Provided by: collectd-core_4.10.1-2.1ubuntu7_amd64
collectd-snmp - Documentation of collectd's "snmp plugin"
LoadPlugin snmp # ... <Plugin snmp> <Data "powerplus_voltge_input"> Type "voltage" Table false Instance "input_line1" Scale 0.1 Values "SNMPv2-SMI::enterprises.6050.5.4.1.1.2.1" </Data> <Data "hr_users"> Type "users" Table false Instance "" Shift -1 Values "HOST-RESOURCES-MIB::hrSystemNumUsers.0" </Data> <Data "std_traffic"> Type "if_octets" Table true Instance "IF-MIB::ifDescr" Values "IF-MIB::ifInOctets" "IF-MIB::ifOutOctets" </Data> <Host "some.switch.mydomain.org"> Address "192.168.0.2" Version 1 Community "community_string" Collect "std_traffic" Interval 120 </Host> <Host "some.server.mydomain.org"> Address "192.168.0.42" Version 2 Community "another_string" Collect "std_traffic" "hr_users" </Host> <Host "some.ups.mydomain.org"> Address "192.168.0.3" Version 1 Community "more_communities" Collect "powerplus_voltge_input" Interval 300 </Host> </Plugin>
The "snmp plugin" queries other hosts using SNMP, the simple network management protocol, and translates the value it receives to collectd's internal format and dispatches them. Depending on the write plugins you have loaded they may be written to disk or submitted to another instance or whatever you configured. Because querying a host via SNMP may produce a timeout multiple threads are used to query hosts in parallel. Depending on the number of hosts between one and ten threads are used.
Since the aim of the "snmp plugin" is to provide a generic interface to SNMP, it's configuration is not trivial and may take some time. Since the "Net-SNMP" library is used you can use all the environment variables that are interpreted by that package. See snmpcmd(1) for more details. There are two types of blocks that can be contained in the "<Plugin snmp>" block: Data and Host: The Data block The Data block defines a list of values or a table of values that are to be queried. The following options can be set: Type type collectd's type that is to be used, e. g. "if_octets" for interface traffic or "users" for a user count. The types are read from the TypesDB (see collectd.conf(5)), so you may want to check for which types are defined. See types.db(5) for a description of the format of this file. Table true|false Define if this is a single list of values or a table of values. The difference is the following: When Table is set to false, the OIDs given to Values (see below) are queried using the "GET" SNMP command (see snmpget(1)) and transmitted to collectd. One value list is dispatched and, eventually, one file will be written. When Table is set to true, the OIDs given to Values (see below) are queried using the "GETNEXT" SNMP command until the subtree is left. After all the lists (think: all columns of the table) have been read several values sets will be dispatches and, eventually, several files will be written. If you configure a Type (see above) which needs more than one data source (for example "if_octets" which needs "rx" and "tx") you will need to specify more than one (two, in the example case) OIDs with the Values option. This has nothing to do with the Table setting. For example, if you want to query the number of users on a system, you can use "HOST-RESOURCES-MIB::hrSystemNumUsers.0". This is one value and belongs to one value list, therefore Table must be set to false. Please note that, in this case, you have to include the sequence number (zero in this case) in the OID. Counter example: If you want to query the interface table provided by the "IF-MIB", e. g. the bytes transmitted. There are potentially many interfaces, so you will want to set Table to true. Because the "if_octets" type needs two values, received and transmitted bytes, you need to specify two OIDs in the Values setting, in this case likely "IF-MIB::ifHCInOctets" and "IF-MIB::ifHCOutOctets". But, this is because of the Type setting, not the Table setting. Since the semantic of Instance and Values depends on this setting you need to set it before setting them. Doing vice verse will result in undefined behavior. Instance Instance Sets the type-instance of the values that are dispatched. The meaning of this setting depends on whether Table is set to true or false: If Table is set to true, Instance is interpreted as an SNMP-prefix that will return a list of values. Those values are then used as the actual type-instance. An example would be the "IF-MIB::ifDescr" subtree. variables(5) from the SNMP distribution describes the format of OIDs. If Table is set to true and Instance is omitted, then "SUBID" will be used as the instance. If Table is set to false the actual string configured for Instance is copied into the value-list. In this case Instance may be empty, i. e. "". InstancePrefix String If Table is set to true, you may feel the need to add something to the instance of the files. If set, String is prepended to the instance as determined by querying the agent. When Table is set to false this option has no effect. The "UPS-MIB" is an example where you need this setting: It has voltages of the inlets, outlets and the battery of an UPS. However, it doesn't provide a descriptive column for these voltages. In this case having 1, 2, ... as instances is not enough, because the inlet voltages and outlet voltages may both have the subids 1, 2, ... You can use this setting to distinguish between the different voltages. Values OID [OID ...] Configures the values to be queried from the SNMP host. The meaning slightly changes with the Table setting. variables(5) from the SNMP distribution describes the format of OIDs. If Table is set to true, each OID must be the prefix of all the values to query, e. g. "IF-MIB::ifInOctets" for all the counters of incoming traffic. This subtree is walked (using "GETNEXT") until a value from outside the subtree is returned. If Table is set to false, each OID must be the OID of exactly one value, e. g. "IF-MIB::ifInOctets.3" for the third counter of incoming traffic. Scale Value The gauge-values returned by the SNMP-agent are multiplied by Value. This is useful when values are transfered as a fixed point real number. For example, thermometers may transfer 243 but actually mean 24.3, so you can specify a scale value of 0.1 to correct this. The default value is, of course, 1.0. This value is not applied to counter-values. Shift Value Value is added to gauge-values returned by the SNMP-agent after they have been multiplied by any Scale value. If, for example, a thermometer returns degrees Kelvin you could specify a shift of 273.15 here to store values in degrees Celsius. The default value is, of course, 0.0. This value is not applied to counter-values. The Host block The Host block defines which hosts to query, which SNMP community and version to use and which of the defined Data to query. The argument passed to the Host block is used as the hostname in the data stored by collectd. Address IP-Address|Hostname Set the address to connect to. Version 1|2 Set the SNMP version to use. When giving 2 version "2c" is actually used. Version 3 is not supported by this plugin. Community Community Pass Community to the host. Collect Data [Data ...] Defines which values to collect. Data refers to one of the Data block above. Since the config file is read top-down you need to define the data before using it here. Interval Seconds Collect data from this host every Seconds seconds. This option is meant for devices with not much CPU power, e. g. network equipment such as switches, embedded devices, rack monitoring systems and so on. Since the Step of generated RRD files depends on this setting it's wise to select a reasonable value once and never change it.
collectd(1), collectd.conf(5), snmpget(1), snmpgetnext(1), variables(5), unix(7)
Florian Forster <firstname.lastname@example.org>