Network Time Protocol daemon (简体中文)
本文描述如何设置和运行 NTPd (Network Time Protocol daemon)。NTPd是使用网络时间协议将 GNU/Linux 系统的软件时钟与 Internet 时间服务器同步的最常见的方法。如果正确设置，NTPd 可以使你的计算机作为时间服务器运行。
配置连接到 NTP 服务器
NTP servers are classified in a hierarchical system with many levels called strata: the devices which are considered independent time sources are classified as stratum 0 sources; the servers directly connected to stratum 0 devices are classified as stratum 1 sources; servers connected to stratum 1 sources are then classified as stratum 2 sources and so on.
It has to be understood that a server's stratum cannot be taken as an indication of its accuracy or reliability. Typically, stratum 2 servers are used for general synchronization purposes: if you do not already know the servers you are going to connect to, you should use the pool.ntp.org servers (alternate link) and choose the server pool that is closest to your location.
server 0.pool.ntp.org iburst server 1.pool.ntp.org iburst server 2.pool.ntp.org iburst server 3.pool.ntp.org iburst
iburst 选项是推荐的，如果第一次尝试无法建立连接的话，会发送一系列的包。burst 选项总是发送一系列的包，即使第一次尝试也是这样。如果没有明确的允许的话不要使用 burst 选项，有可能被封禁。
配置自己的 NTP 服务器
如果建立一个 NTP 服务器，你需要添加 local clock 作为一个服务器，这样，即便它失去网络连接，它也可以继续为网络提供服务;添加 local clock 作为一个 stratum 10 服务器 (使用 fudge 命令)这样它就只会在失去连接时使用本地时钟：
server 127.127.1.0 fudge 127.127.1.0 stratum 10
下一步，定义规则允许客户端连接你的服务(localhost 也被认为是一个客户端)。使用 restrict 命令；你应该在文件中已经有一行：
restrict default nomodify nopeer noquery
This restricts everyone from modifying anything and prevents everyone from querying the status of your time server:
nomodify prevents reconfiguring your ntpd (with ntpq or ntpdc), and
noquery prevents dumping status data from your ntpd (also with ntpq or ntpdc).
You can also add other options:
restrict default kod nomodify notrap nopeer noquery
Full docs for the "restrict" option are in
man ntp_acc. See https://support.ntp.org/bin/view/Support/AccessRestrictions for detailed instructions.
Following this line, you need to tell ntpd what to allow through into your server; the following line is enough if you are not configuring an NTP server:
If you want to force DNS resolution to the IPv6 namespace, write
-6 before the IP address or host name (
-4 forces IPv4 instead), for example:
restrict -6 default kod nomodify notrap nopeer noquery restrict -6 ::1 # ::1 is the IPv6 equivalent for 127.0.0.1
Lastly, specify the drift file (which keeps track of your clock's time deviation) and optionally the log file location:
driftfile /var/lib/ntp/ntp.drift logfile /var/log/ntp.log
A very basic configuration file will look like this (all comments have been stripped out for clarity):
server 0.pool.ntp.org iburst server 1.pool.ntp.org iburst server 2.pool.ntp.org iburst server 3.pool.ntp.org iburst restrict default kod nomodify notrap nopeer noquery restrict -6 default kod nomodify notrap nopeer noquery restrict 127.0.0.1 restrict -6 ::1 driftfile /var/lib/ntp/ntp.drift logfile /var/log/ntp.log
其他关于配置 NTP 的资源
In conclusion, never forget man pages:
man ntp.conf is likely to answer any doubts you could still have (see also the related man pages:
# ntpd -qg # hwclock -s
ntpd -qg 与
ntpdate 程序效果相同，而ntpdate 已经不推荐使用.
hwclock -s 把时间存储到硬件时钟上，这样重启的时候就不会丢失了。
-g 选项允许时钟漂移大于警报级别(默认是 15 分钟)而不发出警告。注意这种误差是不正常的，也许意味着失去设置错误，时钟芯片错误，或仅仅是长时间的忽略。如果在这些情况下你不想设置时钟而且输出错误到 syslog，删除
# ntpd -q
Synchronize once at boot time
If you want to synchronize your system clock once every time the system boots, you can add a
ntpd -qg & line to your
/etc/rc.local. See Autostarting for alternative methods.
In order for this method to work you have to make sure that, when
rc.local is executed, the network connection has already been initialized (for example you should not background essential network-related daemons in
ntpd sets 11 minute mode, which syncs the system clock to hardware every 11 minutes. The hwclock daemon measures hardware clock drift and syncs it, which conflicts with ntpd.
Stop the hwclock daemon (if it is running):
# rc.d stop hwclock
Start the ntpd daemon:
# rc.d start ntpd
Add ntpd to your DAEMONS array so it starts automatically on boot and make sure hwclock is disabled:
DAEMONS=(... !hwclock ntpd ...)
ntpd can be brought up/down along with a network connection through the use of NetworkManager's dispatcher scripts. You can install the needed script from [community]:
# pacman -S networkmanager-dispatcher-ntpd
Running in a chroot
/etc/conf.d/ntpd.conf and change
NTPD_ARGS="-g -u ntp:ntp"
NTPD_ARGS="-g -i /var/lib/ntp -u ntp:ntp"
/etc/ntp.conf to change the driftfile path such that it is relative to the chroot directory, rather than to the real system root. Change:
Create a suitable chroot environment so that getaddrinfo() will work by creating pertinent directories and files (as root):
# mkdir /var/lib/ntp/etc /var/lib/ntp/lib /var/lib/ntp/proc # touch /var/lib/ntp/etc/resolv.conf /var/lib/ntp/etc/services
and by bind-mounting the aformentioned files:
... #ntpd chroot mounts /etc/resolv.conf /var/lib/ntp/etc/resolv.conf none bind 0 0 /etc/services /var/lib/ntp/etc/services none bind 0 0 /lib /var/lib/ntp/lib none bind 0 0 /proc /var/lib/ntp/proc none bind 0 0
# mount -a
Finally, restart the daemon again:
# rc.d restart ntpd
It is relatively difficult to be sure that your driftfile configuration is actually working without waiting a while, as ntpd does not read or write it very often. If you get it wrong, it will log an error; if you get it right, it will update the timestamp. If you do not see any errors about it after a full day of running, and the timestamp is updated, you should be confident of success.
Available alternative to NTPd are Chrony, a dial-up friendly and specifically designed for systems that are not online all the time, and OpenNTPD, part of the OpenBSD project and currently not maintained for Linux.
- Time (简体中文) (更多关于计算机计时的信息)