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 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 --altdir directory
172 Specifies the alternatives directory, when this is to be differ‐
173 ent from the default.
174 --admindir directory
176 Specifies the administrative directory, when this is to be dif‐
177 ferent from the default.
178 ACTIONS
180 --install link name path priority [--slave slink sname spath]
181 [--initscript service]...
182 Add a group of alternatives to the system. name is the generic
183 name for the master link, link is the name of its symlink, path
184 is the alternative being introduced for the master link, and
185 priority is the priority of the alternatives group. Higher pri‐
186 orities take precendence if no alternative is manually selected.
187 sname, slink and spath are the generic name, symlink name and
188 alternative for a slave link, and service is the name of any
189 associated initscript for the alternative. NOTE: --initscript
190 and --family are a Red Hat Linux specific options. Zero or more
191 --slave options, each followed by three arguments, may be speci‐
192 fied.
193 If the master symlink specified exists already in the alterna‐
195 tives system's records, the information supplied will be added
196 as a new set of alternatives for the group. Otherwise, a new
197 group, set to automatic mode, will be added with this informa‐
198 tion. If the group is in automatic mode, and the newly added
199 alternatives' priority is higher than any other installed alter‐
200 natives for this group, the symlinks will be updated to point to
201 the newly added alternatives.
202 If --initscript is used, the alternatives system will manage the
204 initscript associated with the alternative via chkconfig, regis‐
205 tering and unregistering the init script depending on which
206 alternative is active.
207 NOTE: --initscript is a Red Hat Linux specific option.
209 --family can be used to group similar alternatives. If the group
212 is in manual mode and the alternative currently used is removed,
213 alternatives will try to change links to different one with same
214 family and highest priority.
215 NOTE: --family is a Red Hat Linux specific option.
217 --remove name path
219 Remove an alternative and all of its associated slave links.
220 name is a name in the alternatives directory, and path is an
221 absolute filename to which name could be linked. If name is
222 indeed linked to path, name will be updated to point to another
223 appropriate alternative, or removed if there is no such alterna‐
224 tive left. Associated slave links will be updated or removed,
225 correspondingly. If the link is not currently pointing to path,
226 no links are changed; only the information about the alternative
227 is removed.
228 --set name path
230 The symbolic link and slaves for link group name set to those
231 configured for path, and the link group is set to manual mode.
232 This option is not in the original Debian implementation.
233 --config name
235 Present the user with a configuration menu for choosing the mas‐
236 ter link and slaves for link group name. Once chosen, the link
237 group is set to manual mode.
238 --auto name
240 Switch the master symlink name to automatic mode. In the
241 process, this symlink and its slaves are updated to point to the
242 highest priority installed alternatives.
243 --display name
245 Display information about the link group of which name is the
246 master link. Information displayed includes the group's mode
247 (auto or manual), which alternative the symlink currently points
248 to, what other alternatives are available (and their correspond‐
249 ing slave alternatives), and the highest priority alternative
250 currently installed.
251 --list Display information about all link groups.
253 --remove-all name
255 Remove the whole link group name. Use with caution.
256 --add-slave name path slink sname spath
258 Add a slave link to an alternative identified by name and path.
259 sname, slink and spath are the generic name, symlink name and
260 alternative for the slave.
261 --remove-slave name path sname
263 Remove slave with generic name sname from alternative identified
264 by name and path.
265
267 /etc/alternatives/
268 The default alternatives directory. Can be overridden by the
269 --altdir option.
270 /var/lib/alternatives/
272 The default administration directory. Can be overridden by the
273 --admindir option.
274
276 0 The requested action was successfully performed.
277 2 Problems were encountered whilst parsing the command line or
279 performing the action.
280
282 alternatives chatters incessantly about its activities on its standard
283 output channel. If problems occur, alternatives outputs error messages
284 on its standard error channel and returns an exit status of 2. These
285 diagnostics should be self-explanatory; if you do not find them so,
286 please report this as a bug.
287
289 If you find a bug, please report it using the Red Hat bug tracking sys‐
290 tem at http://bugzilla.redhat.com.
291 If you find any discrepancy between the operation of alternatives and
293 this manual page, it is a bug, either in the implementation or the doc‐
294 umentation; please report it. Any significant differences between this
295 implementation and Debian's is also a bug and should be reported,
296 unless otherwise noted in this man page.
297
299 alternatives is copyright 2002 Red Hat, Inc.. It is free software; see
300 the GNU General Public Licence version 2 or later for copying condi‐
301 tions. There is NO warranty.
302 This manual page is copyright 1997/98 Charles Briscoe-Smith and 2002
304 Red Hat, Inc. This is free documentation; see the GNU General Public
305 Licence version 2 or later for copying conditions. There is NO WAR‐
306 RANTY.
307
309 ln(1), FHS, the Filesystem Hierarchy Standard. alternatives.c chkcon‐
310 fig.c COPYING leveldb.c leveldb.h Makefile ntsysv.c ook
311 27 January 2001 UPDATE-ALTERNATIVES(8)