nsswitch.conf5

Sources

The following sources are implemented as part of the base system:

Source

Description

files

Local files, such as /etc/hosts, and /etc/passwd.

db

Local database.

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.

cache

makes use of the nscd(8) daemon.

Additional sources might be provided by third party software.

Databases

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

Database

Used by

group

getgrent(3), getgrent_r(3), getgrgid_r(3), getgrnam_r(3), setgrent(3), endgrent(3)

hosts

getaddrinfo(3), gethostbyaddr(3), gethostbyaddr_r(3), gethostbyname(3), gethostbyname2(3), gethostbyname_r(3), getipnodebyaddr(3), getipnodebyname(3)

networks

getnetbyaddr(3), getnetbyaddr_r(3), getnetbyname(3), getnetbyname_r(3)

passwd

getpwent(3), getpwent_r(3), getpwnam_r(3), getpwuid_r(3), setpwent(3), endpwent(3)

shells

getusershell(3)

services

getservent(3)

rpc

getrpcbyname(3), getrpcbynumber(3), getrpcent(3)

proto

getprotobyname(3), getprotobynumber(3), getprotoent(3)

netgroup

getnetgrent(3), getnetgrent_r(3), setnetgrent(3), endnetgrent(3), innetgr(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]).

Cache

You can enable caching for the particular database by specifying “cache” in the nsswitch.conf file. It should come after “files”, but before remote sources like “nis”. You should also enable caching for this database in nscd.conf(5). If for a particular query “cache” source returns success, then 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 the 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 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

services

compat

services_compat

nis