System information

System Monitoring Utilities 49
Points to Notice
• free_mem.png is the filename of the graph to be created.
• --start and --end limit the time range within which the graph will be drawn.
• --step specifies the time resolution (in seconds) of the graph.
• The DEF:... part is a data definition called free_memory. Its data are read from
the free_mem.rrd database and its data source called memory. The average val-
ue points are calculated, because no others were defined in Section2.11.2.2, “Cre-
ating Database” (page46).
• The LINE... part specifies properties of the line to be drawn into the graph. It is
2 pixels wide, its data come from the free_memory definition, and its color is red.
• --vertical-label sets the label to be printed along the y axis, and --title
sets the main label for the whole graph.
• --zoom specifies the zoom factor for the graph. This value must be greater than
zero.
• --x-grid specifies how to draw grid lines and their labels into the graph. Our ex-
ample places them every second, while major grid lines are placed every 4 seconds.
Labels are placed every 10 seconds under the major grid lines.
Figure2.2: Example Graph Created with RRDtool
2.11.3 For More Information
RRDtool is a very complex tool with a lot of sub-commands and command line op-
tions. Some of them are easy to understand, but you have to really study RRDtool to
make it produce the results you want and fine-tune them according to your liking.