Linux时钟简介 RedHat Linux操作系统修改时区的方法

 

Content of this article:

 

Linux时钟简介

Linux Time Zone Configuration guide

RedHat Linux操作系统修改时区的方法

Here is an example of changing the timezone on linux

extern configuration of timezone on linux

How to Set the Time Zone in Unix

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  Linux时钟简介：

Linux将时钟分为系统时钟(System Clock)和硬件(Real Time Clock，简称RTC)时钟两种。系统时间是指当前Linux Kernel中的时钟，而硬件时钟则是主板上由电池供电的那个主板硬件时钟，这个时钟可以在BIOS的“Standard BIOS Feture”项中进行设置。 既然Linux有两个时钟系统，那么大家所使用的Linux默认使用哪种时钟系统呢？会不回出现两种系统时钟冲突的情况呢？这些疑问和担心不无道理。首 先，Linux并没有默认哪个时钟系统。当Linux启动时，系统时钟会去读取硬件时钟的设置，然后系统时钟就会独立于硬件运作。

从Linux启动过程来看，系统时钟和硬件时钟不会发生冲突，但Linux中的所有命令(包括函数)都是采用的系统时钟设置。不仅如此，系统时钟和硬件时 钟还可以采用异步方式，即系统时间和硬件时间可以不同。这样做的好处对于普通用户意义不大，但对于Linux网络管理员却有很大的用处。例如，要将一个很大的网络中(跨越若干时区)的服务器同步，假如位于美国纽约的Linux服务器和北京的Linux服务器，其中一台服务器无须改变硬件时钟 而只需临时设置一个系统时间，如要将北京服务器上的时间设置为纽约时间，两台服务器完成文件的同步后，再与原来的时钟同步一下即可。这样系统和硬件时钟就 提供了更为灵活的操作。

在Linux中，用于时钟查看和设置的命令主要有date、hwclock和clock。其中，clock和hwclock用法相近，只不过clock命 令除了支持x86硬件体系外，还支持Alpha硬件体系。由于目前绝大多数用户使用x86硬件体系，所以可以视这两个命令为一个命令来学习。

 

在虚拟终端中使用date命令来查看和设置系统时间

查看系统时钟的操作：

# date

设置系统时钟的操作：

# date 091713272003.30

通用的设置格式：

# date 月日时分年.秒

使用hwclock或clock命令查看和设置硬件时钟

查看硬件时钟的操作：

# hwclock --show 或# clock –show

2003年09月17日 星期三 13时24分11秒 -0.482735 seconds

设置硬件时钟的操作：

# hwclock --set --date="09/17/2003 13:26:00"

或者# clock --set --date="09/17/2003 13:26:00"

通用的设置格式：hwclock/clock --set --date=“月/日/年 时：分：秒”。

同步系统时钟和硬件时钟

硬件时钟与系统时钟同步：

# hwclock --hctosys

或者

# clock --hctosys

上面命令中，--hctosys表示Hardware Clock to SYStem clock。

系统时钟和硬件时钟同步：

 hwclock --systohc 或者

 clock –systohc

 

Linux Time Zone Configuration guide:

Background - The Earth is divided into time zones that are 15 degrees of longitude each, for this corresponds to the amount of angular distance the Sun appears to travel in 1 hour. 0 degrees longitude runs through the Royal Observatory in Greenwich, England. This is the origin of Greenwich Mean Time, or GMT. For all practical purposes, GMT and UTC are the same. To complicate matters, some countries observe Daylight Savings Time (DST), while others do not. Even within some countries, some states or districts do not observe DST while the rest of the country does! DST can also begin and end on different days in different countries! What a mess...

