clock syncing

[unicorn]

How to adjust time? How to use OpenNTPD and configure it?

[ocicat]

Originally Posted by unicorn

How to adjust time?

https://www.openbsd.org/faq/faq10.html#OpenNTPD

How to use OpenNTPD and configure it?

https://man.openbsd.org/OpenBSD-7.4/rcctl.8

[unicorn]

sorry, I had read the first article but still confused. I want to auto sync time when booting. Which command should I run and add it to which file?

[jggimi]

The ntpd(8) daemon is started on boot by default. It will automatically synchronize the local system clock using a pool of public NTP servers, and checks the supplied time's validity through a separate pool of public HTTPS servers acting as authentication constraints.

If OpenBSD's default time synchronization is not sufficient to your needs, you can use date(8) to set the clock manually or use rdate(8) to set the clock's time using a trusted remote NTP server.

[shep]

OpenNTP is enabled out of the box as a default. Typically, it is within 200 msec and is substantially smaller and more secure (smaller attack surface and fewer cve's) than ntp which is a port option:
net/ntp

[unicorn]

my system current time is Mon Feb 3 05:44:58 GMT 2025, I want to use Shanghai time, I had edit sysctl.conf and add this line:

kern.utc_offset=+500

but I get top levels and second levels offset invalid errors.What's the appropriate parameter?

[Onauk]

To change the timezone you should follow the OpenBSD FAQ[1].

Basically, do not change kern.utc_offset unless you want your hardware clock to be different than UTC, which is only important for multibooting.

To change the time zone to Shanghai you should do (as root) :

# ln -fs /usr/share/zoneinfo/Asia/Shanghai /etc/localtime

[1] https://www.openbsd.org/faq/faq10.html#TimeZone

[unicorn]

thanks, I had executed that command but my time is still incorrect. I have two disks with OpenBSD and linux installed separately. How to do with it?

[jggimi]

Both of your OSes should use UTC for the clock, with a local timezone offset. Windows is the only OS I'm aware of that needs the clock set to local time.

[Head_on_a_Stick]

The ArchWiki claims that Ubuntu & Fedora will use localtime if they detect a Windows system when installing:

https://wiki.archlinux.org/title/Sys..._Ubuntu/Fedora

So if the OP had Windows on that machine when installing Linux they might have to change the Linux system to UTC:

timedatectl set-local-rtc 0

Then make sure the system clock is correct and update the hardware clock:

hwclock --systohc

[unicorn]

Sorry, I don't understand.
My time is 14:56 PM CST, system time is 08:56 AM GMT. I adjusted time use date command and I got 14:56 PM GMT. My time zone is CST not GMT.

[shep]

Most systems have a hardware clock and a system clock.

https://wiki.archlinux.org/title/System_time.

Unix/Linux based systems set the hardware clock to UTC which is preserved by the cmos battery when the system is powered off. On boot, the hardware clock is read and the system offset applied to generate system time, aka local time. The offset for CST is UTC-6.
NTP initially adjusts the System clock which, at some point, updates the hardware clock.

Windows sets the hardware clock to local time. This can have issues with emails sent from an Eastern Time zone, say at 4pm, which arrive at an Pacific Time zone at 1pm. Another issue is with security updates - most systems balk at security updates from the future