About the Name Service Switch
The name service switch is a file which is named, nsswitch.conf. The
name service switch controls how a client machine or application obtains network information. The
name service switch is used by client applications that call any of
the getXbyY() interfaces such as the following.
gethostbyname()
getpwuid()
getpwnam()
getaddrinfo()
Each machine has a switch file in its /etc directory. Each line of
that file identifies a particular type of network information, such as host, password,
and group, followed by one or more locations of that information.
A client can obtain naming information from one or more of the
switch's sources. For example, an NIS+ client could obtain its hosts information from an
NIS+ table and its password information from a local /etc file. In addition,
the client could specify the conditions under which the switch must use each
source. See Table 2-1.
The Solaris system automatically loads an nsswitch.conf file into every machine's /etc directory
as part of the installation process. Four alternate (template) versions of the switch
file are also loaded into /etc for LDAP, NIS, NIS+, or files. See
The nsswitch.conf Template Files.
These four files are alternate default switch files. Each file is designed for
a different primary naming service: /etc files, NIS, NIS+, or LDAP. When
the Solaris software is first installed on a machine, the installer selects the
machine's default naming service: NIS+, NIS, local files, or LDAP. During installation, the
corresponding template file is copied to nsswitch.conf. For example, for a machine client
using LDAP, the installation process copies nsswitch.ldap to nsswitch.conf. Unless you have
an unusual namespace, the default template file as copied to nsswitch.conf should be
sufficient for normal operation.
No default file is provided for DNS, but you can edit any of
these files to use DNS. For more information see DNS and Internet Access.
If you later change a machine's primary naming service, you copy the appropriate
alternate switch file to nsswitch.conf. See The nsswitch.conf Template Files. You can also change the sources
of particular types of network information used by the client by editing the
appropriate lines of the /etc/nsswitch.conf file. The syntax is described below, and additional
instructions are provided in How to Modify the Name Service Switch.
Format of the nsswitch.conf File
The nsswitch.conf file is essentially a list of 16 types of information and
the sources that getXXbyYY() routines search for that information. The 16 types
of information, not necessarily in this order, are the following.
The following table provides a description of the kind of sources that can
be listed in the switch file for the information types above.
Table 2-1 Switch File Information Sources
Information Sources |
Description |
|---|
files |
A
file stored in the client's /etc directory. For example, /etc/passwd |
nisplus |
An NIS+ table. For
example, the hosts table. |
nis |
An NIS map. For example, the hosts map. |
compat |
compat can
be used for password and group information to support old-style + or -
syntax in /etc/passwd, /etc/shadow, and /etc/group files. |
dns |
Can be used to specify that
host information be obtained from DNS. |
ldap |
Can be used to specify entries be
obtained from the LDAP directory. |
Search Criteria
Single Source. If an information type has only one source, such as nisplus a
routine using the switch searches for the information in that source only. If the
routine finds the information, the routine returns a success status message. If the
routine does not find the information, the routine stops searching and returns a
different status message. What the routine does with the status message varies from
routine to routine.
Multiple Sources. If a table contains multiple sources for a given information type,
the switch directs the routine to search in the first listed source.
If the routine finds the information, the routine returns a success status message.
If the routine does not find the information in the first source, the
routine tries the next source. The routine searches all sources until the
routine has found the information, or until the routine is halted by a
return specification. If all of the listed sources are searched without finding the
information, the routine stops searching and returns a non-success status message.
Switch Status Messages
If a routine finds the information, the routine returns a success status
message. If the routine does not find the information, the routine returns one
of three error status messages. Possible status messages are listed in the following
table.
Table 2-2 Switch Search Status Messages
Status Message |
Meaning of Message |
|---|
SUCCESS |
The requested entry was found in the specified source. |
UNAVAIL |
The
source is either unresponsive or unavailable. In other words, neither the NIS+
table, the NIS map, nor the /etc file could be found or be
accessed. |
NOTFOUND |
The source responded with “No such entry.” In other words, the table, map,
or file was accessed but the needed information was not found. |
TRYAGAIN |
The source
is busy. The source might respond next time. In other words, the table,
map, or file was found, but could not respond to the query. |
Switch Action Options
You can instruct the switch to respond to status messages with either of
the two actions shown in the following table.
