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NAME
alternatives - maintain symbolic links determining default commands
SYNOPSIS
alternatives [options] --install link name path priority [--slave link
name path]... [--initscript service]
alternatives [options] --remove name path
alternatives [options] --set name path
alternatives [options] --auto name
alternatives [options] --display name
alternatives [options] --config name
DESCRIPTION
alternatives creates, removes, maintains and displays information
about the symbolic links comprising the alternatives system. The
alternatives system is a reimplementation of the Debian alternatives
system. It was rewritten primarily to remove the dependence on perl;
it is intended to be a drop in replacement for Debian's update-depen-
dencies script. This man page is a slightly modified version of the
man page from the Debian project.
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 of editor to invoke if the user has not specified a
particular preference.
The alternatives system aims to solve this problem. A generic name in
the filesystem is shared by all files providing interchangeable func-
tionality. 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 alter-
native. Instead, it is a symbolic link to a name in the alternatives
directory, which in turn is a symbolic link to the actual file refer-
enced. 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, alternatives is called to update infor-
mation about that file in the alternatives system. alternatives is
usually called from the %post or %pre scripts in RPM packages.
It is often useful for a number of alternatives to be synchronised, 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 refer-
enced by /usr/bin/vi. 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 not change the links; it will leave all the decisions to
the system administrator.
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 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, alternatives will list all of the
choices for the link group of which given name is the master link.
You will then be prompted for which of the choices to use for the link
group. Once you make a change, the link group will no longer be in
auto mode. You will need to use the --auto option in order to return
to the automatic state.
TERMINOLOGY
Since the activities of alternatives are quite involved, some specific
terms will help to explain its operation.
generic name
A name, like /usr/bin/editor, which refers, via the alterna-
tives system, to one of a number of files of similar function.
symlink
Without any further qualification, this means a symbolic link
in the alternatives directory: one which the system administra-
tor is expected to adjust.
alternative
The name of a specific file in the filesystem, which may be
made accessible via a generic name using the alternatives sys-
tem.
alternatives directory
A directory, by default /etc/alternatives, containing the sym-
links.
administrative directory
A directory, by default /var/lib/alternatives, containing
alternatives' state information.
link group
A set of related symlinks, intended to be updated as a group.
master link
The link in a link group which determines how the other links
in the group are configured.
slave link
A 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 alternatives 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 set-
tings.
OPTIONS
Exactly one action must be specified if alternatives is to perform any
meaningful task. Any number of the common options may be specified
together with any action.
COMMON OPTIONS
--verbose
Generate more comments about what alternatives is doing.
--quiet
Don't generate any comments unless errors occur. This option
is not yet implemented.
--test Don't actually do anything, just say what would be done. This
option is not yet implemented.
--help Give some usage information (and say which version of alterna-
tives this is).
--version
Tell which version of alternatives this is (and give some usage
information).
--altdir directory
Specifies the alternatives directory, when this is to be dif-
ferent from the default.
--admindir directory
Specifies the administrative directory, when this is to be dif-
ferent from the default.
ACTIONS
--install link name path pri [--slave slink sname spath] [--initscript
service]...
Add a group of alternatives to the system. name is the generic
name for the master link, link is the name of its symlink, and
path is the alternative being introduced for the master link.
sname, slink and spath are the generic name, symlink name and
alternative for a slave link, and service is the name of any
associated initscript for the alternative. NOTE: --initscript
is a Red Hat Linux specific option. Zero or more --slave
options, each followed by three arguments, may be specified.
If the master symlink specified exists already in the alterna-
tives 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 informa-
tion. 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.
If --initscript is used, the alternatives system will manage
the initscript associated with the alternative via chkconfig,
registering and unregistering the init script depending on
which alternative is active.
NOTE: --initscript is a Red Hat Linux specific option.
--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, or removed if there is no such alter-
native left. Associated slave links will be updated or
removed, correspondingly. If the link is not currently point-
ing to path, no links are changed; only the information about
the alternative is removed.
--set name path
The symbolic link and slaves for link group name set to those
configured for path, and the link group is set to manual mode.
This option is not in the original Debian implementation.
--auto name
Switch the master symlink name to automatic mode. In the pro-
cess, this symlink and its slaves are updated to point to the
highest priority installed alternatives.
--display name
Display information about the link group of which name is the
master link. Information displayed includes the group's mode
(auto or manual), which alternative the symlink currently
points to, what other alternatives are available (and their
corresponding slave alternatives), and the highest priority
alternative currently installed.
FILES
/etc/alternatives/
The default alternatives directory. Can be overridden by the
--altdir option.
/var/lib/alternatives/
The default administration directory. Can be overridden by the
--admindir option.
EXIT STATUS
0 The requested action was successfully performed.
2 Problems were encountered whilst parsing the command line or
performing the action.
DIAGNOSTICS
alternatives chatters incessantly about its activities on its standard
output channel. If problems occur, alternatives outputs error mes-
sages 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.
BUGS
If you find a bug, please report it using the Red Hat bug tracking
system at http://bugzilla.redhat.com.
If you find any discrepancy between the operation of alternatives and
this manual page, it is a bug, either in the implementation or the
documentation; please report it. Any significant differences between
this implementation and Debian's is also a bug and should be reported,
unless otherwise noted in this man page.
AUTHOR
alternatives is copyright 2002 Red Hat, Inc.. It is free software;
see the GNU General Public Licence version 2 or later for copying con-
ditions. There is NO warranty.
This manual page is copyright 1997/98 Charles Briscoe-Smith and 2002
Red Hat, Inc. This is free documentation; see the GNU General Public
Licence version 2 or later for copying conditions. There is NO WAR-
RANTY.
SEE ALSO
ln(1), FHS, the Filesystem Hierarchy Standard.
27 January 2001 UPDATE-ALTERNATIVES(8)
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