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 [--follower
10 link name path]... [--initscript service] [--family name]
11 alternatives [options] --remove name path
13 alternatives [options] --set name path/family
15 alternatives [options] --auto name
17 alternatives [options] --display name
19 alternatives [options] --config name
21 alternatives [options] --list
23 alternatives [options] --remove-all name
25 alternatives [options] --add-follower name path follower_link fol‐
27 lower_name follower_path
28 alternatives [options] --remove-follower name path follower_name
30
32 alternatives creates, removes, maintains and displays information about
33 the symbolic links comprising the alternatives system. The alternatives
34 system is a reimplementation of the Debian alternatives system. It was
35 rewritten primarily to remove the dependence on perl; it is intended to
36 be a drop in replacement for Debian's update-dependencies script. This
37 man page is a slightly modified version of the man page from the Debian
38 project.
39 It is possible for several programs fulfilling the same or similar
41 functions to be installed on a single system at the same time. For ex‐
42 ample, many systems have several text editors installed at once. This
43 gives choice to the users of a system, allowing each to use a different
44 editor, if desired, but makes it difficult for a program to make a good
45 choice of editor to invoke if the user has not specified a particular
46 preference.
47 The alternatives system aims to solve this problem. A generic name in
49 the filesystem is shared by all files providing interchangeable func‐
50 tionality. The alternatives system and the system administrator to‐
51 gether determine which actual file is referenced by this generic name.
52 For example, if the text editors ed(1) and nvi(1) are both installed on
53 the system, the alternatives system will cause the generic name
54 /usr/bin/editor to refer to /usr/bin/nvi by default. The system admin‐
55 istrator can override this and cause it to refer to /usr/bin/ed in‐
56 stead, and the alternatives system will not alter this setting until
57 explicitly requested to do so.
58 The generic name is not a direct symbolic link to the selected alterna‐
60 tive. Instead, it is a symbolic link to a name in the alternatives di‐
61 rectory, which in turn is a symbolic link to the actual file refer‐
62 enced. This is done so that the system administrator's changes can be
63 confined within the /etc directory: the FHS (q.v.) gives reasons why
64 this is a Good Thing.
65 When each package providing a file with a particular functionality is
67 installed, changed or removed, alternatives is called to update infor‐
68 mation about that file in the alternatives system. alternatives is
69 usually called from the %post or %pre scripts in RPM packages.
70 It is often useful for a number of alternatives to be synchronised, so
72 that they are changed as a group; for example, when several versions of
73 the vi(1) editor are installed, the man page referenced by
74 /usr/share/man/man1/vi.1 should correspond to the executable referenced
75 by /usr/bin/vi. alternatives handles this by means of leader and fol‐
76 lower links; when the leader is changed, any associated followers are
77 changed too. A leader link and its associated followers make up a link
78 group.
79 Each link group is, at any given time, in one of two modes: automatic
81 or manual. When a group is in automatic mode, the alternatives system
82 will automatically decide, as packages are installed and removed,
83 whether and how to update the links. In manual mode, the alternatives
84 system will not change the links; it will leave all the decisions to
85 the system administrator.
86 Link groups are in automatic mode when they are first introduced to the
88 system. If the system administrator makes changes to the system's au‐
89 tomatic settings, this will be noticed the next time alternatives is
90 run on the changed link's group, and the group will automatically be
91 switched to manual mode.
92 Each alternative has a priority associated with it. When a link group
94 is in automatic mode, the alternatives pointed to by members of the
95 group will be those which have the highest priority.
96 When using the --config option, alternatives will list all of the
98 choices for the link group of which given name is the leader link. You
99 will then be prompted for which of the choices to use for the link
100 group. Once you make a change, the link group will no longer be in auto
101 mode. You will need to use the --auto option in order to return to the
102 automatic state.
103
105 Since the activities of alternatives are quite involved, some specific
106 terms will help to explain its operation.
107 generic name
109 A name, like /usr/bin/editor, which refers, via the alternatives
110 system, to one of a number of files of similar function.
111 symlink
113 Without any further qualification, this means a symbolic link in
114 the alternatives directory: one which the system administrator
115 is expected to adjust.
116 alternative
118 The name of a specific file in the filesystem, which may be made
119 accessible via a generic name using the alternatives system.
120 alternatives directory
122 A directory, by default /etc/alternatives, containing the sym‐
123 links.
124 administrative directory
126 A directory, by default /var/lib/alternatives, containing alter‐
127 natives' state information.
128 link group
130 A set of related symlinks, intended to be updated as a group.
131 leader link
133 The link in a link group which determines how the other links in
134 the group are configured.
135 follower link
137 A link in a link group which is controlled by the setting of the
138 leader link.
139 automatic mode
141 When a link group is in automatic mode, the alternatives system
142 ensures that the links in the group point to the highest prior‐
143 ity alternatives appropriate for the group.
144 manual mode
146 When a link group is in manual mode, the alternatives system
147 will not make any changes to the system administrator's set‐
148 tings.
149
151 Exactly one action must be specified if alternatives is to perform any
152 meaningful task. Any number of the common options may be specified to‐
153 gether with any action.
154 COMMON OPTIONS
156 --verbose
157 Generate more comments about what alternatives is doing.
158 --quiet
160 Don't generate any comments unless errors occur. This option is
161 not yet implemented.
162 --test Don't actually do anything, just say what would be done. This
164 option is not yet implemented.
165 --help Give some usage information (and say which version of alterna‐
167 tives this is).
168 --version
170 Tell which version of alternatives this is (and give some usage
171 information).
