Beyond Linux® From Scratch - Version 7.4

Chapter 15. Networking Programs

ntp-4.2.6p5

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.

This package is known to build and work properly using an LFS-7.4 platform.

Package Information

ntp Dependencies

Required

libcap2-2.22

Optional

OpenSSL-1.0.1e and libedit

User Notes: http://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

Install ntp by running the following commands: 


./configure --prefix=/usr         \
            --sysconfdir=/etc     \
            --enable-linuxcaps    \
            --with-binsubdir=sbin \
            --with-lineeditlibs=readline &&
make

To test the results, issue: make check.

Now, as the root user: 

make install &&
install -v -o ntp -g ntp -d /var/lib/ntp &&
install -v -m755 -d /usr/share/doc/ntp-4.2.6p5 &&
cp -v -R html/* /usr/share/doc/ntp-4.2.6p5/

Command Explanations

--with-binsubdir=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 option enables Readline support for ntpdc and ntpq programs. If omitted, libedit will be used if installed, otherwise no readline capabilites will be compiled.

Configuring ntp

Config Files

/etc/ntp.conf

Configuration Information

The following configuration file defines various ntp servers with open access from different continents. It also 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 http://www.ntp.org/ and http://www.pool.ntp.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   /var/run/ntpd.pid
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 /etc/rc.d/init.d/ntp init script included in the blfs-bootscripts-20130908 package. 

make install-ntpd

If you prefer to run ntpd periodically, add the following command to root's crontab: 

ntpd -q

Execute the following command if you would like to set the hardware clock to the current system time at shutdown and reboot: 

ln -v -sf ../init.d/setclock /etc/rc.d/rc0.d/K46setclock &&
ln -v -sf ../init.d/setclock /etc/rc.d/rc6.d/K46setclock

The other way around is already set up by LFS.

Contents

Installed Programs: ntp-keygen, ntp-wait, ntpd, ntpdate, ntpdc, ntpq, ntptime, ntptrace, sntp and tickadj
Installed Libraries: None
Installed Directory: /usr/share/doc/ntp-4.2.6p5

Short Descriptions

ntp-keygen

generates cryptographic data files used by the NTPv4 authentication and identification schemes.

ntp-wait

is useful at boot time, to delay the boot sequence until ntpd has set the time.

ntpd

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 server.

ntpdate

is a client program that sets the date and time based on the response from an ntp server. This command is deprecated.

ntpdc

is used to query the ntp daemon about its current state and to request changes in that state.

ntpq

is an utility program used to monitor ntpd operations and determine performance.

ntptime

reads and displays time-related kernel variables.

ntptrace

traces a chain of ntp servers back to the primary source.

sntp

is a Simple Network Time Protocol (SNTP) client.

tickadj

reads, and optionally modifies, several timekeeping-related variables in older kernels that do not have support for precision timekeeping.

Last updated on 2013-08-20 18:40:33 -0700