从某种程度上讲，在研究这个问题时，我已经变得疯狂到检查“主机名”的源代码并编写脚本以打印调查结果（Fedora 19）。缺少的是查看“ / etc / hosts”，以我的拙见，应该首先将其排除在所有这些之外。
#!/bin/bash
function pad {
if [[ $1 == '?' ]]; then
printf "%-23s" "?"
else
printf "%-23s" "'$1'"
fi
}
# ----- Kernel -----
# Two ways to configure the kernel values:
# 1) Put FQDN into "kernel.hostname" and nothing into "kernel.domainname"
# 2) Put machine name into "kernel.hostname" and DNS domain name into "kernel.domainname" (makes more sense)
echo "== Kernel values =="
echo
H=`/sbin/sysctl -n kernel.hostname`
D=`/sbin/sysctl -n kernel.domainname`
echo "Kernel hostname: '$H'"
echo "Kernel domainname: '$D'"
# ----- What does bash say -----
echo
echo "== According to bash =="
echo
echo "HOSTNAME = '$HOSTNAME'"
# ----- Hostname config file ------
echo
echo "== Hostname config file =="
echo
ETCH="/etc/hostname"
if [[ -f $ETCH ]]; then
CONTENTS=`cat $ETCH`
echo "File '$ETCH' contains: '$CONTENTS'"
else
echo "File '$ETCH' does not exist"
fi
# ----- Network config file ------
echo
echo "== Network config file =="
echo
SYSN="/etc/sysconfig/network"
if [[ -f $SYSN ]]; then
LINE=`grep -e "^HOSTNAME=" $SYSN`
if [[ -n $LINE ]]; then
echo "File '$SYSN' contains: '$LINE'"
else
echo "File '$SYSN' exists but does not contain a line for 'HOSTNAME'"
fi
else
echo "File '$SYSN' does not exist"
fi
# ----- Nodename -------
echo
echo "== Nodename =="
echo
UNAME=`uname --nodename` # On Linux, this is the hostname
echo "The 'nodename' given by 'uname --nodename' is: '$UNAME'"
# ----- The 'hostname' mess ------
THE_HOSTNAME=`hostname`
SHORT_NAME=`hostname --short`
NIS_DNAME=`domainname`
YP_DNAME=`hostname --yp` # Same as `nisdomainname` ; this may fail with "hostname: Local domain name not set"
if [[ $? != 0 ]]; then
YP_DNAME="?"
fi
echo
echo "== 'hostname' directly obtained values =="
echo
echo "The result of gethostname();"
echo "...obtained by running 'hostname'"
echo "Hostname: $(pad $THE_HOSTNAME)"
echo
echo "The part before the first '.' of the value returned by gethostname();"
echo "...obtained by running 'hostname --short'"
echo "Short name: $(pad $SHORT_NAME)"
echo
echo "The result of getdomainname(); the code of 'hostname' seems to call this the 'NIS domain name';"
echo "...on Linux, this is the kernel-configured domainname;"
echo "...obtained by running 'domainname'"
echo "NIS domain name: $(pad $NIS_DNAME)"
echo
echo "The result of yp_get_default_domain(), which may fail;"
echo "...obtained by running 'ĥostname --yp'"
echo "YP default domain: $(pad $YP_DNAME)"
DNS_DNAME=`hostname --domain` # Same as `dnsdomainname`'
FQDN_NAME=`hostname --fqdn`
ALIAS_NAME=`hostname --alias`
echo
echo "== 'hostname' values obtained via DNS =="
echo
echo "The part after the first '.' of the 'canonical name' value returned by getaddrinfo(gethostname());"
echo "...obtained by running 'hostname --domain'"
echo "DNS domain name: $(pad $DNS_DNAME)"
echo
echo "The 'canonical name' value returned by getaddrinfo(gethostname());"
echo "...obtained by running 'hostname --fqdn'"
echo "Fully qualified hostname: $(pad $FQDN_NAME)"
echo
echo "Alias obtained by gethostbyname(gethostname());"
echo "...obtained by running 'hostname --alias'"
echo "Hostname alias: $(pad $ALIAS_NAME)"
BY_IP_ADDR=`hostname --ip-address`
ALL_IP_ADDR=`hostname --all-ip-addresses`
ALL_FQDN_NAMES=`hostname --all-fqdn`
echo
echo "== 'hostname' values obtained by collecting configured network addresses =="
echo
echo "Collect the IP addresses from getaddrinfo(gethostname()), apply getnameinfo(ip) to all those addresses;"
echo "...obtained by running 'hostname --ip-address'"
echo "By IP address: $BY_IP_ADDR"
echo
echo "Call getnameinfo(NI_NUMERICHOST) on all addresses snarfed from active interfaces;"
echo "...obtained by running 'hostname --all-ip-addresses'"
echo "All IP addresses: $ALL_IP_ADDR"
echo
echo "Call getnameinfo(NI_NAMEREQD) on all addresses snarfed from active interfaces (involves lookup in /etc/hosts);"
echo "...obtained by running 'hostname --all-fqdn'"
echo "All fully qualified hostnames: $ALL_FQDN_NAMES"
手动设置内核值并填充/etc/hostname，但未更改后，运行Fedora 19的Amazon EC2 VM上的输出/etc/hosts可能是这样的：
