=head1 NAME

collectd-snmp - Documentation of collectd's C<snmp plugin>

=head1 SYNOPSIS

  LoadPlugin snmp
  # ...
  <Plugin snmp>
    <Data "powerplus_voltge_input">
      Type "voltage"
      Table false
      Instance "input_line1"
      Values "SNMPv2-SMI::enterprises.6050.5.4.1.1.2.1"
    </Data>
    <Data "hr_users">
      Type "users"
      Table false
      Instance ""
      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"
      Inverval 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>

=head1 DESCRIPTION

The C<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.

=head1 CONFIGURATION

Since the aim of the C<snmp plugin> is to provide a generic interface to SNMP,
it's configuration is not trivial and may take some time.

There are two types of blocks that can be contained in the
C<E<lt>PluginE<nbsp>snmpE<gt>> block: B<Data> and B<Host>:

=head2 The B<Data> block

The B<Data> block defines a list of values or a table of values that are to be
queried. The following options can be set:

=over 4

=item B<Type> I<type>

collectd's type that is to be used, e.E<nbsp>g. "if_octets" for interface
traffic or "users" for a user count. The types are read from the B<TypesDB>
(see L<collectd.conf(5)>), so you may want to check for which types are
defined.

=item B<Table> I<true|false>

Define if this is a single list of values or a table of values. The difference
is that when querying a list of values from SNMP that data is going to be
dispatched as one value-list to the daemon (i.E<nbsp>e.  one RRD file will be
created). If the correcponding data-set needs more than one value (has more
than one data-source) you will still need to configure more than one B<Values>
(see below).

If B<Table> is set to I<true> then the plugin will search the entire subtree
and dispatch all values it can find. This is handy for the typical SNMP
tables, such as the interface table (C<IF-MIB::ifTable>).

Since the semantic of B<Instance> and B<Values> depends on this setting you
need to set it before setting them. Doing vice verse will result in undefined
behavior.

=item B<Instance> I<Instance>

Sets the type-instance of the values that are dispatched. The meaning of this
setting depends on wether B<Table> is set to I<true> or I<false>:

If B<Table> is set to I<true>, I<Instance> is interpreted as an SNMP-prefix
that will return a list of strings. Those strings are then used as the actual
type-instance. An example would be the C<IF-MIB::ifDescr> subtree.
L<variables(5)> from the SNMP distribution describes the format of OIDs.

If B<Table> is set to I<false> the actual string configured for I<Instance> is
copied into the value-list. In this case I<Instance> may be empty, i.E<nbsp>e.
"".

=item B<Values> I<OID> [I<OID> ...]

Configures the values to be queried from the SNMP host. The meaning slightly
changes with the B<Table> setting. L<variables(5)> from the SNMP distribution
describes the format of OIDs.

If B<Table> is set to I<true>, each I<OID> must be the prefix of all the
values to query, e.E<nbsp>g. C<IF-MIB::ifInOctets> for all the counters of
incoming traffic. This subtree is walked (using C<GETNEXT>) until a value from
outside the subtree is returned.

If B<Table> is set to I<false>, each I<OID> must be the OID of exactly one
value, e.E<nbsp>g. C<IF-MIB::ifInOctets.3> for the third counter of incoming
traffic.

=back

=head2 The Host block

The B<Host> block defines which hosts to query, which SNMP community and
version to use and which of the defined B<Data> to query.

The argument passed to the B<Host> block is used as the hostname in the data
stored by collectd.

=over 4

=item B<Address> I<IP-Address>|I<Hostname>

Set the address to connect to.

=item B<Version> B<1>|B<2>

Set the SNMP version to use. When giving B<2> version 2c is actually used.
Version 3 is not supported by this plugin.

=item B<Community> I<Community>

Pass I<Community> to the host.

=item B<Collect> I<Data> [I<Data> ...]

Defines which values to collect. I<Data> refers to one of the B<Data> block
above. Since the config file is read top-down you need to define the data
before using it here.

=item B<Interval> I<Seconds>

Collect data from this host every I<Seconds> seconds. This value needs to be a
multiple of the global B<Interval> setting and, if it is not, will be rounded
B<down> to one and a warning is logged in this case. So if your global
B<Interval> is set to I<10> and you configure I<25> here, it's rounded down to
I<20>. By default the global B<Interval> setting will be used.

This option is meant for devices with not much CPU power, e.E<nbsp>g. network
equipment such as switches, embedded devices, rack monitoring systems and so
on. Since the B<Step> of generated RRD files depends on this setting it's
wise to select a reasonable value once and never change it.

=back

=head1 BUGS

All configured hosts are queried sequencially, so timeouts may cause gaps in
graphs.

=head1 SEE ALSO

L<collectd(1)>,
L<collectd.conf(5)>,
L<snmpget(1)>,
L<snmpgetnext(1)>,
L<variables(5)>,
L<unix(7)>

=head1 AUTHOR

Florian Forster E<lt>octo@verplant.orgE<gt>

=cut