[RndTbl] LibreNMS installation _now_ working as it should

Gilbert E. Detillieux gedetil at cs.umanitoba.ca
Wed May 12 10:51:17 CDT 2021

On 2021-05-12 9:27 a.m., Adam Thompson wrote:
> Rubber Ducky Debugging.
> Because you may as well be explaining the problem to your rubber duck 
> bath toy, for all the actual assistance you actually needed from the 
> other person.

I thought I had another great original quote from Adam, but I found out 
this is an actual thing!...


But in fairness to Alberto, he was more than a passive rubber duck in 
this case.  He pointed me back in the direction of cron, when I had 
already dismissed it out of hand as the problem.  By doing so, he 
encouraged me to look more carefully at the cron entries themselves 
(which hadn't changed), allowing me to notice the explicit username in 
the cron entries, which made me think "this thing needs to run as root 
to begin with" (so it can setuid), and "will cron reject a 
non-root-owned file as a security risk?"  And bingo!

So, yeah, talking things through (even with a rubber ducky, or your 
favourite stuffie) definitely helps with the thinking process, but a 
persistent line of questioning back is even more helpful.

Two take-homes for me:

1. Don't quickly dismiss things as irrelevant or too obvious.  Look at 
it from different angles.  (The answer may not be blowing in the wind, 
but stuck to the bottom of your shoe!)

2. When deviating from exact instructions (because I think I know 
better), be careful of subtle side effects.  (Using "cp -p" is usually 
preferable to just "cp", but not always!)


> On May 12, 2021 7:14:20 a.m. CDT, Alberto Abrao <alberto at abrao.net> wrote:
>     On 2021-05-11 10:27 p.m., Gilbert E. Detillieux wrote:
>         OK, I'm a bit sheepish to admit what the problem appears to have
>         been:
>         wrong ownership on the crontab file.  I've made it owned by root
>         now,
>         and this seems to have fixed my issues.
>     "he who is without sin among you, let he be the first to throw a stone..."
>     If anyone here thinks Gilbert should be ashamed, show your face and
>     we'll be sure to point and laugh when your turn comes.
>     Because *it will*.
>         Thanks for Alberto for getting me to re-examine my cron file, which
>         got me thinking about permissions and ownership of the file, after
>         seeing no problem with the content itself.
>     I did not do a thing!
>     I was reading an anecdote that some coders ask for another coder to hear
>     an explanation of what they are trying to do, when baffled that
>     something does not work as it should.
>     Most of the time, during the explanation, the baffled coder end up
>     finding something he/she missed on his/her own, usually trivial, but
>     perfectly OK to skip, considering all that is going on while they're "in
>     the zone".
>     You fixed your own problem. I was just trying to recap what threw me for
>     a loop when I was setting up LibreNMS. In my case - if I recall
>     correctly - I skipped the cron file entirely. But that was a while ago,
>     and it was past 10PM after a looong day (yep, that I do remember...
>     sigh), so... yeah.
>     I am glad it helped, but all I really did was take you out of "the zone"
>     for a little while.
>     For the record, without the cron file with all the housekeeping duties,
>     LibreNMS will cough up a hairball and not give you a clue of what's
>     really going on.
>     Thus, make sure you have your /etc/cron.d/librenms file properly set up,
>     both content (hi!) and permissions/ownership (hi Gilbert!).
>     :)
>     Kind regards,
>     Alberto Abrao

Gilbert E. Detillieux        E-mail:  <gedetil at cs.umanitoba.ca>
Dept. of Computer Science    Web:     http://cs.umanitoba.ca/~gedetil/
University of Manitoba
Winnipeg MB CANADA  R3T 2N2

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