=head1 NAME

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

=head1 SYNOPSIS

  # See collectd.conf(5)
  LoadPlugin exec
  # ...
  <Plugin exec>
    Exec "myuser:mygroup" "myprog"
    Exec "otheruser" "/path/to/another/binary"
    NotificationExec "user" "/usr/lib/collectd/exec/handle_notification"
    NagiosExec "nagios:nagios" "/usr/lib/nagios/plugins/check_something"
  </Plugin>

=head1 DESCRIPTION

The C<exec plugin> forks of an executable either to receive values, to dispatch
notifications to the outside world or to be able to use Nagios plugins.

If you want/need better performance or more functionality you should take a
long look at the C<perl plugin>, L<collectd-perl(5)>.

=head1 EXECUTABLE TYPES

There are currently three types of executables that can be executed by the
C<exec plugin>:

=over 4

=item C<Exec>

These programs are forked and values that it writes to C<STDOUT> are read back.
The executable is forked in a fashion similar to L<init>: It is forked once and
not again until it exits. If it exited, it will be forked again after at most
I<Interval> seconds. It is perfectly legal for the executable to run for a long
time and continuously write values to C<STDOUT>.

See L<EXEC DATA FORMAT> below for a description of the output format expected
from these programs.

B<Warning:> If the executable only writes one value and then exits I will be
executed every I<Interval> seconds. If I<Interval> is short (the default is 10
seconds) this may result in serious system load.

=item C<NotificationExec>

The program is forked once for each notification that is handled by the daemon.
The notification is passed to the program on C<STDIN> in a fashion similar to
HTTP-headers. In contrast to programs specified with C<Exec> the execution of
this program is not serialized, so that several instances of this program may
run at once if multiple notifications are received.

See L<NOTIFICATION DATA FORMAT> below for a description of the data passed to
these programs.

=item C<NagiosExec>

The executable is treated as a Nagios plugin. That means that the first line
printed to C<STDOUT> by this program is used as the text of a notification and
the severity of the notification depends on the exit status of the executable
only.

For information on how to write Nagios plugins please refer to the Nagios
documentation. If a plugin works with Nagios but not with collectd please
complain on the collectd mailing list instead.

=back

=head1 EXEC DATA FORMAT

The forked executable is expected to print values to C<STDOUT>. The expected
format is as follows:

=over 4

=item

Each line beginning with a C<#> (hash mark) is ignored.

=item

Other lines must consist of an I<Identifier>, an optional I<Option-List> and a
I<Value-List>, separated by a spaces. A description of these two parts follows:

An I<Identifier> is of the form
C<I<host>B</>I<plugin>B<->I<instance>B</>I<type>B<->I<instance>> with both
I<instance>-parts being optional. If they're omitted the hyphen must be
omitted, too. I<plugin> and each I<instance>-part may be chosen freely as long
as the tuple (plugin, plugin instance, type instance) uniquely identifies the
plugin within collectd. I<type> identifies the type and number of values
(i.E<nbsp>e. data-set) passed to collectd. A large list of predefined
data-sets is available in the B<types.db> file. See L<types.db(5)> for a
description of the format of this file.

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

I<Valuelist> is a colon-separated 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).

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 B<all> following values, so you don't need
to re-set an option over and over again.

The currently defined B<Options> are:

=over 4

=item B<interval=>I<seconds>

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

=back

Please note that this is the same format as used in the B<unixsock plugin>, see
L<collectd-unixsock(5)>. There's also a bit more information on identifiers in
case you're confused.

Since examples usually let one understand a lot better, here are some:

  leeloo/cpu-0/cpu-idle N:2299366
  alice/interface/if_octets-eth0 interval=10 1180647081:421465:479194

=back

When collectd exits it sends a B<SIGTERM> to all still running
child-processes upon which they have to quit.

=head1 NOTIFICATION DATA FORMAT

The notification executables receive values rather than providing them. In
fact, after the program is started C<STDOUT> is connected to C</dev/null>.

The data is passed to the executables over C<STDIN> in a format very similar to
HTTP-headers: There is one line per field. Every line consists of a field name,
ended by a colon, and the associated value until end-of-line. The input is
ended by two newlines immediately following another.

The following is an example notification passed to a program:

  Severity: FAILURE
  Time: 1200928930
  Host: myhost.mydomain.org
  Message: This is a test notification to demonstrate the format
  <newline>

The following header files are currently used. Please note, however, that you
should ignore unknown header files to be as forward-compatible as possible.

=over 4

=item B<Severity>

Severity of the notification. May either be B<FAILURE>, B<WARNING>, or B<OKAY>.

=item B<Time>

The time in epoch, i.E<nbsp>e. as seconds since 1970-01-01 00:00:00 UTC.

=item B<Host>

Name of the host concerned.

=item B<Message>

Message of the notification. This message should be made accessible to the
user somehow.

=back

=head1 CAVEATS

=over 4

=item

The user, the binary is executed as, may not have root privileges, i.E<nbsp>e.
must have an UID that is non-zero. This is for your own good.

=back

=head1 SEE ALSO

L<collectd(1)>,
L<collectd.conf(5)>,
L<collectd-perl(5)>,
L<collectd-unixsock(5)>,
L<fork(2)>, L<exec(3)>

=head1 AUTHOR

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

=cut