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nss: Use "files dns" as the default for the hosts database (bug 28700)

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This matches what is currently in nss/nsswitch.conf.  The new ordering
matches what most distributions use in their installed configuration
files.

It is common to add localhost to /etc/hosts because the name does not
exist in the DNS, but is commonly used as a host name.

With the built-in "dns [!UNAVAIL=return] files" default, dns is
searched first and provides an answer for "localhost" (NXDOMAIN).
We never look at the files database as a result, so the contents of
/etc/hosts is ignored.  This means that "getent hosts localhost"
fail without a /etc/nsswitch.conf file, even though the host name
is listed in /etc/hosts.

Reviewed-by: Carlos O'Donell <carlos@redhat.com>
This commit is contained in:
Florian Weimer 2021-12-17 12:01:20 +01:00
parent ce1e5b1122
commit b99b0f93ee
3 changed files with 5 additions and 6 deletions
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5
manual/nss.texi
View File

@ -324,9 +324,8 @@ missing.
@cindex default value, and NSS
For the @code{hosts} and @code{networks} databases the default value is
@code{dns [!UNAVAIL=return] files}. I.e., the system is prepared for
the DNS service not to be available but if it is available the answer it
returns is definitive.
@code{files dns}. I.e., local configuration will override the contents
of the domain name system (DNS).
The @code{passwd}, @code{group}, and @code{shadow} databases was
traditionally handled in a special way. The appropriate files in the

2
nss/XXX-lookup.c
View File

@ -28,7 +28,7 @@
|* ALTERNATE_NAME - name of another service which is examined in *|
|* case DATABASE_NAME is not found *|
|* *|
|* DEFAULT_CONFIG - string for default conf (e.g. "dns files") *|
|* DEFAULT_CONFIG - string for default conf (e.g. "files dns") *|
|* *|
\*******************************************************************/

4
nss/nss_database.c
View File

@ -80,7 +80,7 @@ enum nss_database_default
{
nss_database_default_defconfig = 0, /* "nis [NOTFOUND=return] files". */
nss_database_default_compat, /* "compat [NOTFOUND=return] files". */
nss_database_default_dns, /* "dns [!UNAVAIL=return] files". */
nss_database_default_dns, /* "files dns". */
nss_database_default_files, /* "files". */
nss_database_default_nis, /* "nis". */
nss_database_default_nis_nisplus, /* "nis nisplus". */
@ -133,7 +133,7 @@ nss_database_select_default (struct nss_database_default_cache *cache,
#endif
case nss_database_default_dns:
line = "dns [!UNAVAIL=return] files";
line = "files dns";
break;
case nss_database_default_files: