1UPDATE-ALTERNATIVES(8) System Manager's Manual UPDATE-ALTERNATIVES(8)
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6 alternatives - maintain symbolic links determining default commands
7
9 alternatives [options] --install link name path priority [--slave link
10 name path]... [--initscript service] [--family name]
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 alternatives [options] --list
23 alternatives [options] --remove-all name
25 alternatives [options] --add-slave name path slink sname spath
27 alternatives [options] --remove-slave name path sname
29
31 alternatives creates, removes, maintains and displays information about
32 the symbolic links comprising the alternatives system. The alternatives
33 system is a reimplementation of the Debian alternatives system. It was
34 rewritten primarily to remove the dependence on perl; it is intended to
35 be a drop in replacement for Debian's update-dependencies script. This
36 man page is a slightly modified version of the man page from the Debian
37 project.
38 It is possible for several programs fulfilling the same or similar
40 functions to be installed on a single system at the same time. For
41 example, many systems have several text editors installed at once.
42 This gives choice to the users of a system, allowing each to use a dif‐
43 ferent editor, if desired, but makes it difficult for a program to make
44 a good choice of editor to invoke if the user has not specified a par‐
45 ticular preference.
46 The alternatives system aims to solve this problem. A generic name in
48 the filesystem is shared by all files providing interchangeable func‐
49 tionality. The alternatives system and the system administrator
50 together determine which actual file is referenced by this generic
51 name. For example, if the text editors ed(1) and nvi(1) are both
52 installed on the system, the alternatives system will cause the generic
53 name /usr/bin/editor to refer to /usr/bin/nvi by default. The system
54 administrator can override this and cause it to refer to /usr/bin/ed
55 instead, and the alternatives system will not alter this setting until
56 explicitly requested to do so.
57 The generic name is not a direct symbolic link to the selected alterna‐
59 tive. Instead, it is a symbolic link to a name in the alternatives
60 directory, which in turn is a symbolic link to the actual file refer‐
61 enced. This is done so that the system administrator's changes can be
62 confined within the /etc directory: the FHS (q.v.) gives reasons why
63 this is a Good Thing.
64 When each package providing a file with a particular functionality is
66 installed, changed or removed, alternatives is called to update infor‐
67 mation about that file in the alternatives system. alternatives is
68 usually called from the %post or %pre scripts in RPM packages.
69 It is often useful for a number of alternatives to be synchronised, so
71 that they are changed as a group; for example, when several versions of
72 the vi(1) editor are installed, the man page referenced by
73 /usr/share/man/man1/vi.1 should correspond to the executable referenced
74 by /usr/bin/vi. alternatives handles this by means of master and slave
75 links; when the master is changed, any associated slaves are changed
76 too. A master link and its associated slaves make up a link group.
77 Each link group is, at any given time, in one of two modes: automatic
79 or manual. When a group is in automatic mode, the alternatives system
80 will automatically decide, as packages are installed and removed,
81 whether and how to update the links. In manual mode, the alternatives
82 system will not change the links; it will leave all the decisions to
83 the system administrator.
84 Link groups are in automatic mode when they are first introduced to the
86 system. If the system administrator makes changes to the system's
87 automatic settings, this will be noticed the next time alternatives is
88 run on the changed link's group, and the group will automatically be
89 switched to manual mode.
90 Each alternative has a priority associated with it. When a link group
92 is in automatic mode, the alternatives pointed to by members of the
93 group will be those which have the highest priority.
94 When using the --config option, alternatives will list all of the
96 choices for the link group of which given name is the master link. You
97 will then be prompted for which of the choices to use for the link
98 group. Once you make a change, the link group will no longer be in auto
99 mode. You will need to use the --auto option in order to return to the
100 automatic state.
101
103 Since the activities of alternatives are quite involved, some specific
104 terms will help to explain its operation.
105 generic name
107 A name, like /usr/bin/editor, which refers, via the alternatives
108 system, to one of a number of files of similar function.
109 symlink
111 Without any further qualification, this means a symbolic link in
112 the alternatives directory: one which the system administrator
113 is expected to adjust.
114 alternative
116 The name of a specific file in the filesystem, which may be made
117 accessible via a generic name using the alternatives system.
118 alternatives directory
120 A directory, by default /etc/alternatives, containing the sym‐
121 links.
122 administrative directory
124 A directory, by default /var/lib/alternatives, containing alter‐
125 natives' state information.
126 link group
128 A set of related symlinks, intended to be updated as a group.
129 master link
131 The link in a link group which determines how the other links in
132 the group are configured.
133 slave link
135 A link in a link group which is controlled by the setting of the
136 master link.
137 automatic mode
139 When a link group is in automatic mode, the alternatives system
140 ensures that the links in the group point to the highest prior‐
141 ity alternatives appropriate for the group.
142 manual mode
144 When a link group is in manual mode, the alternatives system
145 will not make any changes to the system administrator's set‐
146 tings.
147
149 Exactly one action must be specified if alternatives is to perform any
150 meaningful task. Any number of the common options may be specified
151 together with any action.
152 COMMON OPTIONS
154 --verbose
155 Generate more comments about what alternatives is doing.
156 --quiet
158 Don't generate any comments unless errors occur. This option is
159 not yet implemented.
