32
votes
Accepted
What are examples of software that may be seriously affected by a time jump?
This is a bit of open question but let me give some examples:
databases - most of them rely a lot of precise time for storing records, indexes, etc
security - precise time is very important for ...
- 5,318
18
votes
Force chrony time check
If chronyd isn't already running, a command similar to 'ntpdate
pool.ntp.org' could be (since version 1.30):
chronyd -q 'server pool.ntp.org iburst'
If it's already running and it has some servers ...
- 618
13
votes
What are examples of software that may be seriously affected by a time jump?
I recently got bit by a bug that dates back to 1999 and affects both the JVM and Android Runtime: https://bugs.java.com/bugdatabase/view_bug.do?bug_id=4290274
... two extra executions are fired (...
- 231
10
votes
Accepted
ntpd synchronizes but chronyd fails
The difference is that chronyd by default uses a random source port for each client request. If the firewall doesn't allow client requests from other ports than 123, you will need to specify the port ...
- 116
9
votes
Chrony time synchronization on huge time diff
If your time is way off (days or even months), time synchronization will not work ("it will take a long time") because NTP clients like Chrony adjust the clock gradually by slowing it down or ...
- 353
9
votes
What are examples of software that may be seriously affected by a time jump?
All software that interacts with real-live hardware. If you have a toaster that toasts bread for 20 seconds, and its software is stupid enough to check against the wall clock, you'll either get white ...
- 569
7
votes
Accepted
Chrony doesn't appear to be syncing with the servers I've specified
The servers you've specified:
server 0.us.pool.ntp.org
server 1.us.pool.ntp.org
server 2.us.pool.ntp.org
server 3.us.pool.ntp.org
are, as the names suggest, pools. When you look up one of these ...
- 244k
6
votes
Accepted
Verify internal NTP server is sending the correct time?
TL;DR:
Configure your NTP server according to best current practices.
(Shameless self-promotion warning.) Use my ntpmon check if your monitoring solution uses collectd, Nagios, or telegraf.
Long ...
- 4,367
6
votes
Accepted
The "least bad" settings for Chrony as the NTP server on a virtual machine
The question you linked to is a good example of received wisdom in an established answer becoming so out-of-date as to be just plain wrong for the majority of use cases. Running NTP servers in VMs on ...
- 4,367
5
votes
Accepted
Chrony time synchronization on huge time diff
Your problem seems to be that you're trying to accomplish a six year time change by skewing the clock, and giving up after one day.
If the skew algorithm drifts the clock by as much as one percent - ...
- 79.8k
5
votes
Accepted
"system clock synchronized: no", flip it to yes
chronyc sources indicates that it does not have connectivity to any of the available NTP servers. This is what the ? in the S column means, from the man page:
This column indicates the state of the ...
- 244k
4
votes
Accepted
Chronyc equivalent for ntpdate -q
-Q
This option is similar to the -q option, except it only prints the offset without making any corrections of the clock and it allows chronyd to be started without root privileges.
- 8,777
4
votes
What are examples of software that may be seriously affected by a time jump?
We had an issue with an on-vehicle embedded system where the clock would significant lose time (due to an electrical problem). But the wireless connections were intermittent, so the time only ...
- 141
3
votes
Decentralized NTP in network with only sporadic internet connectivity?
The simplest and best (but not least expensive) solution to your problem is to set up a small radio clock device (either GPS or WWVB/shortwave) on that network. Have devices use that as a server in ...
- 3,762
3
votes
Programmatically detect Chrony time sync events
438 million second offset is 13 years. If this system has a real time clock, check it is functional.
Decide if, on system boot, you wish to wait for NTP to be synchronized before starting your ...
- 32.1k
3
votes
Chrony stepping instead of slewing clock
If anyone is interested the cause of my problem was the initstepslew directive in chrony.conf. In the manual it states that this can be used to allow the clock to be stepped at boot time. However, ...
- 51
3
votes
Accepted
chrony does not log anything on my ec2 instance
I just verified chrony logging by doing the following:
created a default Ubuntu 18.04 LTS EC2 instance - AMI id: ubuntu/images/hvm-ssd/ubuntu-bionic-18.04-amd64-server-20180912 (ami-07a3bd4944eb120a0)...
- 4,367
3
votes
Verify internal NTP server is sending the correct time?
Sure, the standard approach is to use the bundled NTP client called ntpq. This utility can be used to display the connected servers, their reachability, time difference and jitter. Here's the example:...
- 8,690
3
votes
How do I tell if chronyd is actually self-synchronising correctly?
You might want to consider the Information at
https://chrony.tuxfamily.org/doc/3.3/chrony.conf.html
according to what it says at Isolated Networks.
There are several options to help configure a ...
3
votes
Accepted
chrony and gpsd: socket or PPS connection
First, pps is NOT available via USB. You need to use a direct connection. USB is polled and thus cannot provide an accurate enough signal. I learned this trying to set up some Windows boxes at work....
- 46
3
votes
NTP/Chrony not keeping time synchronized on CentOS 7.9 (VM running on VMware ESXi)
I think I have solved it now.
Basically, chrony thought that the time varied too much. So following the link by Peter Rosenberg (and the resources it linked to) I got on the track....
I've put this ...
- 203
3
votes
Accepted
What does 0.0.0.0/0 mean?
It literally means all or any hosts - 99.99% of the time.
The only exception I can provide at hand is the whitelist of Cisco routers, where such "zero whitelist" means negating all hosts. It ...
- 47.9k
2
votes
Accepted
CentOS, Chrony, and AWS Ports
No, because acquisitionport can be configured.
Even if the software didn't allow for such convenience, and a firewall didn't allow the return traffic of a flow, you still could open just a ...
- 32.1k
2
votes
Chrony time synchronization on huge time diff
If the time difference is huge chrony might not accept your source. My clock was a few years back and chronyc tracking was reporting:
> chronyc tracking
Ref time (UTC) : Thu Jan 01 00:00:00 1970
...
- 121
2
votes
Accepted
Synch Clock Per Request
First, understand what software running would be seriously affected by jumps from stepping the time. It may be safer to wait until you can bring databases down.
Start chronyd, wait a few seconds for ...
- 32.1k
2
votes
Decentralized NTP in network with only sporadic internet connectivity?
Try not to do this. Per your reply to @rmalayter's answer, NTP is not a descentralized protocol. Accurate time relies on the "central" (i.e. higher stratum) servers supplying time to their clients. ...
- 4,367
2
votes
Accepted
Why is the /var/log/chrony folder empty?
As well as having a logdir defined, you must also enable logging with the log directive. Here's an extract from the default RHEL 7.2 /etc/chrony.conf:
...
# Specify directory for log files.
logdir /...
- 4,367
2
votes
chrony startup marks all sources as falseticker
In short, I believe this is because you have two pairs of time servers at the same Stratum. If the two servers at the same Stratum differ in the time they report, chronyd will not be able to determine ...
- 21
2
votes
Accepted
Why is chrony reporting low offset when my system times are so far apart?
Yes, there is a limit. The same limit that means NTP will roll over in the year 2036.
NTP timestamp format is based on 32 bit seconds (and 32 bit fractions of a second) or 136 years, also known as an ...
- 32.1k
2
votes
What are examples of software that may be seriously affected by a time jump?
Dovecot IMAP server is affected and (in older versions) it (deliberately) suicides if it detects the system time having jumped backwards. In v2.0, it at least tries to remedy the situation.
See https:...
- 131
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