npt server 設定檔問題

funlonkon

想請教在課本3037 volume 2 的第九章有關於ntp.conf的一段設定內容:
The next entry in /etc/ntp.conf is for the time servers that are to be asked for the current time:
## Outside source of synchronized time
server ptbtime1.ptb.de
server ptbtime2.ptb.de

這意思是說在我這台ntp server 上去設定要指定跟上層的哪台time server作同步對嗎?

There are 2 possible methods of synchronization between the time server and the client？
上面那行是說我這台ntp server 與上層的time server 有兩種同步方式是嗎?

Polling. With polling,the client asds the server for the current time.
Polling starts at 1 minute intervals. If the time interval is determined to be trustworthy,the interval is reset to once every 1024 seconds.
You can set the minimum and maximum limits of the polling in /etc/ntp.conf,as in the following:

server ptbtime1.ptb.de minpoll 4 maxpoll 12

The minpoll and maxpoll values are interpreted as powers of 2(in seconds).The default settings are 6(26=64 seconds) or 10 (210=1024 seconds). Values between 4 and 17 are premitted.
看了半天實在不知道那個minpoll及maxpoll 到底是甚麼意思?

另外我的ntp server啟動後，要如何設定與我指定的上層time server在固定時間就同步?
用crontab 可以達成，但server裡有沒有參數可以設定？
不然我ntp server啟動後，過了幾天時間又跑掉怎麼半?