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Annotation of src/share/man/man7/hostname.7, Revision 1.11

1.11    ! wiz         1: .\" $NetBSD$
        !             2: .\"
1.10      christos    3: .\" Copyright (c) 2004 by Internet Systems Consortium, Inc. ("ISC")
1.4       jtc         4: .\"
1.10      christos    5: .\" Permission to use, copy, modify, and distribute this software for any
                      6: .\" purpose with or without fee is hereby granted, provided that the above
                      7: .\" copyright notice and this permission notice appear in all copies.
1.1       cgd         8: .\"
1.10      christos    9: .\" THE SOFTWARE IS PROVIDED "AS IS" AND ISC DISCLAIMS ALL WARRANTIES
                     10: .\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
                     11: .\" MERCHANTABILITY AND FITNESS.  IN NO EVENT SHALL ISC BE LIABLE FOR
                     12: .\" ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
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                     14: .\" ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT
                     15: .\" OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
1.1       cgd        16: .\"
1.10      christos   17: .\" Copyright (c) 1987 The Regents of the University of California.
                     18: .\" All rights reserved.
1.1       cgd        19: .\"
1.10      christos   20: .\" Redistribution and use in source and binary forms are permitted
                     21: .\" provided that the above copyright notice and this paragraph are
                     22: .\" duplicated in all such forms and that any documentation,
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                     24: .\" distribution and use acknowledge that the software was developed
                     25: .\" by the University of California, Berkeley.  The name of the
                     26: .\" University may not be used to endorse or promote products derived
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                     29: .\" IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
                     30: .\" WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
                     31: .\"
                     32: .\"    @(#)hostname.7  6.4 (Berkeley) 1/16/90
                     33: .\"
                     34: .Dd February 16, 1994
1.1       cgd        35: .Dt HOSTNAME 7
1.11    ! wiz        36: .Os
1.1       cgd        37: .Sh NAME
1.11    ! wiz        38: .Nm hostname
1.1       cgd        39: .Nd host name resolution description
                     40: .Sh DESCRIPTION
1.11    ! wiz        41: Hostnames are domains.
        !            42: A domain is a hierarchical, dot-separated list of subdomains.
        !            43: For example, the machine
        !            44: .Dq Li monet ,
        !            45: in the
1.10      christos   46: .Dq Li Berkeley
1.11    ! wiz        47: subdomain of the
1.10      christos   48: .Dq Li EDU
                     49: subdomain of the Internet Domain Name System would be represented as
1.1       cgd        50: .Pp
                     51: .Dl monet.Berkeley.EDU
                     52: .Pp
                     53: (with no trailing dot).
                     54: .Pp
                     55: Hostnames are often used with network client and server programs,
                     56: which must generally translate the name to an address for use.
1.10      christos   57: (This task is usually performed by the library routine
                     58: .Xr gethostbyname  3 . )
                     59: The default method for resolving hostnames by the Internet name resolver is
1.11    ! wiz        60: to follow RFC 1535's security recommendations.
        !            61: Actions can be taken by the administrator to override these
        !            62: recommendations and to have the resolver behave the same as earlier,
        !            63: non-RFC 1535 resolvers.
1.10      christos   64: .Pp
                     65: The default method (using RFC 1535 guidelines) follows:
                     66: .Pp
                     67: If the name consists of a single component, i.e. contains no dot, and if the
1.11    ! wiz        68: environment variable
        !            69: .Dq Ev HOSTALIASES
1.1       cgd        70: is set to the name of a file,
1.11    ! wiz        71: that file is searched for a string matching the input hostname.
        !            72: The file
1.10      christos   73: should consist of lines made up of two strings separated by white-space, the
                     74: first of which is the hostname alias, and the second of which is the complete
1.11    ! wiz        75: hostname to be substituted for that alias.
        !            76: If a case-insensitive match is
1.10      christos   77: found between the hostname to be resolved and the first field of a line in
                     78: the file, the substituted name is looked up with no further processing.
                     79: .Pp
1.11    ! wiz        80: If there is at least one dot in the name, then the name is first tried
        !            81: .Dq as-is .
1.10      christos   82: The number of dots to cause this action is configurable by setting the
1.11    ! wiz        83: threshold using the
1.10      christos   84: .Dq Li ndots
1.11    ! wiz        85: option in
1.10      christos   86: .Pa /etc/resolv.conf
1.11    ! wiz        87: (default: 1).
