These can all be found via the "snmpwalk" command in CentOS 5.4 (or RHEL 5.4).

# snmp -v 1 -c public localhost | less

The above assumes that you have configured the SNMP agent on the server to allow read-only access to SNMP v1 clients via the "public" community string.

Approximate number of users logged in

HOST-RESOURCES-MIB::hrSystemNumUsers.0 = Gauge32: 3

Number of logged in users. As you can see, this is a gauge value which means (in SNMP terms) that it is a value that can increase or decrease over time. By default, MRTG assumes that the value is monotonically increasing.

Note: Since MRTG only samples once every 5 minutes, this value is very approximate.

Approximate number of system processes

HOST-RESOURCES-MIB::hrSystemProcesses.0 = Gauge32: 171

Current number of processes running. This often makes a good second number to pair up with the number of users. Or you could choose to display them on separate graphs.

Note: Same issue as logging the number of users, MRTG only samples every 5 minutes which makes this an estimation at best.

MRTG: Reporting on processes and users

Here's a fragment from my MRTG configuration file that shows how I reported on the number of users and processes. I could not get MRTG to resolve the plain names to OIDs automatically, so I had to put in the full numeric OIDs.

### PROCESSES & USERS
Options[_]: gauge, integer, noborder, noinfo, nolegend, noo, nopercent, pngdate, printrouter, transparent
WithPeak[_]: ymw
Legend2[_]:
Legend3[_]:
Legend4[_]:

#Target[localhost.system.users]: hrSystemNumUsers.0&hrSystemNumUsers.0:public@localhost
Target[localhost.system.users]: .1.3.6.1.2.1.25.1.5.0&.1.3.6.1.2.1.25.1.5.0:public@localhost
MaxBytes[localhost.system.users]: 50
YLegend[localhost.system.users]: Users
LegendI[localhost.system.users]: Users
Legend1[localhost.system.users]: Approximate number of users logged in
ShortLegend[localhost.system.users]: ~
Title[localhost.system.users]: firewall:Users - Approximate System Users
PageTop[localhost.system.users]: <h1>firewall: Approximate System Users</h1>
    <div id="sysdetails">
    </div>

#Target[localhost.system.processes]: hrSystemProcesses.0&hrSystemProcesses.0:public@localhost
Target[localhost.system.processes]: .1.3.6.1.2.1.25.1.6.0&.1.3.6.1.2.1.25.1.6.0:public@localhost
MaxBytes[localhost.system.processes]: 5000
YLegend[localhost.system.processes]: Processes
LegendI[localhost.system.processes]: Processes
Legend1[localhost.system.processes]: Approximate number of processes
ShortLegend[localhost.system.processes]: ~
Title[localhost.system.processes]: firewall:Procs - Approximate System Processes
PageTop[localhost.system.processes]: <h1>firewall: Approximate System Processes</h1>
    <div id="sysdetails">
    </div>

Real Memory in Use

HOST-RESOURCES-MIB::hrStorageType.2 = OID: HOST-RESOURCES-TYPES::hrStorageRam
HOST-RESOURCES-MIB::hrStorageDescr.2 = STRING: Real Memory
HOST-RESOURCES-MIB::hrStorageAllocationUnits.2 = INTEGER: 1024 Bytes
HOST-RESOURCES-MIB::hrStorageSize.2 = INTEGER: 8043628
HOST-RESOURCES-MIB::hrStorageUsed.2 = INTEGER: 7962536

Swap (Virtual) Memory in Use

HOST-RESOURCES-MIB::hrStorageType.3 = OID: HOST-RESOURCES-TYPES::hrStorageVirtualMemory
HOST-RESOURCES-MIB::hrStorageDescr.3 = STRING: Swap Space
HOST-RESOURCES-MIB::hrStorageAllocationUnits.3 = INTEGER: 1024 Bytes
HOST-RESOURCES-MIB::hrStorageSize.3 = INTEGER: 4021814
HOST-RESOURCES-MIB::hrStorageUsed.3 = INTEGER: 8292

Processor Utilization

First, we need to find the OIDs of the CPUs.

# snmpwalk -v 1 -c public localhost | grep "HOST-RESOURCES" | egrep "hrDeviceProcessor"
HOST-RESOURCES-MIB::hrDeviceType.768 = OID: HOST-RESOURCES-TYPES::hrDeviceProcessor
HOST-RESOURCES-MIB::hrDeviceType.769 = OID: HOST-RESOURCES-TYPES::hrDeviceProcessor
HOST-RESOURCES-MIB::hrSWRunParameters.32755 = STRING: "hrDeviceProcessor"

That gives us 768 and 769 to look at.

