UPDATE-ALTERNATIVES(8) System Manager's Manual 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]
[--family name]
alternatives [options] --remove name path
alternatives [options] --set name path
alternatives [options] --auto name
alternatives [options] --display name
alternatives [options] --config name
alternatives [options] --list 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 sys‐
tem 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 deter‐
mine 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, alterna‐
tives 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 correspond 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
order to return to the automatic state.
TERMINOLOGY
Since the activities of alternatives are quite involved, some specific terms will help to explain its opera‐
tion.
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 alternatives 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
administrator'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.
--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 alternatives 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 and
--family are a Red Hat Linux specific options. 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 sym‐
links will be updated to point to the newly added alternatives.
If --initscript is used, the alternatives system will manage the initscript associated with the alter‐
native via chkconfig, registering and unregistering the init script depending on which alternative is
active.
NOTE: --initscript is a Red Hat Linux specific option.
--family can be used to group similar alternatives. If the group is in manual mode and the alternative
currently used is removed, alternatives will try to change links to different one with same family and
highest priority.
NOTE: --family 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 direc‐
tory, 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 chosen, 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.
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 implementation or the documentation; please report it. Any significant differences between this implemen‐
tation 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 documenta‐
tion; 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 Make‐
file ntsysv.c ook
27 January 2001 UPDATE-ALTERNATIVES(8)
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