####################################################################### # # This is an example chrony configuration file. You should copy it to # /etc/chrony.conf after uncommenting and editing the options that you # want to enable. The more obscure options are not included. Refer # to the documentation for these. # # Copyright 2002 Richard P. Curnow # # This program is free software; you can redistribute it and/or modify # it under the terms of version 2 of the GNU General Public License as # published by the Free Software Foundation. # # This program is distributed in the hope that it will be useful, but # WITHOUT ANY WARRANTY; without even the implied warranty of # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU # General Public License for more details. # # You should have received a copy of the GNU General Public License along # with this program; if not, write to the Free Software Foundation, Inc., # 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. # # ####################################################################### ### 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://www.eecis.udel.edu/~mills/ntp/servers.htm. ! server ntp0.your-isp.com ! server ntp1.your-isp.com ! server ntp.public-server.org # However, for dial-up use you probably want these instead. The word # 'offline' means that the server is not visible at boot time. Use # chronyc's 'online' command to tell chronyd that these servers have # become visible after you go on-line. ! server ntp0.your-isp.com offline ! server ntp1.your-isp.com offline ! server ntp.public-server.org offline # You may want to specify NTP 'peers' instead. If you run a network # with a lot of computers and want several computers running chrony to # have the 'front-line' interface to the public NTP servers, you can # 'peer' these machines together to increase robustness. ! peer ntp0.my-company.com # There are other options to the 'server' and 'peer' directives that you # might want to use. For example, you can ignore measurements whose # round-trip-time is too large (indicating that the measurement is # probably useless, because you don't know which way the measurement # message got held up.) Consult the full documentation for details. ####################################################################### ### 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, you might want to enable # one of the following lines. The first seems good for dial-up (or # other high-latency connections like slow leased lines), the second # seems OK for a LAN environment. ! maxupdateskew 100 ! maxupdateskew 5 ####################################################################### ### 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 /etc/chrony.drift # If you want to use the program called chronyc to configure aspects of # chronyd's operation once it is running (e.g. tell it the Internet link # has gone up or down), you need a password. This is stored in the # following keys file. (You also need keys to support authenticated NTP # exchanges between cooperating machines.) Again, this option is # assumed by default. keyfile /etc/chrony.keys # Tell chronyd which numbered key in the file is used as the password # for chronyc. (You can pick any integer up to 2**32-1. '1' is just a # default. Using another value will _NOT_ increase security.) commandkey 1 # chronyd can save the measurement history for the servers to files when # it it exits. This is useful in 2 situations: # # 1. On Linux, if you stop chronyd and restart it 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. # # 2. Again on Linux, if you use the RTC support and start chronyd with # '-r -s' on bootup, measurements from the last boot will still be # useful (the real time clock is used to 'flywheel' chronyd between # boots). # # Enable these two options to use this. ! dumponexit ! dumpdir /var/log/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 /var/run/chronyd.pid ####################################################################### ### INITIAL CLOCK CORRECTION # This option is only useful if your NTP servers are visible at boot # time. This probably means you are on a LAN. If so, the following # option will choose the best-looking of the servers and correct the # system time to that. The value '10' means that if the error is less # than 10 seconds, it will be gradually removed by speeding up or # slowing down your computer's clock until it is correct. If the error # is above 10 seconds, an immediate time jump will be applied to correct # it. Some software can get upset if the system clock jumps (especially # backwards), so be careful! ! initstepslew 10 ntp0.your-company.com ntp1.your-company.com ntp2.your-company.com ####################################################################### ### 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 /var/log/chrony ! 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 192.168/16 # .. 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. ! noclientlog # The clientlog size is limited to 512KB by default. If you have many # clients, especially in many different subnets, you might want to # increase the limit. ! clientloglimit 4194304 ####################################################################### ### 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@foobar.org 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. # 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. # NOTE, even if the host where you run chronyc is granted access, you # still need a command key set up and you have to know the password to # put into chronyc to allow you to modify chronyd's parameters. By # default all you can do is view information about chronyd's operation. # Some people have reported that the need the following line to allow # chronyc to work even on the same machine. This should not be # necessary, and the problem is being investigated. You can leave this # line enabled, as it's benign otherwise. cmdallow 127.0.0.1 ####################################################################### ### REAL TIME CLOCK # chronyd can characterise the system's real-time clock. This is the # clock that keeps running when the power is turned off, so that the # machine knows the approximate time when it boots again. The error at # a particular epoch and gain/loss rate can be written to a file and # used later by chronyd when it is started with the '-s' option. # # You need to have 'enhanced RTC support' compiled into your Linux # kernel. (Note, these options apply only to Linux.) ! rtcfile /etc/chrony.rtc # Your RTC can be set to keep Universal Coordinated Time (UTC) or local # time. (Local time means UTC +/- the effect of your timezone.) If you # use UTC, chronyd will function correctly even if the computer is off # at the epoch when you enter or leave summer time (aka daylight saving # time). However, if you dual boot your system with Microsoft Windows, # that will work better if your RTC maintains local time. You take your # pick! ! rtconutc # By default chronyd assumes that the enhanced RTC device is accessed as # /dev/rtc. If it's accessed somewhere else on your system (e.g. you're # using devfs), uncomment and edit the following line. ! rtcdevice /dev/misc/rtc ####################################################################### ### 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
