update-alternatives(1) dpkg utilities update-alternatives(1)NAMEupdate-alternatives - maintain symbolic links determining default com‐
mands
SYNOPSISupdate-alternatives [option...] command
DESCRIPTIONupdate-alternatives creates, removes, maintains and displays informa‐
tion about the symbolic links comprising the Debian alternatives sys‐
tem.
It is possible for several programs fulfilling the same or similar
functions 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 a dif‐
ferent editor, if desired, but makes it difficult for a program to make
a good choice for an editor to invoke if the user has not specified a
particular preference.
Debian's alternatives system aims to solve this problem. A generic
name in the filesystem is shared by all files providing interchangeable
functionality. The alternatives system and the system administrator
together determine which actual file is referenced by this generic
name. For example, if the text editors ed(1) and nvi(1) are both
installed on the system, the alternatives system will cause the generic
name /usr/bin/editor to refer to /usr/bin/nvi by default. The system
administrator can override this and cause it to refer to /usr/bin/ed
instead, and the alternatives system will not alter this setting until
explicitly requested to do so.
The generic name is not a direct symbolic link to the selected alterna‐
tive. Instead, it is a symbolic link to a name in the alternatives
directory, which in turn is a symbolic link to the actual file refer‐
enced. This is done so that the system administrator's changes can be
confined within the /etc directory: the FHS (q.v.) gives reasons why
this is a Good Thing.
When each package providing a file with a particular functionality is
installed, changed or removed, update-alternatives is called to update
information about that file in the alternatives system. update-alter‐
natives is usually called from the postinst (configure) or prerm
(remove and deconfigure) scripts in Debian packages.
It is often useful for a number of alternatives to be synchronized, so
that they are changed as a group; for example, when several versions of
the vi(1) editor are installed, the man page referenced by
/usr/share/man/man1/vi.1 should correspond to the executable referenced
by /usr/bin/vi. update-alternatives handles this by means of master
and slave links; when the master is changed, any associated slaves are
changed too. A master link and its associated slaves make up a link
group.
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
will automatically decide, as packages are installed and removed,
whether and how to update the links. In manual mode, the alternatives
system will retain the choice of the administrator and avoid changing
the links (except when something is broken).
Link groups are in automatic mode when they are first introduced to the
system. If the system administrator makes changes to the system's
automatic settings, this will be noticed the next time update-alterna‐
tives is run on the changed link's group, and the group will automati‐
cally be switched to manual mode.
Each alternative has a priority associated with it. When a link group
is in automatic mode, the alternatives pointed to by members of the
group will be those which have the highest priority.
When using the --config option, update-alternatives will list all of
the choices for the link group of which given name is the master alter‐
native name. The current choice is marked with a ‘*’. You will then
be prompted for your choice regarding this link group. Depending on
the choice made, the link group might no longer be in auto mode. You
will need to use the --auto option in order to return to the automatic
mode (or you can rerun --config and select the entry marked as auto‐
matic).
If you want to configure non-interactively you can use the --set option
instead (see below).
Different packages providing the same file need to do so cooperatively.
In other words, the usage of update-alternatives is mandatory for all
involved packages in such case. It is not possible to override some
file in a package that does not employ the update-alternatives mecha‐
nism.
TERMINOLOGY
Since the activities of update-alternatives are quite involved, some
specific terms will help to explain its operation.
generic name (or alternative link)
A name, like /usr/bin/editor, which refers, via the alternatives
system, to one of a number of files of similar function.
alternative name
The name of a symbolic link in the alternatives directory.
alternative (or alternative path)
The name of a specific file in the filesystem, which may be made
accessible via a generic name using the alternatives system.
alternatives directory
A directory, by default /etc/alternatives, containing the sym‐
links.
administrative directory
A directory, by default /var/lib/dpkg/alternatives, containing
update-alternatives' state information.
link group
A set of related symlinks, intended to be updated as a group.
master link
The alternative link in a link group which determines how the
other links in the group are configured.
slave link
An alternative link in a link group which is controlled by the
setting of the master link.
automatic mode
When a link group is in automatic mode, the alternatives system
ensures that the links in the group point to the highest prior‐
ity alternative appropriate for the group.
manual mode
When a link group is in manual mode, the alternatives system
will not make any changes to the system administrator's set‐
tings.
