alternatives



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 dif-
       ferent 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 par-
       ticular preference.

       The alternatives system aims to solve this problem.  A generic name  in
       the  filesystem  is shared by all files providing interchangeable func-
       tionality.   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 alterna-
       tive.  Instead, it is a symbolic link to a  name  in  the  alternatives
       directory,  which  in turn is a symbolic link to the actual file refer-
       enced.  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 infor-
       mation about that file in the  alternatives  system.   alternatives  is
       usually called from the %post or %pre scripts in RPM packages.

       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 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 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
       automatic 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  sym-
              links.

       administrative directory
              A directory, by default /var/lib/alternatives, containing alter-
              natives’ 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 set-
              tings.


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 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  alterna-
              tives 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 differ-
              ent from the default.

       --admindir directory
              Specifies  the administrative directory, when this is to be dif-
              ferent 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 alterna-
              tives 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  informa-
              tion.   If  the  group is in automatic mode, and the newly added
              alternatives’ priority is higher than any other installed alter-
              natives for this group, the symlinks will be updated to point to
              the newly added alternatives.

              If --initscript is used, the alternatives system will manage the
              initscript associated with the alternative via chkconfig, regis-
              tering 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 alterna-
              tive 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.

       --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.

       --config name
              Present the user with a configuration menu for choosing the mas-
              ter link and slaves for link group name. Once chosen,  the  link
              group is set to manual mode.

       --auto name
              Switch  the  master symlink name to automatic mode.  In the pro-
              cess, 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.  Information displayed includes  the  group’s  mode
              (auto or manual), which alternative the symlink currently points
              to, what other alternatives are available (and their correspond-
              ing  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 sys-
       tem 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 doc-
       umentation; please report it.  Any significant 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 condi-
       tions.  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  WAR-
       RANTY.


SEE ALSO

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



                                27 January 2001         UPDATE-ALTERNATIVES(8)

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