man pages section 4: File Formats

nsswitch.conf(4)

Name

nsswitch.conf– configuration file for the name service switch

Synopsis

/etc/nsswitch.conf

Description

The operating system uses a number of databases of information about hosts, ipnodes, users (passwd(4), shadow(4), and user_attr(4)), and groups. Data for these can come from a variety of sources: hostnames and host addresses, for example, can be found in /etc/hosts, NIS, NIS+, LDAP, or DNS. Zero or more sources may be used for each database; the sources and their lookup order are specified in the /etc/nsswitch.conf file.

The following databases use the switch file:

Database	Used By
`aliases`	sendmail(1M)
`auth_attr`	getauthnam(3SECDB)
`automount`	automount(1M)
`bootparams`	rpc.bootparamd(1M)
`ethers`	ethers(3SOCKET)
`group`	getgrnam(3C)
`hosts`	gethostbyname(3NSL), getaddrinfo(3SOCKET). See `Interaction with netconfig`.
`ipnodes`	Same as `hosts`.
`netgroup`	innetgr(3C)
`netmasks`	ifconfig(1M)
`networks`	getnetbyname(3SOCKET)
`passwd`	getpwnam(3C), getspnam(3C), getauusernam(3BSM), getusernam(3SECDB)
`printers`	lp(1), lpstat(1), cancel(1), lpr(1B), lpq(1B), lprm(1B), in.lpd(1M), lpadmin(1M), lpget(1M), lpset(1M)
`prof_attr`	getprofnam(3SECDB), getexecprof(3SECDB)
`project`	getprojent(3PROJECT), getdefaultproj(3PROJECT), inproj(3PROJECT), newtask(1), setproject(3PROJECT)
`protocols`	getprotobyname(3SOCKET)
`publickey`	getpublickey(3NSL), secure_rpc(3NSL)
`rpc`	getrpcbyname(3NSL)
`services`	getservbyname(3SOCKET).
	See `Interaction with netconfig`.
`user_attr`	getuserattr(3SECDB)

The following sources may be used:

Source	Uses
`files`	`/etc/hosts`, `/etc/passwd`, `/etc/inet/ipnodes`, `/etc/shadow`, `/etc/security/auth_attr`, `/etc/user_attr`
`nis`	NIS(YP)
`nisplus`	NIS+
`ldap`	LDAP
`dns`	Valid only for hosts and ipnodes. Uses the Internet Domain Name Service.
`compat`	Valid only for `passwd` and `group`. Implements `+` and `-.` See `Interaction with +/- syntax`.
`user`	Valid only for printers. Implements support for `${HOME}/.printers`.

Note that /etc/inet/ipnodes is a symbolic link to /etc/hosts.

There is an entry in /etc/nsswitch.conf for each database. Typically these entries will be simple, such as protocols: files or networks: files nisplus. However, when multiple sources are specified, it is sometimes necessary to define precisely the circumstances under which each source will be tried. A source can return one of the following codes:

Status	Meaning
`SUCCESS`	Requested database entry was found.
`UNAVAIL`	Source is not configured on this system or internal failure.
`NOTFOUND`	Source responded “`no such entry`”
`TRYAGAIN`	Source is busy or not responding, might respond to retries.

For each status code, two actions are possible:

Action	Meaning
`continue`	Try the next source in the list.
`return`	Return now.

Additionally, for TRYAGAIN only, the following actions are possible:

Action	Meaning
`forever`	Retry the current source forever.
`n`	Retry the current source `n` more times, where `n` is an integer between `0` and `MAX_INT` (that is, 2.14 billion). After `n` retries has been exhausted, the `TRYAGAIN` action transitions to `continue`, until a future request receives a response, at which time `TRYAGAIN`=`n` is restored.

The complete syntax of an entry is:

<entry>     ::= <database> ":" [<source> [<criteria>]]*
<criteria>  ::= "[" <criterion>+ "]"
<criterion> ::= <status> "=" <action>
<status>    ::= "success" | "notfound" | "unavail" | "tryagain"

For every status except TRYAGAIN, the action syntax is:

<action>    ::= "return"  | "continue"

For the TRYAGAIN status, the action syntax is:

<action>    ::= "return"  | "continue" | "forever" | <n>
<n>         ::= 0...MAX_INT

Each entry occupies a single line in the file. Lines that are blank, or that start with white space, are ignored. Everything on a line following a # character is also ignored; the # character can begin anywhere in a line, to be used to begin comments. The <database> and <source> names are case-sensitive, but <action> and <status> names are case-insensitive.

The library functions contain compiled-in default entries that are used if the appropriate entry in nsswitch.conf is absent or syntactically incorrect.

