Installation of ntp
There should be a dedicated user and group to take control of the
ntpd daemon after it
is started. Issue the following commands as the
groupadd -g 87 ntp &&
useradd -c "Network Time Protocol" -d /var/lib/ntp -u 87 \
-g ntp -s /bin/false ntp
Install ntp by running the
./configure --prefix=/usr \
To test the results, issue: make
Now, as the
make install &&
install -v -o ntp -g ntp -d /var/lib/ntp
parameter places the administrative programs in
--enable-linuxcaps: ntpd is
run as user ntp, so use Linux capabilities for non-root clock
option enables Readline support
for ntpdc and
ntpq programs. If
omitted, libedit will be used if
installed, otherwise no readline capabilites will be compiled.
The following configuration file first defines various ntp
servers with open access from different continents. Second, it
creates a drift file where ntpd stores the frequency
offset and a pid file to store the ntpd process ID. Third, it
defines the location for the leap-second definition file
/etc/ntp.leapseconds, that the
checks and updates, when necessary. This script can be run as a
cron job and the ntp developers
recommend a frequency of about three weeks for the updates. Since
the documentation included with the package is sparse, visit the
ntp website at http://www.ntp.org/ and http://www.pool.ntp.org/ for more
cat > /etc/ntp.conf << "EOF"
# North America
# South America
You may wish to add a “Security
session”. For explanations, see
cat >> /etc/ntp.conf << "EOF"
# Security session
restrict default limited kod nomodify notrap nopeer noquery
restrict -6 default limited kod nomodify notrap nopeer noquery
Synchronizing the Time
There are two options. Option one is to run ntpd continuously and allow it
to synchronize the time in a gradual manner. The other option is
to run ntpd
periodically (using cron) and update the time each time
ntpd is scheduled.
If you choose Option one, then install the
ntpd.service unit included in the
If you prefer to run ntpd periodically, add the
following command to
calc_tickadj, ntp-keygen, ntp-wait, ntpd,
ntpdate, ntpdc, ntpq, ntptime, ntptrace, sntp, tickadj and
calculates optimal value for tick given ntp drift file.
generates cryptographic data files used by the NTPv4
authentication and identification schemes.
is useful at boot time, to delay the boot sequence until
set the time.
is a ntp daemon that runs in the background and keeps the
date and time synchronized based on response from
configured ntp servers. It also functions as a ntp
is a client program that sets the date and time based on
the response from an ntp server. This command is
is used to query the ntp daemon about its current state
and to request changes in that state.
is a utility program used to monitor ntpd operations and
reads and displays time-related kernel variables.
traces a chain of ntp servers back to the primary source.
is a Simple Network Time Protocol (SNTP) client.
reads, and optionally modifies, several
timekeeping-related variables in older kernels that do
not have support for precision timekeeping.
is a script to verify and, if necessary, update the
leap-second definition file.
Last updated on 2016-06-11 00:26:20 -0500