possibly need this option. What CA certificates come bundled with C<libcurl>
and are checked by default depends on the distribution you use.
+=item B<MeasureResponseTime> B<true>|B<false>
+
+Measure response time for the request. Disabled by default.
+
=item B<E<lt>MatchE<gt>>
One or more B<Match> blocks that define how to match information in the data
=back
+=head2 Plugin C<curl_json>
+
+The B<curl_json plugin> uses B<libcurl> (L<http://curl.haxx.se/>) and
+B<libyajl> (L<http://www.lloydforge.org/projects/yajl/>) to retrieve JSON data
+via cURL. This can be used to collect values from CouchDB documents (which are
+stored JSON notation), for example.
+
+The following example will collect several values from the built-in `_stats'
+runtime statistics module of CouchDB
+(L<http://wiki.apache.org/couchdb/Runtime_Statistics>).
+
+ <Plugin curl_json>
+ <URL "http://localhost:5984/_stats">
+ Instance "httpd"
+ <Key "httpd/requests/count">
+ Type "http_requests"
+ </Key>
+
+ <Key "httpd_request_methods/*/count">
+ Type "http_request_methods"
+ </Key>
+
+ <Key "httpd_status_codes/*/count">
+ Type "http_response_codes"
+ </Key>
+ </URL>
+ </Plugin>
+
+Another CouchDB example:
+The following example will collect the status values from each database:
+
+ <URL "http://localhost:5984/_all_dbs">
+ Instance "dbs"
+ <Key "*/doc_count">
+ Type "gauge"
+ </Key>
+ <Key "*/doc_del_count">
+ Type "counter"
+ </Key>
+ <Key "*/disk_size">
+ Type "bytes"
+ </Key>
+ </URL>
+
+In the B<Plugin> block, there may be one or more B<URL> blocks, each defining
+a URL to be fetched via HTTP (using libcurl) and one or more B<Key> blocks.
+The B<Key> string argument must be in a path format, of which is used to collect
+a value from a JSON map object. If a B<Key> path element is that of a I<*> wildcard,
+the values for all keys will be collectd.
+
+The following options are valid within B<URL> blocks:
+
+=over 4
+
+=item B<Instance> I<Instance>
+
+Sets the plugin instance to I<Instance>.
+
+=item B<User> I<Name>
+
+Username to use if authorization is required to read the page.
+
+=item B<Password> I<Password>
+
+Password to use if authorization is required to read the page.
+
+=item B<VerifyPeer> B<true>|B<false>
+
+Enable or disable peer SSL certificate verification. See
+L<http://curl.haxx.se/docs/sslcerts.html> for details. Enabled by default.
+
+=item B<VerifyHost> B<true>|B<false>
+
+Enable or disable peer host name verification. If enabled, the plugin checks if
+the C<Common Name> or a C<Subject Alternate Name> field of the SSL certificate
+matches the host name provided by the B<URL> option. If this identity check
+fails, the connection is aborted. Obviously, only works when connecting to a
+SSL enabled server. Enabled by default.
+
+=item B<CACert> I<file>
+
+File that holds one or more SSL certificates. If you want to use HTTPS you will
+possibly need this option. What CA certificates come bundled with C<libcurl>
+and are checked by default depends on the distribution you use.
+
+=back
+
+The following options are valid within B<Key> blocks:
+
+=over 4
+
+=item B<Type> I<Type>
+
+Sets the type used to dispatch the values to the daemon. Detailed information
+about types and their configuration can be found in L<types.db(5)>. This
+option is mandatory.
+
+=item B<Instance> I<Instance>
+
+Type-instance to use. Defaults to the current map key or current string array element value.
+
+=back
+
=head2 Plugin C<dbi>
This plugin uses the B<dbi> library (L<http://libdbi.sourceforge.net/>) to
Select partitions based on the filesystem type.
-=item B<IgnoreSelected> I<true>|I<false>
+=item B<IgnoreSelected> B<true>|B<false>
Invert the selection: If set to true, all partitions B<except> the ones that
match any one of the criteria are collected. By default only selected
partitions are collected if a selection is made. If no selection is configured
at all, B<all> partitions are selected.
+=item B<ReportByDevice> B<true>|B<false>
+
+Report using the device name rather than the mountpoint. i.e. with this I<false>,
+(the default), it will report a disk as "root", but with it I<true>, it will be
+"sda1" (or whichever).
