报错

root@xianchaomaster1:~# apt-get update 
Get:1 http://mirrors.ustc.edu.cn/kubernetes/apt kubernetes-xenial InRelease [8,993 B]
Hit:2 https://mirrors.ustc.edu.cn/docker-ce/linux/ubuntu focal InRelease                                                                                          
Err:1 http://mirrors.ustc.edu.cn/kubernetes/apt kubernetes-xenial InRelease                                                     
  The following signatures couldn't be verified because the public key is not available: NO_PUBKEY B53DC80D13EDEF05
Hit:3 http://security.ubuntu.com/ubuntu focal-security InRelease                                          
Hit:4 http://us.archive.ubuntu.com/ubuntu focal InRelease
Hit:5 http://us.archive.ubuntu.com/ubuntu focal-updates InRelease
Hit:6 http://us.archive.ubuntu.com/ubuntu focal-backports InRelease
Fetched 8,993 B in 1s (6,350 B/s)
Reading package lists... Done
W: An error occurred during the signature verification. The repository is not updated and the previous index files will be used. GPG error: http://mirrors.ustc.edu.cn/kubernetes/apt kubernetes-xenial InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY B53DC80D13EDEF05
W: Failed to fetch http://mirrors.ustc.edu.cn/kubernetes/apt/dists/kubernetes-xenial/InRelease  The following signatures couldn't be verified because the public key is not available: NO_PUBKEY B53DC80D13EDEF05
W: Some index files failed to download. They have been ignored, or old ones used instead.

解决方案

sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys  B53DC80D13EDEF05

其中B53DC80D13EDEF05为报错中的PUBKEY