ntpd seems to add offsets instead of subtracting them

[Thomas Schweikle]

ntpd seems to add offsets instead of subtracting them from the running synchronized clock, leading to time running away fast in one direction -- forward if the offset is positive, -- backward if the offset is negative, until the offset reaches its maximum.

ProblemType: Bug
DistroRelease: Ubuntu 14.04
Package: ntp 1:4.2.6.p5+dfsg-3ubuntu2.14.04.1
ProcVersionSignature: Ubuntu 3.13.0-44.73-generic 3.13.11-ckt12
Uname: Linux 3.13.0-44-generic x86_64
ApportVersion: 2.14.1-0ubuntu3.6
Architecture: amd64
Date: Tue Jan 27 08:25:55 2015
InstallationDate: Installed on 2014-02-10 (350 days ago)
InstallationMedia: Xubuntu 13.10 "Saucy Salamander" - Release amd64 (20131016)
KernLog:

NtpStatus: ntpq: read: Connection refused
ProcEnviron:
 TERM=screen
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=de_DE.UTF-8
 SHELL=/bin/bash
SourcePackage: ntp
UpgradeStatus: Upgraded to trusty on 2014-02-18 (342 days ago)
modified.conffile..etc.ntp.conf: [modified]
mtime.conffile..etc.ntp.conf: 2015-01-27T07:41:51.747605

[Thomas Schweikle (tps)]

Seeing this behaviour on all distributions using ntp 4.2.6p5:

- Ubuntu 14.04
- CentOS 6.5
- Orcale Linux 6.5
- Debian 7

Bug seems resolved in ntp 4.2.8 as available from http://www.ntp.org

[Thomas Schweikle (tps)]

maybe it is a security problem if kerberos used: after a while your clock is of too much and you can't login any more.

[Liam Young (gnuoy)]

Hi Thomas,
    I've tried to recreate this bug by having ntp correct a clock that is fast and also one that is slow and ntp seems to be working fine for me. I'll attach the output of the commands I tested with. Could you include the exact steps you went through please ?
Thanks
Liam