chrony.conf

#######################################################################
#
# This is a chrony configuration file.  You can edit the options that you
# want to enable.  The more obscure options are not included.  Refer
# to the documentation for these.
#
#######################################################################
### COMMENTS
# Any of the following lines are comments (you have a choice of
# comment start character):
# a comment
% a comment
! a comment
; a comment
#
# Below, the '!' form is used for lines that you might want to
# uncomment and edit to make your own chrony.conf file.
#
#######################################################################
#######################################################################
### SPECIFY YOUR NTP SERVERS
# Most computers using chrony will send measurement requests to one or
# more 'NTP servers'.  You will probably find that your Internet Service
# Provider or company have one or more NTP servers that you can specify.
# Failing that, there are a lot of public NTP servers.  There is a list
# you can access at http://support.ntp.org/bin/view/Servers/WebHome or
# you can use servers from the pool.ntp.org project.

! pool time.cloudflare.com iburst nts

! server 0.pool.ntp.org iburst
! server 1.pool.ntp.org iburst
! server 2.pool.ntp.org iburst
! server 3.pool.ntp.org iburst

pool pool.ntp.org iburst

#######################################################################
### AVOIDING POTENTIALLY BOGUS CHANGES TO YOUR CLOCK
#
# To avoid changes being made to your computer's gain/loss compensation
# when the measurement history is too erratic

maxupdateskew 5

# If you want to increase the minimum number of selectable sources
# required to update the system clock in order to make the
# synchronisation more reliable, uncomment (and edit) the following
# line.

! minsources 2

# If your computer has a good stable clock (e.g. it is not a virtual
# machine), you might also want to reduce the maximum assumed drift
# (frequency error) of the clock (the value is specified in ppm).

! maxdrift 100

#######################################################################
### FILENAMES ETC
# Chrony likes to keep information about your computer's clock in files.
# The 'driftfile' stores the computer's clock gain/loss rate in parts
# per million.  When chronyd starts, the system clock can be tuned
# immediately so that it doesn't gain or lose any more time.  You
# generally want this, so it is uncommented.

driftfile /opt/var/lib/chrony/drift

# If you want to enable NTP authentication with symmetric keys, you will need
# to uncomment the following line and edit the file to set up the keys.

! keyfile /opt/etc/chrony/chrony.keys

# chronyd can save the measurement history for the servers to files when
# it it exits.  This is useful on Linux, if you stop chronyd and restart
# tt with '-r' (e.g. after # an upgrade), the old measurements will still
# be relevant when chronyd is restarted.  This will reduce the time needed
# to get accurate gain/loss measurements, especially with a dial-up link.
#
# Enable these two options to use this.

dumponexit
dumpdir /opt/var/lib/chrony

# chronyd writes its process ID to a file.  If you try to start a second
# copy of chronyd, it will detect that the process named in the file is
# still running and bail out.  If you want to change the path to the PID
# file, uncomment this line and edit it.  The default path is shown.

pidfile /opt/var/run/chrony/chronyd.pid

# NTS dir for keys and cookies

! ntsdumpdir /opt/var/lib/chrony

#######################################################################
### INITIAL CLOCK CORRECTION
# This option is useful to quickly correct the clock on start if it's
# off by a large amount.  The value '1.0' means that if the error is less
# than 1 second, it will be gradually removed by speeding up or slowing
# down your computer's clock until it is correct.  If the error is above
# 1 second, an immediate time jump will be applied to correct it.  The
# value '3' means the step is allowed only in the first three updates of
# the clock.  Some software can get upset if the system clock jumps
# (especially backwards), so be careful!

! makestep 1.0 3

#######################################################################
### LOGGING
# If you want to log information about the time measurements chronyd has
# gathered, you might want to enable the following lines.  You probably
# only need this if you really enjoy looking at the logs, you want to
# produce some graphs of your system's timekeeping performance, or you
# need help in debugging a problem.

