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 and certain other applications to deter‐
11 mine the sources from which to obtain name-service information in a
12 range of categories, and in what order. Each category of information
13 is identified by a database name.
14 The file is plain ASCII text, with columns separated by spaces or tab
16 characters. The first column specifies the database name. The remain‐
17 ing columns describe the order of sources to query and a limited set of
18 actions that can be performed by lookup result.
19 The following databases are understood by the GNU C Library:
21 aliases Mail aliases, used by getaliasent(3) and related functions.
23 ethers Ethernet numbers.
25 group Groups of users, used by getgrent(3) and related functions.
27 hosts Host names and numbers, used by gethostbyname(3) and
29 related functions.
30 initgroups Supplementary group access list, used by getgrouplist(3)
32 function.
33 netgroup Network-wide list of hosts and users, used for access
35 rules. C libraries before glibc 2.1 supported netgroups
36 only over NIS.
37 networks Network names and numbers, used by getnetent(3) and related
39 functions.
40 passwd User passwords, used by getpwent(3) and related functions.
42 protocols Network protocols, used by getprotoent(3) and related func‐
44 tions.
45 publickey Public and secret keys for Secure_RPC used by NFS and NIS+.
47 rpc Remote procedure call names and numbers, used by getrpcby‐
49 name(3) and related functions.
50 services Network services, used by getservent(3) and related func‐
52 tions.
53 shadow Shadow user passwords, used by getspnam(3) and related
55 functions.
56 The GNU C Library ignores databases with unknown names. Some applica‐
58 tions use this to implement special handling for their own databases.
59 For example, sudo(8) consults the sudoers database.
60 Here is an example /etc/nsswitch.conf file:
62 passwd: compat
64 group: compat
65 shadow: compat
66 hosts: dns [!UNAVAIL=return] files
68 networks: nis [NOTFOUND=return] files
69 ethers: nis [NOTFOUND=return] files
70 protocols: nis [NOTFOUND=return] files
71 rpc: nis [NOTFOUND=return] files
72 services: nis [NOTFOUND=return] files
73 The first column is the database name. The remaining columns specify:
75 * One or more service specifications, for example, "files", "db", or
77 "nis". The order of the services on the line determines the order
78 in which those services will be queried, in turn, until a result is
79 found.
80 * Optional actions to perform if a particular result is obtained from
82 the preceding service, for example, "[NOTFOUND=return]".
83 The service specifications supported on your system depend on the pres‐
85 ence of shared libraries, and are therefore extensible. Libraries
86 called /lib/libnss_SERVICE.so.X will provide the named SERVICE. On a
87 standard installation, you can use "files", "db", "nis", and "nisplus".
88 For the hosts database, you can additionally specify "dns". For the
89 passwd, group, and shadow databases, you can additionally specify "com‐
90 pat" (see Compatibility mode below). The version number X may be 1 for
91 glibc 2.0, or 2 for glibc 2.1 and later. On systems with additional
92 libraries installed, you may have access to further services such as
93 "hesiod", "ldap", "winbind" and "wins".
94 An action may also be specified following a service specification. The
96 action modifies the behavior following a result obtained from the pre‐
97 ceding data source. Action items take the general form:
98 [STATUS=ACTION]
100 [!STATUS=ACTION]
101 where
103 STATUS => success | notfound | unavail | tryagain
105 ACTION => return | continue | merge
106 The ! negates the test, matching all possible results except the one
108 specified. The case of the keywords is not significant.
109 The STATUS value is matched against the result of the lookup function
111 called by the preceding service specification, and can be one of:
112 success No error occurred and the requested entry is returned.
114 The default action for this condition is "return".
115 notfound The lookup succeeded, but the requested entry was not
117 found. The default action for this condition is "con‐
118 tinue".
119 unavail The service is permanently unavailable. This can mean
121 either that the required file cannot be read, or, for
122 network services, that the server is not available or
123 does not allow queries. The default action for this
124 condition is "continue".
