November 17, 2000 HOSTS 5

### NAME

hosts - host name data base

### DESCRIPTION

The hosts file contains information regarding the known hosts on the network. It can be used in conjunction with the DNS, and the NIS maps `hosts.byaddr', and `hosts.byname', as controlled by nsswitch.conf(5).

For each host a single line should be present with the following information:
```address` `hostname``[alias``...]`

These are:

address
  Internet address
hostname
  Official host name
alias
  Alias host name

Items are separated by any number of blanks and/or tab characters. A hash sign (``#'') indicates the beginning of a comment; characters up to the end of the line are not interpreted by routines which search the file.

When using the name server named(8), or ypserv(8), this file provides a backup when the name server is not running. For the name server, it is suggested that only a few addresses be included in this file. These include address for the local interfaces that ifconfig(8) needs at boot time and a few machines on the local network.

This file may be created from the official host data base maintained at the Network Information Control Center (NIC), though local changes may be required to bring it up to date regarding unofficial aliases and/or unknown hosts. As the data base maintained at NIC is incomplete, use of the name server is recommended for sites on the DARPA Internet.

As network addresses, both IPv4 and IPv6 addresses are allowed. IPv4 addresses are specified in the conventional dot (``.'') notation using the inet_pton(3) routine from the Internet address manipulation library, inet(3). IPv6 addresses are specified in the standard hex-and-colon notation. Host names may contain any printable character other than a field delimiter, newline, or comment character.

### FILES

```/etc/hosts`
  The hosts file resides in ```/etc`.

### SEE ALSO

gethostbyname(3), nsswitch.conf(5), ifconfig(8), named(8)

### HISTORY

The hosts file format appeared in 4.2BSD.