

       update-alternatives [options] --config name

DESCRIPTION    [Toc]    [Back]

       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 of editor to invoke if the user has not specified a  particular

       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 /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-alter-
       natives is usually called from the postinst or prerm scripts in	Debian

       It  is often useful for a number of alternatives to be synchronised, 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

       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 not change the links; it will leave all  the  decisions  to
       the system administrator.

       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-alterna-
       tives 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  link.
       You  will then be prompted for which of the choices to use for the link
       group. Once you make a change, the link group will no longer be in auto
       mode.  You will need to use the --auto option in order to return to the
       automatic state.

TERMINOLOGY    [Toc]    [Back]

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

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

	      Without any further qualification, this means a symbolic link in
	      the  alternatives  directory: one which the system administrator
	      is expected to adjust.

	      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 /etc/alternatives, containing the symlinks.

       administrative directory
	      A directory, by default  /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 link in a link group which determines how the other links in
	      the group are configured.

       slave link
	      A 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
 alternatives 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.

OPTIONS    [Toc]    [Back]

       Exactly	one action must be specified if update-alternatives is to perform
 any meaningful task.  Any number of  the  common  options  may  be
       specified together with any action.

   COMMON OPTIONS    [Toc]    [Back]
	      Generate	more comments about what update-alternatives is doing.

	      Don't generate any comments unless errors occur.	This option is
	      not yet implemented.

       --test Don't  actually  do anything, just say what would be done.  This
	      option is not yet implemented.

       --help Give some usage information (and say which  version  of  update-
	      alternatives this is).

	      Tell which version of update-alternatives this is (and give some
	      usage information).

       --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.

   ACTIONS    [Toc]    [Back]
       --install link gen path pri [--slave slink sgen spath] ...
	      Add a group of alternatives to the system.  gen is  the  generic
	      name  for  the master link, link is the name of its symlink, and
	      path is the alternative being introduced for  the  master  link.
	      sgen,  slink  and  spath	are the generic name, symlink name and
	      alternative for a slave link.  Zero  or  more  --slave  options,
	      each followed by three arguments, may be specified.

	      If  the  master symlink 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.

       --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, 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.

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

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

FILES    [Toc]    [Back]

	      The  default  alternatives  directory.  Can be overridden by the
	      --altdir option.

	      The default administration directory.  Can be overridden by  the
	      --admindir option.

EXIT STATUS    [Toc]    [Back]

       0      The requested action was successfully performed.

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

DIAGNOSTICS    [Toc]    [Back]

       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.

BUGS    [Toc]    [Back]

       If you find a bug, please report it using the Debian bug-tracking  system,
 or, if that is not possible, email the author directly.

       If  you	find  any discrepancy between the operation of update-alterna-
       tives and this manual page, it is a bug, either in  the	implementation
       or the documentation; please report it.

AUTHOR    [Toc]    [Back]

       Debian  update-alternatives  is copyright 1995 Ian Jackson.  It is free
       software; see the GNU General Public Licence version  2	or  later  for
       copying conditions.  There is NO warranty.

       This  manual  page is copyright 1997/98 Charles Briscoe-Smith.  This is
       free documentation; see the GNU General Public  Licence	version  2  or
       later for copying conditions.  There is NO WARRANTY.

       You  can  find  the  GNU  GPL  in /usr/share/common-licenses/GPL on any
       Debian system.

SEE ALSO    [Toc]    [Back]

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

Debian Project			19 January 1998 	UPDATE-ALTERNATIVES(8)
[ Back ]
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