Linux Administration
Simple Network Management Protocol (SNMP) is an «Internet-standard protocol for managing devices on IP networks. It is used mostly in network management systems to monitor network-attached devices for conditions that warrant administrative attention. SNMP is a component of the Internet Protocol Suite as defined by the Internet Engineering Task Force (IETF). It consists of a set of standards for network management, including an application layer protocol, a database schema, and a set of data objects.
SNMP exposes management data in the form of variables on the managed systems, which describe the system configuration. These variables can then be queried (and sometimes set) by managing applications.
SNMP itself does not define which information (which variables) a managed system should offer. Rather, SNMP uses an extensible design, where the available information is defined by management information bases (MIBs). MIBs describe the structure of the management data of a device subsystem; they use a hierarchical namespace containing object identifiers (OID). Each OID identifies a variable that can be read or set via SNMP. OIDs or Object Identifiers uniquely identify manged objects in a MIB hierarchy. This can be depicted as a tree, the levels of which are assigned by different organizations. Top level MIB object IDs (OIDs) belong to different standard organizations. Vendors define private branches including managed objects for their own products.
Using SNMP to monitor disk space on CentOS
The task here is to set up a Nagios test to monitor disk space on a CentOS box. Ive had the firewall protecting the remote CentOS box set up to allow UDP port 161 through so we need to set up SNMP on the box.
Install the SNMP software
yum install net-snmp-utils yum install net-snmp
Now set up the config file
cd /etc/snmp mv snmpd.conf old_snmpd.conf echo 'syslocation "My Location"' >> snmpd.conf echo 'syscontact "Dan Massey"' >> snmpd.conf echo 'sysservices 76' >> snmpd.conf echo '' >> snmpd.conf echo 'rocommunity public localhost' >> snmpd.conf echo 'rocommunity mycommstring ip address' >> snmpd.conf echo '' >> snmpd.conf echo 'disk /' >> snmpd.conf
Make snmpd start up when we reboot
OK, so now we need to check its working locally:
# snmpwalk -v 2c -c public localhost system SNMPv2-MIB::sysDescr.0 = STRING: Linux my.domain.com 2.6.32-358.14.1.el6.i686 #1 SMP Tue Jul 16 21:12:30 UTC 2013 i686 SNMPv2-MIB::sysObjectID.0 = OID: NET-SNMP-MIB::netSnmpAgentOIDs.10 DISMAN-EVENT-MIB::sysUpTimeInstance = Timeticks: (458) 0:00:04.58 SNMPv2-MIB::sysContact.0 = STRING: "Dan Massey" SNMPv2-MIB::sysName.0 = STRING: my.domain.com SNMPv2-MIB::sysLocation.0 = STRING: "My Location" SNMPv2-MIB::sysServices.0 = INTEGER: 76 SNMPv2-MIB::sysORLastChange.0 = Timeticks: (2) 0:00:00.02 SNMPv2-MIB::sysORID.1 = OID: SNMP-MPD-MIB::snmpMPDMIBObjects.3.1.1 SNMPv2-MIB::sysORID.2 = OID: SNMP-USER-BASED-SM-MIB::usmMIBCompliance SNMPv2-MIB::sysORID.3 = OID: SNMP-FRAMEWORK-MIB::snmpFrameworkMIBCompliance SNMPv2-MIB::sysORID.4 = OID: SNMPv2-MIB::snmpMIB SNMPv2-MIB::sysORID.5 = OID: TCP-MIB::tcpMIB SNMPv2-MIB::sysORID.6 = OID: IP-MIB::ip SNMPv2-MIB::sysORID.7 = OID: UDP-MIB::udpMIB SNMPv2-MIB::sysORID.8 = OID: SNMP-VIEW-BASED-ACM-MIB::vacmBasicGroup SNMPv2-MIB::sysORDescr.1 = STRING: The MIB for Message Processing and Dispatching. SNMPv2-MIB::sysORDescr.2 = STRING: The MIB for Message Processing and Dispatching. SNMPv2-MIB::sysORDescr.3 = STRING: The SNMP Management Architecture MIB. SNMPv2-MIB::sysORDescr.4 = STRING: The MIB module for SNMPv2 entities SNMPv2-MIB::sysORDescr.5 = STRING: The MIB module for managing TCP implementations SNMPv2-MIB::sysORDescr.6 = STRING: The MIB module for managing IP and ICMP implementations SNMPv2-MIB::sysORDescr.7 = STRING: The MIB module for managing UDP implementations SNMPv2-MIB::sysORDescr.8 = STRING: View-based Access Control Model for SNMP. SNMPv2-MIB::sysORUpTime.1 = Timeticks: (2) 0:00:00.02 SNMPv2-MIB::sysORUpTime.2 = Timeticks: (2) 0:00:00.02 SNMPv2-MIB::sysORUpTime.3 = Timeticks: (2) 0:00:00.02 SNMPv2-MIB::sysORUpTime.4 = Timeticks: (2) 0:00:00.02 SNMPv2-MIB::sysORUpTime.5 = Timeticks: (2) 0:00:00.02 SNMPv2-MIB::sysORUpTime.6 = Timeticks: (2) 0:00:00.02 SNMPv2-MIB::sysORUpTime.7 = Timeticks: (2) 0:00:00.02 SNMPv2-MIB::sysORUpTime.8 = Timeticks: (2) 0:00:00.02
So that worked fine, let test the disk – i’m only monitoring the ‘/’ partition here so the test and the output looks like:
# /usr/bin/snmpwalk -v 2c -c public localhost .1.3.6.1.4.1.2021.9 UCD-SNMP-MIB::dskIndex.1 = INTEGER: 1 UCD-SNMP-MIB::dskPath.1 = STRING: / UCD-SNMP-MIB::dskDevice.1 = STRING: /dev/mapper/vg_cube-LogVol01 UCD-SNMP-MIB::dskMinimum.1 = INTEGER: 100000 UCD-SNMP-MIB::dskMinPercent.1 = INTEGER: -1 UCD-SNMP-MIB::dskTotal.1 = INTEGER: 1918094464 UCD-SNMP-MIB::dskAvail.1 = INTEGER: 1576078080 UCD-SNMP-MIB::dskUsed.1 = INTEGER: 244582816 UCD-SNMP-MIB::dskPercent.1 = INTEGER: 13 UCD-SNMP-MIB::dskPercentNode.1 = INTEGER: 3 UCD-SNMP-MIB::dskTotalLow.1 = Gauge32: 1918094464 UCD-SNMP-MIB::dskTotalHigh.1 = Gauge32: 0 UCD-SNMP-MIB::dskAvailLow.1 = Gauge32: 1576078080 UCD-SNMP-MIB::dskAvailHigh.1 = Gauge32: 0 UCD-SNMP-MIB::dskUsedLow.1 = Gauge32: 244582816 UCD-SNMP-MIB::dskUsedHigh.1 = Gauge32: 0 UCD-SNMP-MIB::dskErrorFlag.1 = INTEGER: noError(0) UCD-SNMP-MIB::dskErrorMsg.1 = STRING: