UNIX for Dummies Questions & Answers

Hello everyone
I am currently exploring the different time keeping commands in linux. and I having a lot of trouble figuring out the advantages and disadvantages of using daytime command rdate and hwclock and such commands.

Can someone link me to good articles or just give me the answer

What do you mean by "timekeeping"? Execution time of a script/an application, time based resource accounting, or time synchronization?

time synchronization and time based resource accounting. For system admin purpose basically

For time synchronization I'd suggest using an NTP daemon that synchs either against a local stable clock (eg. a radio clock or GPS receiver) or one of the many public accessible time servers.

For time accounting, take a look at the GNU Accounting Utilities. They should be available in the repos of most distributions.

what is the DisadvantagesHwclock

rdate is real old and obsolete program. Few servers still run the daytime service needed to accommodate it. ntp comes with ntpdate which is a better program.

When you first turn a computer on, you need some way to set the time close to being correct. Then ntpd will correct it the rest of the way. One way is for the computer to have a battery operated clock that runs while the system is off. Most computers have this and it usually is managed automatically by the OS. In Linux we have hwclock to do it and by making it command we have explicit control over the process. In general it's better than nothing and it's worth doing... as a first step.

But then I would try an ntpdate command. The ntp server must be running for this to work. But if it is ntpdate will give a more accurate initial setting. This should be done in the ntp start up script before starting ntpd.

Since everyone runs ntpdate followed by ntpd it makes since to build an option into ntpd to effective do what ntpdate does as it starts. I notice the docs for the latest ntpd suggests that we retire ntpdate. But I still run it anyway...old habits die hard.