# systemctl enable chronyd.service
# systemctl restart chronyd.service
# systemctl status chronyd.service查看时间同步源：
# chronyc sources -v
210 Number of sources = 1.-- Source mode  '^' = server, '=' = peer, '#' = local clock./ .- Source state '*' = current synced, '+' = combined , '-' = not combined,
| /   '?' = unreachable, 'x' = time may be in error, '~' = time too variable.
||                                                 .- xxxx [ yyyy ] +/- zzzz
||                                                /   xxxx = adjusted offset,
||         Log2(Polling interval) -.             |    yyyy = measured offset,
||                                  \            |    zzzz = estimated error.
||                                   |           |
MS Name/IP address         Stratum Poll Reach LastRx Last sample
===============================================================================
^? ys-ad1.ys.com      3   6     3     1    +12ms[  +12ms] +/-  268ms查看时间同步源状态：
# chronyc sourcestats -v
210 Number of sources = 1.- Number of sample points in measurement set./    .- Number of residual runs with same sign.|    /    .- Length of measurement set (time).|   |    /      .- Est. clock freq error (ppm).|   |   |      /           .- Est. error in freq.|   |   |     |           /         .- Est. offset.|   |   |     |          |          |   On the -.|   |   |     |          |          |   samples. \|   |   |     |          |          |             |
Name/IP Address            NP  NR  Span  Frequency  Freq Skew  Offset  Std Dev
==============================================================================
ys-ad1.ys.com    4   3     6   -939.214  56272.109  -4371us  5267us

# cat /etc/chrony.conf
# 该参数可以多次用于添加时钟服务器，必须以"server "格式使用。一般而言，你想添加多少服务器，就可以添加多少服务器。
server 0.rhel.pool.ntp.org iburst
server 1.rhel.pool.ntp.org iburst
server 2.rhel.pool.ntp.org iburst
server 3.rhel.pool.ntp.org iburst# Ignore stratum in source selection.
# stratumweight指令设置当chronyd从可用源中选择同步源时，每个层应该添加多少距离到同步距离。默认情况下，设置为0，让chronyd在选择源时忽略源的层级。
stratumweight 0# Record the rate at which the system clock gains/losses time.
# chronyd程序的主要行为之一，就是根据实际时间计算出计算机增减时间的比率，将它记录到一个文件中是最合理的，它会在重启后为系统时钟作出补偿，甚至可能的话，会从时钟服务器获得较好的估值。
driftfile /var/lib/chrony/drift# Enable kernel RTC synchronization.
# rtcsync指令将启用一个内核模式，在该模式中，系统时间每11分钟会拷贝到实时时钟（RTC）。
rtcsync# In first three updates step the system clock instead of slew
# if the adjustment is larger than 10 seconds.
通常，chronyd将根据需求通过减慢或加速时钟，使得系统逐步纠正所有时间偏差。在某些特定情况下，系统时钟可能会漂移过快，导致该调整过程消耗很长的时间来纠正系统时钟。该指令强制chronyd在调整期大于某个阀值时步进调整系统时钟，但只有在因为chronyd启动时间超过指定限制（可使用负值来禁用限制），没有更多时钟更新时才生效。
makestep 10 3# Allow NTP client access from local network.
# 这里你可以指定一台主机、子网，或者网络以允许或拒绝NTP连接到扮演时钟服务器的机器。
#allow 192.168.56.6
#deny 192.168/16# Listen for commands only on localhost.
# 该指令允许你限制chronyd监听哪个网络接口的命令包（由chronyc执行）。该指令通过cmddeny机制提供了一个除上述限制以外可用的额外的访问控制等级。
bindcmdaddress 127.0.0.1
bindcmdaddress ::1# Serve time even if not synchronized to any NTP server.
#local stratum 10keyfile /etc/chrony.keys# Specify the key used as password for chronyc.
commandkey 1# Generate command key if missing.
generatecommandkey# Disable logging of client accesses.
noclientlog# Send a message to syslog if a clock adjustment is larger than 0.5 seconds.
logchange 0.5logdir /var/log/chrony
#log measurements statistics tracking

# cat /etc/chrony.keys
1 MD5 HEX:BD359B2633CD6105AB8820E47A8D8EAB

# cat/etc/chrony.keys
1 xyzzy