Ubuntu Manpage: timemaster - run NTP with PTP as reference clocks

NAME

       timemaster - run NTP with PTP as reference clocks

SYNOPSIS

       timemaster [ -nmqv ] [ -l print-level ] -f file

DESCRIPTION

       timemaster is a program that uses ptp4l and phc2sys in combination with chronyd or ntpd to
       synchronize the system clock to NTP and PTP time sources. The  PTP  time  is  provided  by
       phc2sys  and  ptp4l  via  SHM reference clocks to chronyd/ntpd, which can compare all time
       sources and use the best sources to synchronize the system clock.

       On start, timemaster reads a configuration file  that  specifies  the  NTP  and  PTP  time
       sources,  checks  which  network  interfaces  have  and  share a PTP hardware clock (PHC),
       generates configuration files for ptp4l and chronyd/ntpd, and start  the  ptp4l,  phc2sys,
       chronyd/ntpd  processes  as  needed.  Then,  it  waits for a signal to kill the processes,
       remove the generated configuration files and exit.

OPTIONS

       -f file
              Specify the path to the timemaster configuration file.

       -n     Don't start the programs, only print their configuration  files  and  the  commands
              that would be executed if this option wasn't specified.

       -l level
              Set  the  maximum  syslog  level of messages which should be printed or sent to the
              system logger. The default value is 6 (LOG_INFO).

       -m     Print messages to the standard output.

       -q     Don't send messages to the system logger.

       -v     Print the software version and exit.

       -h     Display a help message and exit.

CONFIGURATION FILE

The configuration file is divided into sections. Each section starts with a line
containing its name enclosed in brackets and it follows with settings. Each setting is
placed on a separate line, it contains the name of the option and the value separated by
whitespace characters. Empty lines and lines starting with # are ignored.

Sections that can used in the configuration file and options that can be set in them are
described below.

[timemaster]
ntp_program
Select which NTP implementation should be used. Possible values are chronyd and
ntpd. The default value is chronyd. Limitations of the implementations relevant to
the timemaster configuration are listed in NOTES.

rundir Specify the directory where should be generated chronyd, ntpd and ptp4l
configuration files and sockets. The directory will be created if it doesn't exist.
The default value is /var/run/timemaster.

first_shm_segment
Specify the first number in a sequence of SHM segments that will be used by ptp4l
and phc2sys. The default value is 0. Increasing the number can be useful to avoid
conflicts with time sources that are not started by timemaster, e.g. gpsd using
segments number 0 and 1.

restart_processes
Enable or disable restarting of processes started by timemaster. If the option is
set to a non-zero value, all processes except chronyd and ntpd will be
automatically restarted when terminated and timemaster is running for at least one
second (i.e. the process did not terminate due to a configuration error). If a
process was terminated and is not started again, timemaster will kill the other
processes and exit with a non-zero status. The default value is 1 (enabled).

[ntp_server address]
The ntp_server section specifies an NTP server that should be used as a time source. The
address of the server is included in the name of the section.

minpoll
maxpoll
Specify the minimum and maximum NTP polling interval as powers of two in seconds.
The default values are 6 (64 seconds) and 10 (1024 seconds) respectively. Shorter
polling intervals usually improve the accuracy significantly, but they should be
used only when allowed by the operators of the NTP service (public NTP servers
generally don't allow too frequent queries). If the NTP server is located on the
same LAN, polling intervals around 4 (16 seconds) might give best accuracy.

iburst Enable or disable sending a burst of NTP packets on start to speed up the initial
synchronization. Possible values are 1 and 0. The default value is 0 (disabled).

ntp_options
Specify extra options that should be added for this source to the server directive
in the configuration file of the selected NTP implementation. No extra options are
added by default.

[ptp_domain number]
The ptp_domain section specifies a PTP domain that should be used as a time source. The
PTP domain number is included in the name of the section. The ptp4l instances are
configured to run in the slaveOnly mode. In this section at least the interfaces option
needs to be set, other options are optional.

interfaces
Specify which network interfaces should be used for this PTP domain. A separate
ptp4l instance will be started for each group of interfaces sharing the same PHC
and for each interface that supports only SW time stamping. HW time stamping is
enabled automatically. If an interface with HW time stamping is specified also in
other PTP domains, only the ptp4l instance from the first PTP domain will be using
HW time stamping.

ntp_poll
Specify the polling interval of the NTP SHM reference clock reading samples from
ptp4l or phc2sys. It's specified as a power of two in seconds. The default value
is 2 (4 seconds).

phc2sys_poll
Specify the polling interval used by phc2sys to read a PTP clock synchronized by
ptp4l and update the SHM sample for chronyd/ntpd. It's specified as a power of two
in seconds. The default value is 0 (1 second).

delay Specify the maximum assumed roundtrip delay to the primary source of the time in
this PTP domain. This value is included in the distance used by chronyd in the
source selection algorithm to detect falsetickers and assign weights for source
combining. The default value is 1e-4 (100 microseconds). With ntpd, the tos mindist
command can be used to set a limit with similar purpose globally for all time
sources.

ntp_options
Specify extra options that should be added for this source to the refclock or
server directives in the configuration file of the selected NTP implementation. No
extra options are added by default.

ptp4l_option
Specify an extra ptp4l option specific to this PTP domain that should be added to
the configuration files generated for ptp4l. This option may be used multiple times
in one ptp_domain section.

