=head1 NAME

rrdtool update - Store a new set of values into the rrd

=for html <div align="right"><a href="rrdupdate.pdf">PDF</a> version.</div>

=head1 SYNOPSIS

B<rrdtool> B<update> I<filename> 
S<[B<--template>|B<-t> I<ds-name>[B<:>I<ds-name>]...]> 
S<B<N>|I<timestamp>B<:>I<value>[B<:>I<value>...]> 
S<[I<timestamp>B<:>I<value>[B<:>I<value>...] ...]>

=head1 DESCRIPTION

The B<update> function feeds new data values into an B<RRD>. The
data gets time aligned according to the properties of the B<RRD> to
which the data is written.

=over 8

=item I<filename>

The name of the B<RRD> you want to update.

=item B<--template>|B<-t> I<ds-name>[B<:>I<ds-name>]...

by default, the update function expects the data input in the order,
the data sources are defined in the RRD. This is not very error
resistant, as you might be sending the wrong data into a RRD.

The template switch allows you to specify which data sources you are
going to update and in which order. If the data sources specified in
the template are not available in the rrd file, the update process
will abort with an error message.

=item B<N>|I<timestamp>B<:>I<value>[B<:>I<value>...]

The data used for updating the RRD was acquired at a certain time. This
time can either be defined in seconds since 1970-01-01. Or by using the
letter 'N' the update time is set to be the current time. Negative time
values are subtracted from the current time.
Getting the timing right to the second is especially
important when you are working with data-sources of type B<COUNTER>,
B<DERIVE> or B<ABSOLUTE>. 

The remaining elements of the argument are DS updates. The order of this list is
the same as the order the data sources were defined in the rra.
If there is no data for a certain data-source, the letter 
B<U> (eg. N:0.1:U:1) can be defined.

The format of the value acquired from the data source is dependent of the
data source type chosen. Normally it will be numeric, but the data acquisition
modules may impose their very own parsing of this parameter as long as the colon
(B<:>) remains the data source value separator.

=back

=head1 EXAMPLE

C<rrdtool update demo1.rrd N:3.44:3.15:U:23>

Update the database file demo1.rrd with 3 known and one I<*UNKNOWN*>
value. Use the current time as the update time.

C<rrdtool update demo2.rrd 887457267:U 887457521:22 88745790:2.7>

Update the database file demo2.rrd which expects data from a single
data-source, three times. First with an I<*UNKNOWN*> value then with two
normal readings. The update interval seems to be around 300 seconds.

=head1 AUTHOR

Tobias Oetiker <oetiker@ee.ethz.ch>