Disk Space Alert Shell Script

Before no space left on device stops MySQL, a simple df threshold script buys you time. This checks each mount (skipping tmpfs) and emails when usage exceeds your percentage.

What this script does

Configurable THRESHOLD percent (default 85)
Uses df -P for portable parsing
Skips tmpfs and devtmpfs mounts
One email bundles all offending filesystems
Exit 1 if any mount over threshold (hook to monitoring)

Prerequisites

df from coreutils
bc or awk for integer compare
mail for notifications

Step 1: Save the script

sudo nano /usr/local/bin/disk-alert.sh
sudo chmod +x /usr/local/bin/disk-alert.sh

Step 2: Full script (scroll to read)

disk-alert.sh

#!/usr/bin/env bash
set -euo pipefail

THRESHOLD="${THRESHOLD:-85}"
ALERT_TO="${ALERT_TO:[email protected]}"
LOG="/var/log/disk-alert.log"
FSTYPE_SKIP='^(tmpfs|devtmpfs|overlay|squashfs)$'

log(){ echo "[$(date '+%F %T')] $*" | tee -a "$LOG"; }

warn=""
while read -r fs size used avail pct mount; do
  [[ "$fs" == Filesystem ]] && continue
  fstype=$(findmnt -n -o FSTYPE "$mount" 2>/dev/null || echo unknown)
  if [[ "$fstype" =~ $FSTYPE_SKIP ]]; then
    continue
  fi
  pct_num=${pct%%%}
  if [[ "$pct_num" -ge "$THRESHOLD" ]]; then
    warn+="$mount at ${pct} (threshold ${THRESHOLD}%)\n"
    log "WARN $mount ${pct}"
  fi
done < <(df -P)

if [[ -z "$warn" ]]; then
  log "OK all mounts under ${THRESHOLD}%"
  exit 0
fi

{
  echo "Disk usage warning on $(hostname -f)"
  echo -e "$warn"
  echo "--- df -h ---"
  df -h
} | mail -s "[disk] $(hostname -s) usage high" "$ALERT_TO" 2>/dev/null || log "mail send failed"

exit 1

Scroll inside the box to read the full script.

Step 3: Configure settings

Cleanup automation: disk monitor & cleanup
Find large files: find large files guide
Inode full: inode monitor script

Disk space alert shell script sending email on high df usage

Step 4: Test manually

THRESHOLD=50 sudo /usr/local/bin/disk-alert.sh

df -h /

Schedule with cron

sudo crontab -e

Add:

0 * * * * /usr/local/bin/disk-alert.sh >> /var/log/disk-alert.log 2>&1

Disk Space Alert Shell Script (df Threshold, Email, Cron)