设置主机名：FQDN 还是短名称？

Question

我注意到设置系统主机名的“首选”方法在 Red Hat/CentOS 和 Debian/Ubuntu 系统之间有着根本的不同。

CentOS 文档和RHEL 部署指南说主机名应该是 FQDN：

HOSTNAME=<value>, 哪里<value>应该是完全限定域名 (FQDN)，例如hostname.example.com，但可以是任何必要的主机名。

在RHEL安装指南稍微有些含糊：

安装程序会提示您为此计算机提供主机名，可以是格式为hostname.domainname的 完全限定域名(FQDN)，也可以是格式为hostname 的短主机名。

Debian 参考说主机名不应该使用 FQDN：

3.5.5. 主机名

内核维护系统主机名。运行级别 S 中的 init 脚本符号链接到“ /etc/init.d/hostname.sh ”，它在启动时（使用hostname命令）将系统主机名设置为存储在“ /etc/hostname ”中的名称。此文件应仅包含系统主机名，而不是完全限定的域名。

我还没有看到 IBM 提出任何关于使用哪个的具体建议，但某些软件似乎有偏好。

我的问题：

• 在异构环境中，是使用供应商建议更好，还是选择一个并在所有主机上保持一致？
• 您遇到过哪些软件对主机名是设置为 FQDN 还是短名称敏感？

Answer 1

我会在整个环境中选择一致的方法。这两种解决方案都可以正常工作，并且将与大多数应用程序保持兼容。但是，在可管理性方面存在差异。

我使用短名称作为 HOSTNAME 设置，并将 FQDN 设置/etc/hosts为服务器 IP的第一列，然后是短名称。

我还没有遇到过许多强制执行或显示两者之间偏好的软件包。我发现对于某些应用程序来说，短名称更清晰，特别是日志记录。也许我很不幸看到像server.northside.chicago.rizzomanufacturing.com. 谁想在日志或shell 提示中看到它？

有时，我会参与内部域和/或子域发生变化的公司收购或重组。我喜欢在这些情况下使用短主机名，因为日志记录、kickstarts、打印、系统监控等不需要完全重新配置来解释新域名。

内部域为“ifp.com”的名为“rizzo”的服务器的典型 RHEL/CentOS 服务器设置如下所示：

/etc/sysconfig/network:
HOSTNAME=rizzo
...

——

/etc/hosts:
127.0.0.1   localhost localhost.localdomain localhost4 localhost4.localdomain4
::1         localhost localhost.localdomain localhost6 localhost6.localdomain6

172.16.100.13   rizzo.ifp.com rizzo

——

[root@rizzo ~]# hostname 
rizzo

——

/var/log/messages snippet:
Dec 15 10:10:13 rizzo proftpd[19675]: 172.16.100.13 (::ffff:206.15.236.182[::ffff:206.15.236.182]) - Preparing to               
 chroot to directory '/app/upload/GREEK'
Dec 15 10:10:51 rizzo proftpd[20660]: 172.16.100.13 (::ffff:12.28.170.2[::ffff:12.28.170.2]) - FTP session opened.
Dec 15 10:10:51 rizzo proftpd[20660]: 172.16.100.13 (::ffff:12.28.170.2[::ffff:12.28.170.2]) - Preparing to chroot                
to directory '/app/upload/ftp/SRRID'

Answer 2

几乎所有软件都对正确设置主机名很敏感。当我在 Digg 工作时，我曾经将整个站点关闭了 2 个小时，因为我做了一个看似无害的更改/etc/hosts，影响了系统的主机名概念。轻踩。话虽如此，您在这里可能会有些困惑。我不认为该HOSTNAME=设置直接等同于基于 Debian 的发行版如何使用/etc/hostname.

在异构环境中对我有用的是：

1. 在您的配置管理软件中使用条件以供应商推荐的方式设置主机名。
2. 使用hostname命令设置内核使用的主机名等。

3. 在/etc/hosts：

   127.0.0.1    localhost
   10.0.0.1     hostname.example.com     hostname
   

这个配置还没有让我失望。

Answer 3

您当然可以在网上找到参考资料，这会告诉您一定要以一种或另一种方式去做。然而，在我看来，使用短名称作为主机名并在 /etc/hosts 中使用完全限定名称肯定要普遍得多。这似乎是更明智的方式，因为需要完全限定名称的服务可以改为调用hostname --fqdn。

我最近只遇到过一个软件，它严格要求由 返回 fqdn hostname，这就是 ganeti。他们在这里记录了这一点。hostname --fqdn然而，我看不出有任何理由让他们无法适应。

Answer 4

有点切题的是，在研究这个问题时，我已经疯狂到检查“主机名”的源代码并编写一个脚本来打印调查结果（Fedora 19）。缺少的是查看“/etc/hosts”，以我的拙见，首先应该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 '?ostname --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"

运行 Fedora 19 的 Amazon EC2 VM 上的输出，在手动设置内核值和填充后/etc/hostname，但没有更改，/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 '?ostname --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 中获取完全限定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}"
      }
   }
}

在 bash 中，它将是：

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 1：HOSTNAME 是 bash 提供的 shell 变量（“自动设置为当前主机的名称。”）但没有关于 bash 到达该值的指示。

注意 2：永远不要忘记 /boot/initrams-FOO.img 中的 /etc/hostname ...