Tag Info

Hot answers tagged

19

Well for one your timestamps on all your logs will be off and out of sync with other servers making it very hard to figure out when things happened. Also, time synchronization is relied upon for some security protocols (kerberos for example). So what I'm saying is, most things will continue working normally, some protocols or applications relying on ...


15

Make both machines be NTP clients. That should make their clocks correct to within a rather short interval, and is already developed, tested, and available. According to the Wikipedia page on NTP, you should expect around 10 ms over Internet, far less if you have a local time server on your LAN, which should be quite easy to set up.


13

First off, the default max difference is 1000s as others have mentioned. As @kyle stated you can use the -g flag to ignore this ONE time only to initially set your clock. After that you really shouldn't see your clock drifting by 1000s between updates even under highload, and if you do you really need to replace the clock. The settings in the configuration ...


7

Here's just a few: MySQL replication Database queries using now() for current date/time rsync backup scripts any other inter-server communication NTP is the best way to keep your time correct.


7

NTP is the answer. NTP is always the answer to "How do I synchronize the clocks on some machines?" A full tutorial on setting up NTP is far beyond the scope of this site, however you will find tutorials all over the internet. The gist of it is: Install the NTP software if your OS doesn't already come with it. (If you're really in a bind and need to build ...


7

NTPD can adjust your clock in slow increments if it's off, clock slewing. The idea behind that is that slow steps won't cause issues with software timers, strange gaps in log files etc. The maximum slew rate possible is limited to 500 parts-per-million (PPM) by the Unix kernel. As a result, the clock can take 2000s for each second the clock is ...


6

This is specified in man ntpd, and you override it you might be interested in the -g option (Note the "which is 1000 s by default": -g Normally, ntpd exits with a message to the system log if the offset exceeds the panic threshold, which is 1000 s by default. This option allows the time to be set to any value without restriction; however, ...


4

I would change the time on the clock back, personally. Depending on how your domain synchronizes time, you'd take different approaches, but generally the easiest way is to just change the clock in Windows back. Synchronization isn't instantaneous, (it works by speeding or slowing clock ticks until your reach the "correct" time) so you shouldn't have to ...


4

Probably belongs on serverfault, but you're looking for ntp (Network Time Protocol). The daemon on linux is ntpd, and I think it's "Windows Time Service Tools" on windows.


3

Just something to watch out for...may not practically apply if the test you're doing is fairly short in duration: Be aware of the time synchronization interval, especially if the Windows client is in a domain (where the domain source and interval would override anything you set manually for your test). It might muddy your results if you sync the times ...


3

Are there any ntpd messages in /var/log/messages? As I was dealing with my EC2 NTP issues I noticed that NTP didn't like being too far out of sync and wanted a manual update. Perhaps you're too far out for it to decide it will update for you.


3

One potential source of problems I found today comes from backup or snapshots rotation scripts that rely on the fact that your clock will never go backward, or in other words, that you will never have backups named with dates and times "from the future", which may cause them to just remove those future backups / snapshots (depends on how the scripts are ...


3

I'll add that two ISC DHCP servers running in failover mode will fail when the time differs by a certain threshold. They will refuse to restart after having been stopped. Edit: depending on how it's configured, DNS can fail too because slaves won't be able to download zones from their masters and their cached zones will eventually expire.


3

I definitely can recommend the Meinberg devices. We were using a 19" device which got it's time from DCF77 (Europe) in a large, but closed network (it was a closed production plant network with an Active Directory (don't ask..), so a proper time sync was inevitable for authentication/kerberos etc. The Mainberg device was rock solid, once set up, ran ...


3

If you have a convienent window nearby a GPS dongle can provide time information in addition to location.


3

Virtual servers have notoriously unreliable clocks, since they don't get reliable ticks from the CPU. They're even worse than the clocks in physical machines. It depends mostly on the load of the hypervisor your VPS is running on, so maybe you're seeing more drift since the load of the physical server has increased. Simply enable NTPD, and point it to some ...


3

Turn ntpd back on. It's job is to figure out how fast the clock is running and apply an appropriate correction.


3

I would either verify that the server time is synchronized with XEN host echo 0 > /proc/sys/xen/independent_wallclock or I would disable this method and configure standalone time synchronisation via NTP echo 1 > /proc/sys/xen/independent_wallclock yum install ntp service ntpd start chkconfig ntpd on Put this line to /etc/sysctl.conf to make ...


3

Does Windows internet time settings operate over NTP? Yes. Will I run into clock drifting issues by using it? Assuming you're using a stable time source and you have things configured correctly, no, this should prevent drift.


3

VMware tools might do this for you, but Gentoo is not in the guest compatibility list so it may not work, or may take a lot of effort to get working. You could use ntp to keep the clock up to date, or schedule ntpdate to run. I am not sure if these are better methods than hwclock -s. One thing you may want to avoid is a method that simply changes the ...


3

This has been addressed before: What are the limits of running NTP servers in virtual machines? Short answer: Don't do it. The accuracy of your local clock is still important when setting up an NTP server, and there are too many variables when using virtual machines to guarantee reasonable accuracy.


2

On an AD domain member, I would definitely use only w32time. On a non-domain server, it's probably a matter of personal preference.


2

VMware recommends a slightly different set of parameters for SLES 10 SP1: clock=pmtmr hpet=disable I normally run only Windows guests under Hyper-V, so I am not sure whether this is equally relevant to your environment. It is certainly worth a try.


2

Simple: DO NOT VIRTUALIZE. Virtualization per definition has time skew. High precision software does not work well with virtualization. I have a similar system here (telling me every hour it synced by 36ms) getting a constant 100 packet per second or so data stream to keep it in sync. Simply did not work under virtualization. Virtualiaztion Hyper-Visors ...


2

Here is a link to the VMware paper "Timekeeping in VMware Virtual Machines" (2008): http://www.vmware.com/pdf/vmware_timekeeping.pdf


2

The best option for a precise clock on the guest is to use the kvm-clock source (pvclock) which is synchronized with clock's host.


2

My most annoying problem yet : Expiring SSL certificates. Very annoying when you can't figure out why they do not work.


2

Remote desktop and other remote access tools may stop working as they rely on time to authenticate. This can make troubleshooting very frustrating (you try to remote on to fix the problem, but can't even do that). I had this on a machine that thought somehow thought the year was 8011 rather than 2011. SSL certificates were also expired.


2

The "operation not permitted" errors make me wonder if NTP is trying to talk from or open its privileged port (123) but is not running as root. Can you confirm that either NTP is running as root, or is running a version with the appropriate permissions to open port 123?


2

How about isolating this group of time-travelling machines and pointing them to a dedicated NTPD service on a server with some spare resources? There are NTP commands available to make/allow big NTP jumps, so you can either push them out over the network or embed them as local commands in your training simulation system/scripts? Or disable NTP on these ...



Only top voted, non community-wiki answers of a minimum length are eligible