NTP

• 推荐使用 chrony
• busybox 的 ntpd 能用
• pools
  • https://www.pool.ntp.org/zone/hk
  • pool.ntp.org
  • time.nist.gov
• twekkel/htpdate
  • HTTP Time protocol

adjtimex

• ppm - parts per million
  • 1ppm - system’s clock thinks it has advanced 1 second, it has actually advanced by 1.000001 seconds relative to true time
    • 0.1ppm
• adjtime.3

adjtimex # 系统同步状态

    mode:         0
-o  offset:       0 us
-f  freq.adjust:  515115 (65536 = 1ppm)
    maxerror:     88986
    esterror:     323
    status:       0 ()
-p  timeconstant: 2
    precision:    1 us
    tolerance:    32768000
-t  tick:         10000 us
    time.tv_sec:  1656320448
    time.tv_usec: 568452
    return value: 0 (clock synchronized)