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~]${nbsp}cd /sys/devices/system/clocksource/clocksource0/
clocksource0]$ cat available_clocksource
kvm-clock tsc hpet acpi_pm
clocksource0]$ cat current_clocksource
~]${nbsp}pass:attributes[{blank}][command]#less /etc/ntp.conf#
synchronised to NTP server ( at stratum 2
time correct to within 52 ms
polling server every 1024 s
time server re-starting
polling server every 64 s
~]${nbsp}pass:attributes[{blank}][command]#systemctl status chronyd#
~]${nbsp}pass:attributes[{blank}][command]#systemctl status ntpd#
~]${nbsp}pass:attributes[{blank}][command]#systemctl status ntpdate#
Accurate time keeping is important for a number of reasons in IT. In networking for example, accurate time stamps in packets and logs are required. Logs are used to investigate service and security issues and so time stamps made on different systems must be made by synchronized clocks to be of real value. As systems and networks become increasingly faster, there is a corresponding need for clocks with greater accuracy and resolution. In some countries there are legal obligations to keep accurately synchronized clocks. Please see [citetitle]_www.ntp.org_ for more information. In Linux systems, `NTP` is implemented by a daemon running in user space. The default `NTP` user space daemon in {MAJOROSVER} is `chronyd`. It must be disabled if you want to use the `ntpd` daemon. See xref:servers/Configuring_NTP_Using_the_chrony_Suite.adoc#ch-Configuring_NTP_Using_the_chrony_Suite[Configuring NTP Using the chrony Suite] for information on [application]*chrony*.
Adding a Broadcast Client Address
Adding a Broadcast or Multicast Server Address
Adding a Manycast Client Address
Adding a Manycast Server Address
Adding a Multicast Client Address
Adding a Peer Address
Adding a Server Address
Additional Resources
Addresses can be added underneath if specifically required by another application.
Addresses within the range `` are sometimes required by various processes or applications. As the "restrict default" line above prevents access to everything not explicitly allowed, access to the standard loopback address for `IPv4` and `IPv6` is permitted by means of the following lines:
A mask of `` is applied if none is specified.
An attacker on the network can attempt to disrupt a service by sending `NTP` packets with incorrect time information. On systems using the public pool of `NTP` servers, this risk is mitigated by having more than three `NTP` servers in the list of public `NTP` servers in `/etc/ntp.conf`. If only one time source is compromised or spoofed, `ntpd` will ignore that source. You should conduct a risk assessment and consider the impact of incorrect time on your applications and organization. If you have internal time sources you should consider steps to protect the network over which the `NTP` packets are distributed. If you conduct a risk assessment and conclude that the risk is acceptable, and the impact to your applications minimal, then you can choose not to use authentication.