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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 sym-
bolic links comprising the alternatives system. The alternatives system is a reim-
plementation 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 sev-
eral 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 filesys-
tem is shared by all files providing interchangeable functionality. The alterna-
tives 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 alterna-
tives 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 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 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 auto-
matic 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 alter-
natives 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 appropri-
ate 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.
--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 informa-
tion).
--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 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 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 chosen, the link group is set to manual
mode.
--auto name
Switch the master symlink name to automatic mode. In the process, this sym-
link 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 pri-
ority 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 chan-
nel. If problems occur, alternatives outputs error messages on its standard error
channel and returns an exit status of 2. These diagnostics should be self-explana-
tory; 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 conditions. There is NO war-
ranty.
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.
27 January 2001 UPDATE-ALTERNATIVES(8)
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On Apache/1.3.41 (Unix) PHP/5.2.5 mod_perl/1.30 mod_gzip/1.3.26.1a
Under GNU General Public License
2009-01-08 06:37 @38.103.63.58 CrawledBy CCBot/1.0 (+http://www.commoncrawl.org/bot.html)