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/proc/filesystems is the file used to detect filesystems supported by running kernel. You can quickly run grep or cat command to display the list of all supported file system. nodev indicates that the file system is not associated with a physical device such as /dev/sdb1. If you see ext3 or vfat, it means you will be able to mount ext3 and vfat based file systems.

Following cat command will quickly tell you what filesystems supported by currently running Linux kernel:

$ cat /proc/filesystems

nodev   sysfs
nodev   rootfs
nodev   proc
nodev   usbfs

For example, if the iso9660 fllesystem not listed, you can not mount standard CD-ROM file system. To add support simply recompile kernel with iso9660 filesystem support.

Shell script to watch the disk space

df displays the amount of disk space available on the file system containing each file name argument. If no file name is given, the space available on all currently mounted file systems is shown. Read man page of df if you are new to df command.


=> Find disk space using df

=> Filter out filesystem and find out the percentage of space using grep

=> Write a shell script

Step # 1: First get disk space:

$ df -H


Filesystem             Size   Used  Avail Use% Mounted on
/dev/hdb1               20G    14G   5.5G  71% /
tmpfs                  394M   4.1k   394M   1% /dev/shm
/dev/hdb5               29G    27G   654M  98% /nas/www

Step # 2: Next filter out filesystem and find out the percentage of space

$ df -H | grep -vE '^Filesystem|tmpfs|cdrom' | awk '{ print $5 " " $1 }'


71% /dev/hdb1
98% /dev/hdb5

Step # 3: Write a shell script

Above command displays field 5 and 1 of df command. Now all you need to do is write a script to see if the percentage of space is >= 90% (download script):

df -H | grep -vE '^Filesystem|tmpfs|cdrom' | awk '{ print $5 " " $1 }' | while read output;
  echo $output
  usep=$(echo $output | awk '{ print $1}' | cut -d'%' -f1  )
  partition=$(echo $output | awk '{ print $2 }' )
  if [ $usep -ge 90 ]; then
    echo "Running out of space \"$partition ($usep%)\" on $(hostname) as on $(date)" |
     mail -s "Alert: Almost out of disk space $usep%" you@somewhere.com

Setup Cron job

Save and install script as cronjob. Copy script to /etc/cron.daily/ (script downolad link)
# cp diskAlert /etc/cron.daily/
# chmod +x /etc/cron.daily/diskAlert

OR install as cronjob:
crontab -e

Write cronjob as per your requirement
10 0 * * * /path/to/diskAlert

Updated script version

Tony contributed and updated my script - You can exclude selected filesystem in case you don't want monitor all filesystems.

# set -x
# Shell script to monitor or watch the disk space
# It will send an email to $ADMIN, if the (free available) percentage of space is >= 90%.
# -------------------------------------------------------------------------
# Set admin email so that you can get email.
# set alert level 90% is default
# Exclude list of unwanted monitoring, if several partions then use "|" to separate the partitions.
# An example: EXCLUDE_LIST="/dev/hdd1|/dev/hdc5"
function main_prog() {
while read output;
#echo $output
  usep=$(echo $output | awk '{ print $1}' | cut -d'%' -f1)
  partition=$(echo $output | awk '{print $2}')
  if [ $usep -ge $ALERT ] ; then
     echo "Running out of space \"$partition ($usep%)\" on server $(hostname), $(date)" | \
     mail -s "Alert: Almost out of disk space $usep%" $ADMIN
if [ "$EXCLUDE_LIST" != "" ] ; then
  df -H | grep -vE "^Filesystem|tmpfs|cdrom|${EXCLUDE_LIST}" | awk '{print $5 " " $6}' | main_prog
  df -H | grep -vE "^Filesystem|tmpfs|cdrom" | awk '{print $5 " " $6}' | main_prog