I am running check_disk 1.64 , nagios-plugins-1.4.3. I am seeing incorrect results for free disk space and the perf data is also wrong. I am running the check_disk on Redhat ES, centos machines. Is anybody seeing the same problem.
[root@caitmon plugins]# ./check_disk -w 20% -c 10% -p /data
DISK OK - free space: /data 17652 MB (95% inode=100%);| /data=1025MB;14941;16809;99;18677
[root@caitmon plugins]# df -h /data
Filesystem Size Used Avail Use% Mounted on
/dev/sda10 19G 77M 18G 1% /data
I think the 1.3 versions of plugins used to use df -pk and they seem to be reporting the results correctly.
/usr/lib/nagios/plugins/check_disk -w 20 -c 10 -p /home
Try looking at /usr/lib/nagios/plugins/check_disk --help.
It tells you that if you use an integer like 20, then that means 20 MB must be all that is left, until you get a warning. So, from your defintion, you want a warning when there is 20MB or less, and a critical if there is 10MB or less. So the plugin output is NOT wrong.