There are several files and directories that are used for time zones, and several tools:

l         /etc/sysconfig/clock- this is a short text file that defines the timezone, whether or not the hardware clock is using UTC, and an ARC option that is only relevant to DEC systems.

      eg：/ect/sysconfig/clock file content on jstest3:

       ZONE="Asia/Shanghai"

       UTC=true

       ARC=false

    

l         /etc/localtime - this is a symbolic link to the appropriate time zone file in /usr/share/zoneinfo

l         /usr/share/zoneinfo - this directory contains the time zone files that were compiled by zic(The time zone compiler. Zic creates the time conversion information files.)These are binary files and cannot be viewed with a text viewer. The files contain information such as rules about DST. They allow the kernel to convert UTC UNIX time into appropriate local dates and times.

l         /etc/rc.d/rc.sysinit- This script runs once, at boot time. A section of this script sets the system time from the hardware clock and applies the local time zone information.

l         /etc/init.d/halt- This script runs during system shutdown. A section of this script synchronizes the hardware clock from the system clock.

l         /etc/adjtime - This file is used by the adjtimex function, which can smoothly adjust system time while the system runs. settimeofday is a related function.

l         redhat-config-date or dateconfig - These commands start the Red Hat date/time/time zone configuration GUI.

l         zdump - This utility prints the current time and date in the specified time zone. Example:

# zdump Japan

Japan Sat Mar 29 00:47:57 2003 JST

# zdump Iceland

Iceland Fri Mar 28 15:48:02 2003 GMT

RedHat Linux操作系统修改时区的方法

Most modern Linux distributions have user-friendly programs to set the timezone, often accesible through the program menus or right-clicking the clock in a desktop environment such as KDE or GNOME. Failing that it's possible to manually change the system timezone in Linux in a few short steps.

It's possible to change the system timezone in Linux in a few short steps.

Steps

1.     Logged in as root, check which timezone your machine is currently using by executing `date`. You'll see something like "Mon 17 Jan 2005 12:15:08 PM PST -0.461203 seconds", PST in this case is the current timezone.

2.     Change to the directory to /usr/share/zoneinfo, here you will find a list of time zone regions. Choose the most appropriate region, if you live in Canada or the US this directory is the "Americas" directory.

3.     If you wish, backup the previous timezone configuration by copying it to a different location. Such as `mv /etc/localtime /etc/localtime-old`.

4.     Create a symbolic link from the appropiate timezone to /etc/localtime. Example: `ln -s /usr/share/zoneinfo/Europe/Amsterdam /etc/localtime`.

5.     If you have the utility rdate, update the current system time by executing `/usr/bin/rdate -s time.nist.gov`. (This step can be skip!)

6.     Set the ZONE entry in the file /etc/sysconfig/clock file (e.g. "America/Los_Angeles")

7.     Set the hardware clock by executing: ` /sbin/hwclock --systohc`

Tips

·       On some versions of RedHat Linux, Slackware, Gentoo, SuSE, Debian, Ubuntu, and anything else that is "normal", the command to display and change the time is 'date', not 'clock'

·       On RedHat Linux there is a utility called "Setup" that allows one to select the timezone from a list, but you must have installed the 'redhat-config-date' package.

Warnings

·       Some applications (such as PHP) have separate timezone settings from the system timezone.

·       On some systems, /etc/localtime is actually a symlink to the appropriate file under the /usr/share/zoneinfo directory (rather than a copy of that file).

·       On some systems, there is a system utility provided that will prompt for the correct timezone and make the proper changes to the system configuration. For example,Debianprovides the "tzsetup" utility.

Here is an example of changing the timezone: (Logged in as root)

In order to manually change the timezone, you can edit the /etc/sysconfig/clockfile and then make a new soft link to /etc/localtime. Here is an example of changing the timezone manually to "America/Denver":

1. Select the appropriate time zone from the /usr/share/zoneinfo directory. Time zone names are relative to that directory. In this case, we will select "America/Denver"

2. Edit the /etc/sysconfig/clocktext file so that it looks like this:

ZONE="America/Denver"

UTC=true

ARC=false

Of course, this assumes that your hardware clock is running UTC time...