172 --keep-missing
174 When switching between alternatives, if the new variant does not
175 provide some files, keep the links pointed to the previous im‐
176 plementation. It prevents issues with missing files due to
177 switching between versions.
178 --keep-foreign
180 When removing, adding or switching between alternatives, check
181 if the link does not point to some other location than altdir
182 (/etc/alternatives/ by default). In such case the link is not
183 modified.
184 --altdir directory
186 Specifies the alternatives directory, when this is to be differ‐
187 ent from the default.
188 --admindir directory
190 Specifies the administrative directory, when this is to be dif‐
191 ferent from the default.
192 ACTIONS
194 --install link name path priority [--follower follower_link fol‐
195 lower_name follower_path] [--initscript service]...
196 Add a group of alternatives to the system. name is the generic
197 name for the leader link, link is the name of its symlink, path
198 is the alternative being introduced for the leader link, and
199 priority is the priority of the alternatives group. Higher pri‐
200 orities take precendence if no alternative is manually selected.
201 follower_name, follower_link and follower_path are the generic
202 name, symlink name and alternative for a follower link, and ser‐
203 vice is the name of any associated initscript for the alterna‐
204 tive. NOTE: --initscript and --family are a Red Hat Linux spe‐
205 cific options. Zero or more --follower options, each followed
206 by three arguments, may be specified.
207 If the leader symlink specified exists already in the alterna‐
209 tives system's records, the information supplied will be added
210 as a new set of alternatives for the group. Otherwise, a new
211 group, set to automatic mode, will be added with this informa‐
212 tion. If the group is in automatic mode, and the newly added
213 alternatives' priority is higher than any other installed alter‐
214 natives for this group, the symlinks will be updated to point to
215 the newly added alternatives.
216 If --initscript is used, the alternatives system will manage the
218 initscript associated with the alternative via chkconfig, regis‐
219 tering and unregistering the init script depending on which al‐
220 ternative is active.
221 NOTE: --initscript is a Red Hat Linux specific option.
223 --family can be used to group similar alternatives. If the group
226 is in manual mode and the alternative currently used is removed,
227 alternatives will try to change links to different one with same
228 family and highest priority.
229 NOTE: --family is a Red Hat Linux specific option.
231 --remove name path
233 Remove an alternative and all of its associated follower links.
234 name is a name in the alternatives directory, and path is an ab‐
235 solute filename to which name could be linked. If name is in‐
236 deed linked to path, name will be updated to point to another
237 appropriate alternative, or removed if there is no such alterna‐
238 tive left. Associated follower links will be updated or re‐
239 moved, correspondingly. If the link is not a symlink, no links
240 are changed; only the information about the alternative is re‐
241 moved.
242 --set name path/family
244 The symbolic link and followers for link group name set to those
245 configured for path, and the link group is set to manual mode.
246 If you use family, then the links and group is configured to the
247 member of given family with highest priority (and moved to man‐
248 ual mode). This option is not in the original Debian implemen‐
249 tation.
250 --config name
252 Present the user with a configuration menu for choosing the
253 leader link and followers for link group name. Once chosen, the
254 link group is set to manual mode.
255 --auto name
257 Switch the leader symlink name to automatic mode. In the
258 process, this symlink and its followers are updated to point to
259 the highest priority installed alternatives.
260 --display name
262 Display information about the link group of which name is the
263 leader link. Information displayed includes the group's mode
264 (auto or manual), which alternative the symlink currently points
265 to, what other alternatives are available (and their correspond‐
266 ing follower alternatives), and the highest priority alternative
267 currently installed.
268 --list Display information about all link groups.
270 --remove-all name
272 Remove the whole link group name. Use with caution.
273 --add-follower name path follower_link follower_name follower_path
275 Add a follower link to an alternative identified by name and
276 path. follower_name, follower_link and follower_path are the
277 generic name, symlink name and alternative for the follower.
278 --remove-follower name path follower_name
280 Remove follower with generic name follower_name from alternative
281 identified by name and path.
282
284 /etc/alternatives/
285 The default alternatives directory. Can be overridden by the
286 --altdir option.
287 /var/lib/alternatives/
289 The default administration directory. Can be overridden by the
290 --admindir option.
291
293 0 The requested action was successfully performed.
294 2 Problems were encountered whilst parsing the command line or
296 performing the action.
297
299 alternatives chatters incessantly about its activities on its standard
300 output channel. If problems occur, alternatives outputs error messages
301 on its standard error channel and returns an exit status of 2. These
302 diagnostics should be self-explanatory; if you do not find them so,
303 please report this as a bug.
304
306 If you find a bug, please report it using the Red Hat bug tracking sys‐
307 tem at http://bugzilla.redhat.com.
308 If you find any discrepancy between the operation of alternatives and
310 this manual page, it is a bug, either in the implementation or the doc‐
311 umentation; please report it. Any significant differences between this
312 implementation and Debian's is also a bug and should be reported, un‐
313 less otherwise noted in this man page.
314
316 alternatives is copyright 2002 Red Hat, Inc.. It is free software; see
317 the GNU General Public Licence version 2 or later for copying condi‐
318 tions. There is NO warranty.
319 This manual page is copyright 1997/98 Charles Briscoe-Smith and 2002
321 Red Hat, Inc. This is free documentation; see the GNU General Public
322 Licence version 2 or later for copying conditions. There is NO WAR‐
323 RANTY.
324
326 ln(1), FHS, the Filesystem Hierarchy Standard.
327 27 January 2001 UPDATE-ALTERNATIVES(8)