+
+=item B<ReportReserved> B<true>|B<false>
+
+When enabled, the blocks reserved for root are reported separately. When
+disabled (the default for backwards compatibility reasons) the reserved space
+will be included in the "free" space.
+
+When disabled, the "df" type will be used to store "free" and "used" space. The
+mount point or disk name (see option B<ReportByDevice>) is used as type
+instance in this case (again: backwards compatibility).
+
+When enabled, the type "df_complex" is used and three files are created. The
+mount point or disk name is used as plugin instance and the type instance is
+set to "free", "reserved" and "used" as appropriate.
+
+Enabling this option is recommended.
+
+=item B<ReportInodes> B<true>|B<false>
+
+Enables or disables reporting of free, reserved and used inodes. Defaults to
+inode collection being disabled.
+
+Enable this option if inodes are a scarce resource for you, usually because
+many small files are stored on the disk. This is a usual scenario for mail
+transfer agents and web caches.
+
=back
=head2 Plugin C<disk>
Ignore packets that originate from this address.
+=item B<SelectNumericQueryTypes> B<true>|B<false>
+
+Enabled by default, collects unknown (and thus presented as numeric only) query types.
+
=back
=head2 Plugin C<email>
=back
+=head2 Plugin C<GenericJMX>
+
+The I<GenericJMX plugin> is written in I<Java> and therefore documented in
+L<collectd-java(5)>.
+
=head2 Plugin C<gmond>
The I<gmond> plugin received the multicast traffic sent by B<gmond>, the
=back
+=head2 Plugin C<netapp>
+
+The netapp plugin can collect various performance and capacity informations
+from a NetApp filer using the NetApp API.
+
+To collect these data collectd will log in to the NetApp via HTTP(S) and HTTP
+basic authentication.
+
+B<Do not use a regular user for this!> Create a special collectd user with just
+the minimum of capabilities needed. The user only needs the "login-http-admin"
+capability as well as a few more depending on which data will be collected.
+Required capabilities are documented below.
+
+=head3 Synopsis
+
+ <Plugin "netapp">
+ <Host "netapp1.example.com">
+ Protocol "https"
+ Address "10.0.0.1"
+ Port 443
+ User "username"
+ Password "aef4Aebe"
+ Interval 30
+
+ <WAFL>
+ Interval 30
+ GetNameCache true
+ GetDirCache true
+ GetBufferCache true
+ GetInodeCache true
+ </WAFL>
+
+ <Disks>
+ Interval 30
+ GetBusy true
+ </Disks>
+
+ <VolumePerf>
+ Interval 30
+ GetIO "volume0"
+ IgnoreSelectedIO false
+ GetOps "volume0"
+ IgnoreSelectedOps false
+ GetLatency "volume0"
+ IgnoreSelectedLatency false
+ </VolumePerf>
+
+ <VolumeUsage>
+ Interval 30
+ GetCapacity "vol0"
+ GetCapacity "vol1"
+ IgnoreSelectedCapacity false
+ GetSnapshot "vol1"
+ GetSnapshot "vol3"
+ IgnoreSelectedSnapshot false
+ </VolumeUsage>
+
+ <System>
+ Interval 30
+ GetCPULoad true
+ GetInterfaces true
+ GetDiskOps true
+ GetDiskIO true
+ </System>
+ </Host>
+ </Plugin>
+
+The netapp plugin accepts the following configuration options:
+
+=over 4
+
+=item B<Host> I<Name>
+
+A host block defines one NetApp filer. It will appear in collectd with the name
+you specify here which does not have to be its real name nor its hostname.
+
+=item B<Protocol> B<httpd>|B<http>
+
+The protocol collectd will use to query this host.
+
+Optional
+
+Type: string
+
+Default: https
+
+Valid options: http, https
+
+=item B<Address> I<Address>
+
+The hostname or IP address of the host.
+
+Optional
+
+Type: string
+
+Default: The "host" block's name.
+
+=item B<Port> I<Port>
+
+The TCP port to connect to on the host.
+
+Optional
+
+Type: integer
+
+Default: 80 for protocol "http", 443 for protocol "https"
+
+=item B<User> I<User>
+
+=item B<Password> I<Password>
+
+The username and password to use to login to the NetApp.