3. Delete the following file: /etc/localtime (backup it when you need it !)

4. Create a new soft link for /etc/localtime. Here is an example of step 3 and step 4:

# cd /etc

# ls -al localtime

lrwxrwxrwx 1 root root 39 Mar 28 07:00 localtime -> /usr/share/zoneinfo/America/Los_Angeles

# rm /etc/localtime

# ln -s /usr/share/zoneinfo/America/Denver /etc/localtime

# ls -al localtime

lrwxrwxrwx 1 root root 34 Mar 28 08:59 localtime -> /usr/share/zoneinfo/America/Denver

# date

Fri Mar 28 09:00:04 MST 2003

 

extern configuration of timezone:

           ---- allows computers, servers, and network devices to synchronize their internal clock systems

NTP Configuration and Usage:

Background - Network Time Protocol (NTP) allows computers, servers, and network devices to synchronize their internal clock systems to an external reference source. In some cases, the reference source can be an atomic clock or GPS receiver. This is useful for a number of reasons. If you would like to automatically keep the time on your Linux system synchronized to standard world times, you have two built-in tools to do this:
ntpdate and ntpd (NTP Daemon)

ntpdate:

ntpdate was written by David L. Mills at the University of Delaware. For details on Dr. Mills, enter this:
$ finger David.L.Mills@udel.eduntpdate allows you to view or set system time from one or more NTP servers. The first thing you need to do is find a time server you can query. Here is a list of public time servers, or you can use one of the following:
clock.redhat.com
clock2.redhat.com
ns1.tuxfamily.org
time.nist.gov
For example, if you only want to query an NTP server and make sure that you can reach it, use the following command:

# ntpdate -q clock2.redhat.com
server 66.187.224.4, stratum 1, offset -0.067532, delay 0.38452
28 Mar 18:14:20 ntpdate[10724]: adjust time server 66.187.224.4 offset -0.067532 sec
Note that some firewall systems do not allow NTP traffic. NTP uses UDP port 123. If you would like to query more than one server and
# ntpdate clock2.redhat.com clock.redhat.com
28 Mar 18:20:59 ntpdate[10754]: adjust time server 66.187.233.4 offset -0.043222 sec
You can add the -v
This command is very similar to the rdate command. The ntpdate command can be used in startup scripts or cron jobs to automatically set the system time without running a dedicated server process. You will definitely want to try to retrieve the time from an NTP server with ntpdate before setting up your own NTP server. This will ensure that (a) you have connectivity (b) your firewall does not block NTP. Another thing to note about the ntpdate command is that it will not work in update mode if you are running a local NTP server process. It will work in query mode.

flag for verbose output.set your system clock with the result, use the following:

NTP Server:

The NTP server (ntpd) can be setup to run continuously. This will keep the system clock synchronized. You will also be able to server NTP clients on your LAN, if you wish. I had problems with the Red Hat configuration GUI not setting the NTP server up correctly.

The configuration file is /etc/ntp.conf, and there is also an /etc/ntp directory which contains keys and the drift file. I will show you a working configuration file, with comments:

