网上很多资料说用这个命令来安装ntp服务：yum -y install ntp
其实这是老系统才能用的了，新版本 CentOS 里不能这么安装了。
宇润给出最新的 CentOS 时间同步的解决方案：
yum -y install chrony && \
systemctl enable chronyd.service && \
systemctl restart chronyd.service
安装 chrony 并启用和启动服务，这样就可以自动同步服务器时间了。
到此为止已经可以解决你的问题了，下面的是可以选择性阅读的内容。
chrony 的 配置文件路径是：/etc/chrony.conf
# Use public servers from the pool.ntp.org project.
# Please consider joining the pool (http://www.pool.ntp.org/join.html).
pool 2.centos.pool.ntp.org iburst
# Record the rate at which the system clock gains/losses time.
driftfile /var/lib/chrony/drift
# Allow the system clock to be stepped in the first three updates
# if its offset is larger than 1 second.
makestep 1.0 3
# Enable kernel synchronization of the real-time clock (RTC).
rtcsync
# Enable hardware timestamping on all interfaces that support it.
#hwtimestamp *
# Increase the minimum number of selectable sources required to adjust
# the system clock.
#minsources 2
# Allow NTP client access from local network.
#allow 192.168.0.0/16
# Serve time even if not synchronized to a time source.
#local stratum 10
# Specify file containing keys for NTP authentication.
keyfile /etc/chrony.keys
# Get TAI-UTC offset and leap seconds from the system tz database.
leapsectz right/UTC
# Specify directory for log files.
logdir /var/log/chrony
# Select which information is logged.
#log measurements statistics tracking
我们可以修改为想要使用的ntp服务器，虽然默认的服务器，在国内速度也是很快的。
