Tribblix: manual page: hosts.5

HOSTS(5) File Formats and Configurations HOSTS(5)

NAME

hosts - host name database

SYNOPSIS

/etc/inet/hosts

/etc/hosts

/etc/inet/ipnodes

DESCRIPTION

The hosts file is a local database that associates the names of hosts
with their Internet Protocol (IP) addresses. An IP address can be in
either IPv4 or IPv6 format. The hosts file can be used in conjunction
with, or instead of, other hosts databases, including the Domain Name
System (DNS), the NIS hosts map, or information from an LDAP server.
Programs use library interfaces to access information in the hosts
file.

Note that /etc/hosts and /etc/inet/ipnodes are symbolic links to
/etc/inet/hosts.

The hosts file has one entry for each IP address of each host. If a
host has more than one IP address, it will have one entry for each,
on consecutive lines. The format of each line is:

IP-address official-host-name nicknames...

Items are separated by any number of SPACE and/or TAB characters.
The first item on a line is the host's IP address. The second entry
is the host's official name. Subsequent entries on the same line are
alternative names for the same machine, or "nicknames." Nicknames are
optional.

For a host with more than one IP address, consecutive entries for
these addresses may contain the same or differing nicknames.
Different nicknames are useful for assigning distinct names to
different addresses.

A call to gethostbyname(3NSL) returns a hostent structure containing
the union of all IPv4 addresses and nicknames from each line
containing a matching official name or nickname. A call to
getipnodebyname(3SOCKET) is similar, but is capable of returning
hostent structures containing IPv4 and IPv6 addresses. Applications
might prefer to use the address-family independent
getaddrinfo(3SOCKET) API for name-to-address lookups.

A `#' indicates the beginning of a comment; characters up to the end
of the line are not interpreted by routines that search the file.

Network addresses are written in one of two ways:

o The conventional "decimal dot" notation and interpreted
using the inet_addr routine from the Internet address
manipulation library, inet(3C).

o The IP Version 6 protocol [IPV6], defined in RFC 1884 and
interpreted using the inet_pton() routine from the
Internet address manipulation library. See inet(3C).

This interface supports node names as defined in Internet RFC 952,
which states:

A "name" (Net, Host, Gateway, or Domain name) is a text string up to
24 characters drawn from the alphabet (A-Z), digits (0-9), minus sign
(-), and period (.). Note that periods are only allowed when they
serve to delimit components of "domain style names". (See RFC 921,
"Domain Name System Implementation Schedule," for background). No
blank or space characters are permitted as part of a name. No
distinction is made between uppercase and lowercase. The first
character must be an alpha character [or a digit. (RFC 1123 relaxed
RFC 952's limitation of the first character to only alpha
characters.)] The last character must not be a minus sign or period.

Host names must not consist of numbers only. A host name must contain
at least one alphabetical or special character.

Although the interface accepts host names longer than 24 characters
for the host portion (exclusive of the domain component), choosing
names for hosts that adhere to the 24 character restriction will
insure maximum interoperability on the Internet.

A host which serves as a GATEWAY should have "-GATEWAY" or "-GW" as
part of its name. Hosts which do not serve as Internet gateways
should not use "-GATEWAY" and "-GW" as part of their names. A host
which is a TAC should have "-TAC" as the last part of its host name,
if it is a DoD host. Single character names or nicknames are not
allowed.

EXAMPLES

Example 1: Example hosts File Entry

The following is a typical line from the hosts file:

192.9.1.20 gaia # John Smith

Example 2: Example IPv6 Address Entry

The following is an example of an IPv6 hosts entry:

2001:0db8:3c4d:55:a00:20ff:fe8e:f3ad myhost # John Smith

NOTES

/etc/inet/hosts is the official SVR4 name of the hosts file. The
symbolic link /etc/hosts exists for BSD compatibility.

The symbolic link /etc/net/ipnodes exists for backwards compatibility
with previous Solaris releases.

March 30, 2022 HOSTS(5)