COMMANDS--install link name path priority [--slave link name path]...
Add a group of alternatives to the system. link is the generic
name for the master link, name is the name of its symlink in the
alternatives directory, and path is the alternative being intro‐
duced for the master link. The arguments after --slave are the
generic name, symlink name in the alternatives directory and the
alternative path for a slave link. Zero or more --slave
options, each followed by three arguments, may be specified.
Note that the master alternative must exist or the call will
fail. However if a slave alternative doesn't exist, the corre‐
sponding slave alternative link will simply not be installed (a
warning will still be displayed). If some real file is installed
where an alternative link has to be installed, it is kept unless
--force is used.
If the alternative name specified exists already in the alterna‐
tives system's records, the information supplied will be added
as a new set of alternatives for the group. Otherwise, a new
group, set to automatic mode, will be added with this informa‐
tion. If the group is in automatic mode, and the newly added
alternatives' priority is higher than any other installed alter‐
natives for this group, the symlinks will be updated to point to
the newly added alternatives.
--set name path
Set the program path as alternative for name. This is equiva‐
lent to --config but is non-interactive and thus scriptable.
--remove name path
Remove an alternative and all of its associated slave links.
name is a name in the alternatives directory, and path is an
absolute filename to which name could be linked. If name is
indeed linked to path, name will be updated to point to another
appropriate alternative (and the group is put back in automatic
mode), or removed if there is no such alternative left. Associ‐
ated slave links will be updated or removed, correspondingly.
If the link is not currently pointing to path, 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.
name is a name in the alternatives directory.
--all Call --config on all alternatives. It can be usefully combined
with --skip-auto to review and configure all alternatives which
are not configured in automatic mode. Broken alternatives are
also displayed. Thus a simple way to fix all broken alterna‐
tives is to call yes '' | update-alternatives--force --all.
--auto name
Switch the link group behind the alternative for name to auto‐
matic mode. In the process, the master symlink and its slaves
are updated to point to the highest priority installed alterna‐
tives.
--display name
Display information about the link group. Information displayed
includes the group's mode (auto or manual), the master and slave
links, which alternative the master link currently points to,
what other alternatives are available (and their corresponding
slave alternatives), and the highest priority alternative cur‐
rently installed.
--get-selections
List all master alternative names (those controlling a link
group) and their status (since version 1.15.0). Each line con‐
tains up to 3 fields (separated by one or more spaces). The
first field is the alternative name, the second one is the sta‐
tus (either auto or manual), and the last one contains the cur‐
rent choice in the alternative (beware: it's a filename and thus
might contain spaces).
--set-selections
Read configuration of alternatives on standard input in the for‐
mat generated by --get-selections and reconfigure them accord‐
ingly (since version 1.15.0).
--query name
Display information about the link group like --display does,
but in a machine parseable way (since version 1.15.0, see sec‐
tion QUERY FORMAT below).
--list name
Display all targets of the link group.
--config name
Show available alternatives for a link group and allow the user
to interactively select which one to use. The link group is
updated.
--help Show the usage message and exit.
--version
Show the version and exit.
OPTIONS--altdir directory
Specifies the alternatives directory, when this is to be differ‐
ent from the default.
--admindir directory
Specifies the administrative directory, when this is to be dif‐
ferent from the default.
--log file
Specifies the log file (since version 1.15.0), when this is to
be different from the default (/var/log/alternatives.log).
--force
Allow replacing or dropping any real file that is installed
where an alternative link has to be installed or removed.
