Let’s play spot the difference:

[root@localhost ~]# /usr/lib64/nagios/plugins/check_disk -w 20 -c 10 -p /home
DISK OK – free space: /home 111715 MB (4% inode=99%);| /home=2498209MB;2609905;2609915;0;2609925

[root@localhost ~]# /usr/lib64/nagios/plugins/check_disk -w 20% -c 10% -p /home
DISK CRITICAL – free space: /home 111715 MB (4% inode=99%);| /home=2498209MB;2087940;2348932;0;2609925

Make sure you that you define your units of disk or add % to your Nagios checks otherwise you might suddenly find yourself running to add more disk….