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-.TH NSSWITCH.CONF 5 2013-02-12 "Linux" "Linux Programmer's Manual"
-.SH NAME
-nsswitch.conf \- Name Service Switch configuration file
-.SH DESCRIPTION
-The Name Service Switch (NSS) configuration file,
-.IR /etc/nsswitch.conf ,
-is used by the GNU C Library to determine
-the sources from which to obtain name-service information in
-a range of categories,
-and in what order.
-Each category of information is identified by a database name.
-.LP
-The file is plain ASCII text, with columns separated by spaces or tab
-characters.
-The first column specifies the database name.
-The remaining columns describe the order of sources to query and a
-limited set of actions that can be performed by lookup result.
-.LP
-The following databases are understood by the GNU C Library:
-.TP 12
-.B aliases
-Mail aliases, used by
-.BR getaliasent (3)
-and related functions.
-.TP
-.B ethers
-Ethernet numbers.
-.TP
-.B group
-Groups of users, used by
-.BR getgrent (3)
-and related functions.
-.TP
-.B hosts
-Host names and numbers, used by
-.BR gethostbyname (3)
-and related functions.
-.TP
-.B initgroups
-Supplementary group access list, used by
-.BR getgrouplist (3)
-function.
-.TP
-.B netgroup
-Network-wide list of hosts and users, used for access rules.
-C libraries before glibc 2.1 supported netgroups only over NIS.
-.TP
-.B networks
-Network names and numbers, used by
-.BR getnetent (3)
-and related functions.
-.TP
-.B passwd
-User passwords, used by
-.BR getpwent (3)
-and related functions.
-.TP
-.B protocols
-Network protocols, used by
-.BR getprotoent (3)
-and related functions.
-.TP
-.B publickey
-Public and secret keys for Secure_RPC used by NFS and NIS+.
-.TP
-.B rpc
-Remote procedure call names and numbers, used by
-.BR getrpcbyname (3)
-and related functions.
-.TP
-.B services
-Network services, used by
-.BR getservent (3)
-and related functions.
-.TP
-.B shadow
-Shadow user passwords, used by
-.BR getspnam (3)
-and related functions.
-.LP
-Here is an example
-.I /etc/nsswitch.conf
-file:
-.LP
-.RS 4
-.PD 0
-.TP 16
-passwd:
-compat
-.TP
-group:
-compat
-.TP
-shadow:
-compat
-.sp 1n
-.TP
-hosts:
-dns [!UNAVAIL=return] files
-.TP
-networks:
-nis [NOTFOUND=return] files
-.TP
-ethers:
-nis [NOTFOUND=return] files
-.TP
-protocols:
-nis [NOTFOUND=return] files
-.TP
-rpc:
-nis [NOTFOUND=return] files
-.TP
-services:
-nis [NOTFOUND=return] files
-.PD
-.RE
-.LP
-The first column is the database name.
-The remaining columns specify:
-.IP * 3
-One or more service specifications, for example, "files", "db", or "nis".
-The order of the services on the line determines the order in which
-those services will be queried, in turn, until a result is found.
-.IP *
-Optional actions to perform if a particular result is obtained
-from the preceding service, for example, "[NOTFOUND=return]".
-.LP
-The service specifications supported on your system depend on the
-presence of shared libraries, and are therefore extensible.
-Libraries called
-.IB /lib/libnss_SERVICE.so. X
-will provide the named
-.IR SERVICE .
-On a standard installation, you can use
-"files", "db", "nis", and "nisplus".
-For the
-.B hosts
-database, you can additionally specify "dns".
-For the
-.BR passwd ,
-.BR group ,
-and
-.BR shadow
-databases, you can additionally specify
-"compat" (see
-.B "Compatibility mode"
-below).
-The version number
-.B X
-may be 1 for glibc 2.0, or 2 for glibc 2.1 and later.
-On systems with additional libraries installed, you may have access to
-further services such as "hesiod", "ldap", "winbind" and "wins".
-.LP
-An action may also be specified following a service specification.
-The action modifies the behavior following a result obtained
-from the preceding data source.
-Action items take the general form:
-.LP
-.RS 4
-.RI [ STATUS = ACTION ]
-.br
-.RI [! STATUS = ACTION ]
-.RE
-.LP
-where
-.LP
-.RS 4
-.I STATUS
-=>
-.B success
-|
-.B notfound
-|
-.B unavail
-|
-.B tryagain
-.br
-.I ACTION
-=>
-.B return
-|
-.B continue
-.RE
-.LP
-The ! negates the test, matching all possible results except the
-one specified.