--skip-auto
Skip configuration prompt for alternatives which are properly
configured in automatic mode. This option is only relevant with
--config or --all.
--verbose
Generate more comments about what is being done.
--quiet
Don't generate any comments unless errors occur.
EXIT STATUS
0 The requested action was successfully performed.
2 Problems were encountered whilst parsing the command line or
performing the action.
ENVIRONMENT
DPKG_ADMINDIR
If set and the --admindir option has not been specified, it will
be used as the base administrative directory.
FILES
/etc/alternatives/
The default alternatives directory. Can be overridden by the
--altdir option.
/var/lib/dpkg/alternatives/
The default administration directory. Can be overridden by the
--admindir option.
QUERY FORMAT
The --query format is using an RFC822-like flat format. It's made of n
+ 1 blocks where n is the number of alternatives available in the
queried link group. The first block contains the following fields:
Name: name
The alternative name in the alternative directory.
Link: link
The generic name of the alternative.
Slaves: list-of-slaves
When this field is present, the next lines hold all slave links
associated to the master link of the alternative. There is one
slave per line. Each line contains one space, the generic name
of the slave alternative, another space, and the path to the
slave link.
Status: status
The status of the alternative (auto or manual).
Best: best-choice
The path of the best alternative for this link group. Not
present if there is no alternatives available.
Value: currently-selected-alternative
The path of the currently selected alternative. It can also take
the magic value none. It is used if the link doesn't exist.
The other blocks describe the available alternatives in the
queried link group:
Alternative: path-of-this-alternative
Path to this block's alternative.
Priority: priority-value
Value of the priority of this alternative.
Slaves: list-of-slaves
When this field is present, the next lines hold all slave
alternatives associated to the master link of the alter‐
native. There is one slave per line. Each line contains
one space, the generic name of the slave alternative,
another space, and the path to the slave alternative.
Example
$ update-alternatives--query editor
Name: editor
Link: /usr/bin/editor
Slaves:
editor.1.gz /usr/share/man/man1/editor.1.gz
editor.fr.1.gz /usr/share/man/fr/man1/editor.1.gz
editor.it.1.gz /usr/share/man/it/man1/editor.1.gz
editor.pl.1.gz /usr/share/man/pl/man1/editor.1.gz
editor.ru.1.gz /usr/share/man/ru/man1/editor.1.gz
Status: auto
Best: /usr/bin/vim.basic
Value: /usr/bin/vim.basic
Alternative: /bin/ed
Priority: -100
Slaves:
editor.1.gz /usr/share/man/man1/ed.1.gz
Alternative: /usr/bin/vim.basic
Priority: 50
Slaves:
editor.1.gz /usr/share/man/man1/vim.1.gz
editor.fr.1.gz /usr/share/man/fr/man1/vim.1.gz
editor.it.1.gz /usr/share/man/it/man1/vim.1.gz
editor.pl.1.gz /usr/share/man/pl/man1/vim.1.gz
editor.ru.1.gz /usr/share/man/ru/man1/vim.1.gz
DIAGNOSTICS
With --verboseupdate-alternatives chatters incessantly about
its activities on its standard output channel. If problems
occur, update-alternatives outputs error messages on its stan‐
dard error channel and returns an exit status of 2. These diag‐
nostics should be self-explanatory; if you do not find them so,
please report this as a bug.
EXAMPLES
There are several packages which provide a text editor compati‐
ble with vi, for example nvi and vim. Which one is used is con‐
trolled by the link group vi, which includes links for the pro‐
gram itself and the associated manpage.
To display the available packages which provide vi and the cur‐
rent setting for it, use the --display action:
update-alternatives--display vi
To choose a particular vi implementation, use this command as
root and then select a number from the list:
update-alternatives--config vi
To go back to having the vi implementation chosen automatically,
do this as root:
update-alternatives--auto vi
SEE ALSOln(1), FHS, the Filesystem Hierarchy Standard.
Debian Project 2012-07-31 update-alternatives(1)
