我对 Linux 还很陌生，
当我第一次通过 SSH 进入我的 Pi（通过我的无线路由器）时，我收到以下消息。
0 packages can be updated.
0 updates are security updates.
Failed to connect to https://changelogs.ubuntu.com/meta-release-lts. Check your Internet connection or proxy settings
sudo apt-get update更新失败。
连接 HDMI 端口并使用 GUI，我可以验证我已连接到我的 Wifi，Firefox 将无法工作。
Ubuntu 18.04.02 LTS
以下是 sudo apt-get update 的输出
Err:1 http://ports.ubuntu.com bionic InRelease
Temporary failure resolving 'ports.ubuntu.com'
Err:2 http://ppa.launchpad.net/ubuntu-pi-flavour-makers/ppa/ubuntu bionic InRelease
Temporary failure resolving 'ppa.launchpad.net'
Err:3 http://ports.ubuntu.com bionic-updates InRelease
Temporary failure resolving 'ports.ubuntu.com'
Err:4 http://ports.ubuntu.com bionic-security InRelease
Temporary failure resolving 'ports.ubuntu.com'
Err:5 http://ports.ubuntu.com bionic-backports InRelease
Temporary failure resolving 'ports.ubuntu.com'
Reading package lists... Done
W: Failed to fetch http://ports.ubuntu.com/dists/bionic/InRelease Temporary failure resolving 'ports.ubuntu.com'
W: Failed to fetch http://ports.ubuntu.com/dists/bionic-updates/InRelease Temporary failure resolving 'ports.ubuntu.com'
W: Failed to fetch http://ports.ubuntu.com/dists/bionic-security/InRelease Temporary failure resolving 'ports.ubuntu.com'
W: Failed to fetch http://ports.ubuntu.com/dists/bionic-backports/InRelease Temporary failure resolving 'ports.ubuntu.com'
W: Failed to fetch http://ppa.launchpad.net/ubuntu-pi-flavour-makers/ppa/ubuntu/dists/bionic/InRelease Temporary failure resolving 'ppa.launchpad.net'
W: Some index files failed to download. They have been ignored, or old ones used instead.
@RPi:~$ Err:1 http://ports.ubuntu.com bionic InRelease
Err:1: command not found
@RPi:~$ Temporary failure resolving 'ports.ubuntu.com'
Temporary: command not found
@RPi:~$ Err:2 http://ppa.launchpad.net/ubuntu-pi-flavour-makers/ppa/ubuntu bionic InRele ase
Err:2: command not found
@RPi:~$ Temporary failure resolving 'ppa.launchpad.net'
Temporary: command not found
@RPi:~$ Err:3 http://ports.ubuntu.com bionic-updates InRelease
Err:3: command not found
@RPi:~$ Temporary failure resolving 'ports.ubuntu.com'
Temporary: command not found
@RPi:~$ Err:4 http://ports.ubuntu.com bionic-security InRelease
Err:4: command not found
@RPi:~$ Temporary failure resolving 'ports.ubuntu.com'
Temporary: command not found
@RPi:~$ Err:5 http://ports.ubuntu.com bionic-backports InRelease
Err:5: command not found
@RPi:~$ Temporary failure resolving 'ports.ubuntu.com'
Temporary: command not found
@RPi:~$ Reading package lists... Done
Reading: command not found
今天随机出现了这个问题，请帮忙！