doc: improve FAQ
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Miroslav Lichvar
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1 changed files with 37 additions and 16 deletions
53
doc/faq.adoc
53
doc/faq.adoc
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@ -79,7 +79,7 @@ rtcsync
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You need to add an `allow` directive to the _chrony.conf_ file in order to open
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the NTP port and allow `chronyd` to reply to client requests. `allow` with no
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specified subnet allows all IPv4 and IPv6 addresses.
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specified subnet allows access from all IPv4 and IPv6 addresses.
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=== I have several computers on a LAN. Should be all clients of an external server?
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@ -97,7 +97,7 @@ _chrony.conf_ file. This configuration will be better because
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No. Starting from version 1.25, `chronyd` will keep trying to resolve
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the names specified by the `server`, `pool`, and `peer` directives in an
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increasing interval until it succeeds. The `online` command can be issued from
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`chronyc` to try to resolve them immediately.
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`chronyc` to force `chronyd` to try to resolve the names immediately.
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=== How can I make `chronyd` more secure?
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@ -161,7 +161,7 @@ The first three options set the minimum and maximum allowed polling interval,
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and how should be the actual interval adjusted in the specified range. Their
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default values are 6 (64 seconds) for `minpoll`, 10 (1024 seconds) for
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`maxpoll` and 8 (samples) for `polltarget`. The default values should be used
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for general servers on the Internet. With your own NTP servers or if have
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for general servers on the Internet. With your own NTP servers, or if you have
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permission to poll some servers more frequently, setting these options for
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shorter polling intervals may significantly improve the accuracy of the system
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clock.
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@ -195,15 +195,27 @@ server ntp.local minpoll 2 maxpoll 4 polltarget 30 maxdelaydevratio 2
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----
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If your server supports the interleaved mode, the `xleave` option should be
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added to the `server` directive in order to receive server's more accurate
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hardware or kernel transmit timestamps. When combined with local hardware
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timestamping, a sub-microsecond accuracy may be possible. An example could be
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added to the `server` directive in order to allow the server to send the
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client more accurate hardware or kernel transmit timestamps. When combined with
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local hardware timestamping, sub-microsecond accuracy may be possible. An
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example could be
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----
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server ntp.local minpoll 2 maxpoll 2 xleave
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hwtimestamp eth0
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----
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=== Does `chronyd` have an ntpdate mode?
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Yes. With the `-q` option `chronyd` will set the system clock once and exit.
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With the `-Q` option it will print the measured offset without setting the
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clock. If you don't want to use a configuration file, NTP servers can be
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specified on the command line. For example:
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----
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# chronyd -q 'pool pool.ntp.org iburst'
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----
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=== What happened to the `commandkey` and `generatecommandkey` directives?
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They were removed in version 2.2. Authentication is no longer supported in the
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@ -242,8 +254,17 @@ MS Name/IP address Stratum Poll Reach LastRx Last sample
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=== Are NTP servers specified with the `offline` option?
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Check that you're using ``chronyc``'s `online` and `offline` commands
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appropriately. Again, check in _measurements.log_ to see if you're getting any
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data back from the server.
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appropriately. The `activity` command prints the number of sources that are
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currently online and offline. For example:
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----
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200 OK
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3 sources online
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0 sources offline
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0 sources doing burst (return to online)
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0 sources doing burst (return to offline)
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0 sources with unknown address
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----
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=== Is `chronyd` allowed to step the system clock?
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@ -396,15 +417,15 @@ option for all time sources in the _chrony.conf_ file.
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=== What happens if the network connection is dropped without using ``chronyc``'s `offline` command first?
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`chronyd` will keep trying to access the server(s) that it thinks are online.
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When the network is connected again, it will take some time (on average half of
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the maximum polling interval) before new measurements are made and the clock is
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corrected. If the servers were set to offline and the `online` command was
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issued when the network was connected, `chronyd` would make new measurements
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immediately.
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`chronyd` will keep trying to access the sources that it thinks are online, and
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it will take longer before new measurements are actually made and the clock is
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corrected when the network is connected again. If the sources were set to
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offline, `chronyd` would make new measurements immediately after issuing the
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`online` command.
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The `auto_offline` option to the `server` entry in the _chrony.conf_ file may
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be useful to switch the servers to the offline state automatically.
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Unless the network connection lasts only few minutes (less than the maximum
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polling interval), the delay is usually not a problem, and it may be acceptable
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to keep all sources online all the time.
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== Operating systems
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