The Name Service Switch (Overview)

This chapter describes the name service switch. You use the name service switch to coordinate usage of different naming services.

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 operating environment 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.

• aliases

• bootparams

• ethers

• group

• hosts

• ipnodes

• netgroup

• netmasks

• networks

• passwd, which includes shadow information

• protocols

• publickey

• rpc

• services

• automount

• sendmailvars

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

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