Domain Time Sync – OS Test

Time synchronization is one of the most important dependencies of Linux. A time protocol is responsible for determining the best available time information and converging the clocks to ensure that a consistent time is maintained across systems. By default, Linux support a tolerance of plus or minus five minutes for clocks. If the time variance exceeds this setting, clients will be unable to authenticate and in the case of domain controllers, replication will not occur. It implements a time synchronization system based on Network Time Protocol (NTP).

NTP is a fault-tolerant, highly scalable time protocol and it is used for synchronizing computer clocks by using a designated reference clock. A reference clock is some device or machinery that spits out the current time. The special thing about these things is accuracy. Reference clocks must be accurately following some time standard. NTP will compute some additional statistical values based on the current time reported by the reference clock, which will describe the quality of time it sees. Among these values are: offset (or phase), jitter (or dispersion), frequency error, and stability. Thus each NTP server will maintain an estimate of the quality of its reference clocks and of itself.

This test reports the time difference between the reference clock and that of the target environment, and thus helps assess the quality of time seen by the system. With the help of this test, you can also easily determine whether the reference time changed recently.

Target of the test : A Linux Systems Group

Agent deploying the test : A remote agent

Outputs of the test : One set of results for each Linux system in the target Linux Systems Group

Configurable parameters for the test

Parameter	Description
Test Period	How often should the test be executed.
Host	The nick name of the Linux Systems Group component for which this test is to be configured.
Port	Refers to the port at which the specified host listens to. By default, this is NULL.
Inside View Using	To obtain the 'inside view' of performance of the systems - i.e., to measure the internal performance of the systems - this test uses a light-weight eG VM Agent software deployed on each of the systems. Accordingly, this parameter is by default set to eG VM Agent.
Report By User	This flag is set to No by default. This implies that the Linux systems in environments will always be identified using the system name. In other words, this test will, by default, report measures for every systemname. On the other hand, if you want this test to report the measures for every user on a system, then set this flag to Yes. In such a case, this test will report the measures for every username_on_systemname.
Report Powered OS	By default, this flag is set to Yes, then the 'inside view' tests will report measures for even those Linux systems that do not have any users logged in currently. The systems will be identified by their name and not by the username_on_systemname. On the other hand, if this flag is set to No, then this test will not report measures for those systems to which no users are logged in currently.
Is Cloud VMs?	This flag is set to Yes by default. The value of this flag cannot be changed. This implies that the cloud-based Linux systems in environments will always be identified using the login name of the user. In other words, in cloud environments, this test will, by default, report measures for every username_on_systemname.

Measurements made by the test

Measurement	Description	Measurement Unit	Interpretation
NTP offset	Indicates the time difference between the local clock and the designated reference clock.	Secs	For a tiny offset, NTP will adjust the local clock; for small and larger offsets, NTP will reject the reference time for a while. In the latter case, the operating system’s clock will continue with the last corrections effective while the new reference time is being rejected. After some time, small offsets (significantly less than a second) will be slewed (adjusted slowly), while larger offsets will cause the clock to be stepped (set anew). Huge offsets are rejected, and NTP will terminate itself, believing something very strange must have happened.