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On my main server I see unexplainable time jumps backwards in the syslog. Those jumps affect CRON.
Example:

Feb 10 06:48:01 nostromo CRON[20351]: (root) CMD (    /storage/exec/checkinternet.sh 2>/dev/null 1>/dev/null)
Feb 10 06:49:01 nostromo CRON[20364]: (root) CMD (    /storage/exec/checkinternet.sh 2>/dev/null 1>/dev/null)
Feb 10 06:50:01 nostromo CRON[20386]: (root) CMD (    /storage/exec/status-nostromo.sh >/dev/null 2>&1)
Feb  7 05:40:01 nostromo CRON[20389]: (root) CMD (    /storage/exec/checkinternet.sh 2>/dev/null 1>/dev/null)
Feb 10 06:50:01 nostromo CRON[20390]: (root) CMD (    /storage/exec/checkinternet.sh 2>/dev/null 1>/dev/null)
Feb 10 06:50:01 nostromo CRON[20391]: (root) CMD (    /storage/exec/checkip.sh 2>/dev/null 1>/dev/null)

For debugging I did the following:
Start xclock and watch xclock and tail -f /var/log/syslog in parallel. When CRON logged a wrong time, xclock did NOT show any time jump but seemed to freeze for a fraction of a second.
Open a screen and start a script that will once per second read the time (in unix seconds) and compare the read time with the time read a second ago. If the current time was smaller, the script would send an email with a process list from before and after the jump. The script also never detected any time jump.

In summary, my current impression is that there might be a bug in CRON because no other programm seems to be able to see the "wrong" time. The server in question is syslog server for 4 servers and 3 network devices. The time jumps exclusively show in syslog entries from the local CRON instance. Not in any remote syslog entry and not in any other local syslog entry, e.g. from DHCPD, bind, tftpd, etc. etc.
Also, after a reboot, things work ok for several days upto about 2 or 3 weeks. Then the "time jumps" start to occur with increasing frequency.

I don't use user crontabs but maintain all jobs in /etc/crontab. I have
number of jobs which are triggered every minute and another number of
jobs which are triggered every 5 minutes (maybe some CRON internal
counter overflow problem?).

Hardware:
Asus P9D-V
Intel Xeon E3-1240L V3
16GB ECC RAM
128GB SSD System
3x3TB ZFS RaidZ2 storage
1x3TB Misc. data

CMOS battery already changed and board inspected.

nostromo:~ # lsb_release -rd
Description:    Ubuntu 14.04.2 LTS
Release:        14.04

nostromo:~ # apt-cache policy cron
cron:
  Installed: 3.0pl1-124ubuntu2
  Candidate: 3.0pl1-124ubuntu2
  Version table:
 *** 3.0pl1-124ubuntu2 0
        500 http://us.archive.ubuntu.com/ubuntu/ trusty/main amd64 Packages
        100 /var/lib/dpkg/status

** Affects: cron (Ubuntu)
     Importance: Undecided
         Status: New

-- 
Unexplainable time jumps in CRON
https://bugs.launchpad.net/bugs/1429427
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