The default criteria for DNS and the NIS server in “DNS-forwarding mode” is [SUCCESS=return NOTFOUND=continue UNAVAIL=continue TRYAGAIN=3].

The default criteria for all other sources is [SUCCESS=return NOTFOUND=continue UNAVAIL=continue TRYAGAIN=forever].

The default, or explicitly specified, criteria are meaningless following the last source in an entry; and they are ignored, since the action is always to return to the caller irrespective of the status code the source returns.

Interaction with `netconfig`

In order to ensure that they all return consistent results, gethostbyname(3NSL), getaddrinfo(3SOCKET), getservbyname(3SOCKET), and netdir_getbyname(3NSL) functions are all implemented in terms of the same internal library function. This function obtains the system-wide source lookup policy for hosts, ipnodes, and services based on the inet family entries in netconfig(4) and uses the switch entries only if the netconfig entries have a - (hyphen) in the last column for nametoaddr libraries. See the Notes section in gethostbyname(3NSL) and getservbyname(3SOCKET) for details.

YP-compatibility Mode

The NIS+ server can be run in YP-compatibility mode, where it handles NIS (YP) requests as well as NIS+ requests. In this case, the clients get much the same results (except for getspnam(3C)) from the nis source as from nisplus; however, nisplus is recommended instead of nis.

Interaction with server in DNS-forwarding Mode

The NIS (YP) server can be run in DNS-forwarding mode, where it forwards lookup requests to DNS for host-names and -addresses that do not exist in its database. In this case, specifying nis as a source for hosts is sufficient to get DNS lookups; dns need not be specified explicitly as a source.

In SunOS 5.3 (Solaris 2.3) and compatible versions, the NIS+ server in NIS/YP-compatibility mode can also be run in DNS-forwarding mode (see rpc.nisd(1M)). Forwarding is effective only for requests originating from its YP clients; hosts policy on these clients should be configured appropriately.

Interaction with Password Aging

When password aging is turned on, only a limited set of possible name services are permitted for the passwd: database in the /etc/nsswitch.conf file:

passwd:: files
passwd:: files nis
passwd:: files nisplus
passwd:: files ldap
passwd:: compat
passwd_compat:: nisplus
passwd_compat:: ldap

Any other settings will cause the passwd(1) command to fail when it attempts to change the password after expiration and will prevent the user from logging in. These are the only permitted settings when password aging has been turned on. Otherwise, you can work around incorrect passwd: lines by using the -r repository argument to the passwd(1) command and using passwd -r repository to override the nsswitch.conf settings and specify in which name service you want to modify your password.

Interaction with +/- syntax

Releases prior to SunOS 5.0 did not have the name service switch but did allow the user some policy control. In /etc/passwd one could have entries of the form +user (include the specified user from NIS passwd.byname), -user (exclude the specified user) and + (include everything, except excluded users, from NIS passwd.byname). The desired behavior was often everything in the file followed by everything in NIS, expressed by a solitary + at the end of /etc/passwd. The switch provides an alternative for this case (passwd: files nis) that does not require + entries in /etc/passwd and /etc/shadow (the latter is a new addition to SunOS 5.0, see shadow(4)).

If this is not sufficient, the NIS/YP compatibility source provides full +/- semantics. It reads /etc/passwd for getpwnam(3C) functions and /etc/shadow for getspnam(3C) functions and, if it finds +/- entries, invokes an appropriate source. By default, the source is nis, but this may be overridden by specifying nisplus or ldap as the source for the pseudo-database passwd_compat.

Note that in compat mode, for every /etc/passwd entry, there must be a corresponding entry in the /etc/shadow file.

The NIS/YP compatibility source also provides full +/- semantics for group; the relevant pseudo-database is group_compat.

Useful Configurations

The compiled-in default entries for all databases use NIS (YP) as the enterprise level name service and are identical to those in the default configuration of this file:

passwd:: files nis
group:: files nis
hosts:: nis [NOTFOUND=return] files
ipnodes:: nis [NOTFOUND=return] files
networks:: nis [NOTFOUND=return] files
protocols:: nis [NOTFOUND=return] files
rpc:: nis [NOTFOUND=return] files
ethers:: nis [NOTFOUND=return] files
netmasks:: nis [NOTFOUND=return] files
bootparams:: nis [NOTFOUND=return] files
publickey:: nis [NOTFOUND=return] files
netgroup:: nis
automount:: files nis
aliases:: files nis
services:: files nis
printers:: user files nis nisplus
auth_attr: files nis
prof_attr: files nis
project: files nis

Note that the files source for the ipnodes and hosts databases is identical, as /etc/inet/ipnodes is a symbolic link to /etc/hosts. Because other sources for the ipnodes and hosts databases are different, do not remove the ipnodes line from the /etc/nsswitch.conf file.

