SNMP ssCPUIdle Incorrect on CentOS 5.2

I use SNMP to monitor ssCPUIdle on CentOS 5.2. Today, after 248 days of uptime, it started returning 0% idle:

$snmpwalk -v 1 localhost –c public .
UCD-SNMP-MIB::ssCpuIdle.0 = INTEGER: 0

I logged in to the CentOS command line and ran top and vmstat 5 (credit). Both showed id (idle) of 97% or more, so the CPU is fine; SNMP is returning an incorrect value.

I stopped and started the SNMP daemon:

service snmpd stop
service snmpd start

After that, SNMP again returned correct values (96 or more). For about a minute. Then it drops back to 0.

Turns out this is a RHEL 5.2 bug that may or may not be fixed in 5.3: wrong CPU idle (ssCpuIdle.0) reported after certain uptime. Interesting that the bug submitter noticed the problem after 62 days with a 4-CPU machine. I get the error after 248 days on a 1-CPU machine. 62 x 4 = 248.

Fortunately a reboot solves the problem:

shutdown –r now

Remind me to check this again in 248 days!

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