Network Time Protocol daemon (简体中文)

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本文介绍Arch Linux中,如何让系统时间和标准时间同步的方法。第一种是openntpd:一种比较简单的方法;第二种,最完备的方法:ntpd。

OpenNTPD

用OpenNTPD替代ntpd

OpenNTPD is a FREE, easy to use implementation of the Network Time Protocol. 能够使本地时间和NTP服务器的时间同步,同时也能使本地时间变成一个NTP服务器,发布给其他用户。

OpenNTPD is primarily developed by Henning Brauer as part of the OpenBSD Project.

OpenNTPD is a brand new implementation of the ntp protocol. 相对于NTPD,OpenNTPD比较容易配置和使用。

首先,安装 OpenNTPD package ——这包Arch Linux社区已经提供了(in the Arch Linux community repository)。

pacman -S openntpd

安装完后,必须编辑配置文件: /etc/ntpd.conf

默认配置已经做好,本身就能够同步网络和本地时间。

# $OpenBSD: ntpd.conf,v 1.7 2004/07/20 17:38:35 henning Exp $
# sample ntpd configuration file, see ntpd.conf(5)

# Addresses to listen on (ntpd does not listen by default)
#listen on *
#listen on 127.0.0.1
#listen on ::1

# sync to a single server
#server ntp.example.org

# use a random selection of 8 public stratum 2 servers
# see http://twiki.ntp.org/bin/view/Servers/NTPPoolServers
servers pool.ntp.org

如果要和特定的服务器时间同步,去掉注释,并把服务器地址替换掉 "ntp.example.org"。

server ntp.example.org

The "servers" directive works the same as the "server" directive, however, if the dns name resolves to multiple IP address, ALL of them will be synced to. 其实,默认的 "pool.ntp.org"已经可以满足大部分要求了。具体的时间服务器可以到这查看:www.pool.ntp.org/zone/asia

pool.ntp.org

Any number of "server" or "servers" directives may be used.

If you want the computer you run OpenNTPD on to also be a time server, simply uncomment and edit the "listen" directive.

For example:

listen on *

will listen on all interfaces.

and

listen on 127.0.0.1

will only listen on the loopback interface.

If you would like to run OpenNTPD at boot, add openntpd the DAEMONS variable in your /etc/rc.conf.

查看同步进度,可以查看 /var/log/daemon.log

即刻同步时间:

net time set /bin/date

ntp

pacman -S ntp

/etc/ntp.conf Configuration

The very first line of your ntp.conf file should contain a line such as the following:

restrict default noquery notrust nomodify

This essentially restricts everyone from modifying anything. Following this, you need to let ntpd know what you want to let through into your NTP server. Here is where you would specify any other ip addresses you would like to synchronize on your NTP server. For example:

restrict 1.2.3.4
restrict 192.168.0.0 mask 255.255.255.0 nomodify

This tells ntpd that 1.2.3.4 and all ip addresses from the 192.168.0.0 range will be allowed to synchronize on this server, but they will not be allowed to modify anything. All other IP addresses in the world will still obey the default restrictions (the first line in the ntp.conf).

Now, is where the stratum 2 servers that our server will synchronize with come into play. The lines in ntp.conf will be used to tell ntpd what servers we would like to use for synchronizing (these are just examples; use ntp servers that are closest to your location). Please see http://ntp.isc.org/bin/view/Servers/NTPPoolServers for a list a closer servers.

server ntp1.cs.wisc.edu
server ntp3.cs.wisc.edu
server ntp3.sf-bay.org

Unless you have a good reason not to, it is advisable to use the pool.ntp.org servers: http://www.pool.ntp.org/. Alternatively, a list of ntp servers is available at http://www.eecis.udel.edu/~mills/ntp/clock2a.html. Please pay attention to the Access Policies.

If we left it alone right now, we would never connect to a server because the response from any of the three servers listed above would never be allowed back into our server due to the fact that our default restrict statement would be in use (since we did not add the servers to our lesser restrictions (like we did with 127.0.0.1 and the subnet of 192.168.0.0).

To correct this, enter the following lines in ntp.conf:

restrict ntp1.cs.wisc.edu noquery nomodify
restrict ntp3.cs.wisc.edu noquery nomodify
restrict ntp3.sf-bay.org noquery nomodify

This will allow the response from the above servers into our system so our local clock can be synchronized. The noquery restriction will not allow any of the above three servers to query for information from our server. The nomodify restriction will not allow the three servers to modify anything (synchronization will still take place).

The only thing left to do is add the drift file (which keeps track of yours clocks time deviation). and the log file location:

driftfile /etc/ntp.drift
logfile /var/log/ntp.log

The complete file will look like this:

# default restrictions
restrict default noquery notrust nomodify

# override the default restrictions here
restrict 10.1.1.0 mask 255.255.255.0 nomodify

# public NTP servers to sync with (all stratum 2)
server ntp1.cs.wisc.edu
server ntp3.cs.wisc.edu
server ntp3.sf-bay.org

restrict ntp1.cs.wisc.edu noquery nomodify
restrict ntp3.cs.wisc.edu noquery nomodify
restrict ntp3.sf-bay.org noquery nomodify

