Um tanto quanto tangencial, enquanto pesquisava esta questão, eu fiquei louco o suficiente para checar o código-fonte do "hostname" e escrever um script para imprimir resultados investigativos (Fedora 19). O que está faltando é uma olhada em "/ etc / hosts", que na minha humilde opinião deve ser mantida fora de tudo isso em primeiro lugar.
#!/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"
A saída em uma VM do Amazon EC2 executando o Fedora 19 , depois de definir manualmente os valores do kernel e preencher /etc/hostname , mas sem alterações em /etc/hosts pode ser assim:
== 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
A maneira resiliente de obter o nome de host totalmente qualificado no perl seria:
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}"
}
}
}
e no bash seria:
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
}
Notas
Nota 1: HOSTNAME é uma variável do shell que o bash fornece ("Definido automaticamente para o nome do host atual"), mas não há nenhuma indicação de que o bash chega a esse valor.
Nota 2: Nunca esqueça o / etc / hostname em /boot/initrams-FOO.img ...