! logdir /opt/var/log/
! log measurements statistics tracking

# If you have real time clock support enabled (see below), you might want
# this line instead:

! log measurements statistics tracking rtc

#######################################################################
### ACTING AS AN NTP SERVER
# You might want the computer to be an NTP server for other computers.
# e.g.  you might be running chronyd on a dial-up machine that has a LAN
# sitting behind it with several 'satellite' computers on it.
#
# By default, chronyd does not allow any clients to access it.  You need
# to explicitly enable access using 'allow' and 'deny' directives.
#
# e.g. to enable client access from the 192.168.*.* class B subnet,

allow 10.0.0.0/8
allow 172.16.0.0/12
allow 192.168.0.0/16

# .. but disallow the 192.168.100.* subnet of that,

! deny 192.168.100/24

# You can have as many allow and deny directives as you need.  The order
# is unimportant.

# If you want chronyd to act as an NTP broadcast server, enable and edit
# (and maybe copy) the following line.  This means that a broadcast
# packet is sent to the address 192.168.1.255 every 60 seconds.  The
# address MUST correspond to the broadcast address of one of the network
# interfaces on your machine.  If you have multiple network interfaces,
# add a broadcast line for each.

! broadcast 60 192.168.1.255

# If you want to present your computer's time for others to synchronise
# with, even if you don't seem to be synchronised to any NTP servers
# yourself, enable the following line.  The value 10 may be varied
# between 1 and 15.  You should avoid small values because you will look
# like a real NTP server.  The value 10 means that you appear to be 10
# NTP 'hops' away from an authoritative source (atomic clock, GPS
# receiver, radio clock etc).

local stratum 10

# Normally, chronyd will keep track of how many times each client
# machine accesses it.  The information can be accessed by the 'clients'
# command of chronyc.  You can disable this facility by uncommenting the
# following line.  This will save a bit of memory if you have many
# clients and it will also disable support for the interleaved mode.

! noclientlog

# The clientlog size is limited to 512KB by default.  If you have many
# clients, you might want to increase the limit.

! clientloglimit 4194304

# By default, chronyd tries to respond to all valid NTP requests from
# allowed addresses.  If you want to limit the response rate for NTP
# clients that are sending requests too frequently, uncomment and edit
# the following line.

ratelimit interval 3 burst 8

#######################################################################
### REPORTING BIG CLOCK CHANGES
# Perhaps you want to know if chronyd suddenly detects any large error
# in your computer's clock.  This might indicate a fault or a problem
# with the server(s) you are using, for example.
#
# The next option causes a message to be written to syslog when chronyd
# has to correct an error above 0.5 seconds (you can use any amount you
# like).

logchange 0.5

# The next option will send email to the named person when chronyd has
# to correct an error above 0.5 seconds.  (If you need to send mail to
# several people, you need to set up a mailing list or sendmail alias
# for them and use the address of that.)

! mailonchange wibble@foo.example.net 0.5

#######################################################################
### COMMAND ACCESS
# The program chronyc is used to show the current operation of chronyd
# and to change parts of its configuration whilst it is running.

# By default chronyd binds to the loopback interface.  Uncomment the
# following lines to allow receiving command packets from remote hosts.

! bindcmdaddress 0.0.0.0
! bindcmdaddress ::

# Normally, chronyd will only allow connections from chronyc on the same
# machine as itself.  This is for security.  If you have a subnet
# 192.168.*.* and you want to be able to use chronyc from any machine on
# it, you could uncomment the following line.  (Edit this to your own
# situation.)

! cmdallow 192.168/16

# You can add as many 'cmdallow' and 'cmddeny' lines as you like.  The
# syntax and meaning is the same as for 'allow' and 'deny', except that
# 'cmdallow' and 'cmddeny' control access to the chronyd's command port.

# Rate limiting can be enabled also for command packets.  (Note,
# commands from localhost are never limited.)

! cmdratelimit interval -4 burst 16

#######################################################################
### REAL TIME SCHEDULER
# This directive tells chronyd to use the real-time FIFO scheduler with the
# specified priority (which must be between 0 and 100).  This should result
# in reduced latency.  You don't need it unless you really have a requirement
# for extreme clock stability.  Works only on Linux.  Note that the "-P"
# command-line switch will override this.

! sched_priority 1

#######################################################################
### LOCKING CHRONYD INTO RAM
# This directive tells chronyd to use the mlockall() syscall to lock itself
# into RAM so that it will never be paged out.  This should result in reduced
# latency.  You don't need it unless you really have a requirement
# for extreme clock stability.  Works only on Linux.  Note that the "-m"
# command-line switch will also enable this feature.

lock_all