MAN page from Mandriva 2008 update-alternatives-1.9.0-1mdv2008.0.noarch.rpm
Section: Mandriva Linux (8)
update-alternatives - maintain symbolic links determining default commands
creates, removes, maintains and displays information about the symboliclinks comprising the Mandriva Linux alternatives system.
It is possible for several programs fulfilling the same or similarfunctions to be installed on a single system at the same time.For example, many systems have several text editors installed at once.This gives choice to the users of a system, allowing each to use adifferent editor, if desired, but makes it difficult for a programto make a good choice for an editor to invoke if theuser has not specified a particular preference.
Mandriva's alternatives system aims to solve this problem.A generic name in the filesystem isshared by all files providing interchangeable functionality.The alternatives system and the system administratortogether determine which actual file is referenced by this generic name.For example, if the text editorsed(1)andnvi(1)are both installed on the system, the alternatives system will causethe generic name/usr/bin/editorto refer to/usr/bin/nviby default. The system administrator can override this and causeitto refer to/usr/bin/edinstead,and the alternatives system will not alter this setting until explicitlyrequested to do so.
The generic name is not a direct symbolic link to the selected alternative.Instead, it is a symbolic link to a name in thealternativesdirectory,which in turn is a symbolic link to the actual file referenced.This is done so that the system administrator's changes can be confinedwithin the/etcdirectory: the FHS (q.v.) gives reasons why this is a Good Thing.
When each packageproviding a file with a particular functionality isinstalled, changed or removed,update-alternativesis called to update information about that file in the alternatives system.update-alternativesis usually called from thepostorpostunscripts in Mandriva Linux packages.
It is often useful for a number of alternatives to be synchronised,so that they are changed as a group; for example, when several versionsof thevi(1)editor are installed, the man page referenced by/usr/share/man/man1/vi.1should correspond to the executable referenced by/usr/bin/vi.update-alternativeshandles this by means ofmasterandslavelinks; when the master is changed, any associated slaves are changedtoo.A master link and its associated slaves make up alinkgroup.
Each link group is, at any given time,in one of two modes: automatic or manual.When a group is in automatic mode, the alternatives system willautomatically decide, as packages are installed and removed,whether and how to update the links.In manual mode, the alternatives system will not change the links;it will leave all the decisions to the system administrator.
Link groups are in automatic mode when they are first introduced tothe system.If the system administrator makes changes to the system'sautomatic settings,this will be noticed the next timeupdate-alternativesis run on the changed link's group,and the group will automatically be switched to manual mode.
Each alternative has apriorityassociated with it.When a link group is in automatic mode,the alternatives pointed to by members of the groupwill be those which have the highest priority.
When using the--configoption,update-alternativeswill list all of the choices for the link groupof which givennameis the master link. The current choice is marked with a '*' and thechoice with the highest priority with a '+'.You will then be prompted for your choice regarding this link group.Once you make a change, the link group will no longer be inautomode. You will need to use the--autooption in order to return to the automatic mode.
If you want to configure non-interactively you can use the--setoption instead (see below).
Different packages providing the same file need to do socooperatively.That is - the usage ofupdate-alternativesismandatoryfor all involved packages in such case - it is not possible tooverride some file in a package that does not employ theupdate-alternativesmechanism.
Since the activities ofupdate-alternatives
are quite involved, some specific terms will help to explain itsoperation.
- generic name
- A name, like/usr/bin/editor,which refers, via the alternatives system, to one of a number offiles of similar function.
- Without any further qualification, this means a symbolic link in thealternatives directory: one which the system administrator is expectedto adjust.
- The name of a specific file in the filesystem, which may be madeaccessible via a generic name using the alternatives system.
- alternatives directory
- A directory, by default/etc/alternatives,containing the symlinks.
- administrative directory
- A directory, by default/var/lib/dpkg/alternatives,containingupdate-alternatives'state information.
- link group
- A set of related symlinks, intended to be updated as a group.
- master link
- The link in a link group which determines how the other links in thegroup are configured.
- slave link
- A link in a link group which is controlled by the setting ofthe master link.
