apt install -y chrony
timedatectl set-timezone Asia/Seoul
vi /etc/chrony/chrony.conf
### vi ###
# pool 2.debian.pool.ntp.org iburst
allow 0.0.0.0/0
local stratum 1
### vi ###
systemctl restart chrony
timedatectl
vi /etc/chrony/chrony.conf
### vi ###
# pool 2.debian.pool.ntp.org iburst
server 1.1.1.100
### vi ###
systemctl restart chrony
chronyc sources