The NTP "ntpdc" shell command "peers" returns "localhost: timed out, nothing received"

Question

I'm running Ubuntu MATE 16.04 (Xenial Xerus) - 64-bit "Desktop" version - in a HP laptop computer.

I have a question regarding NTP (Network Time Protocol): if i run the command "ntpq -p", I then get the following results:

$ ntpq -p
     remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
 0.ubuntu.pool.n .POOL.          16 p    -   64    0    0.000    0.000   0.000
 1.ubuntu.pool.n .POOL.          16 p    -   64    0    0.000    0.000   0.000
 2.ubuntu.pool.n .POOL.          16 p    -   64    0    0.000    0.000   0.000
 3.ubuntu.pool.n .POOL.          16 p    -   64    0    0.000    0.000   0.000
 ntp.ubuntu.com  .POOL.          16 p    -   64    0    0.000    0.000   0.000
-mirrors.dominio 195.220.94.163   3 u   43  256  377   15.209    0.548   0.786
+ntp02.oal.ul.pt 194.117.9.138    2 u  194  256  377   10.934   -0.398   0.783
+a88-157-128-22. 212.113.174.246  3 u    7  256  377    7.905   -0.105   0.156
-smtp-in1.aqea.n 194.117.9.136    3 u  120  256  377   10.117    0.000   0.269
*ns.rnl.tecnico. 131.188.3.222    2 u   56  256  377   11.111    0.135   9.384

However, if I run the "peers" command in an "ntpdc" shell, I get an error message:

$ ntpdc
ntpdc> peers
localhost: timed out, nothing received
***Request timed out
ntpdc> quit

I haven't changed the NTP configuration file (/etc/ntp.conf) from its default configuration. The drift file / driftfile "/var/lib/ntp/ntp.drift" did not exist, so I created it using "touch /var/lib/ntp/ntp.drift", changed its ownership to the "ntp" user and group (using "chown ntp:ntp /var/lib/ntp/ntp.drift") and even rebooted the computer. This did not make any difference.

The "localhost: timed out, nothing received" error happens regardless if I run it as "ntpdc" or "sudo ntpdc", and it happens regardless if I'm running the "ufw" firewall or not.

The log file /var/log/syslog has the following seemingly related entries:

Jul 17 14:48:08 myhostname ntpd[1467]: kernel reports TIME_ERROR: 0x41: Clock Unsynchronized
Jul 17 14:52:16 myhostname ntpd[1467]: 91.189.89.199 local addr 192.168.1.2 -> <null>
Jul 17 14:52:20 myhostname ntpd[1467]: 91.189.94.4 local addr 192.168.1.2 -> <null>
Jul 17 14:52:34 myhostname ntpd[1467]: 5.135.59.152 local addr 192.168.1.2 -> <null>
Jul 17 14:52:40 myhostname ntpd[1467]: 62.48.148.210 local addr 192.168.1.2 -> <null>

I'm guessing that the error "kernel reports TIME_ERROR: 0x41: Clock Unsynchronized" is relevant.

The "ntp" service is running:

$ systemctl status ntp
● ntp.service - LSB: Start NTP daemon
   Loaded: loaded (/etc/init.d/ntp; bad; vendor preset: enabled)
   Active: active (running) since Dom 2016-07-17 14:42:23 WEST; 1h 20min ago
     Docs: man:systemd-sysv-generator(8)
  Process: 1442 ExecStart=/etc/init.d/ntp start (code=exited, status=0/SUCCESS)
   CGroup: /system.slice/ntp.service
           └─1467 /usr/sbin/ntpd -p /var/run/ntpd.pid -g -u 109:116

Jul 17 14:42:27 myhostname ntpd[1467]: Soliciting pool server 62.48.148.210
Jul 17 14:42:27 myhostname ntpd[1467]: receive: Unexpected origin timestamp from 5.135.59.152
Jul 17 14:42:28 myhostname ntpd[1467]: Soliciting pool server 2001:690:2100:80::1
Jul 17 14:42:28 myhostname ntpd[1467]: Soliciting pool server 91.189.89.199
Jul 17 14:42:29 myhostname ntpd[1467]: Soliciting pool server 91.189.94.4
Jul 17 14:48:08 myhostname ntpd[1467]: kernel reports TIME_ERROR: 0x41: Clock Unsynchronized
Jul 17 14:52:16 myhostname ntpd[1467]: 91.189.89.199 local addr 192.168.1.2 -> <null>
Jul 17 14:52:20 myhostname ntpd[1467]: 91.189.94.4 local addr 192.168.1.2 -> <null>
Jul 17 14:52:34 myhostname ntpd[1467]: 5.135.59.152 local addr 192.168.1.2 -> <null>
Jul 17 14:52:40 myhostname ntpd[1467]: 62.48.148.210 local addr 192.168.1.2 -> <null>

Could you help me to troubleshoot this, please?

Answer 1

ntpdc uses mode 7 requests and ntpq uses mode 6 requests. Mode 7 requests are often used as a DDoS and therefore newer default configurations have mode 7 requests blocked. You can get all of the information you need from ntpq -p. There is no need to use ntpdc, but do not take my word for it:

ntpdc is deprecated - please use ntpq now, as it uses a more sane interface and can provide all of the information that ntpdc used to provide.

https://www.eecis.udel.edu/~mills/ntp/html/ntpdc.html

Answer 2

To enable mode 7 use the following option in the ntp config file

# enable mode 7 to support ntpdc
enable mode7