1UPDATE-ALTERNATIVES(8) System Manager's Manual UPDATE-ALTERNATIVES(8)
2
6 alternatives - maintain symbolic links determining default commands
7
9 alternatives [options] --install link name path priority [--slave link
10 name path]... [--initscript service]
11 alternatives [options] --remove name path
13 alternatives [options] --set name path
15 alternatives [options] --auto name
17 alternatives [options] --display name
19 alternatives [options] --config name
21
23 alternatives creates, removes, maintains and displays information about
24 the symbolic links comprising the alternatives system. The alternatives
25 system is a reimplementation of the Debian alternatives system. It was
26 rewritten primarily to remove the dependence on perl; it is intended to
27 be a drop in replacement for Debian's update-dependencies script. This
28 man page is a slightly modified version of the man page from the Debian
29 project.
30 It is possible for several programs fulfilling the same or similar
32 functions to be installed on a single system at the same time. For
33 example, many systems have several text editors installed at once.
34 This gives choice to the users of a system, allowing each to use a dif‐
35 ferent editor, if desired, but makes it difficult for a program to make
36 a good choice of editor to invoke if the user has not specified a par‐
37 ticular preference.
38 The alternatives system aims to solve this problem. A generic name in
40 the filesystem is shared by all files providing interchangeable func‐
41 tionality. The alternatives system and the system administrator
42 together determine which actual file is referenced by this generic
43 name. For example, if the text editors ed(1) and nvi(1) are both
44 installed on the system, the alternatives system will cause the generic
45 name /usr/bin/editor to refer to /usr/bin/nvi by default. The system
46 administrator can override this and cause it to refer to /usr/bin/ed
47 instead, and the alternatives system will not alter this setting until
48 explicitly requested to do so.
49 The generic name is not a direct symbolic link to the selected alterna‐
51 tive. Instead, it is a symbolic link to a name in the alternatives
52 directory, which in turn is a symbolic link to the actual file refer‐
53 enced. This is done so that the system administrator's changes can be
54 confined within the /etc directory: the FHS (q.v.) gives reasons why
55 this is a Good Thing.
56 When each package providing a file with a particular functionality is
58 installed, changed or removed, alternatives is called to update infor‐
59 mation about that file in the alternatives system. alternatives is
60 usually called from the %post or %pre scripts in RPM packages.
61 It is often useful for a number of alternatives to be synchronised, so
63 that they are changed as a group; for example, when several versions of
64 the vi(1) editor are installed, the man page referenced by
65 /usr/share/man/man1/vi.1 should correspond to the executable referenced
66 by /usr/bin/vi. alternatives handles this by means of master and slave
67 links; when the master is changed, any associated slaves are changed
68 too. A master link and its associated slaves make up a link group.
69 Each link group is, at any given time, in one of two modes: automatic
71 or manual. When a group is in automatic mode, the alternatives system
72 will automatically decide, as packages are installed and removed,
73 whether and how to update the links. In manual mode, the alternatives
74 system will not change the links; it will leave all the decisions to
75 the system administrator.
76 Link groups are in automatic mode when they are first introduced to the
78 system. If the system administrator makes changes to the system's
79 automatic settings, this will be noticed the next time alternatives is
80 run on the changed link's group, and the group will automatically be
81 switched to manual mode.
82 Each alternative has a priority associated with it. When a link group
84 is in automatic mode, the alternatives pointed to by members of the
85 group will be those which have the highest priority.
86 When using the --config option, alternatives will list all of the
88 choices for the link group of which given name is the master link. You
89 will then be prompted for which of the choices to use for the link
90 group. Once you make a change, the link group will no longer be in auto
91 mode. You will need to use the --auto option in order to return to the
92 automatic state.
93
95 Since the activities of alternatives are quite involved, some specific
96 terms will help to explain its operation.
97 generic name
99 A name, like /usr/bin/editor, which refers, via the alternatives
100 system, to one of a number of files of similar function.
101 symlink
103 Without any further qualification, this means a symbolic link in
104 the alternatives directory: one which the system administrator
105 is expected to adjust.
106 alternative
108 The name of a specific file in the filesystem, which may be made
109 accessible via a generic name using the alternatives system.
110 alternatives directory
112 A directory, by default /etc/alternatives, containing the sym‐
113 links.
114 administrative directory
116 A directory, by default /var/lib/alternatives, containing alter‐
117 natives' state information.
118 link group
120 A set of related symlinks, intended to be updated as a group.
121 master link
123 The link in a link group which determines how the other links in
124 the group are configured.
125 slave link
127 A link in a link group which is controlled by the setting of the
128 master link.
129 automatic mode
131 When a link group is in automatic mode, the alternatives system
132 ensures that the links in the group point to the highest prior‐
133 ity alternatives appropriate for the group.
134 manual mode
136 When a link group is in manual mode, the alternatives system
137 will not make any changes to the system administrator's set‐
138 tings.
