how check diskspace in linux

df -h - show filesystem free space
du -sh - show current directory size
du --max-depth=1 -h - show size subdirs max to 1 level
df -T - show disks type
du -h | sort -rn - show filesize all dirs and sorting by size
lsblk - show disks tree
ls -l --block-size=G - list files with size in Gigabytes

/* Bash script for notification about critical disk space */

#!/bin/bash
CURRENT=$(df / | grep / | awk '{ print $5}' | sed 's/%//g')
THRESHOLD=90
if [ "$CURRENT" -gt "$THRESHOLD" ] ; then
mail -s 'Your disk space finished' -r admin@example.com << EOF
Stats: $CURRENT%
EOF
fi