January 29, 2015

How to Get an Alert When Your Disk Is Full on Unix, Linux and BSD Systems

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Do you want to get an alert once your disk is full on Unix, Linux or BSD Systems? In this tutorial we will show you to set up a simple cron script which sends you an email once a specific disk limit is reached.
We use the df command which reports the file system disk space usage including the amount of disk space available.

Root access is required to edit the following files and to execute commands. Log in as root (su) or simply prepend sudo to all commands that require root privileges.

Skript preparation

We use the df command with the -P option which make the output POSIX compliant.

df -P /usr

This is a sample output of a RAID 1 disk:

Filesystem      512-blocks    Used    Avail Capacity  Mounted on
/dev/mirror/usr   20308312 2966100 15717548    16%    /usr

With the grep and awk command we can print out the used disk space for /usr.

df -P /usr | grep /usr | awk '{ print $5}' | sed 's/%//g'

You can also assign the output to a variable:

output=$(df -P /usr | grep /usr | awk '{ print $5}' | sed 's/%//g')
echo $output

Indexed arrays can be used under BASH:

output=($(df -P /usr))
echo "${output[11]}"

Cron skript

This is an example of a BASH cron skript. Change the threshold according to your needs.

OUTPUT=($(LC_ALL=C df -P ${FS}))
CURRENT=$(echo ${OUTPUT[11]} | sed 's/%//')
[ $CURRENT -gt $THRESHOLD ] && echo "$FS file system usage $CURRENT" | mail -s "$FS file system" mail@domain.com

Use the appropriate syntax for CSH or KSH. Now save the script and place the following line into your /etc/crontab to run it as a daily task:

@daily /path/to/script.sh