ubuntu 22.04版本修改服务器名、ip，dns信息的操作方法

总结
1、ubuntu修改服务器名重启后生效的方法是直接修改/etc/hostname文件

2、ubuntu 22.04操作系统配置ip和dns信息，一般只需要使用netplan命令行工具来配置就行，在/etc/netplan/在目录下创建一个yaml文件就可以实现ip和dns的配置，当然如果/etc/netplan下有多个yaml文件，则所有/etc/netplan/*.yaml文件都将被netplan命令行使用，参见官方文档https://ubuntu.com/server/docs/network-configuration和https://manpages.ubuntu.com/manpages/jammy/man5/netplan.5.html

3、个人不建议使用/etc/resolve.conf来配置ubuntu 22.04操作系统的dns信息，因为太复杂了，这个文件是被systemd-resolved服务托管。ubuntu操作系统/etc/resolve.conf中默认使用的是 nameserver 127.0.0.53回环地址,/etc/resolve.conf文中有这么一句话This is /run/systemd/resolve/stub-resolv.conf managed by man:systemd-resolved(8). Do not edit。说明这个文件是被systemd-resolved这个服务托管的。通过 netstat -tnpl| grep systemd-resolved 查看到这个服务是监听在 53 号端口上。为啥要用127.0.0.53作为回环地址而不是127.0.0.1，因为127网段都是回环地址(127.0.0.1 - 127.255.255.254),不过通常用大家只喜欢用127.0.0.1来表示而已，53表示dns端口
3.1、新安装的ubuntu 22.04环境不做其他改动的情况下，/etc/resolv.conf是/run/systemd/resolve/stub-resolv.conf的软链接，如果只是手工更改/etc/resolv.conf中的内容，重启会后发现/etc/resolv.conf中的内容又恢复成原样了，比如注释/etc/resolv.conf文件中的nameserver 127.0.0.53这一行，重启系统后被注释掉的nameserver 127.0.0.53这一行又回来了，如果不想重启后/etc/resolv.conf中的内容恢复成原样，则执行systemctl stop systemd-resolved和systemctl disable systemd-resolved，或把/etc/resolv.conf对应的软链接删除，再手工建立一个/etc/resolv.conf
3.2、使用/etc/netplan/00-installer-config.yaml配置DNS 172.22.10.66并执行netplan apply使之生效，再修改/etc/systemd/resolved.conf内容里的DNS为172.22.136.2，然后执行systemctl restart systemd-resolved，发现/etc/resolv.conf中的内容没变还是127.0.0.53，再执行resolvectl status可以看到/etc/systemd/resolved.conf中的DNS 172.22.136.2存在，/etc/netplan/00-installer-config.yaml中的DNS 172.22.10.66也在，就是没有/etc/resolv.conf中的127.0.0.53。重启操作系统后/etc/resolv.conf中的内容没变还是127.0.0.53，重启操作系统后执行resolvectl status还是只有/etc/systemd/resolved.conf中的DNS 172.22.136.2和/etc/netplan/00-installer-config.yaml中的DNS 172.22.10.66，没有/etc/resolv.conf中的127.0.0.53

4、ubuntu官方不建议使用/etc/resolve.conf来配置ubuntu 的dns信息，ubuntu对于/etc/resolv.conf的官方描述：If you require DNS for your temporary network configuration, you can add DNS server IP addresses in the file /etc/resolv.conf. In general, editing /etc/resolv.conf directly is not recommended, but this is a temporary and non-persistent configuration.

5、ubuntu 22.04查看dns信息的命令是resolvectl status，该命令可以看到全局dns信息和某个网卡的dns信息，全局DNS服务器信息一般来自配置文件/etc/systemd/resolved.conf,仅在/etc/resolv.conf不是一个指向/run/systemd/resolve/stub-resolv.conf, /usr/lib/systemd/resolv.conf, /run/systemd/resolve/resolv.conf 之一的软连接的情况下，且/etc/systemd/resolved.conf中dns被注释掉的情况下，全局DNS服务器才会读取自/etc/resolv.conf，所以这就是不建议大家使用/etc/resolve.conf来配置ubuntu 的dns信息的原因。

