On Sun, Nov 29, 2009 at 7:39 PM, Dave Shield <d.t.shi...@liverpool.ac.uk>wrote:
> 2009/11/29 <a...@lingnu.com>:
> > the issue could have been resolved by sampling the
> > system uptime when the snmp daemon starts, and using
> > it to calculate the sysUptime value, instead of relaying
> > on the system clock
>
> But the value of system uptime when the agent starts is 0,
> by definition.
>
> The SNMP agent needs to relate this point to future
> timestamps, and does so by using the local clock.
>
> Yes - if that clock time changes, you've got a problem.
>
Computing the system uptime via gettimeofday() is wrong. A better solution
would be to let get_uptime() in snmplib/system.c compute the system uptime
using methods that do not depend on the wall clock time, e.g.
clock_gettime(CLOCK_MONOTONIC) on POSIX systems that support monotonic
clocks or GetTickCount() on Windows systems. Note: the clock rate of
CLOCK_MONOTONIC takes the clock drift computed by the NTP algorithm in
account, while GetTickCount() does not.
Bart.
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