切换国内源

cat>/etc/apt/sources.list<<EOF
deb http://mirrors.aliyun.com/ubuntu/ jammy main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ jammy main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ jammy-security main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ jammy-security main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ jammy-updates main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ jammy-updates main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ jammy-proposed main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ jammy-proposed main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ jammy-backports main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ jammy-backports main restricted universe multiverse
EOF

apt-get update
apt-get upgrade

上述更新源命令，报错，错误描述的是公钥不可用，无法验签：

The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 871920D1991BC93C

apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 871920D1991BC93C

再次更新源

apt-get update
apt-get upgrade