系统安装体验建议： 1. ubuntu server 18.04 版本安装时候，选择安装软件步骤: 安装ssh-server，便于远程登录操作，方便进一步配置；

                           2. 个人在安装live版本的18.04及20.10版本时候，在安装下载部分皆发生报错，就算由cn.archive.ubuntu（默认中国镜像源）镜像源改为mirrors.aliyun.com/ubuntu/镜像源，也同样在过程中报错（具体为安装kernel时），查看log文件。。。。。。。。

补充： 安装完之后发现采用aliyun的镜像，有问题，安装R包时，总是找不到；改成清华镜像源，不知道这里修改其他镜像源可不可以成功，对服务器网络这块，我也是一个睁眼瞎。

CutinErrors, 好吧，具体看报错，应该时network的原因, network disabled, 应该是看配置文件：/etc/cloud/cloud.cfg.d/subiquity-dissable-cloudiny-networking.cfg，live版本需要云服务在线下载安装，不知道是我网络的原因还是本身的bug，不过别人安装好像都很顺溜-。。。。。。

报错如下图：

然后根据关键词“CutinErrors /etc/cloud/cloud.cfg.d” 检索(bing 国际版本检索), 这玩意儿是啥

 https://wiki.archlinux.org/index.php/Cloud-init

Cloud-init is a package that contains utilities for early initialization of cloud instances. It is needed in Arch Linux images that are built with the intention of being launched in cloud environments like OpenStack, AWS etc. linux安装镜像云安装的支持包，那应该就是这里了。

以上都是事后回顾整理发现，我已经使用了非live18.04版本，在网上找了一下解决方案，个人服务器没有安装这个包，就不能实施操作测试了，感兴趣的可以查看一下；

另外知乎上有一篇Cloud-init中文博文介绍，https://zhuanlan.zhihu.com/p/27664869

然后根据报错查询，根据 https://support.huaweicloud.com/usermanual-ims/ims_01_0407.html 博客中的说明配置详细信息，也可以查找英文原本配置文件详细说明，根据报错修改，结果未测试

跳入help选项，进入linux进行修改，root账号，Cloud-Init接管网络允许；

vi /etc/cloud/cloud.cfg

network:

config: abled

3. ubuntu server 18.04  apt update 报错： Clearsigned file isn't valid, got 'NOSPLIT' (does the network require authentication?)，应该还是网络的问题

不同ubuntu版本代码名：

14.04 ：trusty 

16.04 ：xenial 

18.04 ： bionic

18.04 ：focal

Get:1 http://mirrors.aliyun.com/ubuntu bionic InRelease [6,910 B]

Get:2 http://mirrors.aliyun.com/ubuntu bionic-security InRelease [6,910 B]

Get:3 http://mirrors.aliyun.com/ubuntu bionic-updates InRelease [6,910 B]

Get:4 http://mirrors.aliyun.com/ubuntu bionic-backports InRelease [6,910 B]

Get:5 http://mirrors.aliyun.com/ubuntu bionic-proposed InRelease [6,910 B]

Err:1 http://mirrors.aliyun.com/ubuntu bionic InRelease

  Clearsigned file isn't valid, got 'NOSPLIT' (does the network require authentication?)

Err:2 http://mirrors.aliyun.com/ubuntu bionic-security InRelease

  Clearsigned file isn't valid, got 'NOSPLIT' (does the network require authentication?)

Err:3 http://mirrors.aliyun.com/ubuntu bionic-updates InRelease

  Clearsigned file isn't valid, got 'NOSPLIT' (does the network require authentication?)

Err:4 http://mirrors.aliyun.com/ubuntu bionic-backports InRelease

  Clearsigned file isn't valid, got 'NOSPLIT' (does the network require authentication?)

Err:5 http://mirrors.aliyun.com/ubuntu bionic-proposed InRelease

  Clearsigned file isn't valid, got 'NOSPLIT' (does the network require authentication?)

Reading package lists... Done      

N: See apt-secure(8) manpage for repository creation and user configuration details.

N: Updating from such a repository can't be done securely, and is therefore disabled by default.

E: The repository 'http://mirrors.aliyun.com/ubuntu bionic InRelease' is not signed.

-------------------------------------------------------------------

Failed to fetch

http://mirrors.aliyun.com/ubuntu/dists/bionic-proposed/InRelease 

Clearsigned file isn't valid, got 'NOSPLIT' (does the network require

authentication?)

E: The repository 'http://mirrors.aliyun.com/ubuntu bionic-proposed InRelease' is not signed.

N: Updating from such a repository can't be done securely, and is therefore disabled by default.

N: See apt-secure(8) manpage for repository creation and user configuration details

修改了镜像源，还是报错，看到有个博文是说DNS配置错误；然后就查看了一下DNS配置文件；

/etc/resolv.conf ，目前DNS是动态的 127.0.0.53，固定一下ip及DNS；

cat /etc/resolv.conf

# This file is managed by man:systemd-resolved(8). Do not edit.

#

# This is a dynamic resolv.conf file for connecting local clients to the

# internal DNS stub resolver of systemd-resolved. This file lists all

# configured search domains.

#

# Run "systemd-resolve --status" to see details about the uplink DNS servers

# currently in use.

#

# Third party programs must not access this file directly, but only through the

# symlink at /etc/resolv.conf. To manage man:resolv.conf(5) in a different way,

# replace this symlink by a static file or a different symlink.

#

# See man:systemd-resolved.service(8) for details about the supported modes of

# operation for /etc/resolv.conf.

nameserver 127.0.0.53

options edns0

# Run "systemd-resolve --status" to see details about the uplink DNS servers currently in use.

运行 systemd-resolve --status 查看当前DNS，

~$ systemd-resolve --status

Global

          DNSSEC NTA: 10.in-addr.arpa

                      16.172.in-addr.arpa

                  --------------

                      31.172.in-addr.arpa

                      corp

                      d.f.ip6.arpa

                      home

                      internal

                      intranet

                      lan

                      local

                      private

                      test

Link 2 (eno1)

      Current Scopes: DNS

       LLMNR setting: yes

MulticastDNS setting: no

      DNSSEC setting: no

    DNSSEC supported: no

         DNS Servers: 114.114.114.114

                                8.8.8.8

ifconfig 查看当前网卡，ip及掩码信息；

route -n 查看网关信息

route -n

Kernel IP routing table

Destination    Gateway        Genmask        Flags Metric Ref    Use Iface

0.0.0.0        192.168.xx.1    0.0.0.0        UG    100    0        0 eno1

192.168.xx.x    0.0.0.0        255.255.255.0  U    0      0        0 eno1

192.168.xx.x    0.0.0.0        255.255.255.255 UH    100    0        0 eno1

然后 配置静态ip及固定DNS

sudo vi /etc/netplan/01-netcfg.yaml

gibh@ubuntu:~$ sudo vi /etc/netplan/01-netcfg.yaml

# This file describes the network interfaces available on your system

# For more information, see netplan(5).

network:

  version: 2

  renderer: networkd

  ethernets:

    eno1:

      dhcp4: no

      dhcp6: no

      adresses: [192.168.xx.xx/24] # 个人想要固定的ip，通常固定的是最后一个地址，24 代表掩码  255.255.255.0

      gateway4: 192.168.xx.1

      nameservers:

              addresses: [114.114.114.114, 8.8.8.8]

最后：~$ sudo netplan apply ，使用配置， 配置成功之后，会自动断网，然后利用新ip进行连接 

然后顺利进行sudo apt update