-The case of the keywords is not significant.
-.LP
-The
-.I STATUS
-value is matched against the result of the lookup function called by
-the preceding service specification, and can be one of:
-.RS 4
-.TP 12
-.B success
-No error occurred and the requested entry is returned.
-The default action for this condition is "return".
-.TP
-.B notfound
-The lookup succeeded, but the requested entry was not found.
-The default action for this condition is "continue".
-.TP
-.B unavail
-The service is permanently unavailable.
-This can mean either that the
-required file cannot be read, or, for network services, that the server
-is not available or does not allow queries.
-The default action for this condition is "continue".
-.TP
-.B tryagain
-The service is temporarily unavailable.
-This could mean a file is
-locked or a server currently cannot accept more connections.
-The default action for this condition is "continue".
-.RE
-.LP
-The
-.I ACTION
-value can be one of:
-.RS 4
-.TP 12
-.B return
-Return a result now.
-Do not call any further lookup functions.
-However, for compatibility reasons, if this is the selected action for the
-.B group
-database and the
-.B notfound
-status, and the configuration file does not contain the
-.B initgroups
-line, the next lookup function is always called,
-without affecting the search result.
-.TP
-.B continue
-Call the next lookup function.
-.RE
-.SS Compatibility mode (compat)
-The NSS "compat" service is similar to "files" except that it
-additionally permits special entries in
-.I /etc/passwd
-for granting users or members of netgroups access to the system.
-The following entries are valid in this mode:
-.RS 4
-.TP 12
-.BI + user
-Include the specified
-.I user
-from the NIS passwd map.
-.TP
-.BI +@ netgroup
-Include all users in the given
-.IR netgroup .
-.TP
-.BI \- user
-Exclude the specified
-.I user
-from the NIS passwd map.
-.TP
-.BI \-@ netgroup
-Exclude all users in the given
-.IR netgroup .
-.TP
-.B +
-Include every user, except previously excluded ones, from the
-NIS passwd map.
-.RE
-.LP
-By default the source is "nis", but this may be
-overridden by specifying "nisplus" as the source for the pseudo-databases
-.BR passwd_compat ,
-.BR group_compat ,
-and
-.BR shadow_compat .
-.SH FILES
-A service named
-.I SERVICE
-is implemented by a shared object library named
-.IB libnss_SERVICE.so. X
-that resides in
-.IR /lib .
-.RS 4
-.TP 25
-.PD 0
-.I /etc/nsswitch.conf
-NSS configuration file.
-.TP
-.IB /lib/libnss_compat.so. X
-implements "compat" source.
-.TP
-.IB /lib/libnss_db.so. X
-implements "db" source.
-.TP
-.IB /lib/libnss_dns.so. X
-implements "dns" source.
-.TP
-.IB /lib/libnss_files.so. X
-implements "files" source.
-.TP
-.IB /lib/libnss_hesiod.so. X
-implements "hesiod" source.
-.TP
-.IB /lib/libnss_nis.so. X
-implements "nis" source.
-.TP
-.IB /lib/libnss_nisplus.so. X
-implements "nisplus" source.
-.PD
-.RE
-.SH NOTES
-Within each process that uses
-.BR nsswitch.conf ,
-the entire file is read only once.
-If the file is later changed, the
-process will continue using the old configuration.
-.LP
-Traditionally, there was only a single source for service information,
-often in the form of a single configuration
-file (e.g., \fI/etc/passwd\fP).
-However, as other name services, such as the Network Information
-Service (NIS) and the Domain Name Service (DNS), became popular,
-a method was needed
-that would be more flexible than fixed search orders coded into
-the C library.
-The Name Service Switch mechanism,
-which was based on the mechanism used by
-Sun Microsystems in the Solaris 2 C library,
-introduced a cleaner solution to the problem.
-.SH SEE ALSO
-.BR getent (1),
-.BR nss (5)
-.SH COLOPHON
-This page is part of release 3.79 of the Linux
-.I man-pages
-project.
-A description of the project,
-information about reporting bugs,
-and the latest version of this page,
-can be found at
-\%http://www.kernel.org/doc/man\-pages/.
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