Introduction to ntp
The ntp package contains a client
and server to keep the time synchronized between various computers
over a network. This package is the official reference
implementation of the NTP protocol.
For most systemd installations systemd-timesyncd provides for
simple time synchronization. This package is not needed unless you
need to run an NTP time Server or want to connect to local hardware
clocks
![[Note]](../images/note.png)
Note
This package is known to build and work
properly using an LFS 13.0 platform.
Package Information
ntp Dependencies
Required
IO-Socket-SSL-2.098
Optional
libcap-2.77 with PAM, libevent-2.1.12,
libedit, and libopts from
AutoGen
Editor Notes: https://wiki.linuxfromscratch.org/blfs/wiki/ntp
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 root user:
groupadd -g 87 ntp &&
useradd -c "Network Time Protocol" -d /var/lib/ntp -u 87 \
-g ntp -s /bin/false ntp
First fix build issues identified when glibc-2.43 was introduced:
sed -i 's/getclock/getclock memchr/' sntp/m4/ntp_libntp.m4 &&
sed -i 's/pthread_detach(NULL)/pthread_detach(0)/' sntp/m4/openldap-thread-check.m4 &&
autoreconf -fiv
Then apply an upstream fix to prevent a segfault:
sed -i "/ep.*FAILED/,+4s/ep/ep2/" ntpd/ntp_io.c
Install ntp by running the
following commands:
./configure --prefix=/usr \
--bindir=/usr/sbin \
--sysconfdir=/etc \
--enable-linuxcaps \
--with-lineeditlibs=readline \
--docdir=/usr/share/doc/ntp-4.2.8p18 &&
make
To test the results, issue: make
check. Three tests (test-crypto,
test-packetHandling, and test-packetProcessing) are known to fail
due to using OpenSSL 3.5.2 and later.
Now, as the root user:
make install &&
install -v -o ntp -g ntp -d /var/lib/ntp
Command Explanations
--bindir=/usr/sbin: This
parameter places the administrative programs in /usr/sbin.
--enable-linuxcaps: ntpd is
run as user ntp, so use Linux capabilities for non-root clock
control.
--with-lineeditlibs=readline: This
switch enables Readline support
for ntpdc and
ntpq programs. If
omitted, libedit will be used if
installed, otherwise no readline capabilities will be compiled.
Configuring ntp
Config Files
/etc/ntp.conf
Configuration Information
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. Since the
documentation included with the package is sparse, visit the ntp
website at https://www.ntp.org/ and https://www.ntppool.org/ for more
information.
cat > /etc/ntp.conf << "EOF"
# Asia
server 0.asia.pool.ntp.org
# Australia
server 0.oceania.pool.ntp.org
# Europe
server 0.europe.pool.ntp.org
# North America
server 0.north-america.pool.ntp.org
# South America
server 2.south-america.pool.ntp.org
driftfile /var/lib/ntp/ntp.drift
pidfile /run/ntpd.pid
EOF
You may wish to add a “Security session.” For explanations, see
https://www.eecis.udel.edu/~mills/ntp/html/accopt.html#restrict.
cat >> /etc/ntp.conf << "EOF"
# Security session
restrict default limited kod nomodify notrap nopeer noquery
restrict -6 default limited kod nomodify notrap nopeer noquery
restrict 127.0.0.1
restrict ::1
EOF
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 blfs-systemd-units-20251204 package.
make install-ntpd
In addition, you should disable an incompatible service. As the
root user:
systemctl disable systemd-timesyncd.service
If you prefer to run ntpd periodically, add the
following command to root's
crontab:
ntpd -q