解决wget访问外网问题：步骤一
解决apt访问外网问题：步骤一到步骤六。其中步骤一（设置用户代理）、步骤二（添加证书）、步骤四（修改DNS等网络参数配置）、步骤六（修改apt全局配置）为关键步骤。供参考。我是从步骤一尝试到步骤六，最后解决的。之后如果问题反复出现，还是可以尝试这几个关键步骤。
主要的报错可以参考后文。
一开始如果wget也不能联网，报错：
$ sudo wget www.baidu.com--2020-04-01 15:23:01-- http://www.baidu.com/
Resolving www.baidu.com (www.baidu.com)... failed: No address associated with hostname.
wget: unable to resolve host address ‘www.baidu.com’
就通过步骤一解决。比较难以解决的是apt联网的问题。详见后文。
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可以按照以下步骤依次尝试：
步骤一：在~/.bashrc中设置代理
$ sudo vi ~/.bashrc在文件后面加入内容
http_proxy=http://10.xx.xx.xxx:8080
https_proxy=http://10.xx.xx.xxx:8080$ source ~/.bashrc如果报错
Proxy request sent, awaiting response... 200 OK
Length: 2250 (2.2K) [text/html]
index.html: Permission denied
Cannot write to ‘index.html’ (Success).
说明你对当前的文件夹没有写入权限，改一下权限就可以了
$ sudo chmod 777 -R temp此时wget能用了。但是apt还是不能用
Something wicked happened resolving 'cn.archive.ubuntu.com:http' (-5 - No address associated with hostname)
E: Failed to fetch http://cn.archive.ubuntu.com/ubuntu/pool/universe/x/xorg/xbase-clients_7.7+13ubuntu3.1_all.deb Something wicked happened resolving 'cn.archive.ubuntu.com:http' (-5 - No address associated with hostname)
E: Failed to fetch http://cn.archive.ubuntu.com/ubuntu/pool/universe/v/vnc4/vnc4server_4.1.1+xorg4.3.0-37.3ubuntu2_amd64.deb Something wicked happened resolving 'cn.archive.ubuntu.com:http' (-5 - No address associated with hostname)
E: Failed to fetch http://security.ubuntu.com/ubuntu/pool/universe/x/xrdp/xrdp_0.6.1-2ubuntu0.3_amd64.deb Something wicked happened resolving 'cn.archive.ubuntu.com:http' (-5 - No address associated with hostname)
E: Unable to fetch some archives, maybe run apt-get update or try with --fix-missing?
如果还不行，就给wget创建专门的配置文件：
$ sudo vi ~/.wgetrc加入
# u can set the default proxies for Wget to use for http, https, and ftp.
# They will override the value in the environment.
https_proxy=http://10.xx.xx.xxx:8080
http_proxy=http://10.xx.xx.xxx:8080
# If you do not want to use proxy at all, set this to off.
use_proxy=on使用：
$ source ~/.wgetrc这时候再试试：
$ wget www.baidu.com参考：https://www.cnblogs.com/cloud2rain/archive/2013/03/22/2976337.html
步骤二：如果还是报错，添加证书：https://blog.csdn.net/qxqxqzzz/article/details/102461881
步骤三：如果还是报错，打开firefox浏览器， $sudo firefox
自动蹦出网关登录，蹦不出来你就手动输入地址打开以下吧，类似于这种东西：
http://10.xxx.xxx.xxx/ac_portal/default/pc.html?template=default&tabs=pwd&vlanid=0&url=http://www.baidu.com/
这里的10.xxx.xxx.xxx和步骤一中的10.xxx.xxx.xxx 相同。然后 输入公司内网域账号密码，登录网关。
如果apt还是不能联网。继续下一步。
步骤四：如果还是报错，修改
$ sudo vi /etc/network/interfaces，内容为：
# interfaces(5) file used by ifup(8) and ifdown(8)
auto lo
iface lo inet loopback
# primary network interface
auto eno2
iface eno2 inet static
address 10.167.xxx.xxx
netmask 255.255.xxx.xxx
gateway 10.167.xxx.xxx
dns-nameservers 10.167.xxx.xxx其中静态ip,掩码，网关，dns由公司IT提供。注意address是IP地址，不要改错了，否则你可能要去机房才能连接上机器！！！
然后重启网络服务。DNS不要用网上说的什么8.8.8.8 / 8.8.4.4 / 等等。这些外网地址在内网环境下是不一定能被允许访问的。应该使用什么DNS应该咨询组织IT。
