Chronyd の時刻が大幅に進んだ、または戻ったことが検出される

Issue

• chronyd: 時刻が変更されました
• 時刻が大幅に進んだことが検出されました
• 時刻が大幅に戻ったことが検出されました
• 同期できません: 選択可能なソースがありません
• 同期できません: 選択可能なソースがありません

• サンプルログ:

  Apr 28 05:33:10 localhost chronyd[1216]: Forward time jump detected!
  Apr 28 05:33:10 localhost chronyd[1216]: Can't synchronise: no selectable sources
  Apr 28 05:36:24 localhost chronyd[1216]: Selected source x.x.x.x
  Apr 28 05:36:24 localhost chronyd[1216]: System clock wrong by -3444.493726 seconds, adjustment started
  Apr 28 05:42:01 localhost chronyd[1216]: Forward time jump detected!
  Apr 28 05:42:01 localhost chronyd[1216]: Can't synchronise: no selectable sources
  Apr 28 05:44:20 localhost chronyd[1216]: Selected source x.x.x.x
  Apr 28 05:44:20 localhost chronyd[1216]: System clock wrong by -3440.590555 seconds, adjustment started
  Apr 28 05:48:42 localhost chronyd[1216]: Selected source x.x.x.x
  Apr 28 10:16:42 localhost chronyd[1216]: chronyd exiting
  Apr 28 10:16:43 localhost chronyd[88511]: chronyd version 3.4 starting (+CMDMON +NTP +REFCLOCK +RTC +PRIVDROP +SCFILTER +SIGND +ASYNCDNS +SECHASH +IPV6 +DEBUG)
  Apr 28 10:16:43 localhost chronyd[88511]: Frequency -15.599 +/- 0.194 ppm read from /var/lib/chrony/drift
  Apr 28 09:44:12 localhost chronyd[88511]: Selected source x.x.x.x
  Apr 28 09:44:12 localhost chronyd[88511]: System clock wrong by -1954.933720 seconds, adjustment started
  Apr 28 09:44:12 localhost chronyd[88511]: System clock was stepped by -1954.933720 seconds