+
+Mandatory
+
+Type: string
+
+=item B<Interval> I<Interval>
+
+B<TODO>
+
+=back
+
+The following options decide what kind of data will be collected. You can
+either use them as a block and fine tune various parameters inside this block,
+use them as a single statement to just accept all default values, or omit it to
+not collect any data.
+
+The following options are valid inside all blocks:
+
+=over 4
+
+=item B<Interval> I<Seconds>
+
+Collect the respective statistics every I<Seconds> seconds. Defaults to the
+host specific setting.
+
+=back
+
+=head3 The System block
+
+This will collect various performance data about the whole system.
+
+B<Note:> To get this data the collectd user needs the
+"api-perf-object-get-instances" capability.
+
+=over 4
+
+=item B<Interval> I<Seconds>
+
+Collect disk statistics every I<Seconds> seconds.
+
+=item B<GetCPULoad> B<true>|B<false>
+
+If you set this option to true the current CPU usage will be read. This will be
+the average usage between all CPUs in your NetApp without any information about
+individual CPUs.
+
+B<Note:> These are the same values that the NetApp CLI command "sysstat"
+returns in the "CPU" field.
+
+Optional
+
+Type: boolean
+
+Default: true
+
+Result: Two value lists of type "cpu", and type instances "idle" and "system".
+
+=item B<GetInterfaces> B<true>|B<false>
+
+If you set this option to true the current traffic of the network interfaces
+will be read. This will be the total traffic over all interfaces of your NetApp
+without any information about individual interfaces.
+
+B<Note:> This is the same values that the NetApp CLI command "sysstat" returns
+in the "Net kB/s" field.
+
+B<Or is it?>
+
+Optional
+
+Type: boolean
+
+Default: true
+
+Result: One value list of type "if_octects".
+
+=item B<GetDiskIO> B<true>|B<false>
+
+If you set this option to true the current IO throughput will be read. This
+will be the total IO of your NetApp without any information about individual
+disks, volumes or aggregates.
+
+B<Note:> This is the same values that the NetApp CLI command "sysstat" returns
+in the "DiskE<nbsp>kB/s" field.
+
+Optional
+
+Type: boolean
+
+Default: true
+
+Result: One value list of type "disk_octets".
+
+=item B<GetDiskOps> B<true>|B<false>
+
+If you set this option to true the current number of HTTP, NFS, CIFS, FCP,
+iSCSI, etc. operations will be read. This will be the total number of
+operations on your NetApp without any information about individual volumes or
+aggregates.
+
+B<Note:> These are the same values that the NetApp CLI command "sysstat"
+returns in the "NFS", "CIFS", "HTTP", "FCP" and "iSCSI" fields.
+
+Optional
+
+Type: boolean
+
+Default: true
+
+Result: A variable number of value lists of type "disk_ops_complex". Each type
+of operation will result in one value list with the name of the operation as
+type instance.
+
+=back
+
+=head3 The WAFL block
+
+This will collect various performance data about the WAFL file system. At the
+moment this just means cache performance.
+
+B<Note:> To get this data the collectd user needs the
+"api-perf-object-get-instances" capability.
+
+B<Note:> The interface to get these values is classified as "Diagnostics" by
+NetApp. This means that it is not guaranteed to be stable even between minor
+releases.
+
+=over 4
+
+=item B<Interval> I<Seconds>
+
+Collect disk statistics every I<Seconds> seconds.
+
+=item B<GetNameCache> B<true>|B<false>
+
+Optional
+
+Type: boolean
+
+Default: true
+
+Result: One value list of type "cache_ratio" and type instance
+"name_cache_hit".
+
+=item B<GetDirCache> B<true>|B<false>
+
+Optional
+
+Type: boolean
+
+Default: true
+
+Result: One value list of type "cache_ratio" and type instance "find_dir_hit".
+
+=item B<GetInodeCache> B<true>|B<false>
+
+Optional
+
+Type: boolean
+
+Default: true
+
+Result: One value list of type "cache_ratio" and type instance
+"inode_cache_hit".
+
+=item B<GetBufferCache> B<true>|B<false>
+
+B<Note:> This is the same value that the NetApp CLI command "sysstat" returns
+in the "Cache hit" field.
