[time-nuts] Comparing the BeagleBone Black & Raspberry Pi as NTP servers

[Attila Kinali]

On Sun, 22 Mar 2015 14:14:01 -0000
"David J Taylor" <david-taylor at blueyonder.co.uk> wrote:

> Yes, my posting was at least in part for help with resolving the much higher 
> CPU load seen on a default BBB installation than on an RPi setup.  If you 
> could provide a list of services and cron jobs to be disabled, and a brief 
> guide to doing so (as I'm a beginner with Linux) that would be appreciated.

Sorry, I cannot. I don't have a BBB to test the image and tell you
what it runs.

But i can at least guide you trough the steps to figure out what's going on.

If you run `ps aux` you will get a list of what processes are active.
This is the low level view.

The high level view is aquired using `systemctl list-units`
You can stop the units you don't need using `systemctl stop <name>`

You can find more information on how to deal with systemd on
https://wiki.archlinux.org/index.php/systemd
Do not get confused by this being an Arch Linux wiki, it applies
to Debian as well.

BTW: As Graham wrote Debian is in kind of a transition, though
nobody has really decided where it will be going (there are too
many people who opose the systemd switch). But unlike what he
wrote, there is no mix of init systems. It's either systemd,
or it isn't. You cannot have both at the same time. The default
image of BBB runs systemd.

The second place where to look at are your cron jobs.
They can be found in:
/etc/crontab
/etc/cron.d
/etc/cron.hourly
/var/spool/cron/crontabs/

The first one (/etc/crontab) is the system wide, old school table
that contains all jobs. On a regular debian system, you should
have only 4 entries, the monthly, weekly, daily and hourly job scripts.
If you have only these, don't touch it. They are necessary.
The second one (/etc/cron.d/) is a directory that contains files of the
same format as /etc/crontab for specific installed packages. Edit them
as you whish (but know what you are doing ;-). The third (/etc/cron.hourly)
contains shell scripts that are run once per hour. They are most likely
necessary, but might not be. If you don't want/need them, it's best
to uninstall the package that they came with. The last one is one 
(/var/spool/cron/crontabs/) is one you shouldn't touch by hand. These
are the files stored by the crontab command, for the respective user.
If you need to disable/edit those, use the crontab command.

BTW: i reccomend you getting a book on linux. Dealing with embedded
devices you will need a good understanding of the inner workings of
linux to effectively deal with them. I have heard good things about
"linux for dummies" but i have never read it myself.


> I had looked at [1] but I'm not using his special timer setup, just GPIO 
> pins.  Unfortunately he doesn't quote any of the usual NTP parameters with 
> which to compare.

Yes. But it gives an idea how stable the oscillator is. You have large
deviations of over 10us, which contradict the number Dan Drown is getting.


HTH

			Attila Kinali
-- 
< _av500_> phd is easy
< _av500_> getting dsl is hard