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NAME | SYNOPSIS | DESCRIPTION | TERMINOLOGY | COMMANDS | OPTIONS | EXIT STATUS | ENVIRONMENT | FILES | QUERY FORMAT | DIAGNOSTICS | EXAMPLES | SEE ALSO | COLOPHON |
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update-alternatives(1) dpkg suite update-alternatives(1)
update-alternatives - maintain symbolic links determining default
commands
update-alternatives [option...] command
update-alternatives creates, removes, maintains and displays
information about the symbolic links comprising the alternatives
system.
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 different 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.
The 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
alternative. Instead, it is a symbolic link to a name in the
alternatives directory, which in turn is a symbolic link to the
actual file referenced. This is done so that the system
administrator's changes can be confined within the /usr/local/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-alternatives is usually called
from the following Debian package maintainer scripts, postinst
(configure) to install the alternative and from prerm and postrm
(remove) to remove the alternative. Note: in most (if not all)
cases no other maintainer script actions should call update-
alternatives, in particular neither of upgrade nor disappear, as
any other such action can lose the manual state of an
alternative, or make the alternative temporarily flip-flop, or
completely switch when several of them have the same priority.
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
manual 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-alternatives is run on the changed link's group, and the
group will automatically 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 alternative 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 automatic).
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 mechanism.
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 /usr/local/etc/alternatives,
containing the symlinks.
administrative directory
A directory, by default /usr/local/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 priority 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
settings.
--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 introduced 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 corresponding 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
alternatives 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 information. If the group is in automatic mode,
and the newly added alternatives' priority is higher than any
other installed alternatives 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
equivalent 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. Associated 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 alternatives is to call yes '' | update-
alternatives --force --all.
--auto name
Switch the link group behind the alternative for name to
automatic mode. In the process, the master symlink and its
slaves are updated to point to the highest priority installed
alternatives.
--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 currently installed.
--get-selections
List all master alternative names (those controlling a link
group) and their status (since version 1.15.0). Each line
contains up to 3 fields (separated by one or more spaces).
The first field is the alternative name, the second one is
the status (either auto or manual), and the last one contains
the current 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
format generated by --get-selections and reconfigure them
accordingly (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
section "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.
--altdir directory
Specifies the alternatives directory, when this is to be
different from the default. Defaults to
«/usr/local/etc/alternatives».
--admindir directory
Specifies the administrative directory, when this is to be
different from the default. Defaults to
«/usr/local/var/lib/dpkg/alternatives» if DPKG_ADMINDIR has
not been set.
--instdir directory
Specifies the installation directory where alternatives links
will be created (since version 1.20.1). Defaults to «/» if
DPKG_ROOT has not been set.
--root directory
Specifies the root directory (since version 1.20.1). This
also sets the alternatives, installation and administrative
directories to match. Defaults to «/» if DPKG_ROOT has not
been set.
--log file
Specifies the log file (since version 1.15.0), when this is
to be different from the default
(/usr/local/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.
--quiet
Do not generate any comments unless errors occur.
--verbose
Generate more comments about what is being done.
--debug
Generate even more comments, helpful for debugging, about
what is being done (since version 1.19.3).
0 The requested action was successfully performed.
2 Problems were encountered whilst parsing the command line or
performing the action.
DPKG_ROOT
If set and the --instdir or --root options have not been
specified, it will be used as the filesystem root directory.
DPKG_ADMINDIR
If set and the --admindir option has not been specified, it
will be used as the base administrative directory.
/usr/local/etc/alternatives/
The default alternatives directory. Can be overridden by the
--altdir option.
/usr/local/var/lib/dpkg/alternatives/
The default administration directory. Can be overridden by
the --admindir option.
The --query format is using an RFC822-like flat format. It's
made of n + 1 stanzas where n is the number of alternatives
available in the queried link group. The first stanza 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 stanzas describe the available alternatives in the
queried link group:
Alternative: path-of-this-alternative
Path to this stanza'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
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
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
With --verbose update-alternatives chatters incessantly about its
activities on its standard output channel. If problems occur,
update-alternatives outputs error messages on its standard error
channel and returns 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 compatible
with vi, for example nvi and vim. Which one is used is
controlled by the link group vi, which includes links for the
program itself and the associated manual page.
To display the available packages which provide vi and the
current 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
ln(1), FHS (the Filesystem Hierarchy Standard).
This page is part of the dpkg (Debian Package Manager) project.
Information about the project can be found at
⟨https://wiki.debian.org/Teams/Dpkg/⟩. If you have a bug report
for this manual page, see
⟨http://bugs.debian.org/cgi-bin/pkgreport.cgi?src=dpkg⟩. This
page was obtained from the project's upstream Git repository ⟨git
clone https://git.dpkg.org/git/dpkg/dpkg.git⟩ on 2024-06-14. (At
that time, the date of the most recent commit that was found in
the repository was 2024-05-21.) If you discover any rendering
problems in this HTML version of the page, or you believe there
is a better or more up-to-date source for the page, or you have
corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
[email protected]
1.22.6-77-g86fe7 2024-03-10 update-alternatives(1)
Pages that refer to this page: dh_installalternatives(1)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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