+
+Optional
+
+Type: boolean
+
+Default: true
+
+Result: One value list of type "cache_ratio" and type instance "buf_hash_hit".
+
+=back
+
+=head3 The Disks block
+
+This will collect performance data about the individual disks in the NetApp.
+
+B<Note:> To get this data the collectd user needs the
+"api-perf-object-get-instances" capability.
+
+=over 4
+
+=item B<Interval> I<Seconds>
+
+Collect disk statistics every I<Seconds> seconds.
+
+=item B<GetBusy> B<true>|B<false>
+
+If you set this option to true the busy time of all disks will be calculated
+and the value of the busiest disk in the system will be written.
+
+B<Note:> This is the same values that the NetApp CLI command "sysstat" returns
+in the "Disk util" field. Probably.
+
+Optional
+
+Type: boolean
+
+Default: true
+
+Result: One value list of type "percent" and type instance "disk_busy".
+
+=back
+
+=head3 The VolumePerf block
+
+This will collect various performance data about the individual volumes.
+
+You can select which data to collect about which volume using the following
+options. They follow the standard ignorelist semantic.
+
+B<Note:> To get this data the collectd user needs the
+I<api-perf-object-get-instances> capability.
+
+=over 4
+
+=item B<Interval> I<Seconds>
+
+Collect volume performance data every I<Seconds> seconds.
+
+=item B<GetIO> I<Volume>
+
+=item B<GetOps> I<Volume>
+
+=item B<GetLatency> I<Volume>
+
+Select the given volume for IO, operations or latency statistics collection.
+The argument is the name of the volume without the C</vol/> prefix.
+
+Since the standard ignorelist functionality is used here, you can use a string
+starting and ending with a slash to specify regular expression matching: To
+match the volumes "vol0", "vol2" and "vol7", you can use this regular
+expression:
+
+ GetIO "/^vol[027]$/"
+
+If no regular expression is specified, an exact match is required. Both,
+regular and exact matching are case sensitive.
+
+If no volume was specified at all for either of the three options, that data
+will be collected for all available volumes.
+
+=item B<IgnoreSelectedIO> B<true>|B<false>
+
+=item B<IgnoreSelectedOps> B<true>|B<false>
+
+=item B<IgnoreSelectedLatency> B<true>|B<false>
+
+When set to B<true>, the volumes selected for IO, operations or latency
+statistics collection will be ignored and the data will be collected for all
+other volumes.
+
+When set to B<false>, data will only be collected for the specified volumes and
+all other volumes will be ignored.
+
+If no volumes have been specified with the above B<Get*> options, all volumes
+will be collected regardless of the B<IgnoreSelected*> option.
+
+Defaults to B<false>
+
+=back
+
+=head3 The VolumeUsage block
+
+This will collect capacity data about the individual volumes.
+
+B<Note:> To get this data the collectd user needs the I<api-volume-list-info>
+capability.
+
+=over 4
+
+=item B<Interval> I<Seconds>
+
+Collect volume usage statistics every I<Seconds> seconds.
+
+=item B<GetCapacity> I<VolumeName>
+
+The current capacity of the volume will be collected. This will result in two
+to four value lists, depending on the configuration of the volume. All data
+sources are of type "df_complex" with the name of the volume as
+plugin_instance.
+
+There will be type_instances "used" and "free" for the number of used and
+available bytes on the volume. If the volume has some space reserved for
+snapshots, a type_instance "snap_reserved" will be available. If the volume
+has SIS enabled, a type_instance "sis_saved" will be available. This is the
+number of bytes saved by the SIS feature.
+
+B<Note:> The current NetApp API has a bug that results in this value being
+reported as a 32E<nbsp>bit number. This plugin tries to guess the correct
+number which works most of the time. If you see strange values here, bug
+NetApp support to fix this.
+
+Repeat this option to specify multiple volumes.
+
+=item B<IgnoreSelectedCapacity> B<true>|B<false>
+
+Specify whether to collect only the volumes selected by the B<GetCapacity>
+option or to ignore those volumes. B<IgnoreSelectedCapacity> defaults to
+B<false>. However, if no B<GetCapacity> option is specified at all, all
+capacities will be selected anyway.
+
+=item B<GetSnapshot> I<VolumeName>
+
+Select volumes from which to collect snapshot information.
