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 name
23 alternatives [options] --remove-all name
25
27 alternatives creates, removes, maintains and displays information about
28 the symbolic links comprising the alternatives system. The alternatives
29 system is a reimplementation of the Debian alternatives system. It was
30 rewritten primarily to remove the dependence on perl; it is intended to
31 be a drop in replacement for Debian's update-dependencies script. This
32 man page is a slightly modified version of the man page from the Debian
33 project.
34 It is possible for several programs fulfilling the same or similar
36 functions to be installed on a single system at the same time. For
37 example, many systems have several text editors installed at once.
38 This gives choice to the users of a system, allowing each to use a dif‐
39 ferent editor, if desired, but makes it difficult for a program to make
40 a good choice of editor to invoke if the user has not specified a par‐
41 ticular preference.
42 The alternatives system aims to solve this problem. A generic name in
44 the filesystem is shared by all files providing interchangeable func‐
45 tionality. The alternatives system and the system administrator
46 together determine which actual file is referenced by this generic
47 name. For example, if the text editors ed(1) and nvi(1) are both
48 installed on the system, the alternatives system will cause the generic
49 name /usr/bin/editor to refer to /usr/bin/nvi by default. The system
50 administrator can override this and cause it to refer to /usr/bin/ed
51 instead, and the alternatives system will not alter this setting until
52 explicitly requested to do so.
53 The generic name is not a direct symbolic link to the selected alterna‐
55 tive. Instead, it is a symbolic link to a name in the alternatives
56 directory, which in turn is a symbolic link to the actual file refer‐
57 enced. This is done so that the system administrator's changes can be
58 confined within the /etc directory: the FHS (q.v.) gives reasons why
59 this is a Good Thing.
60 When each package providing a file with a particular functionality is
62 installed, changed or removed, alternatives is called to update infor‐
63 mation about that file in the alternatives system. alternatives is
64 usually called from the %post or %pre scripts in RPM packages.
65 It is often useful for a number of alternatives to be synchronised, so
67 that they are changed as a group; for example, when several versions of
68 the vi(1) editor are installed, the man page referenced by
69 /usr/share/man/man1/vi.1 should correspond to the executable referenced
70 by /usr/bin/vi. alternatives handles this by means of master and slave
71 links; when the master is changed, any associated slaves are changed
72 too. A master link and its associated slaves make up a link group.
73 Each link group is, at any given time, in one of two modes: automatic
75 or manual. When a group is in automatic mode, the alternatives system
76 will automatically decide, as packages are installed and removed,
77 whether and how to update the links. In manual mode, the alternatives
78 system will not change the links; it will leave all the decisions to
79 the system administrator.
80 Link groups are in automatic mode when they are first introduced to the
82 system. If the system administrator makes changes to the system's
83 automatic settings, this will be noticed the next time alternatives is
84 run on the changed link's group, and the group will automatically be
85 switched to manual mode.
86 Each alternative has a priority associated with it. When a link group
88 is in automatic mode, the alternatives pointed to by members of the
89 group will be those which have the highest priority.
90 When using the --config option, alternatives will list all of the
92 choices for the link group of which given name is the master link. You
93 will then be prompted for which of the choices to use for the link
94 group. Once you make a change, the link group will no longer be in auto
95 mode. You will need to use the --auto option in order to return to the
96 automatic state.
97
99 Since the activities of alternatives are quite involved, some specific
100 terms will help to explain its operation.
101 generic name
103 A name, like /usr/bin/editor, which refers, via the alternatives
104 system, to one of a number of files of similar function.
105 symlink
107 Without any further qualification, this means a symbolic link in
108 the alternatives directory: one which the system administrator
109 is expected to adjust.
110 alternative
112 The name of a specific file in the filesystem, which may be made
113 accessible via a generic name using the alternatives system.
114 alternatives directory
116 A directory, by default /etc/alternatives, containing the sym‐
117 links.
118 administrative directory
120 A directory, by default /var/lib/alternatives, containing alter‐
121 natives' state information.
122 link group
124 A set of related symlinks, intended to be updated as a group.
125 master link
127 The link in a link group which determines how the other links in
128 the group are configured.
129 slave link
131 A link in a link group which is controlled by the setting of the
132 master link.
133 automatic mode
135 When a link group is in automatic mode, the alternatives system
136 ensures that the links in the group point to the highest prior‐
137 ity alternatives appropriate for the group.
138 manual mode
140 When a link group is in manual mode, the alternatives system
141 will not make any changes to the system administrator's set‐
142 tings.
143
145 Exactly one action must be specified if alternatives is to perform any
146 meaningful task. Any number of the common options may be specified
147 together with any action.
148 COMMON OPTIONS
150 --verbose
151 Generate more comments about what alternatives is doing.
152 --quiet
154 Don't generate any comments unless errors occur. This option is
155 not yet implemented.
156 --test Don't actually do anything, just say what would be done. This
158 option is not yet implemented.
