get linux disk space data

freespace:
[root@ip-10-99-41-92 cloudwatch]# df --local --block-size=1M / | grep / |  tr -s ' ' | cut -d ' ' -f 4
6949







usedpercent
[root@ip-10-99-41-92 cloudwatch]# df --local /  | grep /  | tr -s ' ' | cut -d ' ' -f 5 | grep -o "[0-9]*"
13

[root@ip-10-99-41-92 cloudwatch]# df
Filesystem           1K-blocks      Used Available Use% Mounted on
/dev/xvda1             8256952   1057996   7115100  13% /
tmpfs                   304240         0    304240   0% /dev/shm