update-alternatives(1)



update-alternatives(1)            dpkg suite            update-alternatives(1)

NAME
       update-alternatives  -  maintain  symbolic  links  determining  default
       commands

SYNOPSIS
       update-alternatives [option...] command

DESCRIPTION
       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  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
       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-alternatives  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
       the links (except when something is broken).

       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-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, update-alternatives will  list  all  of
       the  choices  for  the  link  group  of  which given name is the master
       alternative 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
       automatic).

       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
       mechanism.

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
              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  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
              ensures that the  links  in  the  group  point  to  the  highest
              priority alternative 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.

COMMANDS
       --install link name path priority [--slave link name path]...
              Add  a group of alternatives to the system.  link is the generic
              name for the master link, name is the name of its symlink in the
              alternatives  directory,  and  path  is  the  alternative  being
              introduced 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
              corresponding  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
              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.

       --set name path
              Set  the  program  path  as  alternative  for  name.   This   is
              equivalent   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.
              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. 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
              alternatives is to call yes  ''  |  update-alternatives  --force
              --all.

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

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

       --get-selections
              List  all  master  alternative  names  (those controlling a link
              group) and their  status  (since  version  1.15.0).   Each  line
              contains  up  to 3 fields (separated by one or more spaces). The
              first field is the alternative  name,  the  second  one  is  the
              status  (either  auto  or manual), and the last one contains the
              current 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
              format  generated  by  --get-selections  and  reconfigure   them
              accordingly (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
              section 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
              different from the default.

       --admindir directory
              Specifies the administrative  directory,  when  this  is  to  be
              different 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.

EXIT STATUS
       0      The requested action was successfully performed.

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

ENVIRONMENT
       DPKG_ADMINDIR
              If set and the --admindir option has not been specified, it will
              be used as the base administrative directory.

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.

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
              alternatives  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
       $ update-alternatives --query editor
       Name: editor
       Link: /usr/bin/editor
       Slaves:
        editor.1.gz /usr/share/man/man1/editor.1.gz
        editor.fr.1.gz /usr/share/man/fr/man1/editor.1.gz
        editor.it.1.gz /usr/share/man/it/man1/editor.1.gz
        editor.pl.1.gz /usr/share/man/pl/man1/editor.1.gz
        editor.ru.1.gz /usr/share/man/ru/man1/editor.1.gz
       Status: auto
       Best: /usr/bin/vim.basic
       Value: /usr/bin/vim.basic

       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
       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.

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
       setting 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.

1.19.0.4                          2017-10-22            update-alternatives(1)

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