if you reinstall agent, you must copy password from master and paste it to /var/lib/rancher/k3s/agent/node-password.txt. the password is from /var/lib/rancher/k3s/server/cred/passwd in master server
if you want to run "sudo kubectl get nodes" in agent, you must copy k3s.yaml(in /etc/rancher/k3s) from master and paste it to /etc/rancher/k3s/ in master
K3S_TOKEN is the content of /var/lib/rancher/k3s/server/node-token in master
if you set the nodename of agent, you must add ip nodename(such as 127.0.0.1 node-1) to /etc/hosts