160 --test Don't actually do anything, just say what would be done. This
162 option is not yet implemented.
163 --help Give some usage information (and say which version of alterna‐
165 tives this is).
166 --version
168 Tell which version of alternatives this is (and give some usage
169 information).
170 --keep-missing
172 When switching between alternatives, if the new variant does not
173 provide some files, keep the links pointed to the previous
174 implementation. It prevents issues with missing files due to
175 switching between versions.
176 --altdir directory
178 Specifies the alternatives directory, when this is to be differ‐
179 ent from the default.
180 --admindir directory
182 Specifies the administrative directory, when this is to be dif‐
183 ferent from the default.
184 ACTIONS
186 --install link name path priority [--slave slink sname spath]
187 [--initscript service]...
188 Add a group of alternatives to the system. name is the generic
189 name for the master link, link is the name of its symlink, path
190 is the alternative being introduced for the master link, and
191 priority is the priority of the alternatives group. Higher pri‐
192 orities take precendence if no alternative is manually selected.
193 sname, slink and spath are the generic name, symlink name and
194 alternative for a slave link, and service is the name of any
195 associated initscript for the alternative. NOTE: --initscript
196 and --family are a Red Hat Linux specific options. Zero or more
197 --slave options, each followed by three arguments, may be speci‐
198 fied.
199 If the master symlink specified exists already in the alterna‐
201 tives system's records, the information supplied will be added
202 as a new set of alternatives for the group. Otherwise, a new
203 group, set to automatic mode, will be added with this informa‐
204 tion. If the group is in automatic mode, and the newly added
205 alternatives' priority is higher than any other installed alter‐
206 natives for this group, the symlinks will be updated to point to
207 the newly added alternatives.
208 If --initscript is used, the alternatives system will manage the
210 initscript associated with the alternative via chkconfig, regis‐
211 tering and unregistering the init script depending on which
212 alternative is active.
213 NOTE: --initscript is a Red Hat Linux specific option.
215 --family can be used to group similar alternatives. If the group
218 is in manual mode and the alternative currently used is removed,
219 alternatives will try to change links to different one with same
220 family and highest priority.
221 NOTE: --family is a Red Hat Linux specific option.
223 --remove name path
225 Remove an alternative and all of its associated slave links.
226 name is a name in the alternatives directory, and path is an
227 absolute filename to which name could be linked. If name is
228 indeed linked to path, name will be updated to point to another
229 appropriate alternative, or removed if there is no such alterna‐
230 tive left. Associated slave links will be updated or removed,
231 correspondingly. If the link is not currently pointing to path,
232 no links are changed; only the information about the alternative
233 is removed.
234 --set name path
236 The symbolic link and slaves for link group name set to those
237 configured for path, and the link group is set to manual mode.
238 This option is not in the original Debian implementation.
239 --config name
241 Present the user with a configuration menu for choosing the mas‐
242 ter link and slaves for link group name. Once chosen, the link
243 group is set to manual mode.
244 --auto name
246 Switch the master symlink name to automatic mode. In the
247 process, this symlink and its slaves are updated to point to the
248 highest priority installed alternatives.
249 --display name
251 Display information about the link group of which name is the
252 master link. Information displayed includes the group's mode
253 (auto or manual), which alternative the symlink currently points
254 to, what other alternatives are available (and their correspond‐
255 ing slave alternatives), and the highest priority alternative
256 currently installed.
257 --list Display information about all link groups.
259 --remove-all name
261 Remove the whole link group name. Use with caution.
262 --add-slave name path slink sname spath
264 Add a slave link to an alternative identified by name and path.
265 sname, slink and spath are the generic name, symlink name and
266 alternative for the slave.
267 --remove-slave name path sname
269 Remove slave with generic name sname from alternative identified
270 by name and path.
271
273 /etc/alternatives/
274 The default alternatives directory. Can be overridden by the
275 --altdir option.
276 /var/lib/alternatives/
278 The default administration directory. Can be overridden by the
279 --admindir option.
280
282 0 The requested action was successfully performed.
283 2 Problems were encountered whilst parsing the command line or
285 performing the action.
286
288 alternatives chatters incessantly about its activities on its standard
289 output channel. If problems occur, alternatives outputs error messages
290 on its standard error channel and returns an exit status of 2. These
291 diagnostics should be self-explanatory; if you do not find them so,
292 please report this as a bug.
293
295 If you find a bug, please report it using the Red Hat bug tracking sys‐
296 tem at http://bugzilla.redhat.com.
297 If you find any discrepancy between the operation of alternatives and
299 this manual page, it is a bug, either in the implementation or the doc‐
300 umentation; please report it. Any significant differences between this
301 implementation and Debian's is also a bug and should be reported,
302 unless otherwise noted in this man page.
303
305 alternatives is copyright 2002 Red Hat, Inc.. It is free software; see
306 the GNU General Public Licence version 2 or later for copying condi‐
307 tions. There is NO warranty.
308 This manual page is copyright 1997/98 Charles Briscoe-Smith and 2002
310 Red Hat, Inc. This is free documentation; see the GNU General Public
311 Licence version 2 or later for copying conditions. There is NO WAR‐
312 RANTY.
313
315 ln(1), FHS, the Filesystem Hierarchy Standard.
316 27 January 2001 UPDATE-ALTERNATIVES(8)