On 19 July 2010 18:09, Steve DeLaney <[email protected]> wrote:
> what we are after for our application is modify ARGS on the fly
> It seems to me that having baked in args in snmpd.conf is far to
> restrictive and it would be better to exploit the power of
> extend by allowing on-the-fly updates to arguments and input


I agree that allowing SET requests to update this sort of config
would definitely be useful.   And as the link you refer to mentions,
this is  certainly possible for entries that are set up dynamically.
   Unfortunately there's a fundamental problem with extending this
to entries that are set up via the config file.

Consider what happens if you have an "extend" entry set up in
the snmpd.conf file, amended via SET requests, and then the
agent is re-started.

  It will re-read the config file, including the "extend" entry, and
configure this - using the *original* arguments.   So from the view
of an external network manager, the changes would have been lost.

  Several years ago we took the decision that such behaviour was
not acceptable.   If changes were made via SET requests, these
should be persistent across restarts.
So rather than applying SET requests which could subsequently
be silently reversed, the policy of the Net-SNMP agent is that
entries in the snmpd.conf files are "permanent", and hence read-only.
Note that this issue is not specific to the "extend" directive - it applies
to *all* the snmpd.conf settings.


One way around this might be to allow the agent to update the
config files automatically.   But that's not something we've ever felt
comfortable with.  So the only config file that the agent can
legitimately update is the one in /var/net-snmp.

  I'm not quite sure what would happen if you put the "extend"
line into /var/net-snmp/snmpd.conf,  updated it via SET and then
restarted the agent.   That would certainly be a possible way
forward.
   But allowing general updating of (static) snmpd.conf settings
is not as simple as you may think.   I don't think it's likely to make
it into 5.6  (though the others may well overrule me!)

Dave

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