=head1 NAME

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

=head1 SYNOPSIS

  # See collectd.conf(5)
  LoadPlugin exec
  # ...
  <Plugin exec>
    Exec myuser myprog
    Exec otheruser /path/to/another/binary
  </Plugin>

=head1 DESCRIPTION

The C<exec plugin> forks of an executable and reads back values that it writes
to C<STDOUT>. 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>.

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 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> and a I<Value-List>, separated by
a space. 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.

A I<Value-List> is a colon-separated list of values, prepended by the time
stamp in epoch, i.E<nbsp>e. the same format RRDTool uses, see L<rrdupdate(1)>.
As with the argument passed to RRDTool you can use B<N> as the current time and
B<U> for undefined values. However, undefined values can only passed for
B<GAUGE> values. When setting B<U> for a B<COUNTER> data source the behavior is
undefined.

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

  leeloo/cpu-0/cpu-idle N:2299366
  alice/interface/if_octets-eth0 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 CAVEATS

=over 4

=item

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

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

=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