The policy nis [NOTFOUND=return] files implies: if nis is UNAVAIL, continue on to files, and if nis returns NOTFOUND, return to the caller. In other words, treat nis as the authoritative source of information and try files only if nis is down. This, and other policies listed in the default configuration above, are identical to the hard-wired policies in SunOS releases prior to 5.0.

If compatibility with the +/- syntax for passwd and group is required, simply modify the entries for passwd and group to:

passwd:: compat
group:: compat

If NIS+ is the enterprise level name service, the default configuration should be modified to use nisplus instead of nis for every database on client machines. The file /etc/nsswitch.nisplus contains a sample configuration that can be copied to /etc/nsswitch.conf to set this policy.

If LDAP is the enterprise level name service, the default configuration should be modified to use ldap instead of nis for every database on client machines. The file /etc/nsswitch.ldap contains a sample configuration that can be copied to /etc/nsswitch.conf to set this policy.

If the use of +/- syntax is desired in conjunction with nisplus, use the following four entries:

passwd:: compat
passwd_compat:: nisplus OR ldap
group:: compat
group_compat:: nisplus OR ldap

In order to get information from the Internet Domain Name Service for hosts that are not listed in the enterprise level name service, NIS+ or LDAP, use the following configuration and set up the /etc/resolv.conf file (see resolv.conf(4) for more details):

hosts:: nisplus dns [NOTFOUND=return] files

hosts:: ldap dns [NOTFOUND=return] files

Enumeration - `getXXXent()`

Many of the databases have enumeration functions: passwd has getpwent(), hosts has gethostent(), and so on. These were reasonable when the only source was files but often make little sense for hierarchically structured sources that contain large numbers of entries, much less for multiple sources. The interfaces are still provided and the implementations strive to provide reasonable results, but the data returned may be incomplete (enumeration for hosts is simply not supported by the dns source), inconsistent (if multiple sources are used), formatted in an unexpected fashion (for a host with a canonical name and three aliases, the nisplus source will return four hostents, and they may not be consecutive), or very expensive (enumerating a passwd database of 5,000 users is probably a bad idea). Furthermore, multiple threads in the same process using the same reentrant enumeration function (getXXXent_r() are supported beginning with SunOS 5.3) share the same enumeration position; if they interleave calls, they will enumerate disjoint subsets of the same database.

In general, the use of the enumeration functions is deprecated. In the case of passwd, shadow, and group, it may sometimes be appropriate to use fgetgrent(), fgetpwent(), and fgetspent() (see getgrnam(3C), getpwnam(3C), and getspnam(3C), respectively), which use only the files source.

Files

A source named SSS is implemented by a shared object named nss_SSS.so.1 that resides in /usr/lib.

/etc/nsswitch.conf: Configuration file.
/usr/lib/nss_compat.so.1: Implements compat source.
/usr/lib/nss_dns.so.1: Implements dns source.
/usr/lib/nss_files.so.1: Implements files source.
/usr/lib/nss_nis.so.1: Implements nis source.
/usr/lib/nss_nisplus.so.1: Implements nisplus source.
/usr/lib/nss_ldap.so.1: Implements ldap source.
/usr/lib/nss_user.so.1: Implements user source.
/etc/netconfig: Configuration file for netdir(3NSL) functions that redirects hosts/devices policy to the switch.
/etc/nsswitch.files: Sample configuration file that uses files only.
/etc/nsswitch.nis: Sample configuration file that uses files and nis.
/etc/nsswitch.nisplus: Sample configuration file that uses files and nisplus.
/etc/nsswitch.ldap: Sample configuration file that uses files and ldap.
/etc/nsswitch.dns: Sample configuration file that uses files and dns (but only for hosts).

Notes

Within each process that uses nsswitch.conf, the entire file is read only once; if the file is later changed, the process will continue using the old configuration.

The use of both nis and nisplus as sources for the same database is strongly discouraged since both the name services are expected to store similar information and the lookups on the database may yield different results depending on which name service is operational at the time of the request. The same applies for using ldap along with nis or nisplus.

Misspelled names of sources and databases will be treated as legitimate names of (most likely nonexistent) sources and databases.

The following functions do not use the switch: fgetgrent(3C), fgetprojent(3PROJECT), fgetpwent(3C), fgetspent(3C), getpw(3C), putpwent(3C), shadow(4).

SunOS 5.10 Last Revised 15 Aug 2006