version 1.10, 2010/09/29 13:44:33 |
version 1.11, 2010/09/29 14:34:07 |
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.\" $NetBSD$ |
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.\" |
.\" Copyright (c) 2004 by Internet Systems Consortium, Inc. ("ISC") |
.\" Copyright (c) 2004 by Internet Systems Consortium, Inc. ("ISC") |
.\" |
.\" |
.\" Permission to use, copy, modify, and distribute this software for any |
.\" Permission to use, copy, modify, and distribute this software for any |
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.\" |
.\" |
.Dd February 16, 1994 |
.Dd February 16, 1994 |
.Dt HOSTNAME 7 |
.Dt HOSTNAME 7 |
.Os BSD 4 |
.Os |
.Sh NAME |
.Sh NAME |
.Nm hostname |
.Nm hostname |
.Nd host name resolution description |
.Nd host name resolution description |
.Sh DESCRIPTION |
.Sh DESCRIPTION |
Hostnames are domains. A domain is a hierarchical, dot-separated list |
Hostnames are domains. |
of subdomains. For example, the machine |
A domain is a hierarchical, dot-separated list of subdomains. |
.Dq Li monet , |
For example, the machine |
in the |
.Dq Li monet , |
|
in the |
.Dq Li Berkeley |
.Dq Li Berkeley |
subdomain of the |
subdomain of the |
.Dq Li EDU |
.Dq Li EDU |
subdomain of the Internet Domain Name System would be represented as |
subdomain of the Internet Domain Name System would be represented as |
.Pp |
.Pp |
Line 54 which must generally translate the name |
|
Line 57 which must generally translate the name |
|
(This task is usually performed by the library routine |
(This task is usually performed by the library routine |
.Xr gethostbyname 3 . ) |
.Xr gethostbyname 3 . ) |
The default method for resolving hostnames by the Internet name resolver is |
The default method for resolving hostnames by the Internet name resolver is |
to follow RFC 1535's security recommendations. Actions can be taken |
to follow RFC 1535's security recommendations. |
by the administrator to override these recommendations and to have the |
Actions can be taken by the administrator to override these |
resolver behave the same as earlier, non-RFC 1535 |
recommendations and to have the resolver behave the same as earlier, |
resolvers. |
non-RFC 1535 resolvers. |
.Pp |
.Pp |
The default method (using RFC 1535 guidelines) follows: |
The default method (using RFC 1535 guidelines) follows: |
.Pp |
.Pp |
If the name consists of a single component, i.e. contains no dot, and if the |
If the name consists of a single component, i.e. contains no dot, and if the |
environment variable |
environment variable |
.Dq Ev HOSTALIASES |
.Dq Ev HOSTALIASES |
is set to the name of a file, |
is set to the name of a file, |
that file is searched for a string matching the input hostname. The file |
that file is searched for a string matching the input hostname. |
|
The file |
should consist of lines made up of two strings separated by white-space, the |
should consist of lines made up of two strings separated by white-space, the |
first of which is the hostname alias, and the second of which is the complete |
first of which is the hostname alias, and the second of which is the complete |
hostname to be substituted for that alias. If a case-insensitive match is |
hostname to be substituted for that alias. |
|
If a case-insensitive match is |
found between the hostname to be resolved and the first field of a line in |
found between the hostname to be resolved and the first field of a line in |
the file, the substituted name is looked up with no further processing. |
the file, the substituted name is looked up with no further processing. |
.Pp |
.Pp |
If there is at least one dot in the name, then the name is first tried |
If there is at least one dot in the name, then the name is first tried |
.Dq as-is . |
.Dq as-is . |
The number of dots to cause this action is configurable by setting the |
The number of dots to cause this action is configurable by setting the |
threshold using the |
threshold using the |
.Dq Li ndots |
.Dq Li ndots |
option in |
option in |
.Pa /etc/resolv.conf |
.Pa /etc/resolv.conf |
(default: 1). If the name ends with a dot, the trailing dot is |
(default: 1). |
|
If the name ends with a dot, the trailing dot is |
removed, and the remaining name is looked up (regardless of the setting of |
removed, and the remaining name is looked up (regardless of the setting of |
the |
the |
.Li ndots |
.Li ndots |
option), without further processing. |
option), without further processing. |
.Pp |
.Pp |
If the input name does not end with a trailing dot, it is looked up by |
