The
file specifies how the
nsdispatch(3)
(name-service switch dispatcher) routines in the C library should operate.
The configuration file controls how a process looks up various databases
containing information regarding hosts, users (passwords), groups, etc.
Each database comes from a source (such as local files, DNS,
NIS
and cache), and the order to look up the sources is specified in
.
Each entry in
consists of a database name, and a space separated list of sources.
Each source can have an optional trailing criterion that determines
whether the next listed source is used, or the search terminates at
the current source.
Each criterion consists of one or more status codes, and actions to
take if that status code occurs.
Sources
The following sources are implemented:
Source
Description
files
Local files, such as
/etc/hosts
and
/etc/passwd
dns
Internet Domain Name System.
``hosts''
and
`networks'
use
IN
class entries, all other databases use
HS
class (Hesiod) entries.
nis
NIS (formerly YP)
compat
support
`+/-'
in the
``passwd''
and
``group''
databases.
If this is present, it must be the only source for that entry.
Each entry starts on a new line in the file.
A
`#'
delimits a comment to end of line.
Blank lines are ignored.
A
`\'
at the end of a line escapes the newline, and causes the next line to
be a continuation of the current line.
All entries are case-insensitive.
The default criteria is to return on
``success''
and continue on anything else (i.e,
[success=return notfound=continue unavail=continue tryagain=continue] )
Cache
You can enable caching for the particular database by specifying
``cache''
as the first source in the
nsswitch.conf5
file.
You should also enable caching for this database in
nscd.conf5.
If for the particular query
``cache''
source returns success, no further sources are queried.
On the other hand, if there are no previously cached data, the
query result will be placed into the cache right after
all other sources are processed.
Note, that
``cache''
requires
nscd(8)
daemon to be running.
Compat mode: +/- syntax
In historical multi-source implementations, the
`+'
and
`-'
characters are used to specify the importing of user password and
group information from
NIS
Although
provides alternative methods of accessing distributed sources such as
NIS
specifying a sole source of
``compat''
will provide the historical behaviour.
An alternative source for the information accessed via
`+/-'
can be used by specifying
``passwd_compat: source''
``source''
in this case can be
`dns'
`nis'
or
any other source except for
`files'
and
`compat'
Notes
Historically, many of the databases had enumeration functions, often of
the form
getXXXent (.);
These made sense when the databases were in local files, but do not make
sense or have lesser relevance when there are possibly multiple sources,
each of an unknown size.
The interfaces are still provided for compatibility, but the source
may not be able to provide complete entries, or duplicate entries may
be retrieved if multiple sources that contain similar information are
specified.
To ensure compatibility with previous and current implementations, the
``compat''
source must appear alone for a given database.
Default source lists
If, for any reason,
does not exist, or it has missing or corrupt entries,
nsdispatch(3)
will default to an entry of
``files''
for the requested database.
Exceptions are:
Database
Default source list
group
compat
group_compat
nis
hosts
files dns
passwd
compat
passwd_compat
nis
services
compat
services_compat
nis
FILES
/etc/nsswitch.conf
The file
resides in
/etc
EXAMPLES
To lookup hosts in cache, then in
/etc/hosts
and then from the DNS, and lookup user information from
NIS
then files, use:
hosts:
cache files dns
passwd:
nis [notfound=return] files
group:
nis [notfound=return] files
The criteria
``[notfound=return]''
sets a policy of "if the user is notfound in nis, do not try files."
This treats nis as the authoritative source of information, except
when the server is down.
NOTES
If system got compiled with
WITHOUT_NIS
you have to remove
`nis'
entries.
Fx Ns 's
Lb libc
provides stubs for compatibility with NSS modules
written for the
GNU
C Library
nsswitch
interface.
However, these stubs only support the use of the
``passwd
''
and
``group
''
databases.
The
file format first appeared in
Fx 5.0 .
It was imported from the
Nx Project, where it appeared first in
Nx 1.4 .
AUTHORS
Luke Mewburn
Aq [email protected]
wrote this freely distributable name-service switch implementation,
using ideas from the
ULTRIX
svc.conf5
and
Solaris
nsswitch.conf4
manual pages.
