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UPDATE-ALTERNATIVES(8) UPDATE-ALTERNATIVES(8)
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-dependencies 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 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, alternatives is
called to update information 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 cor-
respond to the executable referenced 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 alternatives 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
administrator 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 alterna-
tives system.
alternatives directory
A directory, by default /etc/alternatives, containing the symlinks.
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 administra-
tor's settings.
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 alternatives 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 different from the default.
--admindir directory
Specifies the administrative directory, when this is to be different from the default.
ACTIONS
--install link name path priority [--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, path is the alternative being introduced for the master link, and priority is the priority of the alter-
natives group. Higher priorities take precendence if no alternative is manually selected. 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 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.
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 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.
--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.
--config name
Present the user with a configuration menu for choosing the master link and slaves for link group name. Once cho-
sen, the link group is set to manual mode.
--auto name
Switch the master symlink name to automatic mode. In the process, 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 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.
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 imple-
mentation 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 conditions. 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 WARRANTY.
SEE ALSO
ln(1), FHS, the Filesystem Hierarchy Standard. alternatives.c chkconfig.c COPYING leveldb.c leveldb.h Makefile ntsysv.c
ook
27 January 2001 UPDATE-ALTERNATIVES(8)
