HOSTS(4) File Formats and Configurations HOSTS(4)
hosts - host name database
SYNOPSIS /etc/inet/hosts /etc/hosts /etc/inet/ipnodes
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
Note that /etc/hosts
are symbolic links to /etc/inet/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
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)
similar, but is capable of returning hostent
structures containing IPv4
and IPv6 addresses. Applications might prefer to use the address-family
API for name-to-address lookups.
' 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
routine from the Internet address manipulation
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(3SOCKET)
This interface supports node names as defined in Internet RFC 952, which
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.
Example 1: Example hosts File Entry
The following is a typical line from the hosts
18.104.22.168 gaia # John Smith
Example 2: Example IPv6 Address Entry
The following is an example of an IPv6 hosts
2001:0db8:3c4d:55:a00:20ff:fe8e:f3ad myhost # John Smith
SEE ALSO gethostbyname(3NSL)
Braden, B., editor, RFC 1123, Requirements for Internet Hosts - Application and Support
, Network Working Group, October, 1989.
Harrenstien, K., Stahl, M., and Feinler, E., RFC 952, DOD Internet Host Table Specification
, Network Working Group, October 1985.
Hinden, R., and Deering, S., editors, RFC 1884, IP Version 6 Addressing Architecture
, Network Working Group, December, 1995.
Postel, Jon, RFC 921, Domain Name System Implementation Schedule (Revised)
, Network Working Group, October 1984.
is the official SVR4 name of the hosts
file. The symbolic
exists for BSD
The symbolic link /etc/net/ipnodes
exists for backwards compatibility
with previous Solaris releases.
February 25, 2017 HOSTS(4)