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.

       --quiet
              Do not generate any comments unless errors occur.

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

       --debug
              Generate even more comments, helpful for debugging, about what is being done (since
              version 1.19.3).

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.

1.19.7                                      2019-06-03                     update-alternatives(1)

Használat: update-alternatives [<opció> ...] <parancs>

Commands:
  --install <link> <name> <path> <priority>
    [--slave <link> <name> <path>] ...
                           add a group of alternatives to the system.
  --remove <name> <path>   remove <path> from the <name> group alternative.
  --remove-all <name>      remove <name> group from the alternatives system.
  --auto <name>            switch the master link <name> to automatic mode.
  --display <name>         display information about the <name> group.
  --query <name>           machine parseable version of --display <name>.
  --list <name>            display all targets of the <name> group.
  --get-selections         list master alternative names and their status.
  --set-selections         read alternative status from standard input.
  --config <name>          show alternatives for the <name> group and ask the
                           user to select which one to use.
  --set <name> <path>      set <path> as alternative for <name>.
  --all                    call --config on all alternatives.

<link> is the symlink pointing to /etc/alternatives/<name>.
  (e.g. /usr/bin/pager)
<name> is the master name for this link group.
  (e.g. pager)
<path> is the location of one of the alternative target files.
  (e.g. /usr/bin/less)
<priority> is an integer; options with higher numbers have higher priority in
  automatic mode.

Options:
  --altdir <directory>     change the alternatives directory.
  --admindir <directory>   change the administrative directory.
  --log <file>             change the log file.
  --force                  allow replacing files with alternative links.
  --skip-auto              skip prompt for alternatives correctly configured
                           in automatic mode (relevant for --config only)
  --quiet                  quiet operation, minimal output.
  --verbose                verbose operation, more output.
  --debug                  debug output, way more output.
  --help                   show this help message.
  --version                show the version.