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NAME | SYNOPSIS | DESCRIPTION | TERMINOLOGY | COMMANDS | OPTIONS | EXIT STATUS | ENVIRONMENT | FILES | QUERY FORMAT | DIAGNOSTICS | EXAMPLES | SEE ALSO | COLOPHON |
update-alternatives(1) dpkg suite update-alternatives(1)
update-alternatives - maintain symbolic links determining default
commands
update-alternatives [option...] command
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 /usr/local/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.
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 /usr/local/etc/alternatives,
containing the symlinks.
administrative directory
A directory, by default /usr/local/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.
--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.
--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
(/usr/local/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.
0 The requested action was successfully performed.
2 Problems were encountered whilst parsing the command line or
performing the action.
DPKG_ADMINDIR
If set and the --admindir option has not been specified, it
will be used as the base administrative directory.
/usr/local/etc/alternatives/
The default alternatives directory. Can be overridden by the
--altdir option.
/usr/local/var/lib/dpkg/alternatives/
The default administration directory. Can be overridden by
the --admindir option.
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
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.
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
ln(1), FHS, the Filesystem Hierarchy Standard.
This page is part of the dpkg (Debian Package Manager) project.
Information about the project can be found at
⟨https://wiki.debian.org/Teams/Dpkg/⟩. If you have a bug report for
this manual page, see
⟨http://bugs.debian.org/cgi-bin/pkgreport.cgi?src=dpkg⟩. This page
was obtained from the project's upstream Git repository
⟨git://git.debian.org/git/dpkg/dpkg.git⟩ on 2017-07-05. If you dis‐
cover any rendering problems in this HTML version of the page, or you
believe there is a better or more up-to-date source for the page, or
you have corrections or improvements to the information in this
COLOPHON (which is not part of the original manual page), send a mail
to man-pages@man7.org
1.18.15-3-ga2ef 1970-01-01 update-alternatives(1)