nsswitch.conf -- name-service switch configuration file
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 sep- arated list of sources. Each source can have an optional trailing crite- rion 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: 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 any- thing 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 access- ing 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 don't make sense or have lesser relevance when there are pos- sibly multiple sources, each of an unknown size. The interfaces are still provided for compatibility, but the source may not be able to pro- vide 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 doesn't 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
/etc/nsswitch.conf The file nsswitch.conf resides in /etc.
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 not- found in nis, don't try files." This treats nis as the authoritative source of information, except when the server is down. Luke Mewburn <email@example.com> wrote this freely distributable name-ser- vice switch implementation, using ideas from the ULTRIX svc.conf(5) and Solaris nsswitch.conf(4) manual pages. FreeBSD 5.4 June 21, 2004 FreeBSD 5.4
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