Proactive monitoring of free space is essential in order to get early warnings to drives or filesystems which could run out of space and affect your application or database. A simple command to check free space on Linux and then integrated into a DBTuna/Alert is as follows:

The logic of this alert is to run df -h to get filesystem information, then grep for a specific filesystem (in this case mysqldata), then awk out the Use% column, then remove the percentage sign using sed, in order to return just a numeric value.

N.B. if the output from df -h displays an lvm which creates a new line due to the length, then switch the column you are awk'ing for to $4 e.g. df -h | grep mysqldata | awk '{print $4}' | sed 's/[[:punct:]]//g'

You can now add this into DBTuna/Alerts and receive a proactive alert as soon as free space becomes an issue e.g. 90% used etc.