Send Email Alerts from Bash

The Script

Save as disk-email-alert.sh (or any name). Set EMAIL and THRESHOLD, install mailutils, then run or cron it.

#!/bin/bash

CHECK="✓"
CROSS="✗"

# --- Configuration ---
THRESHOLD=80
EMAIL="you@example.com"
HOSTNAME=$(hostname)
DATE=$(date '+%Y-%m-%d %H:%M:%S')

# --- Check disk usage on root partition ---
USAGE=$(df / | awk 'NR==2{print $5}' | tr -d '%')

echo "[$DATE] Disk usage: ${USAGE}%"

if [ "$USAGE" -gt "$THRESHOLD" ]; then
  echo "$CROSS Disk at ${USAGE}% — sending alert to $EMAIL"

  MESSAGE="[DISK ALERT] ${HOSTNAME}

Disk usage on / is at ${USAGE}% as of ${DATE}.
Threshold: ${THRESHOLD}%

Top disk consumers:
$(du -sh /* 2>/dev/null | sort -rh | head -5)

-- BashSnippets monitor"

  echo "$MESSAGE" | mail -s "[ALERT] Disk Space on ${HOSTNAME}" "$EMAIL"
  echo "$CHECK Alert sent to $EMAIL"
else
  echo "$CHECK Disk OK at ${USAGE}%"
fi

How It Works

HOSTNAME=$(hostname) runs the hostname command once and stores the machine name in HOSTNAME, so subject lines and the body clearly say which server had the problem (especially useful if you run the same script on several VPS hosts).

The multi-line MESSAGE variable uses double quotes so Bash expands variables like ${USAGE} and embedded command substitution ($(du …)) when the assignment runs. Literal newlines inside the quoted string appear as real line breaks in the email body.

du -sh /* estimates size per top-level directory (human-readable sizes with -h). Piping through sort -rh and head -5 surfaces the worst offenders inside the alert.

echo "$MESSAGE" | mail -s "[ALERT] Disk Space on ${HOSTNAME}" "$EMAIL" sends standard input as the body, -s sets the subject, and the last argument is the recipient. That is the common mailutils pattern on Ubuntu when local/SMTP delivery is configured.

Step-by-Step Setup

Step 1 — Install mailutils

sudo apt update && sudo apt install mailutils

When the installer asks, choose Internet Site and use your server hostname. Test delivery: echo "test" | mail -s "test" you@example.com

Step 2 — Create the script

nano disk-email-alert.sh

Paste the script, then Ctrl+X → Y → Enter to save.

Step 3 — Set your email and threshold

Edit EMAIL="you@example.com" and THRESHOLD=80 to match your inbox and risk tolerance.

Step 4 — Make it executable

chmod +x disk-email-alert.sh

Step 5 — Run it once

./disk-email-alert.sh

Schedule It with Cron

Automation is the point: let the script run while you sleep.

Open your crontab

crontab -e

Example schedules

# Hourly disk email check
0 * * * * /home/user/disk-email-alert.sh

# Daily at 6:15
15 6 * * * /home/user/disk-email-alert.sh

Variations

Use Gmail SMTP via msmtp (config example)

Install msmtp, then configure a relay. Example snippet for ~/.msmtprc — use an App Password, not your normal Gmail password:

defaults
auth           on
tls            on
tls_trust_file /etc/ssl/certs/ca-certificates.crt
logfile        ~/.msmtp.log

account gmail
host           smtp.gmail.com
port           587
from           youraddress@gmail.com
user           youraddress@gmail.com
password       YOUR_APP_PASSWORD_HERE

account default : gmail

Point mail at msmtp per your distro docs, or call msmtp directly from the script.

One email for multiple conditions (disk + RAM + CPU)

Collect flags in variables, build a single BODY, and send once if anything is red:

#!/bin/bash
EMAIL="you@example.com"
DISK=$(df / | awk 'NR==2{print $5}' | tr -d '%')
LOAD=$(awk -v OFMT='%.0f' '{print $1*100}' /proc/loadavg)

WARN=
[[ "$DISK" -gt 80 ]] && WARN+=$(printf 'Disk %s%%\n' "$DISK")
# add free -m / top checks here…
[[ ${#WARN} -gt 0 ]] && printf '%s' "$WARN" | mail -s "[ALERT] $(hostname)" "$EMAIL"

Send at most one alert per 24 hours (lockfile)

Use a sentinel file so a flapping condition does not hammer your inbox:

LOCK=/var/tmp/disk-alert.sent
if [[ "$USAGE" -gt "$THRESHOLD" ]]; then
  ALLOW=0
  [[ ! -e "$LOCK" ]] && ALLOW=1
  [[ -e "$LOCK" ]] && [[ $(date +%s) -gt $(( $(date -r "$LOCK" +%s) + 86400 )) ]] && ALLOW=1
  [[ "$ALLOW" -eq 1 ]] && {
    echo "$MESSAGE" | mail -s "[ALERT] Disk Space on ${HOSTNAME}" "$EMAIL"
    touch "$LOCK"
  }
fi

Common Mistakes

Understanding the Commands

Frequently Asked Questions

How do I send an email from a bash script?

Use the mail command: echo 'Message body' | mail -s 'Subject' you@example.com. Install mailutils first on Ubuntu: sudo apt install mailutils

How do I install mailutils on Ubuntu?

Run: sudo apt update && sudo apt install mailutils. When prompted, choose Internet Site and use your server hostname.

Can I send email alerts automatically from a cron job?

Yes. Schedule your script with crontab -e. When the condition is met, the script sends the email. Add 2>&1 | mail -s 'Cron Error' you@example.com to capture cron output.

What if mail command is not found?

Run: which mail — if it returns nothing, install with: sudo apt install mailutils (Ubuntu/Debian) or sudo yum install mailx (CentOS/RHEL).

How do I send email from bash using SMTP (Gmail)?

Use ssmtp or msmtp with your Gmail SMTP credentials. Configure /etc/ssmtp/ssmtp.conf with your gmail address and an App Password (not your real password).

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