- automatic mode
- When a link group is in automatic mode,the alternatives system ensures that the links in the grouppoint to the highest priority alternativeappropriate for the group.
- manual mode
- When a link group is in manual mode,the alternatives system will not make any changesto the system administrator's settings.
- --install genname symlink altern priority [--slave genname symlink altern]...
- Add a group of alternatives to the system.gennameis the generic name for the master link,symlinkis the name of its symlink in the alternatives directory, andalternis the alternative being introduced for the master link.The arguments after --slave are the generic name, symlink name in thealternatives directory and the alternative for a slave link.Zero or more--slaveoptions, each followed by three arguments,may be specified.
- If the master symlink specified exists alreadyin the alternatives system's records,the information supplied will be added as a newset of alternatives for the group.Otherwise, a new group, set to automatic mode,will be added with this information.If the group is in automatic mode,and the newly added alternatives' priority is higher thanany other installed alternatives for this group,the symlinks will be updated to point to the newly added alternatives.
- --set name path
- Set the programpathas alternative forname.This is equivalent to--configbut is non-interactive and thus scriptable.
- --remove name path
- Remove an alternative and all of its associated slave links.nameis a name in the alternatives directory, andpathis an absolute filename to whichnamecould be linked. Ifnameis indeed linked topath,namewill be updated to point to another appropriate alternative, orremoved if there is no such alternative left.Associated slave links will be updated or removed, correspondingly.If the link is not currently pointing topath,no links are changed;only the information about the alternative is removed.
- --remove-all name
- Remove all alternatives and all of their associated slave links.nameis a name in the alternatives directory.
- --auto link
- Switch the master symlinklinkto automatic mode.In the process, this symlink and its slaves are updatedto point to the highest priority installed alternatives.
- --display link
- Display information about the link group of whichlinkis the master link.Information displayed includes the group's mode(auto or manual),which alternative the symlink currently points to,what other alternatives are available(and their corresponding slave alternatives),and the highest priority alternative currently installed.
- --list link
- Display all targets of the link group.
- --config link
- Show available alternatives for a link group and allow the user tointeractively select which one to use. The link group is updatedand taken out ofautomode.
- Show the usage message and exit.
- Show the version and exit.
- --altdir directory
- Specifies the alternatives directory, when this is to bedifferent from the default.
- --admindir directory
- Specifies the administrative directory, when this is to bedifferent from the default.
- Generate more comments about whatupdate-alternativesis doing.
- Don't generate any comments unless errors occur.This option is not yet implemented.
- Don't actually do anything, just say what would be done.This option is not yet implemented.
- The default alternatives directory.Can be overridden by the--altdiroption.
- The default administration directory.Can be overridden by the--admindiroption.
- The requested action was successfully performed.
- Problems were encountered whilst parsing the command lineor performing the action.
chatters incessantly about its activities on its standard output channel.If problems occur,update-alternatives
outputs error messages on its standard error channel andreturns an exit status of 2.These diagnostics should be self-explanatory;if you do not find them so, please report this as a bug.
There are several packages which provide a text editor compatiblewith vi
, for example nvi
. Which one is usedis controlled by the link group vi
, which includes links for theprogram itself and the associated manpage.
To display the available packages which provide vi and the currentsetting for it, use the --display action:
update-alternatives --display vi
To choose a particular vi implementation, use this command as rootand then select a number from the list:
update-alternatives --config vi
To go back to having the vi implementation chosen automatically, dothis as root:
update-alternatives --auto vi
If you find a bug, please report it using the Mandriva bug-tracking system,or, if that is not possible, email the author directly.
If you find any discrepancy between the operation ofupdate-alternativesand this manual page, it is a bug,either in the implementation or the documentation; please report it.
Copyright (C) 1995 Ian Jackson
This is free software; see the GNU General Public Licence version 2 orlater for copying conditions. There is NO WARRANTY.
This manual page is copyright 1997,1998 Charles Briscoe-Smith.
This is free documentation; see the GNU General Public Licence version 2 orlater for copying conditions. There is NO WARRANTY.
(1),FHS, the Filesystem Hierarchy Standard.
- EXIT STATUS
- SEE ALSO
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