修改服务器名
修改服务器名为FRSBachDEV3，重启后也生效的方法
vi /etc/hostname
FRSBachDEV3
备注：如果/etc/hostname文件中的内容写成hostname FRSBachDEV3，那么重启后服务器名就变成了hostnameFRSBachDEV3

修改IP
https://ubuntu.com/server/docs/network-configuration
https://manpages.ubuntu.com/manpages/jammy/man5/netplan.5.html
netplan是一个命令行工具，用于ubuntu上配置网络，所有/etc/netplan/*.yaml文件都将被使用

root@FRSBachDEV3:~# cat /etc/netplan/00-installer-config.yaml
network:
  ethernets:
    ens160:
      dhcp4: true
  version: 2

root@FRSBachDEV3:~# vim /etc/netplan/00-installer-config.yaml
network:
  ethernets:
    ens160:
      dhcp4: false
      addresses: [172.22.136.147/22]
      routes:
        - to: default
          via: 172.22.136.1
      nameservers:
        search: [dai.netdai.com,netdai.com]
        addresses: [172.22.10.66,172.22.10.67]
  version: 2

备注：
dhcp4中的4表示ipv4
gateway4中的4表示ipv4，不过gateway4已经被废弃，配置了gateway4再执行netplan apply的话会报错** (generate:1426): WARNING **: 09:54:13.918: gateway4 has been deprecated, use default routes instead.See the ‘Default routes’ section of the documentation for more details.
routes项填写网关地址
addresses项填写ip地址
nameservers项填写dns地址或搜索域，其中addresses子项是dns地址列表，search子项是搜索域名列表
version: 2这一项表示YAML版本是2，curtin,MaaS等目前使用的YAML的版本是1

root@FRSBachDEV3:~# netplan apply

root@FRSBachDEV3:~# cat /etc/resolv.conf
nameserver 127.0.0.53
options edns0 trust-ad
search dai.netdai.com netdai.com

root@FRSBachDEV3:~# ifconfig
ens160: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet 172.22.136.147  netmask 255.255.252.0  broadcast 172.22.139.255
        inet6 fe80::250:56ff:fe94:522d  prefixlen 64  scopeid 0x20<link>
        ether 00:50:56:94:52:2d  txqueuelen 1000  (Ethernet)
        RX packets 45071  bytes 3394009 (3.3 MB)
        RX errors 0  dropped 40  overruns 0  frame 0
        TX packets 765  bytes 78732 (78.7 KB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

lo: flags=73<UP,LOOPBACK,RUNNING>  mtu 65536
        inet 127.0.0.1  netmask 255.0.0.0
        inet6 ::1  prefixlen 128  scopeid 0x10<host>
        loop  txqueuelen 1000  (Local Loopback)
        RX packets 2331  bytes 168025 (168.0 KB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 2331  bytes 168025 (168.0 KB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

查看网关

root@FRSBachDEV3:~# ip route | grep default
default via 172.22.136.1 dev ens160 proto static

root@FRSBachDEV3:~# nmcli dev show|grep GATEWAY
IP4.GATEWAY:                            172.22.136.1
IP6.GATEWAY:                            --
IP4.GATEWAY:                            --
IP6.GATEWAY:                            --

查看dns

root@FRSBachDEV3:~# resolvectl status
Global
       Protocols: -LLMNR -mDNS -DNSOverTLS DNSSEC=no/unsupported
resolv.conf mode: stub

Link 2 (ens160)
    Current Scopes: DNS
         Protocols: +DefaultRoute +LLMNR -mDNS -DNSOverTLS DNSSEC=no/unsupported
Current DNS Server: 172.22.10.66
       DNS Servers: 172.22.10.66 172.22.10.67
        DNS Domain: dai.netdai.com netdai.com

实验：如何才会使用到/etc/resolve.conf中的dns信息

/etc/systemd/resolved.conf中dns为172.22.136.2
root@FRSBachDEV3:~# cat /etc/systemd/resolved.conf |grep DNS=
DNS=172.22.136.2

/etc/resolv.conf来自软链接/run/systemd/resolve/stub-resolv.conf
root@FRSBachDEV3:~# ll /etc/resolv.conf
lrwxrwxrwx 1 root root 39 Aug  9  2022 /etc/resolv.conf -> ../run/systemd/resolve/stub-resolv.conf

root@FRSBachDEV3:~# cat /run/systemd/resolve/stub-resolv.conf
nameserver 127.0.0.53
options edns0 trust-ad
search dai.netdai.com netdai.com

