System Administration Guide: IP Services

hosts Database

The hosts database contains the IPv4 addresses and host names of systems on your network. If you use the NIS or DNS name service, or the LDAP directory service, the hosts database is maintained in a database that is designated for host information. For example, on a network that runs NIS, the hosts database is maintained in the hostsbyname file.

If you use local files for the name service, the hosts database is maintained in the /etc/inet/hosts file. This file contains the host names and IPv4 addresses of the primary network interface, other network interfaces that are attached to the system, and any other network addresses that the system must check for.

Note –

For compatibility with BSD-based operating systems, the /etc/hosts file is a symbolic link to /etc/inet/hosts.

/etc/inet/hosts File Format

The /etc/inet/hosts file uses the basic syntax that follows. Refer to the hosts(4) man page for complete syntax information.

IPv4-address hostname [nicknames] [#comment]


Contains the IPv4 address for each interface that the local host must recognize.


Contains the host name that is assigned to the system at setup, plus the host names that are assigned to additional network interfaces that the local host must recognize.


Is an optional field that contains a nickname for the host.


Is an optional field for a comment.

Initial /etc/inet/hosts File

When you run the Oracle Solaris installation program on a system, the program configures the initial /etc/inet/hosts file. This file contains the minimum entries that the local host requires. The entries include the loopback address, the host IPv4 address, and the host name.

For example, the Oracle Solaris installation program might create the following /etc/inet/hosts file for system tenere shown in Figure 5–1:

Example 10–1 /etc/inet/hosts File for System tenere     localhost         loghost    #loopback address   tenere                      #host name

Loopback Address

In Example 10–1, the IPv4 address is the loopback address. The loopback address is the reserved network interface that is used by the local system to allow interprocess communication. This address enables the host to send packets to itself. The ifconfig command uses the loopback address for configuration and testing, as explained in Monitoring the Interface Configuration With the ifconfig Command. Every system on a TCP/IP network must use the IP address for IPv4 loopback on the local host.

Host Name

The IPv4 address and the name tenere are the address and host name of the local system. They are assigned to the system's primary network interface.

Multiple Network Interfaces

Some systems have more than one network interface, because they are either routers or multihomed hosts. Each network interface that is attached to the system requires its own IP address and associated name. During installation, you must configure the primary network interface. If a particular system has multiple interfaces at installation time, the Oracle Solaris installation program also prompts you about these additional interfaces. You can optionally configure one or more additional interfaces at this time, or manually, at a later date.

After the Oracle Solaris installation, you can configure additional interfaces for a router or multihomed host by adding interface information to the systems' /etc/inet/hosts file. For more information on configuring routers and multihomed hosts refer to Configuring an IPv4 Router and Configuring Multihomed Hosts.

Example 10–2 shows the /etc/inet/hosts file for system timbuktu that is shown in Figure 5–1.

Example 10–2 /etc/inet/hosts File for System timbuktu        localhost     loghost   timbuktu      #This is the local host name   timbuktu-201  #Interface to network 192.9.201

With these two interfaces, timbuktu connects networks 192.168.200 and 192.168.201 as a router.

How Name Services Affect the hosts Database

The NIS and DNS name services, and LDAP directory service, maintain host names and addresses on one or more servers. These servers maintain hosts databases that contain information for every host and router (if applicable) on the servers' network. Refer to System Administration Guide: Naming and Directory Services (DNS, NIS, and LDAP) for more information about these services.

When Local Files Provide the Name Service

On a network that uses local files for the name service, systems that run in local files mode consult their individual /etc/inet/hosts files for IPv4 addresses and host names of other systems on the network. Therefore, these system's /etc/inet/hosts files must contain the following:

Figure 10–1 shows the /etc/inet/hosts file for system tenere. This system runs in local files mode. Notice that the file contains the IPv4 addresses and host names for every system on the 192.9.200 network. The file also contains the IPv4 address and interface name timbuktu-201. This interface connects the 192.9.200 network to the 192.9.201 network.

A system that is configured as a network client uses the local /etc/inet/hosts file for its loopback address and IPv4 address.

Figure 10–1 /etc/inet/hosts File for a System Running in Local Files Mode

Shows what the hosts file might look like for a system
that is running in local files mode.