What is Chrony ?
Chrony provides another implementation of NTP. It is designed for systems that are often powered down or disconnected from the network. The main configuration file is /etc/chrony.conf and the parameters are similar to those in the /etc/ntp.conf file. Chronyd is a daemon that runs in user space and also is a command-line program that provides a command prompt and a number of commands.
Examples:
tracking: Displays system time information.
sources: Displays information about current sources.
You can find more about here:
https://chrony.tuxfamily.org/comparison.html
1. Make sure you have your hostnames and /etc/hosts file properly configured
Server (host1.localnet.com)
Client (host2.localnet.com)
/etc/hosts file
127.0.0.1 localhost localhost.localdomain localhost4 localhost4.localdomain4 ::1 localhost localhost.localdomain localhost6 localhost6.localdomain6 192.168.0.200 host2.localnet.com host2 192.168.0.199 host1.localnet.com host1
2. Install chrony package on both the server and the client machine
# yum install chrony
3. Start and enable the daemon on both the server and client machines
# systemctl start chrony # systemctl enable chrony
4. At the server machine, edit the /etc/chrony.conf file and add your client network
## Allow NTP client access from local network. allow 192.168.0.0/24
5. At the client machine, edit the /etc/chrony.conf and add your ntp server IP address
# Use public servers from the pool.ntp.org project. # Please consider joining the pool (http://www.pool.ntp.org/join.html). #server 0.centos.pool.ntp.org iburst #server 1.centos.pool.ntp.org iburst #server 2.centos.pool.ntp.org iburst #server 3.centos.pool.ntp.org iburst server 192.168.0.199 iburst
6. Restart chrony service on both machines
# systemctl restart chrony
7. Make sure you allow ntp service in your firewall on both machines
# firewall-cmd --permanent --zone=public --add-service ntp # firewall-cmd --reload # firewall-cmd --list-all | grep services
8. Verify your sources information
server
# chronyc sources 210 Number of sources = 4 MS Name/IP address Stratum Poll Reach LastRx Last sample =============================================================================== ^? t1.time.ir2.yahoo.com 0 6 0 - +0ns[ +0ns] +/- 0ns ^? bray.walcz.net 0 6 0 - +0ns[ +0ns] +/- 0ns ^? t1.time.ir2.yahoo.com 0 9 0 - +0ns[ +0ns] +/- 0ns ^? tshirt.heanet.ie 0 6 0 - +0ns[ +0ns] +/- 0ns
client
# chronyc sources 210 Number of sources = 1 MS Name/IP address Stratum Poll Reach LastRx Last sample =============================================================================== ^? host1.localnet.com 0 7 0 - +0ns[ +0ns] +/- 0ns
9. Verify your system time information
# chronyc tracking Reference ID : 7F7F0101 () Stratum : 10 Ref time (UTC) : Wed Aug 15 12:16:29 2018 System time : 0.000000020 seconds fast of NTP time Last offset : +0.000000000 seconds RMS offset : 0.000000000 seconds Frequency : 3.440 ppm fast Residual freq : +0.000 ppm Skew : 0.000 ppm Root delay : 0.000000000 seconds Root dispersion : 0.000000000 seconds Update interval : 0.0 seconds Leap status : Normal
Some of the fields
Reference ID: The Reference ID and the name or IP address (if available), of the server to which the computer is currently synchronized.
Stratum: The stratum indicates how many hops away from a computer with an attached reference clock you are.
Ref time: This is the time (UTC) at which the last measurement from the reference source was processed.
10. Verify your sources
# chronyc sources -v 210 Number of sources = 4 .-- Source mode '^' = server, '=' = peer, '#' = local clock. / .- Source state '*' = current synced, '+' = combined , '-' = not combined, | / '?' = unreachable, 'x' = time may be in error, '~' = time too variable. || .- xxxx [ yyyy ] +/- zzzz || Reachability register (octal) -. | xxxx = adjusted offset, || Log2(Polling interval) --. | | yyyy = measured offset, || \ | | zzzz = estimated error. || | | \ MS Name/IP address Stratum Poll Reach LastRx Last sample =============================================================================== ^? mail.thefrown.net 0 6 0 - +0ns[ +0ns] +/- 0ns ^? t2.time.ir2.yahoo.com 0 6 0 - +0ns[ +0ns] +/- 0ns ^? bray.walcz.net 0 9 0 - +0ns[ +0ns] +/- 0ns ^? 193.1.12.167 0 6 0 - +0ns[ +0ns] +/- 0ns
M: The mode of the source, where:
^ means a server
= means a peer
# indicates a locally connected reference clock.
S: The state of the sources, where:
“*” indicates the source to which chronyd is currently synchronized.
“+” indicates acceptable sources that are combined with the selected source.
“-” indicates acceptable sources that are excluded by the combining algorithm.
“?” indicates sources to which connectivity has been lost or whose packets do not pass all tests.
“x” indicates a clock that chronyd thinks is a false ticker, that is, its time is inconsistent with a majority of other sources.
“~” indicates a source whose time appears to have too much variability.
“?” condition is also shown at start-up, until at least three samples have been gathered from it.
Name/IP address: This shows the name or the IP address of the source, or reference ID for reference clocks.