update-alternatives

SYNOPSIS
       update-alternatives [option...] command

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 for an editor to invoke if the user has not specified a
       particular 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  (configure) or prerm
       (remove and deconfigure) scripts in Debian packages.

       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   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  retain the choice of the administrator and avoid changing
       When using the --config option, update-alternatives will  list  all  of
       the choices for the link group of which given name is the master alter-
       native 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  auto-
       matic).

       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 mecha-
       nism.

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 /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  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
              alternatives directory, and path is the alternative being intro-
              duced 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 corre-
              sponding 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 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 (and the group is put back in automatic
              mode), 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.

       --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 alterna-
              tives is to call yes '' | update-alternatives --force --all.

       --auto name
              Switch the link group behind the alternative for name  to  auto-
              matic  mode.   In the process, the master symlink and its slaves
              are updated to point to the highest priority installed  alterna-
              tives.

       --display name
              Display information about the link group.  Information displayed
              rent 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 for-
              mat  generated  by --get-selections and reconfigure them accord-
              ingly (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 sec-
              tion 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 differ-
              ent from the default.

       --admindir directory
              Specifies  the administrative directory, when this is to be dif-
              ferent from the default.

       --log file
              Specifies the log file (since version 1.15.0), when this  is  to
              be different from the default (/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.

       --verbose
              Generate more comments about what is being done.

       --quiet
              Don't generate any comments unless errors occur.

       /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.

QUERY FORMAT
       The --query format is using an RFC822-like flat format. It's made of  n
       +  1  blocks  where  n  is  the number of alternatives available in the
       queried link group. The first block 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 blocks describe the available  alternatives  in  the  queried
       link group:

       Alternative: path-of-this-alternative
              Path to this block'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 alter-
              natives 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

              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 chan-
       nel 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 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

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

Debian Project                    2012-07-31            update-alternatives(1)
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