NSSWITCH.CONF(5) MidnightBSD File Formats Manual NSSWITCH.CONF(5)

NAME

nsswitch.conf — name-service switch configuration file

DESCRIPTION

The nsswitch.conf 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, and NIS), and the order to look up the sources is specified in nsswitch.conf.

Each entry in nsswitch.conf 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.

Databases
The following databases are used by the following C library functions:

Database

Used by

group

getgrent(3)

hosts

gethostbyname(3)

networks

getnetbyname(3)

passwd

getpwent(3)

shells

getusershell(3)

Status codes
The following status codes are available:

Status

Description

success

The requested entry was found.

notfound

The entry is not present at this source.

tryagain

The source is busy, and may respond to retries.

unavail

The source is not responding, or entry is corrupt.

Actions
For each of the status codes, one of two actions is possible:

Action

Description

continue

Try the next source

return

Return with the current result

Format of file
A BNF description of the syntax of nsswitch.conf is:

<entry>

::= <database> ":" [<source> [<criteria>]]*

<criteria>

::= "[" <criterion>+ "]"

<criterion>

::= <status> "=" <action>

<status>

::= "success" | "notfound" | "unavail" | "tryagain"

<action>

::= "return" | "continue"

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]).

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 nsswitch.conf 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, nsswitch.conf 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

FILES
/etc/nsswitch.conf

The file nsswitch.conf resides in /etc.

EXAMPLES

To lookup hosts in /etc/hosts and then from the DNS, and lookup user information from NIS then files, use:

hosts:

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 NO_NIS you have to remove ‘nis’ entries.

SEE ALSO

nsdispatch(3), resolv.conf(5), named(8), ypbind(8)

HISTORY

The nsswitch.conf file format first appeared in FreeBSD 5.0. It was imported from the NetBSD Project, where it appeared first in NetBSD 1.4.

AUTHORS

Luke Mewburn 〈lukem@netbsd.org〉 wrote this freely distributable name-service switch implementation, using ideas from the ULTRIX svc.conf(5) and Solaris nsswitch.conf(4) manual pages.

MidnightBSD 0.3 April 24, 2005 MidnightBSD 0.3