125 tryagain The service is temporarily unavailable. This could
127 mean a file is locked or a server currently cannot
128 accept more connections. The default action for this
129 condition is "continue".
130 The ACTION value can be one of:
132 return Return a result now. Do not call any further lookup
134 functions. However, for compatibility reasons, if this
135 is the selected action for the group database and the
136 notfound status, and the configuration file does not
137 contain the initgroups line, the next lookup function
138 is always called, without affecting the search result.
139 continue Call the next lookup function.
141 merge [SUCCESS=merge] is used between two database entries.
143 When a group is located in the first of the two group
144 entries, processing will continue on to the next one.
145 If the group is also found in the next entry (and the
146 group name and GID are an exact match), the member list
147 of the second entry will be added to the group object
148 to be returned. Available since glibc 2.24. Note that
149 merging will not be done for getgrent(3) nor will
150 duplicate members be pruned when they occur in both
151 entries being merged.
152 Compatibility mode (compat)
154 The NSS "compat" service is similar to "files" except that it addition‐
155 ally permits special entries in corresponding files for granting users
156 or members of netgroups access to the system. The following entries
157 are valid in this mode:
158 For passwd and shadow databases:
160 +user Include the specified user from the NIS
162 passwd/shadow map.
163 +@netgroup Include all users in the given netgroup.
165 -user Exclude the specified user from the NIS
167 passwd/shadow map.
168 -@netgroup Exclude all users in the given netgroup.
170 + Include every user, except previously excluded
172 ones, from the NIS passwd/shadow map.
173 For group database:
175 +group Include the specified group from the NIS group map.
177 -group Exclude the specified group from the NIS group map.
179 + Include every group, except previously excluded
181 ones, from the NIS group map.
182 By default, the source is "nis", but this may be overridden by specify‐
184 ing any NSS service except "compat" itself as the source for the
185 pseudo-databases passwd_compat, group_compat, and shadow_compat.
186
188 A service named SERVICE is implemented by a shared object library named
189 libnss_SERVICE.so.X that resides in /lib.
190 /etc/nsswitch.conf NSS configuration file.
192 /lib/libnss_compat.so.X implements "compat" source.
193 /lib/libnss_db.so.X implements "db" source.
194 /lib/libnss_dns.so.X implements "dns" source.
195 /lib/libnss_files.so.X implements "files" source.
196 /lib/libnss_hesiod.so.X implements "hesiod" source.
197 /lib/libnss_nis.so.X implements "nis" source.
198 /lib/libnss_nisplus.so.X implements "nisplus" source.
199 The following files are read when "files" source is specified for
201 respective databases:
202 aliases /etc/aliases
204 ethers /etc/ethers
205 group /etc/group
206 hosts /etc/hosts
207 initgroups /etc/group
208 netgroup /etc/netgroup
209 networks /etc/networks
210 passwd /etc/passwd
211 protocols /etc/protocols
212 publickey /etc/publickey
213 rpc /etc/rpc
214 services /etc/services
215 shadow /etc/shadow
216
218 Within each process that uses nsswitch.conf, the entire file is read
219 only once. If the file is later changed, the process will continue
220 using the old configuration.
221 Traditionally, there was only a single source for service information,
223 often in the form of a single configuration file (e.g., /etc/passwd).
224 However, as other name services, such as the Network Information Ser‐
225 vice (NIS) and the Domain Name Service (DNS), became popular, a method
226 was needed that would be more flexible than fixed search orders coded
227 into the C library. The Name Service Switch mechanism, which was based
228 on the mechanism used by Sun Microsystems in the Solaris 2 C library,
229 introduced a cleaner solution to the problem.
230
232 getent(1), nss(5)
233
235 This page is part of release 4.16 of the Linux man-pages project. A
236 description of the project, information about reporting bugs, and the
237 latest version of this page, can be found at
238 https://www.kernel.org/doc/man-pages/.
239Linux 2017-05-03 NSSWITCH.CONF(5)