'packagename' has no installation candidate 解决方法

更新软件包和软件源

sudo apt-get update
sudo apt-get upgrade
sudo apt-get install <packagename>

更改 /etc/apt/sources.list

阿里源

# 默认注释了源码镜像以提高 apt update 速度，如有需要可自行取消注释
deb http://mirrors.aliyun.com/ubuntu/ groovy main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ groovy main restricted universe multiverse

deb http://mirrors.aliyun.com/ubuntu/ groovy-security main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ groovy-security main restricted universe multiverse

deb http://mirrors.aliyun.com/ubuntu/ groovy-updates main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ groovy-updates main restricted universe multiverse

deb http://mirrors.aliyun.com/ubuntu/ groovy-backports main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ groovy-backports main restricted universe multiverse

# 预发布软件源，不建议启用
#deb http://mirrors.aliyun.com/ubuntu/ groovy-proposed main restricted universe multiverse
#deb-src http://mirrors.aliyun.com/ubuntu/ groovy-proposed main restricted universe multiverse

清华源

# 默认注释了源码镜像以提高 apt update 速度，如有需要可自行取消注释
deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ groovy main restricted universe multiverse
# deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ groovy main restricted universe multiverse
deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ groovy-updates main restricted universe multiverse
# deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ groovy-updates main restricted universe multiverse
deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ groovy-backports main restricted universe multiverse
# deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ groovy-backports main restricted universe multiverse
deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ groovy-security main restricted universe multiverse
# deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ groovy-security main restricted universe multiverse

# 预发布软件源，不建议启用
# deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ groovy-proposed main restricted universe multiverse
# deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ groovy-proposed main restricted universe multiverse

Ubuntu官方源

deb http://cn.archive.ubuntu.com/ubuntu/ groovy main universe restricted multiverse
deb-src http://cn.archive.ubuntu.com/ubuntu/ groovy main universe restricted multiverse #Added by software-properties
deb http://security.ubuntu.com/ubuntu/ groovy-security main universe restricted multiverse
deb-src http://cn.archive.ubuntu.com/ubuntu/ groovy-security main universe restricted multiverse #Added by software-properties
deb http://cn.archive.ubuntu.com/ubuntu/ groovy-updates main universe restricted multiverse
deb-src http://cn.archive.ubuntu.com/ubuntu/ groovy-updates main universe restricted multiverse #Added by software-properties