NTP client / NTP server

See also NTP

Note: most devices supported by OpenWrt do not have a hardware clock.

You can set the system date and time using one of the following methods:

  • Manually by utilizing busybox-date, e.g.
    date -s  hh:mm[:ss] or [YYYY.]MM.DD-hh:mm[:ss] or YYYY-MM-DD hh:mm[:ss] or [[[[[YY]YY]MM]DD]hh]mm[.ss]
  • Network Time Protocol by invoking busybox-ntpd once, e.g.:
    ntpd -q -p ptbtime1.ptb.de

    , or configure /etc/config/system accordingly to have nptd run as NTP client (and optionally additionally as NTP server) daemon. By default busybox-ntpd runs as a client and does not serve time. You can set the UCI option enable_server in /etc/config/system (in the ntp section) to enable serving time as well.

  1. Other NTP packages If the default busybox-ntpd isn't sufficient, one of the following alternate ntpd packages can be installed:
Name Version Size Description
ntpclient 2007_365-4 12.970 NTP client for setting system time from NTP servers.
ntpd 4.2.6p4-1 168.021 The ISC ntp suite is a collection of tools used to synchronize the system clock with remote NTP time servers and run/montior local NTP servers. This package contains the ntpd server. See ntpd
ntpd-ssl 4.2.6p4-1 179.511 The ISC ntp ... . This package contains the ntpd server with OpenSSL support.
ntpdate 4.2.6p4-1 36.642 The ISC ntp ... . This package contains ntpdate. See ntpdate
ntp-utils 4.2.6p4-1 158.035 The ISC ntp ... . This package contains ntpdc and ntpq.

NTP (Network Time Protocol) is used to keep computer clocks accurate by synchronizing them over the Internet or a local network, or by following an accurate hardware receiver that interprets GPS, DCF-77, NIST or similar time signals.

This package contains the NTP daemon and utility programs. An NTP daemon needs to be running on each host that is to have its clock accuracy controlled by NTP. The same NTP daemon is also used to provide NTP service to other hosts.

In R28612 and R28613 busybox-rdate has been replaced with busybox-ntpd by default.
If you check the entire file Config.in not only the diffs above, you will learn that busybox-ntpd is employable as server as well by default.

The busybox-ntpd will auto-tune its sync rate depending on clock drift and other factors, it varies between 1-60min, and yes its a daemon which keeps syncing the time. When invoking it with -q it would act like ntpdate, means do a burst poll/sync cycle and exit.

See opkg for more details on using the OpenWrt package manager.

By default, busybox-ntpd, can supply both a client for setting time, and a server for supplying time to the local net. This is installed out of the box and should take care of most time syncing needs. It doesnt support advanced features like query, so the server cannot be monitored from other systems like Nagios.

Some packages, such as luci-app-ntpc and ntpclient, may conflict with the built-in busybox-ntpd installation. If an NTP client or server fails to work as expected, you can check if there is another program using the NTP port by calling netstat -np | grep 123 to search for clients, and netstat -nlp | grep 123 to look for servers.

Example (install the real ntpd package (=not busybox-ntpd):

opkg update
opkg install ntpd
/etc/init.d/sysntpd disable
/etc/init.d/ntpd enable
/etc/init.d/ntpd start
netstat -l | grep ntp

When you use ntpd, make sure you disable sysntpd daemon. An ntpd server should be listening on the default NTP port (UDP 123).

By default, it runs as a client and does not serve time to other peers. A server can be enabled by adding the flag “-l” to “local args” in /etc/init.d/sysntpd (line 23). Starting with Backfire 10.3.1 this is not anymore needed and can be also changed in /etc/config/system.

ntpdate is a command line tool that usually is used for one time synchronizations with remote ntp peers:

ntpdate pool.ntp.org

and also in conjuction with /etc/crontabs/root

  • ntpd is a daemon that runs all the time in the background for permanent synchronization.

According to Debian the same NTP daemon is also used to provide NTP service to other hosts.

To use ntpd as NTP client daemon, no change to the firewall is required, to run as NTP server daemon, open port 123 UDP for your NTP clients (which is by default open in LAN). An example to run ntpd as a server:

driftfile  /var/lib/ntp/ntp.drift

server 0.openwrt.pool.ntp.org iburst
server 1.openwrt.pool.ntp.org iburst
server 2.openwrt.pool.ntp.org iburst
server 3.openwrt.pool.ntp.org iburst

#exchange time with everybody but dont allow configuration (noquery to forbid query)
restrict -4 default kod notrap nomodify nopeer
restrict -6 default kod notrap nomodify nopeer

#local users may interrogate the ntp server more closely
restrict ::1

Depending on your configuration ntpd won't start properly when

restrict ::1

is not set. When ntpd is started and it tries to connect to a server for which only a hostname is known, e.g. 0.openwrt.pool.ntp.org, and for some reason DNS service is not available yet (e.g. you are on a dial-up connection and it takes some time to set everything up), then without the above snippet you'll find two processes of ntpd running (one as user 'root', the other as user 'ntp') and you will have errors like this in the log:

ntp_intres.request: permission denied

The explanation I found at https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=571469. The default configuration above sets “nomodify”. That configuration on localhost “will prevent the resolver process from adding the peers.” [...] “The nomodify will only be a problem in case the resolver process needs to be started, which it does when it can't resolve the hostsnames when ntpd starts. So this is mostly when the network isn't up yet.” (explanation by Kurt, from Debian bug report mentioned above) (sic)

First of all: rdate is old, very simple and does not give you highly reliable time. If you still want to run a server for rdate clients for some reason you can use the xinetd package.

After installing xinetd and running “/etc/init.d/xinetd enable”, create a file “/etc/xinetd.d/time-stream” with the following content:

service time
	disable = no
	id		= time-stream
	type		= INTERNAL
	wait		= no
	socket_type	= stream
	flags		= IPv4

Finally run “/etc/init.d/xinetd restart” and your rdate-timeserver should be up and running.

You can test any NTP server (including those in OpenWRT) by using the ntpdate utility, which is available in most Linux distributions.

ntpdate -q [OpenWRT IP Address]

This should return something like:

server, stratum 2, offset -0.909611, delay 0.02853
30 Nov 00:43:21 ntpdate[44]: step time server offset -0.909611 sec

If your system uses chrony instead of ntpdate, you need to add the server to your config file, even if you're just testing it. To do so:

  1. Add server [OpenWRT IP] iburst noselect to your chrony.config - this will allow you to query the server, without using it to set system time.
  2. Run chronyc ntpdata [OpenWRT IP] - this will return data about the NTP server. You may need to be root to execute this command.

To enable syslog to show ntpd updates create /etc/hotplug.d/ntp/20-ntpd-logger and put the following into it. Reboot and ntpd will log updates to syslog.

[ $ACTION = "step" ]    && logger -t ntpd Time set, stratum=$stratum interval=$poll_interval offset=$offset
[ $ACTION = "stratum" ] && logger -t ntpd Stratum change, stratum=$stratum interval=$poll_interval offset=$offset

Log Output:

Wed Jan  5 18:18:54 2022 user.notice ntpd: Stratum change, stratum=2 interval=2048 offset=0.007304
Wed Jan  5 18:18:54 2022 user.notice ntpd: Stratum change, stratum=3 interval=2048 offset=0.009748
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  • Last modified: 2022/01/06 18:47
  • by mercygroundabyss