*:chrony-4.3 released(31 Aug 2022) --->Add selection option to log directive
chrony-4.1 released(13 May 2021 )-->Perform source selection immediately after loading dump files
chrony-4.0 released(7 Oct 2020)-->void replacing NTP sources with sources that have unreachable address
chrony-3.5.1 released(20 Aug 2020)-->When chronyd is configured to save the pidfile in a directory where the chrony user has write permissions (e.g. /var/run/chrony - the default since chrony-3.4), an attacker that compromised the chrony user account could create a symbolic link at the location of the pidfile to make chronyd starting with root privileges follow the symlink and write its process ID to a file for which the chrony user doesn’t have write permissions, causing a denial of service, or data loss.
chrony-3.4 released(19 Sep 2018)-->Change default pidfile to /var/run/chrony/chronyd.pid to allow chronyd without root privileges to remove it on exit
chrony-3.3 released(4 Apr 2018)-->Improve source selection with unreachable sources
1、在chrony.conf开启日志记录，会记录measurements.log statistics.log tracking.log三个日志文件。
# Specify directory for log files.
logdir /var/log/chrony
# Select which information is logged.
#log measurements statistics tracking 2、tracking.log日志：SDFP1直接和持久百城GPS192.168.10.101同步，所以stratum是2，在10:34:20 estimated local offset（normally corrected by slewing the local clock）从(2.9us)2.953e-06改变到-3.245 e-01(320毫秒)增加了10的5次方十万倍，chrony认为出现了跳变,chronyc sources -v显示 'x' = time may be in error，在SMC上提示未同步unsynced。
Date (UTC) Time IP Address St Freq ppm Skew ppm Offset L Co Offset sd Rem. corr. Root delay Root disp. Max. error
===================================================================================================================================
2022-10-04 10:32:10 192.168.10.101 2 -8.932 0.046 2.743e-06 N 1 3.386e-06 2.199e-11 1.125e-04 1.618e-05 1.421e-04
2022-10-04 10:33:15 192.168.10.101 2 -8.926 0.039 2.953e-06 N 1 3.114e-06 -1.234e-06 1.096e-04 1.546e-05 1.435e-04
2022-10-04 10:34:20 192.168.10.101 2 -8.926 0.039 3.245e-01 N 1 2.341e-01 -4.651e-07 1.139e-04 1.207e-03 1.418e-04
2022-10-04 10:35:25 192.168.10.101 2 -8.926 0.039 -1.457e-01 N 1 2.290e-01 -2.415e-02 1.081e-04 5.415e-05 4.203e-01
2022-10-04 10:36:30 192.168.10.101 2 -8.926 0.039 -1.232e-01 N 1 1.714e-01 7.827e-02 1.143e-04 3.099e-04 1.530e-01 3、tracking.log日志：SDFP2与SDFP1同步，所以stratum是3，在10:34:29-34秒 IP Address从192.168.5.50变成192.168.7.50；offset从-2.710e-07改变到 2.014e-01，增加了10的6次方、百万倍，跳跃状态Leap status：N表示正常，频繁出现?表示远程计算机当前未同步；number of combined sources组合源的数量也不稳定，正常应该为3。
Date (UTC) Time IP Address St Freq ppm Skew ppm Offset L Co Offset sd Rem. corr. Root delay Root disp. Max. error
===================================================================================================================================
2022-10-04 10:31:15 192.168.5.50 3 -11.877 0.065 -2.251e-06 N 3 4.257e-06 3.748e-10 1.618e-04 3.120e-05 1.983e-04
2022-10-04 10:32:20 192.168.5.50 3 -11.880 0.045 -1.611e-06 N 3 3.818e-06 1.453e-06 1.618e-04 3.686e-05 1.834e-04
2022-10-04 10:33:24 192.168.5.50 3 -11.879 0.038 -2.710e-07 N 3 4.314e-06 1.429e-06 1.685e-04 3.104e-05 1.883e-04
2022-10-04 10:34:29 0.0.0.0 0 -11.879 0.038 0.000e+00 ? 0 0.000e+00 1.254e-06 1.685e-04 9.808e-05 1.840e-04
2022-10-04 10:34:34 192.168.7.50 3 -11.879 0.038 2.014e-01 N 3 1.102e-01 1.214e-06 1.601e-04 2.196e-02 1.895e-04
2022-10-04 10:35:31 0.0.0.0 0 -11.879 0.038 0.000e+00 ? 0 0.000e+00 -3.294e-03 1.601e-04 6.595e-02 2.674e-01
2022-10-04 10:35:39 192.168.7.50 3 -11.879 0.038 -1.517e-02 N 3 2.942e-02 1.933e-07 1.592e-04 7.077e-03 7.555e-02
2022-10-04 10:36:36 0.0.0.0 0 -11.879 0.038 0.000e+00 ? 0 0.000e+00 1.057e-02 1.592e-04 4.618e-02 6.143e-02
2022-10-04 10:36:44 192.168.7.50 3 -11.879 0.038 -7.103e-02 N 1 4.620e-02 9.971e-03 1.674e-04 4.493e-03 6.194e-02
2022-10-04 10:37:41 192.168.6.50 3 -11.879 0.038 -9.663e-02 N 1 3.840e-02 -4.566e-07 1.879e-04 5.930e-03 9.512e-02 ![logrotate机制与原理[图]](data:image/gif;base64,R0lGODlhAQABAIAAAP///wAAACwAAAAAAQABAAACAkQBADs=)