NTP Server and Client
===

###### tags: `IBM` `Linux Tools`

台灣時區
GMT+8=UTC+8=CST
:::info
CST可能代表4個不同的時區：
* Central Standard Time (USA) UT-6:00
* Central Standard Time (Australia) UT+9:30
* China Standard Time UT+8:00
* Cuba Standard Time UT-4:00
:::

## 設定時區顯示格式
開機時，依據/etc/sysconfig/clock的ZONE，系統會將/usr/share/zoneinfo/Asia/Taipei複製為/etc/localtime

# vi /etc/sysconfig/clock
ZONE="Asia/Taipei"

## 手動校時

# 查看Unix Time
date

# 查看系統時間/硬體時間
hwclock -r

# 手動修改Unix Time
date MMDDhhmmYYYY

# 將Unix Time改到系統時間/硬體時間
hwclock -w

## yum install ntp
### 網路校時

# 透過NTP Client，修改Unix Time
ntpdate <Time Server IP>

# 確認Unix Time
date

# 將Unix Time改到系統時間/硬體時間
hwclock -w

### 架設Time Server

> yum install ntp

> which ntpd

> vi /etc/ntp.conf
# difference of its hardware time and its time server
driftfile /var/lib/ntp/drift

# not allow all
restrict default nomodify notrap nopeer noquery

# allow its time server
restrict tock.stdtime.gov.tw
restrict tick.stdtime.gov.tw
restrict time.stdtime.gov.tw

# allow itself
restrict 127.0.0.1
restrict ::1

# allow client
restrict 192.168.56.0 mask 255.255.255.0 nomodify

# time server
server tock.stdtime.gov.tw prefer
server tick.stdtime.gov.tw
server time.stdtime.gov.tw

> systemctl stop chronyd; systemctl disable chronyd
> systemctl restart ntpd

# check if it has synchronized with its time server (more than 15 minutes after restarting)
> ntpstat

# check its time server status
> ntpq -p

## yum install chrony
- [建立 NTP Server ( chrony 簡介)](https://kenwu0310.wordpress.com/2020/06/20/centos-7-%E5%BB%BA%E7%AB%8B-ntp-server-chrony-%E7%B0%A1%E4%BB%8B/)