$ sudo /etc/init.d/networking restart还是报错：
xfce4-volumed/xfce4-volumed_0.2.0-0ubuntu2_amd64.deb Could not resolve 'cn.archive.ubuntu.com'
E: Failed to fetch http://cn.archive.ubuntu.com/ubuntu/pool/universe/x/xscreensaver/xscreensaver-data_5.34-2ubuntu1_amd64.deb Could not resolve 'cn.archive.ubuntu.com'
E: Failed to fetch http://cn.archive.ubuntu.com/ubuntu/pool/universe/x/xscreensaver/xscreensaver_5.34-2ubuntu1_amd64.deb Could not resolve 'cn.archive.ubuntu.com'
E: Failed to fetch http://cn.archive.ubuntu.com/ubuntu/pool/universe/x/xubuntu-artwork/xubuntu-icon-theme_16.04.2_all.deb Could not resolve 'cn.archive.ubuntu.com'
E: Unable to fetch some archives, maybe run apt-get update or try with --fix-missing?
步骤五：如果还是报错，重启服务器
E: Failed to fetch http://cn.archive.ubuntu.com/ubuntu/pool/universe/x/xfce4-pulseaudio-plugin/xfce4-pulseaudio-plugin_0.2.4-1_amd64.deb Something wicked happened resolving 'cn.archive.ubuntu.com:http' (-5 - No address associated with hostname)
E: Failed to fetch http://cn.archive.ubuntu.com/ubuntu/pool/universe/x/xfce4/xfce4_4.12.2_all.deb Something wicked happened resolving 'cn.archive.ubuntu.com:http' (-5 - No address associated with hostname)
E: Failed to fetch http://cn.archive.ubuntu.com/ubuntu/pool/universe/x/xfce4-notifyd/xfce4-notifyd_0.2.4-3ubuntu1_amd64.deb Something wicked happened resolving 'cn.archive.ubuntu.com:http' (-5 - No address associated with hostname)
E: Failed to fetch http://cn.archive.ubuntu.com/ubuntu/pool/universe/x/xfce4-volumed/xfce4-volumed_0.2.0-0ubuntu2_amd64.deb Something wicked happened resolving 'cn.archive.ubuntu.com:http' (-5 - No address associated with hostname)
E: Failed to fetch http://cn.archive.ubuntu.com/ubuntu/pool/universe/x/xscreensaver/xscreensaver-data_5.34-2ubuntu1_amd64.deb Something wicked happened resolving 'cn.archive.ubuntu.com:http' (-5 - No address associated with hostname)
E: Failed to fetch http://cn.archive.ubuntu.com/ubuntu/pool/universe/x/xscreensaver/xscreensaver_5.34-2ubuntu1_amd64.deb Something wicked happened resolving 'cn.archive.ubuntu.com:http' (-5 - No address associated with hostname)
E: Failed to fetch http://cn.archive.ubuntu.com/ubuntu/pool/universe/x/xubuntu-artwork/xubuntu-icon-theme_16.04.2_all.deb Something wicked happened resolving 'cn.archive.ubuntu.com:http' (-5 - No address associated with hostname)
E: Unable to fetch some archives, maybe run apt-get update or try with --fix-missing?
步骤六：如果还是报错：
1，打开firefox， $ sudo firefox
2，设置代理链接 :菜单-preference-advanced-network-connection-settings-automatic proxy configuration URL-粘贴http://xxx.pac/的代理上网地址（由IT提供）-OK
3，访问www.baidu.com，提示insecure，不管它，加入例外->confirm exceptions。然后再打开百度或者新浪，发现可以打开了。但是APT还是不能用
4，新建或编辑/etc/apt/apt.conf文件，加入代理：
$ sudo vi /etc/apt/apt.conf加入
Acquire::http::Proxy "http://10.xxx.xxx.xxx:8080/";5，重新使用apt
$ sudo apt-get update
$ sudo apt-get install xrdp可以了。