If the input name does not end with a trailing dot, it is looked up by |
searching through a list of domains until a match is found. If neither the |
searching through a list of domains until a match is found. |
search option in the |
If neither the search option in the |
.Pa /etc/resolv.conf |
.Pa /etc/resolv.conf |
file or the |
file or the |
.Dq Ev LOCALDOMAIN |
.Dq Ev LOCALDOMAIN |
environment variable is used, then the |
environment variable is used, then the |
search list of domains contains only the full domain specified by the |
search list of domains contains only the full domain specified by the |
.Li domain |
.Li domain |
option (in |
option (in |
.Pa /etc/resolv.conf ) |
.Pa /etc/resolv.conf ) |
or the domain used in the local hostname. For example, if the |
or the domain used in the local hostname. |
.Dq Li domain |
For example, if the |
option is set to |
.Dq Li domain |
|
option is set to |
.Li CS.Berkeley.EDU , |
.Li CS.Berkeley.EDU , |
then only |
then only |
.Li CS.Berkeley.EDU |
.Li CS.Berkeley.EDU |
will be in the search list, and this will be the only |
will be in the search list, and this will be the only |
domain appended to the partial hostname. For example, if |
domain appended to the partial hostname. |
.Dq Li lithium |
For example, if |
|
.Dq Li lithium |
is the name to be resolved, this would make |
is the name to be resolved, this would make |
.Li lithium.CS.Berkeley.EDU |
.Li lithium.CS.Berkeley.EDU |
the only name to be tried using the search list. |
the only name to be tried using the search list. |
.Pp |
.Pp |
If the |
If the |
.Li search |
.Li search |
option is used in |
option is used in |
.Pa /etc/resolv.conf |
.Pa /etc/resolv.conf |
or the environment variable |
or the environment variable |
.Dq Ev LOCALDOMAIN |
.Dq Ev LOCALDOMAIN |
is set by the user, then |
is set by the user, then |
the search list will include what is set by these methods. For |
the search list will include what is set by these methods. |
example, if the |
For example, if the |
.Dq Li search |
.Dq Li search |
option contained |
option contained |
.Pp |
.Pp |
.Dl CS.Berkeley.EDU CChem.Berkeley.EDU Berkeley.EDU |
.Dl CS.Berkeley.EDU CChem.Berkeley.EDU Berkeley.EDU |
.Pp |
.Pp |
then the partial hostname (e.g., |
then the partial hostname (e.g., |
.Dq Li lithium ) |
.Dq Li lithium ) |
will be tried with |
will be tried with |
.Em each |
.Em each |
domain name appended (in the same order specified); the resulting hostnames |
domain name appended (in the same order specified); the resulting hostnames |
that would be tried are: |
that would be tried are: |
.Bd -literal -offset indent |
.Bd -literal -offset indent |
lithium.CS.Berkeley.EDU |
lithium.CS.Berkeley.EDU |
Line 135 lithium.CChem.Berkeley.EDU |
|
Line 143 lithium.CChem.Berkeley.EDU |
|
lithium.Berkeley.EDU |
lithium.Berkeley.EDU |
.Ed |
.Ed |
.Pp |
.Pp |
The environment variable |
The environment variable |
.Dq Ev LOCALDOMAIN |
.Dq Ev LOCALDOMAIN |
overrides the |
overrides the |
.Dq Li search |
.Dq Li search |
and |
and |
.Dq Li domain |
.Dq Li domain |
options, and if both |
options, and if both |
.Li search |
.Li search |
and |
and |
.Li domain |
.Li domain |
options are present in the resolver configuration file, then only the |
options are present in the resolver configuration file, then only the |
.Em last |
.Em last |
one listed is used (see |
one listed is used (see |
.Xr resolver 5 ) . |
.Xr resolver 5 ) . |
.Pp |
.Pp |
If the name was not previously tried |
If the name was not previously tried |
.Dq as-is |
.Dq as-is |
(i.e., it fell below the |
(i.e., it fell below the |
.Dq Li ndots |
.Dq Li ndots |
threshold or did not contain a dot), then the name as |
threshold or did not contain a dot), then the name as |
originally provided is attempted. |
originally provided is attempted. |
.Sh ENVIRONMENT |
.Sh ENVIRONMENT |
.Bl -tag -width "/etc/resolv.conf " |
.Bl -tag -width "/etc/resolv.conf " |
.It Ev LOCALDOMAIN |
.It Ev LOCALDOMAIN |
Affects domains appended to partial hostnames. |
Affects domains appended to partial hostnames. |
.It Ev HOSTALIASES |
.It Ev HOSTALIASES |
Name of file containing |
Name of file containing |
|
|
.Bl -tag -width "/etc/resolv.conf " -compact |
.Bl -tag -width "/etc/resolv.conf " -compact |
.It Pa /etc/resolv.conf |
.It Pa /etc/resolv.conf |
See |
See |
.Xr resolve 5 . |
.Xr resolver 5 . |
.El |
.El |
.Sh SEE ALSO |
.Sh SEE ALSO |
.Xr gethostbyname 3 , |
.Xr gethostbyname 3 , |
.Xr resolver 5 , |
.Xr resolver 5 , |
.Xr mailaddr 7 , |
.Xr mailaddr 7 |