139
141 Exactly one action must be specified if alternatives is to perform any
142 meaningful task. Any number of the common options may be specified
143 together with any action.
144 COMMON OPTIONS
146 --verbose
147 Generate more comments about what alternatives is doing.
148 --quiet
150 Don't generate any comments unless errors occur. This option is
151 not yet implemented.
152 --test Don't actually do anything, just say what would be done. This
154 option is not yet implemented.
155 --help Give some usage information (and say which version of alterna‐
157 tives this is).
158 --version
160 Tell which version of alternatives this is (and give some usage
161 information).
162 --altdir directory
164 Specifies the alternatives directory, when this is to be differ‐
165 ent from the default.
166 --admindir directory
168 Specifies the administrative directory, when this is to be dif‐
169 ferent from the default.
170 ACTIONS
172 --install link name path priority [--slave slink sname spath]
173 [--initscript service]...
174 Add a group of alternatives to the system. name is the generic
175 name for the master link, link is the name of its symlink, path
176 is the alternative being introduced for the master link, and
177 priority is the priority of the alternatives group. Higher pri‐
178 orities take precendence if no alternative is manually selected.
179 sname, slink and spath are the generic name, symlink name and
180 alternative for a slave link, and service is the name of any
181 associated initscript for the alternative. NOTE: --initscript
182 is a Red Hat Linux specific option. Zero or more --slave
183 options, each followed by three arguments, may be specified.
184 If the master symlink specified exists already in the alterna‐
186 tives system's records, the information supplied will be added
187 as a new set of alternatives for the group. Otherwise, a new
188 group, set to automatic mode, will be added with this informa‐
189 tion. If the group is in automatic mode, and the newly added
190 alternatives' priority is higher than any other installed alter‐
191 natives for this group, the symlinks will be updated to point to
192 the newly added alternatives.
193 If --initscript is used, the alternatives system will manage the
195 initscript associated with the alternative via chkconfig, regis‐
196 tering and unregistering the init script depending on which
197 alternative is active.
198 NOTE: --initscript is a Red Hat Linux specific option.
200 --remove name path
202 Remove an alternative and all of its associated slave links.
203 name is a name in the alternatives directory, and path is an
204 absolute filename to which name could be linked. If name is
205 indeed linked to path, name will be updated to point to another
206 appropriate alternative, or removed if there is no such alterna‐
207 tive left. Associated slave links will be updated or removed,
208 correspondingly. If the link is not currently pointing to path,
209 no links are changed; only the information about the alternative
210 is removed.
211 --set name path
213 The symbolic link and slaves for link group name set to those
214 configured for path, and the link group is set to manual mode.
215 This option is not in the original Debian implementation.
216 --config name
218 Present the user with a configuration menu for choosing the mas‐
219 ter link and slaves for link group name. Once chosen, the link
220 group is set to manual mode.
221 --auto name
223 Switch the master symlink name to automatic mode. In the
224 process, this symlink and its slaves are updated to point to the
225 highest priority installed alternatives.
226 --display name
228 Display information about the link group of which name is the
229 master link. Information displayed includes the group's mode
230 (auto or manual), which alternative the symlink currently points
231 to, what other alternatives are available (and their correspond‐
232 ing slave alternatives), and the highest priority alternative
233 currently installed.
234
236 /etc/alternatives/
237 The default alternatives directory. Can be overridden by the
238 --altdir option.
239 /var/lib/alternatives/
241 The default administration directory. Can be overridden by the
242 --admindir option.
243
245 0 The requested action was successfully performed.
246 2 Problems were encountered whilst parsing the command line or
248 performing the action.
249
251 alternatives chatters incessantly about its activities on its standard
252 output channel. If problems occur, alternatives outputs error messages
253 on its standard error channel and returns an exit status of 2. These
254 diagnostics should be self-explanatory; if you do not find them so,
255 please report this as a bug.
256
258 If you find a bug, please report it using the Red Hat bug tracking sys‐
259 tem at http://bugzilla.redhat.com.
260 If you find any discrepancy between the operation of alternatives and
262 this manual page, it is a bug, either in the implementation or the doc‐
263 umentation; please report it. Any significant differences between this
264 implementation and Debian's is also a bug and should be reported,
265 unless otherwise noted in this man page.
266
268 alternatives is copyright 2002 Red Hat, Inc.. It is free software; see
269 the GNU General Public Licence version 2 or later for copying condi‐
270 tions. There is NO warranty.
271 This manual page is copyright 1997/98 Charles Briscoe-Smith and 2002
273 Red Hat, Inc. This is free documentation; see the GNU General Public
274 Licence version 2 or later for copying conditions. There is NO WAR‐
275 RANTY.
276
278 ln(1), FHS, the Filesystem Hierarchy Standard. alternatives.c chkcon‐
279 fig.c COPYING leveldb.c leveldb.h Makefile ntsysv.c ook
280 27 January 2001 UPDATE-ALTERNATIVES(8)