+
+Usually, the space used for snapshots is included in the space reported as
+"used". If snapshot information is collected as well, the space used for
+snapshots is subtracted from the used space.
+
+To make things even more interesting, it is possible to reserve space to be
+used for snapshots. If the space required for snapshots is less than that
+reserved space, there is "reserved free" and "reserved used" space in addition
+to "free" and "used". If the space required for snapshots exceeds the reserved
+space, that part allocated in the normal space is subtracted from the "used"
+space again.
+
+Repeat this option to specify multiple volumes.
+
+=item B<IgnoreSelectedSnapshot>
+
+Specify whether to collect only the volumes selected by the B<GetSnapshot>
+option or to ignore those volumes. B<IgnoreSelectedSnapshot> defaults to
+B<false>. However, if no B<GetSnapshot> option is specified at all, all
+capacities will be selected anyway.
+
+=back
+
=head2 Plugin C<netlink>
The C<netlink> plugin uses a netlink socket to query the Linux kernel about
That means that multicast packets will be sent with a TTL of C<1> (one) on most
operating systems.
+=item B<MaxPacketSize> I<1024-65535>
+
+Set the maximum size for datagrams received over the network. Packets larger
+than this will be truncated.
+
=item B<Forward> I<true|false>
If set to I<true>, write packets that were received via the network plugin to
1800 seconds, but setting this to 86400 seconds (one day) will not do much harm
either.
+=item B<ReportStats> B<true>|B<false>
+
+The network plugin cannot only receive and send statistics, it can also create
+statistics about itself. Collected data included the number of received and
+sent octets and packets, the length of the receive queue and the number of
+values handled. When set to B<true>, the I<Network plugin> will make these
+statistics available. Defaults to B<false>.
+
=back
=head2 Plugin C<nginx>
=back
+=head2 Plugin C<olsrd>
+
+The I<olsrd> plugin connects to the TCP port opened by the I<txtinfo> plugin of
+the Optimized Link State Routing daemon and reads information about the current
+state of the meshed network.
+
+The following configuration options are understood:
+
+=over 4
+
+=item B<Host> I<Host>
+
+Connect to I<Host>. Defaults to B<"localhost">.
+
+=item B<Port> I<Port>
+
+Specifies the port to connect to. This must be a string, even if you give the
+port as a number rather than a service name. Defaults to B<"2006">.
+
+=item B<CollectLinks> B<No>|B<Summary>|B<Detail>
+
+Specifies what information to collect about links, i.E<nbsp>e. direct
+connections of the daemon queried. If set to B<No>, no information is
+collected. If set to B<Summary>, the number of links and the average of all
+I<link quality> (LQ) and I<neighbor link quality> (NLQ) values is calculated.
+If set to B<Detail> LQ and NLQ are collected per link.
+
+Defaults to B<Detail>.
+
+=item B<CollectRoutes> B<No>|B<Summary>|B<Detail>
+
+Specifies what information to collect about routes of the daemon queried. If
+set to B<No>, no information is collected. If set to B<Summary>, the number of
+routes and the average I<metric> and I<ETX> is calculated. If set to B<Detail>
+metric and ETX are collected per route.
+
+Defaults to B<Summary>.
+
+=item B<CollectTopology> B<No>|B<Summary>|B<Detail>
+
+Specifies what information to collect about the global topology. If set to
+B<No>, no information is collected. If set to B<Summary>, the number of links
+in the entire topology and the average I<link quality> (LQ) is calculated.
+If set to B<Detail> LQ and NLQ are collected for each link in the entire topology.
+
+Defaults to B<Summary>.
+
+=back
+
=head2 Plugin C<onewire>
B<EXPERIMENTAL!> See notes below.
Specifies the location of the status file.
+=item B<Compression> B<true>|B<false>
+
+Sets whether or not statistics about the compression used by OpenVPN should be
+collected. This information is only available in I<single> mode. Enabled by
+default.
+
=back
=head2 Plugin C<oracle>
The B<Query> block defines one database query which may later be used by a
database definition. It accepts a single mandatory argument which specifies
the name of the query. The names of all queries have to be unique (see the
-B<MinPGVersion> and B<MaxPGVersion> options below for an exception to this
+B<MinVersion> and B<MaxVersion> options below for an exception to this
rule). The following configuration options are available to define the query:
In each B<Query> block, there is one or more B<Result> blocks. B<Result>
should be used. The first option specifies the data found in the first column,
the second option that of the second column, and so on.
