1UPDATE-ALTERNATIVES(8)      System Manager's Manual     UPDATE-ALTERNATIVES(8)
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NAME

6       alternatives - maintain symbolic links determining default commands
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SYNOPSIS

9       alternatives  [options] --install link name path priority [--slave link
10       name path]...  [--initscript service] [--family name]
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12       alternatives [options] --remove name path
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14       alternatives [options] --set name path
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16       alternatives [options] --auto name
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18       alternatives [options] --display name
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20       alternatives [options] --config name
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22       alternatives [options] --list name
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DESCRIPTION

25       alternatives creates, removes, maintains and displays information about
26       the symbolic links comprising the alternatives system. The alternatives
27       system is a reimplementation of the Debian alternatives system. It  was
28       rewritten primarily to remove the dependence on perl; it is intended to
29       be a drop in replacement for Debian's update-dependencies script.  This
30       man page is a slightly modified version of the man page from the Debian
31       project.
32
33       It is possible for several programs  fulfilling  the  same  or  similar
34       functions  to  be  installed  on a single system at the same time.  For
35       example, many systems have several  text  editors  installed  at  once.
36       This gives choice to the users of a system, allowing each to use a dif‐
37       ferent editor, if desired, but makes it difficult for a program to make
38       a  good choice of editor to invoke if the user has not specified a par‐
39       ticular preference.
40
41       The alternatives system aims to solve this problem.  A generic name  in
42       the  filesystem  is shared by all files providing interchangeable func‐
43       tionality.   The  alternatives  system  and  the  system  administrator
44       together  determine  which  actual  file  is referenced by this generic
45       name.  For example, if the text  editors  ed(1)  and  nvi(1)  are  both
46       installed on the system, the alternatives system will cause the generic
47       name /usr/bin/editor to refer to /usr/bin/nvi by default.   The  system
48       administrator  can  override  this and cause it to refer to /usr/bin/ed
49       instead, and the alternatives system will not alter this setting  until
50       explicitly requested to do so.
51
52       The generic name is not a direct symbolic link to the selected alterna‐
53       tive.  Instead, it is a symbolic link to a  name  in  the  alternatives
54       directory,  which  in turn is a symbolic link to the actual file refer‐
55       enced.  This is done so that the system administrator's changes can  be
56       confined  within  the  /etc directory: the FHS (q.v.) gives reasons why
57       this is a Good Thing.
58
59       When each package providing a file with a particular  functionality  is
60       installed,  changed or removed, alternatives is called to update infor‐
61       mation about that file in the  alternatives  system.   alternatives  is
62       usually called from the %post or %pre scripts in RPM packages.
63
64       It  is often useful for a number of alternatives to be synchronised, so
65       that they are changed as a group; for example, when several versions of
66       the   vi(1)   editor   are   installed,  the  man  page  referenced  by
67       /usr/share/man/man1/vi.1 should correspond to the executable referenced
68       by /usr/bin/vi.  alternatives handles this by means of master and slave
69       links; when the master is changed, any associated  slaves  are  changed
70       too.  A master link and its associated slaves make up a link group.
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72       Each  link  group is, at any given time, in one of two modes: automatic
73       or manual.  When a group is in automatic mode, the alternatives  system
74       will  automatically  decide,  as  packages  are  installed and removed,
75       whether and how to update the links.  In manual mode, the  alternatives
76       system  will  not  change the links; it will leave all the decisions to
77       the system administrator.
78
79       Link groups are in automatic mode when they are first introduced to the
80       system.   If  the  system  administrator  makes changes to the system's
81       automatic settings, this will be noticed the next time alternatives  is
82       run  on  the  changed link's group, and the group will automatically be
83       switched to manual mode.
84
85       Each alternative has a priority associated with it.  When a link  group
86       is  in  automatic  mode,  the alternatives pointed to by members of the
87       group will be those which have the highest priority.
88
89       When using the --config option,  alternatives  will  list  all  of  the
90       choices for the link group of which given name is the master link.  You
91       will then be prompted for which of the choices  to  use  for  the  link
92       group. Once you make a change, the link group will no longer be in auto
93       mode. You will need to use the --auto option in order to return to  the
94       automatic state.
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TERMINOLOGY

97       Since  the activities of alternatives are quite involved, some specific
98       terms will help to explain its operation.
99
100       generic name
101              A name, like /usr/bin/editor, which refers, via the alternatives
102              system, to one of a number of files of similar function.
103
104       symlink
105              Without any further qualification, this means a symbolic link in
106              the alternatives directory: one which the  system  administrator
107              is expected to adjust.
108
109       alternative
110              The name of a specific file in the filesystem, which may be made
111              accessible via a generic name using the alternatives system.
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113       alternatives directory
114              A directory, by default /etc/alternatives, containing  the  sym‐
115              links.
116
117       administrative directory
118              A directory, by default /var/lib/alternatives, containing alter‐
119              natives' state information.
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121       link group
122              A set of related symlinks, intended to be updated as a group.
123
124       master link
125              The link in a link group which determines how the other links in
126              the group are configured.
127
128       slave link
129              A link in a link group which is controlled by the setting of the
130              master link.
131
132       automatic mode
133              When a link group is in automatic mode, the alternatives  system
134              ensures  that the links in the group point to the highest prior‐
135              ity alternatives appropriate for the group.
136
137       manual mode
138              When a link group is in manual  mode,  the  alternatives  system
139              will  not  make  any  changes to the system administrator's set‐
140              tings.
141