/run/systemd/resolve/resolv.conf有来自/etc/systemd/resolved.conf中dns 172.22.136.2，也有来自/etc/netplan/00-installer-config.yaml中dns 172.22.10.66 172.22.10.67，就是没有来自/etc/resolv.conf的127.0.0.53
root@FRSBachDEV3:~# cat /run/systemd/resolve/resolv.conf
nameserver 172.22.136.2
nameserver 172.22.10.66
nameserver 172.22.10.67
search dai.netdai.com netdai.com

/etc/systemd/resolved.conf中dns 172.22.136.2和/etc/netplan/00-installer-config.yaml中dns 172.22.10.66 172.22.10.67，就是没有来自/etc/resolv.conf的127.0.0.53
root@FRSBachDEV3:~# resolvectl status
Global
         Protocols: -LLMNR -mDNS -DNSOverTLS DNSSEC=no/unsupported
  resolv.conf mode: stub
Current DNS Server: 172.22.136.2
       DNS Servers: 172.22.136.2

Link 2 (ens160)
    Current Scopes: DNS
         Protocols: +DefaultRoute +LLMNR -mDNS -DNSOverTLS DNSSEC=no/unsupported
Current DNS Server: 172.22.10.66
       DNS Servers: 172.22.10.66 172.22.10.67
        DNS Domain: dai.netdai.com netdai.com

删除/etc/resolv.conf来自软链接，并手工建立/etc/resolv.conf文件，其中dns为172.22.136.3
root@FRSBachDEV3:~# ll /etc/resolv.conf
-rw-r--r-- 1 root root 946 Oct 12 10:49 /etc/resolv.conf

root@FRSBachDEV3:~# cat /etc/resolv.conf
nameserver 172.22.136.3
options edns0 trust-ad
search dai.netdai.com netdai.com

保留/etc/systemd/resolved.conf中dns 172.22.136.2的情况下，重启systemd-resolved，发现还是用的/etc/systemd/resolved.conf中dns 172.22.136.2而没有使用手工建立/etc/resolv.conf文件的dns 172.22.136.3
root@FRSBachDEV3:~# systemctl restart systemd-resolved
root@FRSBachDEV3:~# resolvectl status
Global
       Protocols: -LLMNR -mDNS -DNSOverTLS DNSSEC=no/unsupported
resolv.conf mode: foreign
     DNS Servers: 172.22.136.2

Link 2 (ens160)
Current Scopes: DNS
     Protocols: +DefaultRoute +LLMNR -mDNS -DNSOverTLS DNSSEC=no/unsupported
   DNS Servers: 172.22.10.66 172.22.10.67
    DNS Domain: dai.netdai.com netdai.com

注释掉/etc/systemd/resolved.conf中dns再重启systemd-resolved，发现这个时候才真正用上了手工建立/etc/resolv.conf文件的dns 172.22.136.3
root@FRSBachDEV3:~# vim /etc/systemd/resolved.conf
root@FRSBachDEV3:~# cat /etc/systemd/resolved.conf |grep DNS
#DNS

root@FRSBachDEV3:~# systemctl restart systemd-resolved
root@FRSBachDEV3:~# resolvectl status
Global
         Protocols: -LLMNR -mDNS -DNSOverTLS DNSSEC=no/unsupported
  resolv.conf mode: foreign
Current DNS Server: 172.22.136.3
       DNS Servers: 172.22.136.3
        DNS Domain: dai.netdai.com netdai.com

Link 2 (ens160)
Current Scopes: DNS
     Protocols: +DefaultRoute +LLMNR -mDNS -DNSOverTLS DNSSEC=no/unsupported
   DNS Servers: 172.22.10.66 172.22.10.67
    DNS Domain: dai.netdai.com netdai.com

root@FRSBachDEV3:~# cat /run/systemd/resolve/resolv.conf
nameserver 172.22.136.3
nameserver 172.22.10.66
nameserver 172.22.10.67
search dai.netdai.com netdai.com