[chronyd]
path Specify the path to the chronyd binary. The default value is chronyd to search for
the binary in PATH.

options
Specify extra options that should be added to the chronyd command line. No extra
options are added by default.

[chrony.conf]
Settings specified in this section are copied directly to the configuration file generated
for chronyd. If this section is not present in the timemaster configuration file, the
following setting will be added:

makestep 1 3

This configures chronyd to step the system clock in the first three updates if the offset
is larger than 1 second.

[ntpd]
path Specify the path to the ntpd binary. The default value is ntpd to search for the
binary in PATH.

options
Specify extra options that should be added to the ntpd command line. No extra
options are added by default.

[ntp.conf]
Settings specified in this section are copied directly to the configuration file generated
for ntpd. If this section is not present in the timemaster configuration file, the
following settings will be added:

restrict default nomodify notrap nopeer noquery
restrict 127.0.0.1
restrict ::1

This configures ntpd to use safe default restrictions.

[phc2sys]
path Specify the path to the phc2sys binary. The default value is phc2sys to search for
the binary in PATH.

options
Specify extra options that should be added to all phc2sys command lines. By
default, -l 5 is added to the command lines.

[ptp4l]
path Specify the path to the ptp4l binary. The default value is ptp4l to search for the
binary in PATH.

options
Specify extra options that should be added to all ptp4l command lines. By default,
-l 5 is added to the command lines.

[ptp4l.conf]
Settings specified in this section are copied directly to the global section of the
configuration files generated for all ptp4l instances. There is no default content of this
section.

Other sections (e.g. [unicast_master_table]) may be specified here, but lines beginning
with the bracket need to be prefixed with the > character to prevent timemaster from
parsing it as a beginning of another section.

NOTES

For best accuracy, chronyd is usually preferred over ntpd, it also synchronizes the system
clock faster. Both NTP implementations, however, have some limitations that need to be
considered before choosing the one to be used in a given timemaster configuration.

The chronyd limitations are:

In version 1.31 and older, the maximum number of reference clocks used at the same
time is 8. This limits the number of PHCs and interfaces using SW time stamping
that can be used for PTP.

Using polling intervals (minpoll, maxpoll, ntp_poll options) shorter than 2 (4
seconds) is not recommended with versions before 1.30. With 1.30 and later values
of 0 or 1 can be used for NTP sources and negative values for PTP sources
(ntp_poll) to specify a subsecond interval.

The ntpd limitations are:

In versions before 4.2.8p1, only the first two shared-memory segments created by
the ntpd SHM refclock driver have owner-only access. Other segments are created
with world access, which allows any user on the system to write to the segments and
disrupt or take control over the synchronization of the clock. In 4.2.8p1 the
access was made configurable with the mode option, which is set by timemaster for
owner-ownly access.

The shortest polling interval for all sources is 3 (8 seconds).

Nanosecond resolution in the SHM refclock driver is supported in version 4.2.7p303
and later, older versions have only microsecond resolution.

EXAMPLES

       A minimal configuration file using one NTP source and two PTP sources would be:

       [ntp_server 10.1.1.1]

       [ptp_domain 0]
       interfaces eth0

       [ptp_domain 1]
       interfaces eth1

       A more complex example using all timemaster options would be:

       [ntp_server 10.1.1.1]
       minpoll 3
       maxpoll 4
       iburst 1
       ntp_options key 12

       [ptp_domain 0]
       interfaces eth0 eth1
       ntp_poll 0
       phc2sys_poll -2
       delay 10e-6
       ntp_options prefer
       ptp4l_option clock_servo linreg
       ptp4l_option delay_mechanism P2P

       [timemaster]
       ntp_program chronyd
       rundir /var/run/timemaster
       first_shm_segment 1
       restart_processes 0

       [chronyd]
       path /usr/sbin/chronyd
       options

       [chrony.conf]
       makestep 1 3
       logchange 0.5
       rtcsync
       driftfile /var/lib/chrony/drift

       [ntpd]
       path /usr/sbin/ntpd
       options -u ntp:ntp

       [ntp.conf]
       restrict default nomodify notrap nopeer noquery
       restrict 127.0.0.1
       restrict ::1
       driftfile /var/lib/ntp/drift

       [phc2sys]
       path /usr/sbin/phc2sys
       options -l 5

       [ptp4l]
       path /usr/sbin/ptp4l
       options

       [ptp4l.conf]
       logging_level 5