OPTIONS

143       Exactly one action must be specified if alternatives is to perform  any
144       meaningful  task.   Any  number  of the common options may be specified
145       together with any action.
146
147   COMMON OPTIONS
148       --verbose
149              Generate more comments about what alternatives is doing.
150
151       --quiet
152              Don't generate any comments unless errors occur.  This option is
153              not yet implemented.
154
155       --test Don't  actually  do anything, just say what would be done.  This
156              option is not yet implemented.
157
158       --help Give some usage information (and say which version  of  alterna‐
159              tives this is).
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161       --version
162              Tell  which version of alternatives this is (and give some usage
163              information).
164
165       --altdir directory
166              Specifies the alternatives directory, when this is to be differ‐
167              ent from the default.
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169       --admindir directory
170              Specifies  the administrative directory, when this is to be dif‐
171              ferent from the default.
172
173   ACTIONS
174       --install  link  name  path  priority  [--slave  slink   sname   spath]
175       [--initscript service]...
176              Add  a group of alternatives to the system.  name is the generic
177              name for the master link, link is the name of its symlink,  path
178              is  the  alternative  being  introduced for the master link, and
179              priority is the priority of the alternatives group. Higher  pri‐
180              orities take precendence if no alternative is manually selected.
181              sname, slink and spath are the generic name,  symlink  name  and
182              alternative  for  a  slave  link, and service is the name of any
183              associated initscript for the alternative.   NOTE:  --initscript
184              and --family are a Red Hat Linux specific options.  Zero or more
185              --slave options, each followed by three arguments, may be speci‐
186              fied.
187
188              If  the  master symlink specified exists already in the alterna‐
189              tives system's records, the information supplied will  be  added
190              as  a  new  set of alternatives for the group.  Otherwise, a new
191              group, set to automatic mode, will be added with  this  informa‐
192              tion.   If  the  group is in automatic mode, and the newly added
193              alternatives' priority is higher than any other installed alter‐
194              natives for this group, the symlinks will be updated to point to
195              the newly added alternatives.
196
197              If --initscript is used, the alternatives system will manage the
198              initscript associated with the alternative via chkconfig, regis‐
199              tering and unregistering the  init  script  depending  on  which
200              alternative is active.
201
202              NOTE: --initscript is a Red Hat Linux specific option.
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204
205              --family can be used to group similar alternatives. If the group
206              is in manual mode and the alternative currently used is removed,
207              alternatives will try to change links to different one with same
208              family and highest priority.
209
210              NOTE: --family is a Red Hat Linux specific option.
211
212       --remove name path
213              Remove an alternative and all of  its  associated  slave  links.
214              name  is  a  name  in the alternatives directory, and path is an
215              absolute filename to which name could be  linked.   If  name  is
216              indeed  linked to path, name will be updated to point to another
217              appropriate alternative, or removed if there is no such alterna‐
218              tive  left.   Associated slave links will be updated or removed,
219              correspondingly.  If the link is not currently pointing to path,
220              no links are changed; only the information about the alternative
221              is removed.
222
223       --set name path
224              The symbolic link and slaves for link group name  set  to  those
225              configured  for  path, and the link group is set to manual mode.
226              This option is not in the original Debian implementation.
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228       --config name
229              Present the user with a configuration menu for choosing the mas‐
230              ter  link  and slaves for link group name. Once chosen, the link
231              group is set to manual mode.
232
233       --auto name
234              Switch the master  symlink  name  to  automatic  mode.   In  the
235              process, this symlink and its slaves are updated to point to the
236              highest priority installed alternatives.
237
238       --display name
239              Display information about the link group of which  name  is  the
240              master  link.   Information  displayed includes the group's mode
241              (auto or manual), which alternative the symlink currently points
242              to, what other alternatives are available (and their correspond‐
243              ing slave alternatives), and the  highest  priority  alternative
244              currently installed.
245
246       --list Display information about all link groups.
247

FILES

249       /etc/alternatives/
250              The  default  alternatives  directory.  Can be overridden by the
251              --altdir option.
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253       /var/lib/alternatives/
254              The default administration directory.  Can be overridden by  the
255              --admindir option.
256

EXIT STATUS

258       0      The requested action was successfully performed.
259
260       2      Problems  were  encountered  whilst  parsing the command line or
261              performing the action.
262

DIAGNOSTICS

264       alternatives chatters incessantly about its activities on its  standard
265       output channel.  If problems occur, alternatives outputs error messages
266       on its standard error channel and returns an exit status of  2.   These
267       diagnostics  should  be  self-explanatory;  if you do not find them so,
268       please report this as a bug.
269

BUGS

271       If you find a bug, please report it using the Red Hat bug tracking sys‐
272       tem at http://bugzilla.redhat.com.
273
274       If  you  find any discrepancy between the operation of alternatives and
275       this manual page, it is a bug, either in the implementation or the doc‐
276       umentation; please report it.  Any significant differences between this
277       implementation and Debian's is also  a  bug  and  should  be  reported,
278       unless otherwise noted in this man page.
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AUTHOR

281       alternatives is copyright 2002 Red Hat, Inc..  It is free software; see
282       the GNU General Public Licence version 2 or later  for  copying  condi‐
283       tions.  There is NO warranty.
284
285       This  manual  page  is copyright 1997/98 Charles Briscoe-Smith and 2002
286       Red Hat, Inc.  This is free documentation; see the GNU  General  Public
287       Licence  version  2  or later for copying conditions.  There is NO WAR‐
288       RANTY.
289

SEE ALSO

291       ln(1), FHS, the Filesystem Hierarchy Standard.  alternatives.c  chkcon‐
292       fig.c COPYING leveldb.c leveldb.h Makefile ntsysv.c ook
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296                                27 January 2001         UPDATE-ALTERNATIVES(8)
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