On 2/11/2015 5:53 PM, David chen wrote: > A shell script is deployed to synchronize time, the script is invoked hourly by crontab, and its content is as follows: > #!/bin/bash > service ntpd stop > ntpdate 192.168.0.191 #it's a valid ntpd server in LAN > service ntpd start > chkconfig ntpd on huh? ntpd synchronizes time continuously with the given reference servers. why in heck would you stop it to set the clock then restart it ?!? $ uptime 6:37pm up 422 days, 19:38, 1 user, load average: 0.00, 0.04, 0.06 $ ntptrace localhost: stratum 3, offset 0.000015, synch distance 0.05679 enigma.wiredgoats.com: stratum 2, offset 0.000249, synch distance 0.04080 lantime.sonic.net: stratum 1, offset -0.000116, synch distance 0.00044, refid 'PPS' ntpd hasn't been stopped or restarted since that server last booted over a year ago... my time is within 0.000116 seconds, thats 116 microseconds, of the reference server. ntpd works by incrementally fine tuning the speed the system clock runs at, using phase lock loop techniques, so the clock remains monotonic (always increasing) and stable. running a hard time set program can cause the clock to go BACKWARDS if its running fast. if ntpd isn't working for you properly, you should investigate what ntp servers you're using in /etc/ntp.conf -- john r pierce 37N 122W somewhere on the middle of the left coast