# snmpwalk -v 1 -c public localhost | grep "HOST-RESOURCES" | egrep "(768|769)"
HOST-RESOURCES-MIB::hrDeviceIndex.768 = INTEGER: 768
HOST-RESOURCES-MIB::hrDeviceIndex.769 = INTEGER: 769
HOST-RESOURCES-MIB::hrDeviceType.768 = OID: HOST-RESOURCES-TYPES::hrDeviceProcessor
HOST-RESOURCES-MIB::hrDeviceType.769 = OID: HOST-RESOURCES-TYPES::hrDeviceProcessor
HOST-RESOURCES-MIB::hrDeviceDescr.768 = STRING: AuthenticAMD: AMD Athlon(tm) 64 X2 Dual Core Processor 4200+
HOST-RESOURCES-MIB::hrDeviceDescr.769 = STRING: AuthenticAMD: AMD Athlon(tm) 64 X2 Dual Core Processor 4200+
HOST-RESOURCES-MIB::hrDeviceID.768 = OID: SNMPv2-SMI::zeroDotZero
HOST-RESOURCES-MIB::hrDeviceID.769 = OID: SNMPv2-SMI::zeroDotZero
HOST-RESOURCES-MIB::hrProcessorFrwID.768 = OID: SNMPv2-SMI::zeroDotZero
HOST-RESOURCES-MIB::hrProcessorFrwID.769 = OID: SNMPv2-SMI::zeroDotZero
HOST-RESOURCES-MIB::hrProcessorLoad.768 = INTEGER: 1
HOST-RESOURCES-MIB::hrProcessorLoad.769 = INTEGER: 1

So by looking at the hrProcessorLoad for nodes 768 & 769, we can track the CPU utilization on this PC. But unless you can get MRTG to load the MIBs, you'll need to use the numeric OID format.

# snmpwalk -v 1 -c public localhost -On | egrep "(768|769)" | grep "INTEGER"
.1.3.6.1.2.1.25.3.3.1.2.768 = INTEGER: 9
.1.3.6.1.2.1.25.3.3.1.2.769 = INTEGER: 17

Labels: 2009, MRTG, SNMP

The key tool in the toolbox for exploring MIBs and finding things in SNMP is either "snmpwalk" or looking at the actual MIB text definitions. On CentOS 5 (and RHEL 5), the net-snmp package installs a default set of MIBs to "/usr/share/snmp/mibs/".

# snmpwalk -v 2c -c public localhost diskIONReadX

That particular command uses version "2c" of the SNMP protocol to talk to the "public" community on the localhost and looks for "diskIONReadX" (which is a 64bit counter value column from the diskIOTable).

# snmptranslate -m +ALL -IR -Td diskIONReadX

Here, we use "snmptranslate" to report on full details (-Td) of the diskIONReadX property. When looking up SNMP attributes by labels, you'll want to use the above format, but you can change "-Td" to other "-T" options or a "-O" option. Some common choices are:

# snmptranslate -m +ALL -IR -Td diskIONReadX
UCD-DISKIO-MIB::diskIONReadX
diskIONReadX OBJECT-TYPE
-- FROM UCD-DISKIO-MIB
SYNTAX Counter64
MAX-ACCESS read-only
STATUS current
DESCRIPTION "The number of bytes read from this device since boot."
::= { iso(1) org(3) dod(6) internet(1) private(4) enterprises(1) ucdavis(2021) ucdExperimental(13) ucdDiskIOMIB(15) diskIOTable(1) diskIOEntry(1) 12 }

# snmptranslate -m +ALL -IR -On diskIONReadX
.1.3.6.1.4.1.2021.13.15.1.1.12

# snmptranslate -m +ALL -IR -Of diskIONReadX
.iso.org.dod.internet.private.enterprises.ucdavis.ucdExperimental.
ucdDiskIOMIB.diskIOTable.diskIOEntry.diskIONReadX

# snmptranslate -m +ALL -IR -Ou diskIONReadX
enterprises.ucdavis.ucdExperimental.ucdDiskIOMIB.diskIOTable.
diskIOEntry.diskIONReadX

Labels: 2009, SNMP

Reference links:

IETF RFC 3410 - Introduction and Applicability Statements for Internet Standard Management Framework (SNMP) - Dec 2002. An information RFC that covers the basics of SNMP. See also RFC 3411 (Architecture), 3413 (Applications), 3416 (Version 2 of the Protocol Operations), and 3418 (Management Information Base) as well as a few others in the 3400-3499 range.

Simple Network Management Protocol (Wikipedia) - Covers the basics and links to additional reference works.

Labels: 2009, SNMP