53
votes
Accepted
Why is it important that servers have the exact same time?
Security
In general, timestamps are used in various authentication protocols to help prevent replay attacks, where an attacker can reuse an authentication token he was able to steal (e.g. by sniffing ...
- 241k
20
votes
Accepted
How to synchronize time on ESXi Windows virtual machines within one second?
This is 2018. Windows is capable of keeping servers synchronized within 2 ms or so, as required by MIFID II Regulations. So, your problem is a non-problem.
Our sysadmins using windows NTP to sync ...
- 51.4k
17
votes
Why is it important that servers have the exact same time?
Mainly, it's so that you can correlate incidents from logs on different devices. Suppose you have a security incident where someone accesses your database through your web server -- you want the ...
- 7,983
15
votes
Accepted
Time synchronization in an heterogeneous environment
[EDIT] A major rewrite with references as I just jotted down the old answer from memory.
Short answer: no. It is not possible to get near-millisecond accuracy from a run-of-the-mill operating system ...
- 4,726
15
votes
Accepted
How to set up local ntp server without internet access on ubuntu?
Don't do this. Seriously. Just don't. People keep coming up with the idea that NTP is designed to allow a bunch of machines all to have the same time. It isn't. It's designed, quite carefully, to ...
- 79.2k
12
votes
Sync ntp immediately at boot with undiciplined clock
You can use the -g parameter. From the manpage:
-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 ...
- 436
11
votes
Accepted
NTP: How to establish redundant solution for NTP servers?
I suspect this is a non-problem: NTP is resilient to this already.
You don't have a "primary" NTP server, and some secondaries: you have a set of configured servers. NTPd will decide which is ...
- 79.2k
9
votes
Ntpd on local network - Preventing clock drift causing high offsets
A driftfile records the frequency of the local clock, and is a good thing to have to accurately discipline it. Ubuntu /etc/ntp.conf has a driftfile by default.
Appending iburst to the server line ...
- 31.1k
8
votes
Accepted
w32time in domain polling from wrong Domain Controller
From the MS Documentation I can see that computers in a domain should get their time from the PDC domain controller
Not an accurate statement. Domain members need not sync time with the PDCe ...
- 55.3k
8
votes
Accepted
Allow Active Directory users to disable datetime sync
As pointed out by @MDMarra, using a VM is a great way to go because blocking time synchronization can cause significant problems for authentication, TLS certificate validity, etc. However, for true ...
- 3,369
7
votes
Why is it important that servers have the exact same time?
Not only is it important from an administration perspective, but having clocks in sync my be important from application level correlation too. This depends on how solution is designed, how the ...
- 3,413
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 ...
- 241k
7
votes
Allow Active Directory users to disable datetime sync
You really don't want to do this. Time sync is critical to Kerberos functioning properly. Unless you want authentication failures, you'll leave the system clocks where they are.
Perhaps a non-domain ...
- 101k
7
votes
Accepted
no internet time tab on domain controller, Windows Server 2016
However, my computer is a domain controller which should provide the time for clients. Could it be that my domain controller is anyhow configured as both at a time, server and client?
The Domain ...
- 109k
7
votes
Accepted
Ubuntu 20.04 time sync problems and possibly incorrect status information
The timedatectl command reports that NTP is in use when either chronyd or systemd-timesyncd is enabled and running. Both of these are lightweight NTP clients suitable for most servers and workstations....
- 241k
6
votes
Why is it important that servers have the exact same time?
Since you mentioned leap seconds it should be noted that they require particularly difficult handling.
They're usually added by injecting a second as 23:59:60, this is problematic if you're ...
- 1,025
6
votes
Turn OFF NTPD immediatly synchronization
By default, ntpd will step (instead of slew) the time if the offset is greater than 128ms. You can avoid that with the -x command line option, but beware: Correcting one second of offset will take ...
- 98.1k
6
votes
Incorrect Ubuntu server time
How to keep accurate time on Ubuntu continuously?
By enabling the ntpd service and running it continuously.
I synchronized it using sudo ntpdate -s time.nist.gov few months ago but it jumped ...
- 74k
6
votes
Incorrect Ubuntu server time
Unfortunately Ubuntu hasn't added the disclaimer from NTP.org's ntp-4.2.*\html\ntpdate.html manual to Ubuntu's ntpdate(8) manpage, like for example FreeBSD has:
ntpdate - set the date and time via ...
- 44.8k
6
votes
Accepted
hwclock: Cannot access the Hardware Clock via any known method
The problem seems to be connected to clocksource, check available_clocksource:
$ cat /sys/devices/system/clocksource/clocksource0/available_clocksource
tsc hpet acpi_pm
Based on answer to "What does ...
- 2,103
6
votes
How to synchronize time on ESXi Windows virtual machines within one second?
Is it correct for us to ask for "within second" or we need to ditch
Quartz entirely?
There are lots of very good reasons for various application stacks to need tight time control and what Quartz ...
- 101k
6
votes
Sync ntp immediately at boot with undiciplined clock
In addition to the -g flag described above, you should add iburst to the server line on the clients. This will cause them to sync more quickly to the server.
However, you can't expect your server ...
- 4,032
5
votes
How to fix time on NTP server with a lot of machines synchronized by it
When you talk about slewing the time, you are usually talking about small amounts of time. The fix is performed with a call to adjtime(), or on linux maybe adjtimex().
From the ntpd man page:
-x ...
- 5,826
5
votes
Accepted
What problems result from servers not time-sync'd?
Kerberos tickets granted for authentication are very time sensitive and the mechanism breaks down absent accurate time sync between clients, servers and ticket grantors.
- 6,382
5
votes
Why is it important that servers have the exact same time?
Whenever timestamps are involved, de-synchronized devices can create logical incoherences, like: A sends a query to B, and the reply of B comes with a timestamp earlier than that of the query, ...
- 151
5
votes
System time is off by up to hundreds of milliseconds despite NTP sync before boot
I do not have numbers to produce, but it seems probable that the interface used to set the clock at boot only has precision down to the second.
You do not state your OS, but on all Unix-like systems ...
- 3,527
5
votes
Accepted
Why is my internal clock always 1.3 seconds off?
Turns out w32time simply sucks. Microsoft admitted that
w32time cannot reliably maintain sync time to the range of 1 to 2 seconds.
Great software guys...
I installed a different implementation ...
- 163
5
votes
change time grayed out in windows server 2016
I had the same problem and the issue wasn't related to policy. Only changing it in the Local Server section of the Server Manager worked. See this article:
https://www.dtonias.com/set-time-date-...
- 59
5
votes
Ntpd on local network - Preventing clock drift causing high offsets
Your lack of a relation between your NTP server's clock time and the real-world UTC time could be the root of your problem. If your NTP server does not have multiple real-world sources (regardless of ...
- 4,032
4
votes
How to keep time on resumed KVM guest with libvirt?
Many virtualization host operations on the guest can result in a pause - resume. This will negatively effect the system clock at the guest. For example, cloning a VM results in a pause while cloning. ...
- 41
Only top scored, non community-wiki answers of a minimum length are eligible