Manual Pages for UNIX Operating System command usage for man hosts

File Formats                                             hosts(4)



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  char-
     acters.  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 differ-
     ing 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



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File Formats                                             hosts(4)



     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  inter-
              preted  using the inet_addr routine from the Inter-
              net address manipulation library, inet(3SOCKET).

         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 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 com-
     ponents 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 dis-
     tinction  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.




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File Formats                                             hosts(4)



     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



SEE ALSO
     gethostbyname(3NSL),               getipnodebyname(3SOCKET),
     inet(3SOCKET), nsswitch.conf(4), resolv.conf(4)


     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.





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File Formats                                             hosts(4)



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 com-
     patibility with previous Solaris releases.
















































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