我的服务器中主机名文件的内容是：
# cat /etc/hostname
sub.mysite.com
但是当我ping的 CentOS 7 服务器上显示：
# ping sub.mysite.com
64 bytes from sub ...
甚至：
# ping ns1.mysite.com
64 bytes from sub ...
如何告诉我的服务器在 ping 时有以下输出？
64 bytes from sub.mysite.com ...
更新
以我的客户为例：
user@host:~$ ping ns1.mysite.com
PING ns1.mysite.com (x.x.x.x) 56(84) bytes of data.
64 bytes from sub (x.x.x.x): icmp_seq=1 ttl=56 time=7.88 ms
64 bytes from sub (x.x.x.x): icmp_seq=2 ttl=56 time=5.86 ms
64 bytes from sub (x.x.x.x): icmp_seq=3 ttl=56 time=4.99 ms
64 bytes from sub (x.x.x.x): icmp_seq=4 ttl=56 time=4.88 ms
我想要完整的主机名 (sub.mysite.com) 而不是sub.
答案1
ping不用于/etc/hostname解析 IP 到名称映射，它使用名称服务 ( netns) 来执行这些转换。顺便说一下，/etc/hostname它是 systemd 的一部分：
$ rpm -qf /etc/hostname
systemd-219-42.el7_4.10.x86_64
您看到的短名称是通过名称服务sub来自您的文件。/etc/hosts如果您使用，strace您可以看到如何ping找到sub：
$ strace -s 2000 ping -c1 www.google.com |& grep /etc/host
open("/etc/host.conf", O_RDONLY|O_CLOEXEC) = 4
open("/etc/hosts", O_RDONLY|O_CLOEXEC) = 4
open("/etc/hosts", O_RDONLY|O_CLOEXEC) = 4
ping因此，解决问题的简单方法是将要显示的服务器名称放入/etc/hosts文件中。
例子
$ ping -c1 www.google.com
PING www.google.com (74.125.141.99) 56(84) bytes of data.
64 bytes from vl-in-f99.1e100.net (74.125.141.99): icmp_seq=1 ttl=63 time=109 ms
--- www.google.com ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 109.903/109.903/109.903/0.000 ms
Now if we were to add that IP, 74.125.141.103, to your `/etc/hosts` file we could manipulate `ping` into showing whatever we want for it:
将其添加到/etc/hosts：
74.125.141.99 blah.blah.com
现在重复我们的测试：
$ ping -c1 www.google.com
PING www.google.com (74.125.141.99) 56(84) bytes of data.
64 bytes from blah.blah.com (74.125.141.99): icmp_seq=1 ttl=63 time=109 ms
--- www.google.com ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 109.886/109.886/109.886/0.000 ms
/etc/hosts 的顺序
请记住，添加主机的顺序/etc/hosts可能会导致名称按照您所看到的方式显示。
例如，如果我们的/etc/hosts：
74.125.141.99 blah blah.blah.com
将会ping像您所看到的那样显示，并带有一个简短的名称：
$ ping -c1 www.google.com
PING www.google.com (74.125.141.99) 56(84) bytes of data.
64 bytes from blah (74.125.141.99): icmp_seq=1 ttl=63 time=108 ms
--- www.google.com ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 108.065/108.065/108.065/0.000 ms