-=item B<MinPGVersion> I<version>
+=item B<MinVersion> I<version>
-=item B<MaxPGVersion> I<version>
+=item B<MaxVersion> I<version>
Specify the minimum or maximum version of PostgreSQL that this query should be
used with. Some statistics might only be available with certain versions of
and patch-level versions, each represented as two-decimal-digit numbers. For
example, version 8.2.3 will become 80203.
+=item B<MinPGVersion> I<version>
+
+=item B<MaxPGVersion> I<version>
+
+These are deprecated synonyms for B<MinVersion> and B<MaxVersion>
+respectively. They will be removed in version 5 of collectd.
+
=back
The following predefined queries are available (the definitions can be found
Select more detailed statistics of processes matching this name. The statistics
collected for these selected processes are size of the resident segment size
(RSS), user- and system-time used, number of processes and number of threads,
-and minor and major pagefaults.
+io data (where available) and minor and major pagefaults.
=item B<ProcessMatch> I<name> I<regex>
=head2 Plugin C<rrdcached>
-The C<rrdcached> plugin uses the RRDTool accelerator daemon, L<rrdcached(1)>,
+The C<rrdcached> plugin uses the RRDtool accelerator daemon, L<rrdcached(1)>,
to store values to RRD files in an efficient manner. The combination of the
C<rrdcached> B<plugin> and the C<rrdcached> B<daemon> is very similar to the
way the C<rrdtool> plugin works (see below). The added abstraction layer
You can use the settings B<StepSize>, B<HeartBeat>, B<RRARows>, and B<XFF> to
fine-tune your RRD-files. Please read L<rrdcreate(1)> if you encounter problems
-using these settings. If you don't want to dive into the depths of RRDTool, you
+using these settings. If you don't want to dive into the depths of RRDtool, you
can safely ignore these settings.
=over 4
"collection3" you'll end up with a responsive and fast system, up to date
graphs and basically a "backup" of your values every hour.
+=item B<RandomTimeout> I<Seconds>
+
+When set, the actual timeout for each value is chosen randomly between
+I<CacheTimeout>-I<RandomTimeout> and I<CacheTimeout>+I<RandomTimeout>. The
+intention is to avoid high load situations that appear when many values timeout
+at the same time. This is especially a problem shortly after the daemon starts,
+because all values were added to the internal cache at roughly the same time.
+
=back
=head2 Plugin C<sensors>
=back
+=head2 Plugin C<tokyotyrant>
+
+The C<tokyotyrant plugin> connects to a TokyoTyrant server and collects a
+couple metrics: number of records, and database size on disk.
+
+=over 4
+
+=item B<Host> I<Hostname/IP>
+
+The hostname or ip which identifies the server.
+Default: B<127.0.0.1>
+
+=item B<Port> I<Service/Port>
+
+The query port of the server. This needs to be a string, even if the port is
+given in its numeric form.
+Default: B<1978>
+
+=back
+
=head2 Plugin C<unixsock>
=over 4
collect on-wire traffic you could, for example, use the logging facilities of
iptables to feed data for the guest IPs into the iptables plugin.
+=head2 Plugin C<write_http>
+
+This output plugin submits values to an http server by POST them using the
+PUTVAL plain-text protocol. Each destination you want to post data to needs to
+have one B<URL> block, within which the destination can be configured further,
+for example by specifying authentication data.
+
+Synopsis:
+
+ <Plugin "write_http">
+ <URL "http://example.com/post-collectd">
+ User "collectd"
+ Password "weCh3ik0"
+ </URL>
+ </Plugin>
+
+B<URL> blocks need one string argument which is used as the URL to which data
+is posted. The following options are understood within B<URL> blocks.
+
+=over 4
+
+=item B<User> I<Username>
+
+Optional user name needed for authentication.
+
+=item B<Password> I<Password>
+
+Optional password needed for authentication.
+
+=item B<VerifyPeer> B<true>|B<false>
+
+Enable or disable peer SSL certificate verification. See
+L<http://curl.haxx.se/docs/sslcerts.html> for details. Enabled by default.