# NTP drift file - used to keep track of your system clocks
# time deviation
driftfile /etc/ntp.drift

# NTP log file
logfile /var/log/ntp.log

Take note that this is for a client and a server ntp.conf configuration. If you just want to synchronize with a stratum server and are not concerned with other PCs synchronizing with your ntp server, then you can do something like the following (note that only 127.0.0.1 is allowed to be synchronized):

# default restrictions
restrict default noquery notrust nomodify

# Permit all access over the loopback interface
restrict 127.0.0.1

# public NTP servers to sync with (all stratum 2)
server ntp1.cs.wisc.edu
server ntp3.cs.wisc.edu
server ntp3.sf-bay.org

restrict ntp1.cs.wisc.edu noquery nomodify
restrict ntp3.cs.wisc.edu noquery nomodify
restrict ntp3.sf-bay.org noquery nomodify

# NTP drift file - used to keep track of your system clocks
# time deviation
driftfile /etc/ntp.drift

# NTP log file
logfile /var/log/ntp.log

... or if you don't care about restrictions at all, something like this (note there are no restrictions, thus no need to reduce restrictions for 127.0.0.1 to allow your local clock to synchronize):

# public NTP servers to sync with (all stratum 2)
server ntp1.cs.wisc.edu
server ntp3.cs.wisc.edu
server ntp3.sf-bay.org

# NTP drift file - used to keep track of your system clocks
# time deviation
driftfile /etc/ntp.drift

# NTP log file
logfile /var/log/ntp.log


A Note about Security

You may wonder about all of the restrict lines. The reason for them is security. If you don't want a secure NTP server, don't add any restrict lines to your ntp.conf file. If you want a secure NTP server, start out by adding a default restrict that doesn't allow anything to contact your server, then add more (less restrictive) restrict lines - allowing certain addresses various access privileges.


/etc/rc.d/network file modification

One more thing that you may want to do. 大多数情况下, /etc/ntp.conf 会被dhcp重写,为防止发生这情况,编辑 the /etc/conf.d/dhcpcd , add -N to the line that starts with 'dhcpcd -t 10'.


FYI: This was my experience/solution with setting the time.

On my system my /etc/conf.d/dhcpcd contains a single line:

    DHCPCD_ARGS="-t 30 -h $HOSTNAME"

I assume it needs to be changed to:

    DHCPCD_ARGS="-N -t 30 -h $HOSTNAME"

Some have suggested adding -R to preserve /etc/resolv.conf as well.

To fix Time use /etc/rc.local

To set the correct time; Set time and start ntpd at boot via /etc/rc.local


Relevant sections of /etc/rc.conf


    HARDWARECLOCK="UTC"
    TIMEZONE="US/Mountain"
    
    Network/ DHCP section:
       
    lo="lo 127.0.0.1"
    eth0="dhcp"
    INTERFACES=(lo eth0)
    
    Daemons subsection:
    
    DAEMONS=(syslog-ng hotplug !pcmcia network netfs !ntpd crond dbus hal alsa gdm)

This is my /etc/rc.local


    #!/bin/bash
    #
    # /etc/rc.local: Local multi-user startup script.
    #
    
    # Re-copy ntp.conf (was over written by dhcp)
    cp /root/CONFIG.BAK/ntp.conf.bac /etc/ntp.conf
    # I advise you keep your desired /etc/ntp.conf
    # OUTSIDE of /etc
    
    # Set time
    /usr/bin/ntpdate ntp.nasa.gov #Use any time server you like here
    
    # Start ntpd
    /etc/rc.d/ntpd start


And here is my /root/CONFIG.BAK/ntp.conf.bac (this is just a copy of the desired /etc/ntp.conf)


    # default restrictions
    restrict default noquery notrust nomodify
    
    # override the default restrictions here
    restrict 127.0.0.1 nomodify
    restrict 192.168.2.0 mask 255.255.255.0 nomodify
    
    # public NTP servers to sync with (all stratum 2)
    server ntp.nasa.gov #Use any time server you like here
    
    restrict ntp.nasa.gov noquery nomodify
    
    # NTP drift file - used to keep track of your system clocks
    driftfile /etc/ntp.drift
    
    # NTP log file
    logfile /var/log/ntp.log


Leave /etc/conf.d/dhcpcd at default. Mine is a single line and reads


    DHCPCD_ARGS="-t 30 -h $HOSTNAME"


With this configuration I get the correct time and ntpd running at boot. There may be a better way, but this worked for me. I hope it helps.


Updating your system immediately using ntpdate

建议在/etc/rc.local加上下面一行,这样在系统启动时,就能和NTP时间同步 (服务器地址用一个对你来说快点的 NTP 服务器).

/usr/bin/ntpdate ntp1.cs.wisc.edu

Running ntpdate when you boot up is a good idea because ntpd may take a long time to synchronize your local clock depending on how far off the time is. If your clock is synchronized when ntpd starts, then it's sole purpose is to keep it synchronized. To run ntpd at startup, add ntpd to the daemons section of the /etc/rc.conf file.

ntpd will work well if you have a connection to the internet all the time. If you are using dialup, you may just want to stick with using ntpdate via the command line.

Querying your NTP server using ntpq

There is a default restrict statement for the localhost that includes an ignore flag. Without overriding it (adding the line restrict 127.0.0.1) you will not be able to query your NTP server. If that's not a concern to you, then leave out the restrict line for your localhost. You will still be able to synchronize with your stratum 2 servers.

External Resources