Monitoring Data - Big Data Made Easy: A Working Guide to the Complete Hadoop Toolset - page 220

Figure 7-21. Details of the Nagios root partition
To demonstrate what a warning alert looks like, I changed the hc1nn.cfg configuration file on the server hc1nn,
defining the root parition check_command line to provide a warning if free space reaches 90 percent. (A silly measure,
I know, but it will show what a warning alert looks like.)
define service{
use local-service
host_name hc1nn
service_description Root Partition
check_command check_local_disk!90%!10%!/
}
I then saved the configuration file and restarted the Nagios server to pick up the changes:
[root@hc1nn ~]# service nagios restart
Not surprisingly, at the next scheduled check, the alert shown in Figure 7-22 was raised, stating that the root
partition contained less than 90 percent free space.