collectd-unixsock(5) - Linux man page

Name

collectd-unixsock - Documentation of collectd's "unixsock plugin"

Synopsis

# See collectd.conf(5)
LoadPlugin unixsock
# ...
<Plugin unixsock>
  SocketFile "/path/to/socket"
  SocketGroup "collectd"
  SocketPerms "0770"
</Plugin>

Description

The "unixsock plugin" opens an UNIX-socket over which one can interact with the daemon. This can be used to use the values collected by collectd in other applications, such as monitoring, or submit externally collected values to collectd.

This plugin is used by collectd-nagios(1) to check if some value is in a certain range and exit with a Nagios-compatible exit code.

Commands

Upon start the "unixsock plugin" opens a UNIX-socket and waits for connections. Once a connection is established the client can send commands to the daemon which it will answer, if it understand them.

The following commands are implemented:

GETVAL Identifier

If the value identified by Identifier (see below) is found the complete value-list is returned. The response is a space separated list of name-value-pairs:

num name=value[ name=value[ ...]]

If num is less then zero, an error occurred. Otherwise it contains the number of values that follow. Each value is of the form name=value. Counter-values are converted to a rate, e. g. bytes per second. Undefined values are returned as NaN.

Example: -> | GETVAL myhost/cpu-0/cpu-user <- | 1 value=1.260000e+00

LISTVAL

Returns a list of the values available in the value cache together with the time of the last update, so that querying applications can issue a GETVAL command for the values that have changed.

The first line's status number is the number of identifiers returned or less than zero if an error occurred. Each of the following lines contains the update time as an epoch value and the identifier, separated by a space.

PUTVAL Identifier [OptionList] Valuelist

Submits one or more values (identified by Identifier, see below) to the daemon which will dispatch it to all it's write-plugins.

An Identifier is of the form " host / plugin - instance / type - instance " with both instance-parts being optional. If they're omitted the hyphen must be omitted, too. plugin and each instance-part may be chosen freely as long as the tuple (plugin, plugin instance, type instance) uniquely identifies the plugin within collectd. type identifies the type and number of values (i. e. data-set) passed to collectd. A large list of predefined data-sets is available in the types.db file.

The OptionList is an optional list of Options, where each option is a key-value-pair. A list of currently understood options can be found below, all other options will be ignored.

Valuelist is a colon-separated list of the time and the values, each either an integer if the data-source is a counter, or a double if the data-source is of type "gauge". You can submit an undefined gauge-value by using U. When submitting U to a counter the behavior is undefined. The time is given as epoch (i. e. standard UNIX time).

You can mix options and values, but the order is important: Options only effect following values, so specifying an option as last field is allowed, but useless. Also, an option applies to all following values, so you don't need to re-set an option over and over again.

The currently defined Options are:

interval=seconds

Gives the interval in which the data identified by Identifier is being collected.

Please note that this is the same format as used in the exec plugin, see collectd-exec(5).

Example: -> | PUTVAL testhost/interface/if_octets-test0 interval=10 1179574444:123:456 <- | 0 Success

PUTNOTIF [OptionList] message=Message

Submits a notification to the daemon which will then dispatch it to all plugins which have registered for receiving notifications.

The PUTNOTIF if followed by a list of options which further describe the notification. The message option is special in that it will consume the rest of the line as its value. The message, severity, and time options are mandatory.

Valid options are:

message=Message ( REQUIRED )

Sets the message of the notification. This is the message that will be made accessible to the user, so it should contain some useful information. This option must be the last option because the rest of the line will be its value, even if there are spaces and equal-signs following it! This option is mandatory.

severity=failure|warning|okay ( REQUIRED )

Sets the severity of the notification. This option is mandatory.

time=Time ( REQUIRED )

Sets the time of the notification. The time is given as "epoch", i. e. as seconds since January 1st, 1970, 00:00:00. This option is mandatory.

host=Hostname

plugin=Plugin

plugin_instance=Plugin-Instance

type=Type

type_instance=Type-Instance

These "associative" options establish a relation between this notification and collected performance data. This connection is purely informal, i. e. the daemon itself doesn't do anything with this information. However, websites or GUIs may use this information to place notifications near the affected graph or table. All the options are optional, but plugin_instance without plugin or type_instance without type doesn't make much sense and should be avoided.

Please note that this is the same format as used in the exec plugin, see collectd-exec(5).

Example: -> | PUTNOTIF type=temperature severity=warning time=1201094702 message=The roof is on fire! <- | 0 Success

Identifiers
Value or value-lists are identified in a uniform fashion:
Hostname/Plugin/Type
Where Plugin and Type are both either of type "Name" or "Name-Instance". This sounds more complicated than it is, so here are some examples:
myhost/cpu-0/cpu-user myhost/load/load myhost/memory/memory-used myhost/disk-sda/disk_octets
Return values
Unless otherwise noted the plugin answers with a line of the following form:
Num Message
If Num is zero the message indicates success, if Num is non-zero the message indicates failure. Message is a human-readable string that describes the return value further.
Commands that return values may use Num to return the number of values that follow, such as the GETVAL command. These commands usually return a negative value on failure and never return zero.

Abstraction Layer

collectd ships the Perl-Module Collectd::Unixsock which provides an abstraction layer over the actual socket connection. It can be found in the directory bindings/perl/ in the source distribution or (usually) somewhere near /usr/share/perl5/ if you're using a package. If you want to use Perl to communicate with the daemon, you're encouraged to use and expand this module.

Author

Florian Forster <octo@verplant.org>