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Most server hardware clocks are use UTC. UTC stands for the Universal Time, Coordinated, also known as Greenwich Mean Time (GMT). Other time zones are determined by adding or subtracting from the UTC time. Server typically displays local time, which now is subject of DST correction twice a year.
Wikipedia defines DST as follows:
Daylight saving time (DST), also known as summer time in British English, is the convention of advancing clocks so that evenings have more daylight and mornings have less. Typically clocks are adjusted forward one hour in late winter or early spring and are adjusted backward in autumn.
DST patch is only required in few countries such as USA. Please see this wikipedia article.
Linux will change to and from DST when the HWCLOCK setting is set to `-u', i.e. when the hardware clock is set to UTC (which is closely related to GMT), regardless of whether Linux was running at the time DST is entered or left.
When the HWCLOCK setting is set to `--localtime', Linux will not adjust the time, operating under the assumption that your system may be a dual boot system at that time and that the other OS takes care of the DST switch. If that was not the case, the DST change needs to be made manually.
Note:
EST is defined as being GMT -5 all year round. US/Eastern, on the other hand, means GMT-5 or GMT-4 depending on whether Daylight Savings Time (DST) is in effect or not.
The tzdata package contains data files with rules for various timezones around the world. When this package is updated, it will update multiple timezone changes for all previous timezone fixes.
To retrieve the most recent version of tzdata package, run the command:
yum update tzdata
After updating the timezone package, the system must run its timezone configuration
package to update the obsolete /etc/localtime file: Run the command as the superuser root:
1.
# system-config-date
2.
3. Click OK.
====================
Uncheck "Use local time source" and on the time zone tab, check "system clock uses UTC".
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The command I'm using to check that DST will change at the right time reads out of the tzdata file:
zdump -v Australia/Sydney | grep 2008It returns output like so:
Australia/Sydney Sat Apr 5 15:59:59 2008 UTC = Sun Apr 6 02:59:59 2008 EST isdst=1 gmtoff=39600
Australia/Sydney Sat Apr 5 16:00:00 2008 UTC = Sun Apr 6 02:00:00 2008 EST isdst=0 gmtoff=36000
Australia/Sydney Sat Oct 4 15:59:59 2008 UTC = Sun Oct 5 01:59:59 2008 EST isdst=0 gmtoff=36000Australia/Sydney Sat Oct 4 16:00:00 2008 UTC = Sun Oct 5 03:00:00 2008 EST isdst=1 gmtoff=39600
Good for checking that your clocks are in order!
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Wikipedia defines DST as follows:
Daylight saving time (DST), also known as summer time in British English, is the convention of advancing clocks so that evenings have more daylight and mornings have less. Typically clocks are adjusted forward one hour in late winter or early spring and are adjusted backward in autumn.DST patch is only required in few countries such as USA. Please see this wikipedia article. It display usage and a short history of daylight saving time by location in alphabetic order.
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Managing Accurate Date and Time
1. Why do We Need a Precise Clock?
- 1.1. On What Factors Does the Hardware-Clock Depend?
2. Computer Global Date and Time Concept 3. What are Time Zones?
- 3.1. Daylight Savings Time
- 3.2. Time Zones Examples
- 3.3. Time Zone Mechanism on Linux
4. The Correct Settings for Your Linux Box
- 4.1. Setting Time Zone
- 4.2. Setting the Hardware Clock
5. Accurate Global Time Synchronization
- 5.1. NTP: The Network Time Protocol
- 5.2. Building a Simple Time Synchronization Architecture
- 5.3. NTP Configurations
- 5.4. Watching Your Box Synchronizing
- 5.5. Configure to Automatically Run NTP at Boot
6. Precise Time with the chrony Program
- 6.1. How chrony Differs from the ntp Suite?
- 6.2. How to Use chrony?
A. About this Document
14.1. The concept of localtime 14.2. The hardware and software clocks 14.3. Showing and setting time 14.4. When the clock is wrong 14.5. NTP - Network Time Protocol 14.6. Basic NTP configuration 14.7. NTP Toolkit 14.8. Some known NTP servers 14.9. NTP Links
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