Table 2-3 Responses to Switch Status Messages
Action |
Meaning |
|---|
return |
Stop looking for the information. |
continue |
Try
the next source. |
Default Search Criteria
The combination of nsswitch.conf file status message and action option determines what the
routine does at each step. The combination of status and action make up
the search criteria.
The switch's default search criteria are the same for every source. As described
in terms of the status messages listed above, see the following.
SUCCESS=return. Stop looking for the information. Proceed using the information that has been found.
UNAVAIL=continue. Go to the next nsswitch.conf file source and continue searching. If this source is the last or only source, return with a NOTFOUND status.
NOTFOUND=continue. Go to the next nsswitch.conf file source and continue searching. If this source is the last or only source, return with a NOTFOUND status.
TRYAGAIN=continue. Go to the next nsswitch.conf file source and continue searching. If this source is the last or only source, return with a NOTFOUND status.
You can change default search criteria by explicitly specifying some other criteria by
using the STATUS=action syntax shown above. For example, the default action for
a NOTFOUND condition is to continue the search to the next source. For
example, to specify for networks, the search should stop in a
NOTFOUND condition, edit the networks line of the switch file. The
line would read as follows.
networks: nis [NOTFOUND=return] files
The networks: nis [NOTFOUND=return] files line specifies a nondefault criterion for the NOTFOUND status. Nondefault criteria are
delimited by square brackets.
In this example, the search routine behaves as follows:
If the networks map is available, and contains the needed information, the routine returns with a SUCCESS status message.
If the networks map is not available, the routine returns with an UNAVAIL status message. By default, the routine continues to search the appropriate /etc file.
If the networks map is available and found, but the map does not contain the needed information, the routine returns with a NOTFOUND message. But, instead of continuing on to search the appropriate /etc file, which would be the default behavior, the routine stops searching.
If the networks map is busy, the routine returns with an TRYAGAIN status message and by default continues on to search the appropriate /etc file.
Note - Lookups in the nsswitch.conf file are done in the order in which items
are listed. However, password updates are done in reverse order, unless otherwise specified
by using the passwd -r repository command. See The Switch File and Password Information for more information.
What if the Syntax is Wrong?
Client library routines contain compiled-in default entries that are used if an entry
in the nsswitch.conf file is either missing or syntactically incorrect. These entries are
the same as the switch file's defaults.
The name service switch assumes that the table and source names are spelled
correctly. If you misspell a table or source name, the switch uses default
values.
Auto_home and Auto_master
The switch search criteria for the auto_home and auto_master tables and maps
is combined into one category, which is called automount.
Timezone and the Switch File
The timezone table does not use the switch, so the table is not
included in the switch file's list.
Comments in nsswitch.conf Files
Any nsswitch.conf file line beginning with a comment character (#) is interpreted as
a comment line. A comment line is ignored by routines that search the
file.
Characters preceding a comment mark are interpreted by routines that search the nsswitch.conf
file. Characters to the right of the comment mark are interpreted as comments
and ignored.
Table 2-4 Switch File Comment Examples
Type of Line |
Example |
|---|
Comment line. |
# hosts: nisplus [NOTFOUND=return] files |
Interpreted line. |
hosts: nisplus [NOTFOUND=return]
file |
Partially interpreted line. The files element is not interpreted. |
hosts: nisplus [NOTFOUND=return] # files |
Keyserver and publickey Entry in the Switch File
Caution - You must restart the keyserver after you make a change to nsswitch.conf.
The keyserver reads the publickey entry in the name service switch configuration file
only when the keyserver is started. If you change the switch configuration file,
the keyserver does not register the changes until the keyserver is restarted.
