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hbh231:/house/hbh231$man nsswitch.conf
nsswitch.conf(4) 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, users (passwd), groups and so forth. Data for these can come
from a variety of sources: host-names and -addresses, for example,
may be found in /etc/hosts, NIS, LDAP, or DNS. One 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:
Database Used by
aliases sendmail
automount automount
group getgrnam()
hosts gethostbyname()
ipnodes getipnodebyname()
netgroup innetgr()
networks getnetbyname()
passwd getpwnam(), getspnam()
protocols getprotobyname()
publickey getpublickey(), secure_rpc()
rpc getrpcbyname()
sendmailvars sendmail
services getservbyname()
The following sources may be used:
Source Uses
files /etc/hosts, /etc/passwd, and so forth
nis NIS (YP)
ldap LDAP Directory Server
dns Valid only for hosts, ipnodes; uses the Internet
Domain Name Service.
compat Valid only for passwd and group; implements + and
-.
(See Interaction with +/- syntax below)
There is an entry in /etc/nsswitch.conf for each database. Typically
these entries will be simple, like protocols: files or networks: files
nis. 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:
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Status Meaning
SUCCESS Requested database entry was found
UNAVAIL Source is not responding or corrupted
NOTFOUND Source responded "no such entry"
TRYAGAIN Source is busy, 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
The complete syntax of an entry is
<entry> ::= <database> ":" [<source> [<criteria>]]* <source>
<criteria> ::= "[" <criterion>+ "]"
<criterion> ::= <status> "=" <action>
<status> ::= "success" | "notfound" | "unavail" | "tryagain"
<action> ::= "return" | "continue"
Each entry occupies a single line in the file. Lines that are blank,
or that start with white space character 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 default criteria are to continue on anything except SUCCESS; in
other words, [SUCCESS=return NOTFOUND=continue UNAVAIL=continue
TRYAGAIN=continue].
The default, or explicitly specified, criteria are meaningless
following the last source in an entry; and 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 based on
the inet family of entries, gethostbyname(), getservbyname(), and
netdir_getbyname() functions are all implemented in terms of the same
internal switch library functions. These functions obtain the system-
wide source lookup policy for hosts and services based on the inet
family entries in netconfig(). For services and hosts only the "-" in
the last column, which represents nametoaddr libraries, is supported.
NIS (YP) server in DNS-forwarding Mode
The NIS (YP) server can be run in "DNS-forwarding mode" (see
rpc.nisd_resolv(1M)), where it forwards lookup requests to DNS for
host-names and host-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.
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Interaction with +/- syntax
Releases prior to HP-UX 10.30 did not have the name-service switch
support for passwd and group 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.
If this is not sufficient, the compat source provides full +/-
semantics. It reads /etc/passwd for getpwnam() functions and, if it
finds +/- entries, invokes an appropriate source. The only source
supported by pseudo-database passwd_compat is nis.
The compat 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: dns [NOTFOUND=return] nis [NOTFOUND=return] files
ipnodes: dns [NOTFOUND=return] nis [NOTFOUND=return] files
networks: nis [NOTFOUND=return] files
protocols: nis [NOTFOUND=return] files
rpc: nis [NOTFOUND=return] files
publickey: nis [NOTFOUND=return] files
netgroup: nis
automount: files nis
aliases: files nis
services: files nis
sendmailvars: files
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.
If compatibility with the +/- syntax for passwd and group is required,
simply modify the entries for passwd and group to:
passwd: compat
group: compat
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To get information from the Internet Domain Name Service for hosts
that are not listed in the enterprise level name-service, NIS, use the
following configuration and set up the file /etc/resolv.conf. See
resolver(4) for more details.
hosts: nis dns [NOTFOUND=return] files
ipnodes: nis dns [NOTFOUND=return] files
The file /etc/nsswitch.ldap contains an example configuration that can
be copied to /etc/nsswitch.conf to set an LDAP policy. If the +/-
netgroup syntax (used for access control as defined by nis) is
desired, the administrator needs to configure libpam_authz.1 in the
/etc/pam.conf file. See the ldapux(5) manpage for more information
about LDAP-UX, pam_authz(5) manpage for more information on
libpam_authz.1, and passwd(4) for more information about the +/-
netgroup syntax. The ldapux(5) and pam_authz(5) manpages are in the
LDAP-UX Integration product.
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), very expensive
(enumerating a passwd database of 5000 users is probably a bad idea)
or formatted in an unexpected fashion. Furthermore, multiple threads
in the same process using the same reentrant enumeration function
(getXXXent_r() are supported) 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, and group, it may sometimes be appropriate to use
fgetgrent(), fgetpwent(), and fgetspent() (see getgrent(3C), and
getpwent(3C), respectively), which use only the files source.
WARNINGS
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.
Programs that use the getXXbyYY() functions cannot be linked
statically since the implementation of these functions requires
dynamic linker functionality to access the shared objects
/usr/lib/nss_SSS.sl.1 at run time.
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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(),
fgetpwent(), fgetspent(), getpw(), and putpwent().
The functions getipnodebyname() and getipnodebyaddr() were introduced
with libc.2 and not found in libc.1.
Applications linked with libc.1 will display different default actions
for NOTFOUND and TRYAGAIN. Applications linked with libc.1 will have
the switch search terminate if the Name Service returns a result of
NOTFOUND or TRYAGAIN.
This will be an issue for existing nsswitch.conf files that specify
name service lookup criteria that contains no criterion between source
entries.
Example: hosts: dns files
For applications linked with libc.1, the fallback to files will only
occur if DNS returns UNAVAIL. For all other applications, the
fallback to files will occur unless DNS returns SUCCESS.
For applications linked with libc.1 and other applications to have the
same behavior, a criterion must be specified between source.
For libc.1 behavior:
hosts: dns [NOTFOUND=return TRYAGAIN=return] files
For the default system behavior:
hosts: dns [NOTFOUND=continue TRYAGAIN=continue] files
NIS+ is obsoleted on HP-UX 11i Version 3 and is no longer supported.
LDAP is the recommended replacement for NIS+. HP fully supports the
industry standard naming services based on LDAP.
Obsolescence
The ipnodes directive may not be supported in future HP-UX releases.
In order to minimize the impact to applications, it is recommended
that you have the same configuration for the hosts and the ipnodes
directives.
AUTHOR
nsswitch.conf was developed by Sun Microsystems, Inc.
FILES
A source named SSS is implemented by a shared object named nss_SSS.1
that resides in /usr/lib.
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nsswitch.conf(4) nsswitch.conf(4)
/etc/nsswitch.conf configuration file
/usr/lib/nss_compat.1 implements compat source
/usr/lib/nss_dns.1 implements dns source
/usr/lib/nss_files.1 implements files source
/usr/lib/nss_nis.1 implements nis source
/usr/lib/nss_ldap.1 implements ldap source
/etc/netconfig configuration file for netdir() functions
that redirects hosts/services 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.ldap sample configuration file that uses files and
ldap
SEE ALSO
automount(1M), rpc.nisd_resolv(1M), sendmail(1M), getgrent(3C),
getnetgrent(3C), getpwent(3C), getrpcent(3C), gethostent(3N),
getnetent(3N), getprotoent(3N), getpublickey(3N), getservent(3N),
netdir(3N), secure_rpc(3N), netconfig(4), resolver(4), ypfiles(4).
ldapux(5) and pam_authz(5) in the LDAP-UX Integration product.
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发表于 2008-05-22 22:56
