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RedHat 9 (Linux i386) - man page for alternatives (redhat section 8)

UPDATE-ALTERNATIVES(8)							   UPDATE-ALTERNATIVES(8)

NAME
       alternatives - maintain symbolic links determining default commands

SYNOPSIS
       alternatives  [options]	--install  link  name  path  priority [--slave link name path]...
       [--initscript service]

       alternatives [options] --remove name path

       alternatives [options] --set name path

       alternatives [options] --auto name

       alternatives [options] --display name

       alternatives [options] --config name

DESCRIPTION
       alternatives creates, removes, maintains and displays information about the symbolic links
       comprising  the	alternatives system. The alternatives system is a reimplementation of the
       Debian alternatives system. It was rewritten primarily to remove the dependence	on  perl;
       it  is  intended to be a drop in replacement for Debian's update-dependencies script. This
       man page is a slightly modified version of the man page from the Debian project.

       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 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 /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, alternatives is called to update information about that file in  the  alterna-
       tives  system.  alternatives is usually called from the %post or %pre scripts in RPM pack-
       ages.

       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.  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 not change the links; it will leave all the decisions to the sys-
       tem 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 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, 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 auto-
       matic state.

TERMINOLOGY
       Since the activities of 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.

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

       alternative
	      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/alternatives,  containing  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 con-
	      figured.

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

   COMMON OPTIONS
       --verbose
	      Generate more comments about what alternatives is doing.

       --quiet
	      Don't generate any comments unless errors occur.	This option  is  not  yet  imple-
	      mented.

       --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 alternatives this is).

       --version
	      Tell which version of 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
       --install link name path pri [--slave slink sname spath] [--initscript service]...
	      Add a group of alternatives to the system.  name 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.  sname, slink and spath are the generic name, symlink name and
	      alternative  for a slave link, and service is the name of any associated initscript
	      for the alternative.  NOTE: --initscript is a Red Hat Linux specific option.   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 sym-
	      links will be updated to point to the newly added alternatives.

	      If --initscript is used, the alternatives system will manage the initscript associ-
	      ated  with  the  alternative  via chkconfig, registering and unregistering the init
	      script depending on which alternative is active.

	      NOTE: --initscript is a Red Hat Linux specific option.

       --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.  Associ-
	      ated 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.

       --set name path
	      The symbolic link and slaves for link group name set to those configured for  path,
	      and  the	link  group  is  set  to manual mode.  This option is not in the original
	      Debian implementation.

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

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

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

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

EXIT STATUS
       0      The requested action was successfully performed.

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

DIAGNOSTICS
       alternatives chatters incessantly about its activities on its standard output channel.  If
       problems occur, 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
       If you  find  a	bug,  please  report  it  using  the  Red  Hat	bug  tracking  system  at
       http://bugzilla.redhat.com.

       If you find any discrepancy between the operation of alternatives and this manual page, it
       is a bug, either in the implementation or the documentation; please report it.	Any  sig-
       nificant  differences between this implementation and Debian's is also a bug and should be
       reported, unless otherwise noted in this man page.

AUTHOR
       alternatives is copyright 2002 Red Hat, Inc..  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 and 2002 Red Hat, Inc.  This
       is free documentation; see the GNU General Public Licence version 2 or later  for  copying
       conditions.  There is NO WARRANTY.

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

					 27 January 2001		   UPDATE-ALTERNATIVES(8)


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