== Kernel values ==
Kernel hostname: 'kyubee'
Kernel domainname: 'homelinux.org'
== According to bash ==
HOSTNAME = 'ip-172-31-24-249.localdomain'
== Hostname config file ==
File '/etc/hostname' contains: 'kyubee.homelinux.org'
== Network config file ==
File '/etc/sysconfig/network' exists but does not contain a line for 'HOSTNAME'
== Nodename ==
The 'nodename' given by 'uname --nodename' is: 'kyubee'
== 'hostname' directly obtained values ==
The result of gethostname();
...obtained by running 'hostname'
Hostname: 'kyubee'
The part before the first '.' of the value returned by gethostname();
...obtained by running 'hostname --short'
Short name: 'kyubee'
The result of getdomainname(); the code of 'hostname' seems to call this the 'NIS domain name';
...on Linux, this is the kernel-configured domainname;
...obtained by running 'domainname'
NIS domain name: 'homelinux.org'
The result of yp_get_default_domain(), which may fail;
...obtained by running 'ĥostname --yp'
YP default domain: 'homelinux.org'
== 'hostname' values obtained via DNS ==
The part after the first '.' of the 'canonical name' value returned by getaddrinfo(gethostname());
...obtained by running 'hostname --domain'
DNS domain name: ''
The 'canonical name' value returned by getaddrinfo(gethostname());
...obtained by running 'hostname --fqdn'
Fully qualified hostname: 'kyubee'
Alias obtained by gethostbyname(gethostname());
...obtained by running 'hostname --alias'
Hostname alias: ''
== 'hostname' values obtained by collecting configured network addresses ==
Collect the IP addresses from getaddrinfo(gethostname()), apply getnameinfo(ip) to all those addresses;
...obtained by running 'hostname --ip-address'
By IP address: fe80::8f6:8eff:fe49:9e21%eth0 172.31.24.249
Call getnameinfo(NI_NUMERICHOST) on all addresses snarfed from active interfaces;
...obtained by running 'hostname --all-ip-addresses'
All IP addresses: 172.31.24.249
Call getnameinfo(NI_NAMEREQD) on all addresses snarfed from active interfaces (involves lookup in /etc/hosts);
...obtained by running 'hostname --all-fqdn'
All fully qualified hostnames: ip-172-31-24-249.eu-west-1.compute.internal
在perl中获取完全合格的主机名的弹性方法是：
sub getHostname {
my $hostname_short = `/bin/hostname --short`;
if ($? != 0) { print STDERR "Could not execute 'hostname --short' -- exiting\n"; exit 1 }
chomp $hostname_short;
my $hostname_long = `/bin/hostname`;
if ($? != 0) { print STDERR "Could not execute 'hostname' -- exiting\n"; exit 1 }
chomp $hostname_long;
if ($hostname_long =~ /^${hostname_short}\..+$/) {
# "hostname_long" is a qualified version of "hostname_short"
return $hostname_long
}
else {
# both hostnames are "short" (and are equal)
die unless ($hostname_long eq $hostname_short);
my $domainname = `/bin/domainname`;
if ($? != 0) { print STDERR "Could not execute 'domainname' -- exiting\n"; exit 1 }
chomp $domainname;
if ($domainname eq "(none)") {
# Change according to taste
return "${hostname_short}.localdomain"
}
else {
return "${hostname_short}.${domainname}"
}
}
}
而在bash中将是：
function getHostname {
local hostname_short=`/bin/hostname --short`
if [ $? -ne 0 ]; then
echo "Could not execute 'hostname --short' -- exiting" >&2; exit 1
fi
local hostname_long=`/bin/hostname`
if [ $? -ne 0 ]; then
echo "Could not execute 'hostname' -- exiting" >&2; exit 1
fi
if [[ $hostname_long =~ ^"$hostname_short"\..+$ ]]; then
# "hostname_long" is a qualified version of "hostname_short"
echo $hostname_long
else
# both hostnames are "short" (and are equal)
if [[ $hostname_long != $hostname_short ]]; then
echo "Cannot happen: '$hostname_long' <> '$hostname_short' -- exiting" >&2; exit 1
fi
local domainname=`/bin/domainname`
if [ $? -ne 0 ]; then
echo "Could not execute 'domainname' -- exiting" >&2; exit 1
fi
if [[ domainname == '(none)' ]]; then
# Change according to taste
echo "${hostname_short}.localdomain"
else
echo "${hostname_short}.${domainname}"
fi
fi
}
笔记
注意1：HOSTNAME是bash提供的shell变量（“自动设置为当前主机的名称。”），但是没有迹象表明bash达到了该值。
注意2：永远不要忘记/boot/initrams-FOO.img中的/ etc / hostname ...
hostname作为FQDN。仅仅拥有它还/etc/hosts不够。这弄乱了我的一贯性。