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UPDATE-ALTERNATIVES(8)          dpkg utilities          UPDATE-ALTERNATIVES(8)



NAME
       update-alternatives  - maintain symbolic links determining default com-
       mands

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

       update-alternatives [options] --remove name path

       update-alternatives [options] --remove-all name

       update-alternatives [options] --all

       update-alternatives [options] --auto name

       update-alternatives [options] --display name

       update-alternatives [options] --list name

       update-alternatives [options] --config name

       update-alternatives [options] --set name path

DESCRIPTION
       update-alternatives  creates,  removes, maintains and displays informa-
       tion about the symbolic links comprising the Debian  alternatives  sys-
       tem.

       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.

       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 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, 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
       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.   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 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  automati-
       cally 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.

       If you want to configure non-interactivily you can use the --set option
       instead (see below).

TERMINOLOGY
       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.

       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/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 prior-
              ity 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.

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 manpage.

       To display the available packages which provide vi and the current set-
       ting 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

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

   COMMON OPTIONS
       --verbose
              Generate more comments about what update-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
              update-alternatives this is).

       --version
              Tell which version of update-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 gen link alt pri [--slave sgen slink salt] ...
              Add a group of alternatives to the system.  gen is  the  generic
              name for the master link, link is the name of its symlink in the
              alternatives directory, and alt is the alternative being  intro-
              duced for the master link.  sgen, slink and salt are the generic
              name, symlink name in the alternatives directory 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  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.

       --set name path
              Set  the  program path as alternative for name.  This is equiva-
              lent 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, 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.

       --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.

       --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 correspond-
              ing  slave  alternatives),  and the highest priority alternative
              currently installed.

       --list link
              Display all targets of the link group.

       --config link
              Show available alternatives for a link group and allow the  user
              to  interactively  select  which  one to use.  The link group is
              updated and taken out of auto mode.

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

       /var/lib/dpkg/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
       update-alternatives  chatters  incessantly  about its activities on its
       standard output channel.  If problems occur,  update-alternatives  out-
       puts  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 Debian bug-tracking sys-
       tem, 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
       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
       ln(1), FHS, the Filesystem Hierarchy Standard.



Debian Project                  19 January 1998         UPDATE-ALTERNATIVES(8)