---

# Prohibit general access to this service.
restrict default ignore
# Permit all access over the loopback interface. This could
# be tightened as well, but to do so would effect some of
# the administrative functions.
restrict 127.0.0.1
# -- CLIENT NETWORK -------
# Permit systems on this network to synchronize with this
# time service. Do not permit those systems to modify the
# configuration of this service. Also, do not use those
# systems as peers for synchronization.
# This is my internal LAN network address
restrict 192.168.212.0 mask 255.255.255.0 notrust nomodify notrap
# --- OUR TIMESERVERS -----
# or remove the default restrict line
# Permit time synchronization with our time source, but do not
# permit the source to query or modify the service on this system.
# The statements below limit what the servers can do to your server
# I am using IP instead of DNS name because the "restrict" construct
# requires IP addresses
restrict 66.187.224.4 mask 255.255.255.255 nomodify notrap noquery
restrict 80.67.177.2 mask 255.255.255.255 nomodify notrap noquery
# The server listed below is clock2.redhat.com
server 66.187.224.4
# The server listed below is ns1.tuxfamily.org
server 80.67.177.2
# --- NTP MULTICASTCLIENT ---
#multicastclient # listen on default 224.0.1.1
# restrict 224.0.1.1 mask 255.255.255.255 notrust nomodify notrap
# restrict 192.168.1.0 mask 255.255.255.0 notrust nomodify notrap
# I don't want to use multicast for my NTP server
# --- GENERAL CONFIGURATION ---
#
# Undisciplined Local Clock. This is a fake driver intended for backup
# and when no outside source of synchronized time is available. The
# default stratum is usually 3, but in this case we elect to use stratum
# 0. Since the server line does not have the prefer keyword, this driver
# is never used for synchronization, unless no other other
# synchronization source is available. In case the local host is
# controlled by some external source, such as an external oscillator or
# another protocol, the prefer keyword would cause the local host to
# disregard all other synchronization sources, unless the kernel
# modifications are in use and declare an unsynchronized condition.
#
# If you un-comment the two statements below, you could run an NTP server
# off of your local (and inaccurate) system clock.
#restrict 127.127.1.0
#server 127.127.1.0
fudge 127.127.1.0 stratum 10
#
# Drift file. Put this in a directory which the daemon can write to.
# No symbolic links allowed, either, since the daemon updates the file
# by creating a temporary in the same directory and then rename()'ing
# it to the file.
#
driftfile /etc/ntp/drift
broadcastdelay 0.008

#
# Authentication delay. If you use, or plan to use someday, the
# authentication facility you should make the programs in the auth_stuff
# directory and figure out what this number should be on your machine.
#
# I am not using any authentication for this simple setup.
authenticate no

#
# Keys file. If you want to diddle your server at run time, make a
# keys file (mode 600 for sure) and define the key number to be
# used for making requests.
#
# PLEASE DO NOT USE THE DEFAULT VALUES HERE. Pick your own, or remote
# systems might be able to reset your clock at will. Note also that
# ntpd is started with a -A flag, disabling authentication, that
# will have to be removed as well.
#
keys /etc/ntp/keys

---

After you install this new version of the config file, you can start the service with /etc/init.d/ntpd startTo monitor the service, you can run the following command: ntpdc -p or ntpdc -p -n
If you are really impatient, you can use this command to watch the system until it synchronizes: watch nptdc -p -n
The ntpdc command can be run interactively as well. There are a number of informative ntpdc commands, such as iostats, sysstats, and peers.
When enough time has gone by, one of the servers will have an * placed in front of it to tell you that your system is synchronized to it. The lower the stratum number, the more accurate the server.
If you want to have the NTP server start up automatically, you can use the checkconfig command as follows:
# chkconfig --level 345 ntpd on
# chkconfig --level 0126 ntpd off
# chkconfig --list | grep ntpd
ntpd 0:off 1:off 2:off 3:on 4:on 5:on 6:off
To see that your NTP server is listening on UDP port 123, use the following command: netstat -tunaPlease note that the NTP server makes NTP queries from a UDP source port of 123. Some firewalls will not allow this, even if ntpdate worked (ntpdate uses a source port > 1023.)
You can also use the ntpq utility, and the ntptrace utility for additional diagnostic support. For complete documentation on setting up and using NTP servers, see http://www.ntp.org/.

 

 

 

How to Set the Time Zone in Unix:

Step1

Turn your machine on and locate the time zone file. You can do this by entering “command /etc/TIMEZONE.”

Step2

Locate the line within this file that indicates what time zone you’re clock is set to. It will look like this: TZ=US/Pacific. In this example, the time zone is set to the Pacific time zone of the U.S.

Step3

Change the value of the time zone to the desired time zone. This could be, for example, U.S./Eastern. It is important to know what time zone you are in so the time zone function can be set correctly.

Step4

Reboot your machine for the changes to take effect. Shut down and restart your computer. This will cause the computer’s clock to reset and show the correct time zone