+
+=item B<VerifyHost> B<true|false>
+
+Enable or disable peer host name verification. If enabled, the plugin checks if
+the C<Common Name> or a C<Subject Alternate Name> field of the SSL certificate
+matches the host name provided by the B<URL> option. If this identity check
+fails, the connection is aborted. Obviously, only works when connecting to a
+SSL enabled server. Enabled by default.
+
+=item B<CACert> I<File>
+
+File that holds one or more SSL certificates. If you want to use HTTPS you will
+possibly need this option. What CA certificates come bundled with C<libcurl>
+and are checked by default depends on the distribution you use.
+
+=item B<Format> B<Command>|B<JSON>
+
+Format of the output to generate. If set to B<Command>, will create output that
+is understood by the I<Exec> and I<UnixSock> plugins. When set to B<JSON>, will
+create output in the I<JavaScript Object Notation> (JSON).
+
+Defaults to B<Command>.
+
+=back
+
=head1 THRESHOLD CONFIGURATION
Starting with version C<4.3.0> collectd has support for B<monitoring>. By that
missing value is generated once every B<Interval> seconds. If set to B<false>
only one such notification is generated until the value appears again.
+=item B<Percentage> B<true>|B<false>
+
+If set to B<true>, the minimum and maximum values given are interpreted as
+percentage value, relative to the other data sources. This is helpful for
+example for the "df" type, where you may want to issue a warning when less than
+5E<nbsp>% of the total space is available. Defaults to B<false>.
+
=back
=head1 FILTER CONFIGURATION
Satisfy "Any"
</Match>
+=item B<empty_counter>
+
+Matches all values with one or more data sources of type B<COUNTER> and where
+all counter values are zero. These counters usually I<never> increased since
+they started existing (and are therefore uninteresting), or got reset recently
+or overflowed and you had really, I<really> bad luck.
+
+Please keep in mind that ignoring such counters can result in confusing
+behavior: Counters which hardly ever increase will be zero for long periods of
+time. If the counter is reset for some reason (machine or service restarted,
+usually), the graph will be empty (NAN) for a long time. People may not
+understand why.
+
+=item B<hashed>
+
+Calculates a hash value of the host name and matches values according to that
+hash value. This makes it possible to divide all hosts into groups and match
+only values that are in a specific group. The intended use is in load
+balancing, where you want to handle only part of all data and leave the rest
+for other servers.
+
+The hashing function used tries to distribute the hosts evenly. First, it
+calculates a 32E<nbsp>bit hash value using the characters of the hostname:
+
+ hash_value = 0;
+ for (i = 0; host[i] != 0; i++)
+ hash_value = (hash_value * 251) + host[i];
+
+The constant 251 is a prime number which is supposed to make this hash value
+more random. The code then checks the group for this host according to the
+I<Total> and I<Match> arguments:
+
+ if ((hash_value % Total) == Match)
+ matches;
+ else
+ does not match;
+
+Please note that when you set I<Total> to two (i.E<nbsp>e. you have only two
+groups), then the least significant bit of the hash value will be the XOR of
+all least significant bits in the host name. One consequence is that when you
+have two hosts, "server0.example.com" and "server1.example.com", where the host
+name differs in one digit only and the digits differ by one, those hosts will
+never end up in the same group.
+
+Available options:
+
+=over 4
+
+=item B<Match> I<Match> I<Total>
+
+Divide the data into I<Total> groups and match all hosts in group I<Match> as
+described above. The groups are numbered from zero, i.E<nbsp>e. I<Match> must
+be smaller than I<Total>. I<Total> must be at least one, although only values
+greater than one really do make any sense.
+
+You can repeat this option to match multiple groups, for example:
+
+ Match 3 7
+ Match 5 7
+
+The above config will divide the data into seven groups and match groups three
+and five. One use would be to keep every value on two hosts so that if one
+fails the missing data can later be reconstructed from the second host.
+
+=back
+
+Example:
+
+ # Operate on the pre-cache chain, so that ignored values are not even in the
+ # global cache.
+ <Chain "PreCache">
+ <Rule>
+ <Match "hashed">
+ # Divide all received hosts in seven groups and accept all hosts in
+ # group three.
+ Match 3 7
+ </Match>
+ # If matched: Return and continue.
+ Target "return"
+ </Rule>
+ # If not matched: Return and stop.
+ Target "stop"
+ </Chain>
+
=back
=head2 Available targets