vim /etc/ntp.conf
server 0.at.pool.ntp.org ibrust
server 1.at.pool.ntp.org ibrust

Starten / Stoppen

systemctl <start|stop|status| ntp

root@server:~# ntpq -p
     remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
+mail.somenet.or 178.189.127.149  2 u 1011 1024  377    9.694   -0.695   0.873
*194.112.182.172 193.171.23.163   2 u  267 1024  377    8.813   -0.609   1.137

remote – The remote peer or server being synced to. “LOCAL” is this local host (included in case there are no remote peers or servers available);
refid – Where or what the remote peer or server is itself synchronised to;
st – The remote peer or server Stratum
t – Type (u: unicast or manycast client, b: broadcast or multicast client, l: local reference clock, s: symmetric peer, A: manycast server, B: broadcast server, M: multicast server, see “Automatic Server Discovery“);
when – When last polled (seconds ago, “h” hours ago, or “d” days ago);
poll – Polling frequency: rfc5905 suggests this ranges in NTPv4 from 4 (16s) to 17 (36h) (log2 seconds), however observation suggests the actual displayed value is seconds for a much smaller range of 64 (26) to 1024 (210) seconds;
reach – An 8-bit left-shift shift register value recording polls (bit set = successful, bit reset = fail) displayed in octal;
delay – Round trip communication delay to the remote peer or server (milliseconds);
offset – Mean offset (phase) in the times reported between this local host and the remote peer or server (RMS, milliseconds);
jitter – Mean deviation (jitter) in the time reported for that remote peer or server (RMS of difference of multiple time samples, milliseconds);

The first character displayed in the table (Select Field tally code) is a state flag (see Peer Status Word) that follows the sequence ” “, “x”, “-”, “#”, “+”, “*”, “o”:

” ” – No state indicated for:
    non-communicating remote machines,
    “LOCAL” for this local host,
    (unutilised) high stratum servers,
    remote machines that are themselves using this host as their synchronisation reference;
“x” – Out of tolerance, do not use (discarded by intersection algorithm);
“-” – Out of tolerance, do not use (discarded by the cluster algorithm);
“#” – Good remote peer or server but not utilised (not among the first six peers sorted by synchronization distance, ready as a backup source);
“+” – Good and a preferred remote peer or server (included by the combine algorithm);
“*” – The remote peer or server presently used as the primary reference;
“o” – PPS peer (when the prefer peer is valid). The actual system synchronization is derived from a pulse-per-second (PPS) signal, either indirectly via the PPS reference clock driver or directly via kernel interface.

The refid can have the status values:

An IP address – The IP address of a remote peer or server;
.LOCL. – This local host (a place marker at the lowest stratum included in case there are no remote peers or servers available);
.PPS. – “Pulse Per Second” from a time standard;
.IRIG. – Inter-Range Instrumentation Group time code;
.ACTS. – American NIST time standard telephone modem;
.NIST. – American NIST time standard telephone modem;
.PTB. – German PTB time standard telephone modem;
.USNO. – American USNO time standard telephone modem;
.CHU. – CHU (HF, Ottawa, ON, Canada) time standard radio receiver;
.DCFa. – DCF77 (LF, Mainflingen, Germany) time standard radio receiver;
.HBG. – HBG (LF Prangins, Switzerland) time standard radio receiver;
.JJY. – JJY (LF Fukushima, Japan) time standard radio receiver;
.LORC. – LORAN-C station (MF) time standard radio receiver. Note, no longer operational (superseded by eLORAN);
.MSF. – MSF (LF, Anthorn, Great Britain) time standard radio receiver;
.TDF. – TDF (MF, Allouis, France) time standard radio receiver;
.WWV. – WWV (HF, Ft. Collins, CO, America) time standard radio receiver;
.WWVB. – WWVB (LF, Ft. Collins, CO, America) time standard radio receiver;
.WWVH. – WWVH (HF, Kauai, HI, America) time standard radio receiver;
.GOES. – American Geosynchronous Orbit Environment Satellite;
.GPS. – American GPS;
.GAL. – Galileo European GNSS;
.ACST. – manycast server;
.AUTH. – authentication error;
.AUTO. – Autokey sequence error;
.BCST. – broadcast server;
.CRYPT. – Autokey protocol error;
.DENY. – access denied by server;
.INIT. – association initialized;
.MCST. – multicast server;
.RATE. – (polling) rate exceeded;
.TIME. – association timeout;
.STEP. – step time change, the offset is less than the panic threshold (1000ms) but greater than the step threshold (125ms)