159 --help Give some usage information (and say which version of alterna‐
161 tives this is).
162 --version
164 Tell which version of alternatives this is (and give some usage
165 information).
166 --altdir directory
168 Specifies the alternatives directory, when this is to be differ‐
169 ent from the default.
170 --admindir directory
172 Specifies the administrative directory, when this is to be dif‐
173 ferent from the default.
174 ACTIONS
176 --install link name path priority [--slave slink sname spath]
177 [--initscript service]...
178 Add a group of alternatives to the system. name is the generic
179 name for the master link, link is the name of its symlink, path
180 is the alternative being introduced for the master link, and
181 priority is the priority of the alternatives group. Higher pri‐
182 orities take precendence if no alternative is manually selected.
183 sname, slink and spath are the generic name, symlink name and
184 alternative for a slave link, and service is the name of any
185 associated initscript for the alternative. NOTE: --initscript
186 and --family are a Red Hat Linux specific options. Zero or more
187 --slave options, each followed by three arguments, may be speci‐
188 fied.
189 If the master symlink specified exists already in the alterna‐
191 tives system's records, the information supplied will be added
192 as a new set of alternatives for the group. Otherwise, a new
193 group, set to automatic mode, will be added with this informa‐
194 tion. If the group is in automatic mode, and the newly added
195 alternatives' priority is higher than any other installed alter‐
196 natives for this group, the symlinks will be updated to point to
197 the newly added alternatives.
198 If --initscript is used, the alternatives system will manage the
200 initscript associated with the alternative via chkconfig, regis‐
201 tering and unregistering the init script depending on which
202 alternative is active.
203 NOTE: --initscript is a Red Hat Linux specific option.
205 --family can be used to group similar alternatives. If the group
208 is in manual mode and the alternative currently used is removed,
209 alternatives will try to change links to different one with same
210 family and highest priority.
211 NOTE: --family is a Red Hat Linux specific option.
213 --remove name path
215 Remove an alternative and all of its associated slave links.
216 name is a name in the alternatives directory, and path is an
217 absolute filename to which name could be linked. If name is
218 indeed linked to path, name will be updated to point to another
219 appropriate alternative, or removed if there is no such alterna‐
220 tive left. Associated slave links will be updated or removed,
221 correspondingly. If the link is not currently pointing to path,
222 no links are changed; only the information about the alternative
223 is removed.
224 --set name path
226 The symbolic link and slaves for link group name set to those
227 configured for path, and the link group is set to manual mode.
228 This option is not in the original Debian implementation.
229 --config name
231 Present the user with a configuration menu for choosing the mas‐
232 ter link and slaves for link group name. Once chosen, the link
233 group is set to manual mode.
234 --auto name
236 Switch the master symlink name to automatic mode. In the
237 process, this symlink and its slaves are updated to point to the
238 highest priority installed alternatives.
239 --display name
241 Display information about the link group of which name is the
242 master link. Information displayed includes the group's mode
243 (auto or manual), which alternative the symlink currently points
244 to, what other alternatives are available (and their correspond‐
245 ing slave alternatives), and the highest priority alternative
246 currently installed.
247 --list Display information about all link groups.
249 --remove-all name
251 Remove the whole link group name. Use with caution.
252
254 /etc/alternatives/
255 The default alternatives directory. Can be overridden by the
256 --altdir option.
257 /var/lib/alternatives/
259 The default administration directory. Can be overridden by the
260 --admindir option.
261
263 0 The requested action was successfully performed.
264 2 Problems were encountered whilst parsing the command line or
266 performing the action.
267
269 alternatives chatters incessantly about its activities on its standard
270 output channel. If problems occur, alternatives outputs error messages
271 on its standard error channel and returns an exit status of 2. These
272 diagnostics should be self-explanatory; if you do not find them so,
273 please report this as a bug.
274
276 If you find a bug, please report it using the Red Hat bug tracking sys‐
277 tem at http://bugzilla.redhat.com.
278 If you find any discrepancy between the operation of alternatives and
280 this manual page, it is a bug, either in the implementation or the doc‐
281 umentation; please report it. Any significant differences between this
282 implementation and Debian's is also a bug and should be reported,
283 unless otherwise noted in this man page.
284
286 alternatives is copyright 2002 Red Hat, Inc.. It is free software; see
287 the GNU General Public Licence version 2 or later for copying condi‐
288 tions. There is NO warranty.
289 This manual page is copyright 1997/98 Charles Briscoe-Smith and 2002
291 Red Hat, Inc. This is free documentation; see the GNU General Public
292 Licence version 2 or later for copying conditions. There is NO WAR‐
293 RANTY.
294
296 ln(1), FHS, the Filesystem Hierarchy Standard. alternatives.c chkcon‐
297 fig.c COPYING leveldb.c leveldb.h Makefile ntsysv.c ook
298 27 January 2001 UPDATE-ALTERNATIVES(8)