Инсталирайте NTP услуга:
apt-get install ntp

Конфигурираме etc/ntp.conf
#ntp-conf
driftfile /var/lib/ntp/ntp.drift

# Enable this if you want statistics to be logged.
#statsdir /var/log/ntpstats/
statistics loopstats peerstats clockstats
filegen loopstats file loopstats type day enable
filegen peerstats file peerstats type day enable
filegen clockstats file clockstats type day enable

# GUDE Expert mouseCLOCK
server 127.127.8.0 mode 19 prefer
fudge 127.127.8.0 flag2 1 stratum 0 refid DCF

# Specify one or more NTP servers.
# Use servers from the NTP Pool Project. Approved by Ubuntu Technical Board
# on 2011-02-08 (LP: #104525). See http://www.pool.ntp.org/join.html for
# more information.
#server time.fu-berlin.de # time.fu-berlin.de (LCL)
#server ptbtime1.ptb.de
#server ptbtime2.ptb.de

# options
enable calibrate

# By default, exchange time with everybody, but don't allow configuration.
restrict -4 default kod notrap nomodify nopeer noquery
restrict -6 default kod notrap nomodify nopeer noquery

# Local users may interrogate the ntp server more closely.
restrict 127.0.0.1 # Localhost erlauben
restrict 127.127.8.0
restrict ::1

# If you want to provide time to your local subnet, change the next line.
# (Again, the address is an example only.)
broadcast 192.168.1.255

Добавяме устройството:
ln -s /dev/ttyUSB0 /dev/refclock-0

Създаване на UDEV правило:
sudo nano /etc/udev/rules.d/05-persistent-dcf.rules
KERNEL=="ttyUSB*", ATTRS{idProduct}=="e88a", SYMLINK+="refclock-%m"

Рестартирайте услугата:
udevadm trigger
sudo /etc/init.d/ntp restart

Тест на часовника
watch -n1 ntpq -c cv -c rv

Трябва да видите нещо такова:
associd=0 status=0020 , 2 events, clk_unspec,
device="RAW DCF77 CODE (Expert mouseCLOCK USB v2.0)",
timecode="--#--###---------D--S1-4-1-4p-24---p12----1-4---8--2--1---P",
poll=12, noreply=0, badformat=0, baddata=1, fudgetime1=425.000,
stratum=0, refid=DCF, flags=2,
refclock_time="d3c5d844.00000000 Fri, Aug 3 2012 4:55:32.000",
refclock_status="DST; TIME CODE; (LEAP INDICATION; ANTENNA)",
refclock_format="RAW DCF77 Timecode",
refclock_states="*NOMINAL: 00:10:33 (88.16%); ILLEGAL DATE: 00:01:25 (11.83%); running time: 00:11:58"
associd=0 status=0214 leap_none, sync_lf_radio, 1 event, freq_mode,
version="ntpd Този имейл адрес е защитен от спам ботове. Трябва да имате пусната JavaScript поддръжка, за да го видите. Tue Jun 5 20:12:08 UTC 2015 (1)",
processor="x86_64", system="Linux/3.2.0-29-generic", leap=00, stratum=1,
precision=-22, rootdelay=0.000, rootdisp=31.196, refid=DCF,
reftime=d3c5d838.75cb8306 Fri, Aug 3 2015 6:55:20.460,
clock=d3c5d844.8f4457f4 Fri, Aug 3 2012 6:55:32.559, peer=44449, tc=6,
mintc=3, offset=-43.458, frequency=-3.564, sys_jitter=1.685,
clk_jitter=14.366, clk_wander=1.260

Stratum = 1 означава, че сървъра работи като сървър за време с най-висока точност!