        !            88: If the name ends with a dot, the trailing dot is
1.10      christos   89: removed, and the remaining name is looked up (regardless of the setting of
1.11    ! wiz        90: the
        !            91: .Li ndots
        !            92: option), without further processing.
1.10      christos   93: .Pp
                     94: If the input name does not end with a trailing dot, it is looked up by
1.11    ! wiz        95: searching through a list of domains until a match is found.
        !            96: If neither the search option in the
1.10      christos   97: .Pa /etc/resolv.conf
1.11    ! wiz        98: file or the
        !            99: .Dq Ev LOCALDOMAIN
1.10      christos  100: environment variable is used, then the
1.11    ! wiz       101: search list of domains contains only the full domain specified by the
1.10      christos  102: .Li domain
                    103: option (in
                    104: .Pa /etc/resolv.conf )
1.11    ! wiz       105: or the domain used in the local hostname.
        !           106: For example, if the
        !           107: .Dq Li domain
        !           108: option is set to
1.10      christos  109: .Li CS.Berkeley.EDU ,
1.11    ! wiz       110: then only
        !           111: .Li CS.Berkeley.EDU
1.10      christos  112: will be in the search list, and this will be the only
1.11    ! wiz       113: domain appended to the partial hostname.
        !           114: For example, if
        !           115: .Dq Li lithium
1.10      christos  116: is the name to be resolved, this would make
1.11    ! wiz       117: .Li lithium.CS.Berkeley.EDU
1.10      christos  118: the only name to be tried using the search list.
                    119: .Pp
1.11    ! wiz       120: If the
        !           121: .Li search
1.10      christos  122: option is used in
                    123: .Pa /etc/resolv.conf
1.11    ! wiz       124: or the environment variable
        !           125: .Dq Ev LOCALDOMAIN
1.10      christos  126: is set by the user, then
1.11    ! wiz       127: the search list will include what is set by these methods.
        !           128: For example, if the
        !           129: .Dq Li search
1.10      christos  130: option contained
                    131: .Pp
                    132: .Dl CS.Berkeley.EDU CChem.Berkeley.EDU Berkeley.EDU
                    133: .Pp
1.11    ! wiz       134: then the partial hostname (e.g.,
        !           135: .Dq Li lithium )
        !           136: will be tried with
1.10      christos  137: .Em each
1.11    ! wiz       138: domain name appended (in the same order specified); the resulting hostnames
1.10      christos  139: that would be tried are:
                    140: .Bd -literal -offset indent
                    141: lithium.CS.Berkeley.EDU
                    142: lithium.CChem.Berkeley.EDU
                    143: lithium.Berkeley.EDU
                    144: .Ed
                    145: .Pp
1.11    ! wiz       146: The environment variable
        !           147: .Dq Ev LOCALDOMAIN
1.10      christos  148: overrides the
1.11    ! wiz       149: .Dq Li search
        !           150: and
        !           151: .Dq Li domain
        !           152: options, and if both
        !           153: .Li search
        !           154: and
1.10      christos  155: .Li domain
1.11    ! wiz       156: options are present in the resolver configuration file, then only the
1.10      christos  157: .Em last
                    158: one listed is used (see
                    159: .Xr resolver 5 ) .
                    160: .Pp
1.11    ! wiz       161: If the name was not previously tried
        !           162: .Dq as-is
1.10      christos  163: (i.e., it fell below the
1.11    ! wiz       164: .Dq Li ndots
1.10      christos  165: threshold or did not contain a dot), then the name as
                    166: originally provided is attempted.
                    167: .Sh ENVIRONMENT
                    168: .Bl -tag -width "/etc/resolv.conf  "
1.11    ! wiz       169: .It Ev LOCALDOMAIN
1.10      christos  170: Affects domains appended to partial hostnames.
                    171: .It Ev HOSTALIASES
                    172: Name of file containing
                    173: .Pq Ar host alias , full hostname
                    174: pairs.
                    175: .El
                    176: .Sh FILES
                    177: .Bl -tag -width "/etc/resolv.conf  " -compact
                    178: .It Pa /etc/resolv.conf
                    179: See
1.11    ! wiz       180: .Xr resolver 5 .
1.10      christos  181: .El
1.1       cgd       182: .Sh SEE ALSO
                    183: .Xr gethostbyname 3 ,
1.10      christos  184: .Xr resolver 5 ,
1.11    ! wiz       185: .Xr mailaddr 7

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