1NSSWITCH.CONF(5) Linux Programmer's Manual NSSWITCH.CONF(5)
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6 nsswitch.conf - Name Service Switch configuration file
7
9 The Name Service Switch (NSS) configuration file, /etc/nsswitch.conf,
10 is used by the GNU C Library to determine the sources from which to
11 obtain name-service information in a range of categories, and in what
12 order. Each category of information is identified by a database name.
13 The file is plain ASCII text, with columns separated by spaces or tab
15 characters. The first column specifies the database name. The remain‐
16 ing columns describe the order of sources to query and a limited set of
17 actions that can be performed by lookup result.
18 The following databases are understood by the GNU C Library:
20 aliases Mail aliases, used by getaliasent(3) and related functions.
22 ethers Ethernet numbers.
24 group Groups of users, used by getgrent(3) and related functions.
26 hosts Host names and numbers, used by gethostbyname(3) and
28 related functions.
29 initgroups Supplementary group access list, used by getgrouplist(3)
31 function.
32 netgroup Network-wide list of hosts and users, used for access
34 rules. C libraries before glibc 2.1 supported netgroups
35 only over NIS.
36 networks Network names and numbers, used by getnetent(3) and related
38 functions.
39 passwd User passwords, used by getpwent(3) and related functions.
41 protocols Network protocols, used by getprotoent(3) and related func‐
43 tions.
44 publickey Public and secret keys for Secure_RPC used by NFS and NIS+.
46 rpc Remote procedure call names and numbers, used by getrpcby‐
48 name(3) and related functions.
49 services Network services, used by getservent(3) and related func‐
51 tions.
52 shadow Shadow user passwords, used by getspnam(3) and related
54 functions.
55 Here is an example /etc/nsswitch.conf file:
57 passwd: compat
59 group: compat
60 shadow: compat
61 hosts: dns [!UNAVAIL=return] files
63 networks: nis [NOTFOUND=return] files
64 ethers: nis [NOTFOUND=return] files
65 protocols: nis [NOTFOUND=return] files
66 rpc: nis [NOTFOUND=return] files
67 services: nis [NOTFOUND=return] files
68 The first column is the database name. The remaining columns specify:
70 * One or more service specifications e.g., "files", "db", or "nis".
72 The order of the services on the line determines the order in which
73 those services will be queried, in turn, until a result is found.
74 * Optional actions to perform if a particular result is obtained from
76 the preceding service, e.g., "[NOTFOUND=return]".
77 The service specifications supported on your system depend on the pres‐
79 ence of shared libraries, and are therefore extensible. Libraries
80 called /lib/libnss_SERVICE.so.X will provide the named SERVICE. On a
81 standard installation, you can use "files", "db", "nis", and "nisplus".
82 For the hosts database, you can additionally specify "dns". For the
83 passwd, group, and shadow databases, you can additionally specify "com‐
84 pat" (see Compatibility mode below). The version number X may be 1 for
85 glibc 2.0, or 2 for glibc 2.1 and later. On systems with additional
86 libraries installed, you may have access to further services such as
87 "hesiod", "ldap", "winbind" and "wins".
88 An action may also be specified following a service specification. The
90 action modifies the behavior following a result obtained from the pre‐
91 ceding data source. Action items take the general form:
92 [STATUS=ACTION]
94 [!STATUS=ACTION]
95 where
97 STATUS => success | notfound | unavail | tryagain
99 ACTION => return | continue
100 The ! negates the test, matching all possible results except the one
102 specified. The case of the keywords is not significant.
103 The STATUS value is matched against the result of the lookup function
105 called by the preceding service specification, and can be one of:
106 success No error occurred and the requested entry is returned.
108 The default action for this condition is "return".
109 notfound The lookup succeeded, but the requested entry was not
111 found. The default action for this condition is "con‐
112 tinue".
113 unavail The service is permanently unavailable. This can mean
115 either that the required file cannot be read, or, for
116 network services, that the server is not available or
117 does not allow queries. The default action for this
118 condition is "continue".
119 tryagain The service is temporarily unavailable. This could
121 mean a file is locked or a server currently cannot
122 accept more connections. The default action for this
123 condition is "continue".
124 The ACTION value can be one of:
126 return Return a result now. Do not call any further lookup
128 functions. However, for compatibility reasons, if this
129 is the selected action for the group database and the
130 notfound status, and the configuration file does not
131 contain the initgroups line, the next lookup function
132 is always called, without affecting the search result.
133 continue Call the next lookup function.
135 Compatibility mode (compat)
137 The NSS "compat" service is similar to "files" except that it addition‐
138 ally permits special entries in /etc/passwd for granting users or mem‐
139 bers of netgroups access to the system. The following entries are
140 valid in this mode:
141 +user Include the specified user from the NIS passwd map.
143 +@netgroup Include all users in the given netgroup.
145 -user Exclude the specified user from the NIS passwd map.
147 -@netgroup Exclude all users in the given netgroup.
149 + Include every user, except previously excluded ones,
151 from the NIS passwd map.
152 By default the source is "nis", but this may be overridden by specify‐
154 ing "nisplus" as the source for the pseudo-databases passwd_compat,
155 group_compat, and shadow_compat.
156
158 A service named SERVICE is implemented by a shared object library named
159 libnss_SERVICE.so.X that resides in /lib.
160 /etc/nsswitch.conf NSS configuration file.
162 /lib/libnss_compat.so.X implements "compat" source.
163 /lib/libnss_db.so.X implements "db" source.
164 /lib/libnss_dns.so.X implements "dns" source.
165 /lib/libnss_files.so.X implements "files" source.
166 /lib/libnss_hesiod.so.X implements "hesiod" source.
167 /lib/libnss_nis.so.X implements "nis" source.
168 /lib/libnss_nisplus.so.X implements "nisplus" source.
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171 Within each process that uses nsswitch.conf, the entire file is read
172 only once. If the file is later changed, the process will continue
173 using the old configuration.
174 Traditionally, there was only a single source for service information,
176 often in the form of a single configuration file (e.g., /etc/passwd).
177 However, as other name services, such as the Network Information Ser‐
178 vice (NIS) and the Domain Name Service (DNS), became popular, a method
179 was needed that would be more flexible than fixed search orders coded
180 into the C library. The Name Service Switch mechanism, which was based
181 on the mechanism used by Sun Microsystems in the Solaris 2 C library,
182 introduced a cleaner solution to the problem.
183
185 getent(1), nss(5)
186
188 This page is part of release 3.53 of the Linux man-pages project. A
189 description of the project, and information about reporting bugs, can
190 be found at http://www.kernel.org/doc/man-pages/.
191Linux 2013-02-12 NSSWITCH.CONF(5)