поддерживать символические ссылки, определяющие команды по умолчанию (maintain symbolic links determining default commands)
Имя (Name)
update-alternatives - maintain symbolic links determining default
commands
Синопсис (Synopsis)
update-alternatives [option...] command
Описание (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 /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.
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 /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.
Команды (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.
Параметры (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
(/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.
--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).
Статус выхода (Exit)
0 The requested action was successfully performed.
2 Problems were encountered whilst parsing the command line
or performing the action.
Окружение (Environment)
DPKG_ADMINDIR
If set and the --admindir option has not been specified,
it will be used as the base administrative directory.
Файлы (Files)
/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.
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
Диагностика (Diagnostic)
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.
Примеры (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
Смотри также (See also)
ln(1), FHS, the Filesystem Hierarchy Standard.
