collectd-snmp - Documentation of collectd's "snmp plugin"
Values "IF-MIB::ifInOctets" "IF-MIB::ifOutOctets"
Collect "std_traffic" "hr_users"
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
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:
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.
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.
Sets the type-instance of the values that are dispatched. The
meaning of this setting depends on whether Table is set to true or
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. "".
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
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.
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.
Set the address to connect to.
Set the SNMP version to use. When giving 2 version "2c" is actually
used. Version 3 is not supported by this plugin.
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.
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),
Florian Forster <firstname.lastname@example.org>