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Old 02-06-2011, 09:56 PM
Benjamin Donnachie
 
Default system clock

On 6 February 2011 22:33, Keith Roberts <keith@karsites.net> wrote:
> Could do Ben. But the idea of ntp is that it does it for
> you automatically, without having to intervene yourself and
> set the time manually

Agreed but OP asked, "Is there a simple way to adjust the time?".

Ben
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Old 02-06-2011, 10:20 PM
Scott Robbins
 
Default system clock

On Sun, Feb 06, 2011 at 10:56:11PM +0000, Benjamin Donnachie wrote:
> On 6 February 2011 22:33, Keith Roberts <keith@karsites.net> wrote:
> > Could do Ben. But the idea of ntp is that it does it for
> > you automatically, without having to intervene yourself and
> > set the time manually
>
> Agreed but OP asked, "Is there a simple way to adjust the time?".

Depending upon OP's needs, as they are going to be dual booting, as far
as I can tell from the post, the simplest thing would be to set the
CentOS install to use localtime.

To do that, edit /etc/adjtime. You'll see it says UTC. Change that to
LOCAL

Reboot. (Might be a way to put it into effect without a reboot, but I
don't know) Run ntpdate pool.ntp.org which will set the time.

Now, when you boot between the two of them, Windows and Linux, the time
will stay the same. The problem is that both systems set the hardware
to clock time when shutting down.

--
Scott Robbins
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Old 02-06-2011, 11:56 PM
Kwan Lowe
 
Default system clock

On Sun, Feb 6, 2011 at 4:35 PM, Buz Davis <buzdavis@earthlink.net> wrote:
> I am running CntOS 5 with Gnome. *Every *now and then I have noticed
> that the computer will somehow get the time wrong by several hours. *Is
> there a simple way to adjust the time? *So far the only way I have found
> is to boot into windows (it is a dual boot system), make the change
> there, and then get back into CentOS. *Older versions of Red Hat and
> Fedora let you do it by right-clicking on the time display, if I recall
> correctly, but setting the time isn't one of the options in CentOS.

To summarize what others have said:

1) The disparity is caused by using different clock settings from
Linux to Windows. Deselect UTC to make it use local time.
2) Use ntpdate to sync the time.

A few other points:

1) Linux maintains both a system and a hardware clock. On bootup, the
system copies the hardware clock to the system time. There can be
drift between the two clocks (especially in virtual environments), so
on shutdown the system does a sync from the system to the hardware
clock.

2) The ntpd daemon will not adjust the system time beyond a few
minutes. If you want to hard set the time, you need to use ntpdate
first then turn on ntpd to keep it accurate. ntpdate does allow the
system to slowly adjust the clock and this is useful to keep logs
sane.

3) Be careful when forcing a time change on a running system. Time
shifting backwards can wreak havoc on certain applications such as
databases.
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Old 02-07-2011, 04:59 AM
Nico Kadel-Garcia
 
Default system clock

On Sun, Feb 6, 2011 at 7:56 PM, Kwan Lowe <kwan.lowe@gmail.com> wrote:
> On Sun, Feb 6, 2011 at 4:35 PM, Buz Davis <buzdavis@earthlink.net> wrote:
>> I am running CntOS 5 with Gnome. *Every *now and then I have noticed
>> that the computer will somehow get the time wrong by several hours. *Is
>> there a simple way to adjust the time? *So far the only way I have found
>> is to boot into windows (it is a dual boot system), make the change
>> there, and then get back into CentOS. *Older versions of Red Hat and
>> Fedora let you do it by right-clicking on the time display, if I recall
>> correctly, but setting the time isn't one of the options in CentOS.
>
> To summarize what others have said:
>
> 1) The disparity is caused by using different clock settings from
> Linux to Windows. Deselect UTC to make it use local time.
> 2) Use ntpdate to sync the time.
>
> A few other points:
>
> 1) Linux maintains both a system and a hardware clock. On bootup, the
> system copies the hardware clock to the system time. *There can be
> drift between the two clocks (especially in virtual environments), so
> on shutdown the system does a sync from the system to the hardware
> clock.
>
> 2) The ntpd daemon will not adjust the system time beyond a few
> minutes. If you want to hard set the time, you need to use ntpdate
> first then turn on ntpd to keep it accurate. ntpdate does allow the
> system to slowly adjust the clock and this is useful to keep logs
> sane.
>
> 3) Be careful when forcing a time change on a running system. Time
> shifting backwards can wreak havoc on certain applications such as
> databases.

ntpdate is normally executed at boot tiime by the ntp init script. If
you're on an unconnected wireless or modem at the time, this command
will fall through to using the local hardware clock, which is listed
as a "fudge" server in ntp.conf, just in case you can't reach the real
NTP servers.
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Old 02-07-2011, 02:45 PM
Lamar Owen
 
Default system clock

On Sunday, February 06, 2011 04:35:48 pm Buz Davis wrote:
> I am running CntOS 5 with Gnome. Is
> there a simple way to adjust the time?

Use system-config-date (in the GNOME menu: System/Administration/Date&Time)

Make sure 'System clock uses UTC' is unchecked in the timezone tab if you dual-boot with windows and don't have windows set to that setting. You can set up network stime servers in the 'Network Time Protocol' tab, and you can adjust the date and time easily in the 'Date & Time' tab.
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