What does the [DEFAULT] written in the beginning of some files indicate and mean?

Question

I have seen this especially in /etc folder, which perhaps means it should be the default configuration?

P.S.: The main reason behind asking this is, adding [DEFAULT] to the top of file renders all comments in blue colour which are otherwise white in "vi" editor.

Do you have an example? and do those files end in .conf perhaps? — Rinzwind, Jun 27 '13 at 13:15
I don't know which file you are looking at, but in general, it means that is the default behavior of the process, unless you change the file to do something else as needed. — chili555, Jun 27 '13 at 13:17
@Rinzwind: Here, have a look. This is a part of my /etc/nova/nova.conf file. — jobin, Jun 27 '13 at 13:20

score 1 · Accepted Answer · edited Jun 12 '20 at 14:37

The [DEFAULT] in the file you posted in comments is part of an INI file configuration and in that context is called a "section" and can contain 0, 1 or more keys or properties (ie. in the format name=value) (but not other sections).

From the link:

Sections

Keys may (but need not) be grouped into arbitrarily named sections. The section name appears on a line by itself, in square brackets ([ and ]). All keys after the section declaration are associated with that section. There is no explicit "end of section" delimiter; sections end at the next section declaration, or the end of the file. Sections may not be nested.

Regarding Nova itself you can have several other sections (and it also explains DEFAULT):

Sections

Configuration options are grouped by section. The Compute config file supports the following sections.

[DEFAULT]

Almost all of the configuration options are organized into this section. If the documentation for a configuration option does not specify its section, assume that it should be placed in this one.

[cells]

The cells section is used for options for configuring cells functionality. See the Cells section of the OpenStack Compute Admin Manual for more details.

[baremetal]

This section is used for options that relate to the baremetal hypervisor driver.

[conductor]

The conductor section is used for options for configuring the nova-conductor service.

[trusted_computing]

The trusted_computing section is used for options that relate to the trusted computing pools functionality. Options in this section describe how to connect to a remote attestation service.

Regarding the coloring: it is more than likely that the editor you use is aware of INI file configuration and understands "sections" and "keys/properties".

The specific section name "DEFAULT" is a convention encouraged by the Python programming language's standard INI parser. — Matt Nordhoff, Jun 01 '16 at 10:10

What does the [DEFAULT] written in the beginning of some files indicate and mean?

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