error: Waiting for cache lock: Could not get lock /var/lib/dpkg/lock-frontend. It is held by process 20060 (unattended-upgr)

问题：sudo apt upgrade 执行一直等待

报错：Waiting for cache lock: Could not get lock /var/lib/dpkg/lock-frontend. It is held by process 20060 (unattended-upgr)

解决：

unattended-upgr应该是Ubuntu系统自动更新的一部分，可能是在后台自动运行的系统更新进程
运行sudo apt upgrade的时候，系统自动更新进程也在运行，导致锁被占用，无法同时进行。这个时候应该等待自动更新完成，或者手动终止自动更新进程，然后继续手动更新

ps -p 20060
kill -9 20060 # 谨慎
sudo apt upgrade

# 删除残留的锁文件
sudo rm /var/lib/dpkg/lock-frontend
sudo rm /var/lib/dpkg/lock
sudo rm /var/lib/apt/lists/lock

sudo dpkg --config -a # 修复未完成的包配置