update-alternatives
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 2022-05-25 update-alternatives(1)
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