=head1 NAME

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

=head1 SYNOPSIS

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

=head1 DESCRIPTION

The C<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 L<collectd-nagios(1)> to check if some value is in a
certain range and exit with a Nagios-compatible exit code.

=head1 COMMANDS

Upon start the C<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:

=over 4

=item B<GETVAL> I<Identifier>

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

I<num> I<name>B<=>I<value>[ I<name>B<=>I<value>[ ...]]

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

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

=item B<LISTVAL>

Returnes 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 B<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 occured. Each of the following lines containes the
update time as an epoch value and the identifier, seperated by a space.

Example:
  -> | LISTVAL
  <- | 69 Values found
  <- | 1182204284 leeloo/cpu-0/cpu-idle
  <- | 1182204284 leeloo/cpu-0/cpu-nice
  <- | 1182204284 leeloo/cpu-0/cpu-system
  <- | 1182204284 leeloo/cpu-0/cpu-user
  ...

=item B<PUTVAL> I<Identifier> I<Valuelist>

Submits a value (identified by I<Identifier>, see below) to the daemon which
will dispatch it to all it's write-plugins. The I<Valuelist> is a
colon-seperated list of the time and the values, each either an integer if the
data-source is a counter, of a double if the data-source if of type "gauge".
You can submit an undefined gauge-value by using B<U>. When submitting B<U> to
a counter the behavior is undefined. The time is given as epoch (i.E<nbsp>e.
standard UNIX time).

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

=back

=head2 Identifiers

Value or value-lists are identified in a uniform fassion:

I<Hostname>/I<Plugin>/I<Type>

Where I<Plugin> and I<Type> are both either of type "I<Name>" or
"I<Name>-I<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

=head2 Return values

Unless otherwise noted the plugin answers with a line of the following form:

I<Num> I<Message>

If I<Num> is zero the message indicates success, if I<Num> is non-zero the
message indicates failure. I<Message> is a human-readable string that describes
the return value further.

Commands that return values may use I<Num> to return the number of values that
follow, such as the B<GETVAL> command. These commands usually return a negative
value on failure and never return zero.

=head1 ABSTRACTION LAYER

Shipped with the sourcecode comes the Perl-Module L<Collectd::Unixsock> which
provides an abstraction layer over the actual socket connection. It can be
found in the directory F<contrib/PerlLib>. If you want to use Perl to
communicate with the daemon, you're encouraged to use and expand this module.

=head1 SEE ALSO

L<collectd(1)>,
L<collectd.conf(5)>,
L<collectd-nagios(1)>,
L<unix(7)>

=head1 AUTHOR

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

=cut