Email Alert on Failure | Shell Script for Cron

Cron can email output, but many servers disable MTA or bury failures in spam. This wrapper runs your command, captures output to a log, and sends a concise mail alert only when the exit code is non-zero.

What this script does

Runs any command and records combined stdout/stderr
Sends email only on non-zero exit
Includes tail of log in the message body
Returns the same exit code as the wrapped command
Configurable recipient and subject prefix

Prerequisites

mail or mailx package installed
Working local MTA or relay (postfix/nullclient)
Recipient address that accepts server mail

Step 1: Save the script

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

Step 2: Full script (scroll to read)

alert-on-fail.sh

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

ALERT_TO="[email protected]"
SUBJECT_PREFIX="[cron-fail]"
LOG="/var/log/alert-on-fail.log"
CMD=("$@")

[[ ${#CMD[@]} -gt 0 ]] || { echo "usage: alert-on-fail.sh command [args...]"; exit 2; }

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

set +e
"${CMD[@]}" >>"$LOG" 2>&1
ec=$?
set -e

if [[ "$ec" -ne 0 ]]; then
  log "${CMD[*]} failed exit=$ec"
  {
    echo "Command: ${CMD[*]}"
    echo "Exit: $ec"
    echo "Host: $(hostname -f)"
    echo "--- log tail ---"
    tail -n 40 "$LOG"
  } | mail -s "${SUBJECT_PREFIX} $(hostname -s): ${CMD[0]##*/} exit $ec" "$ALERT_TO"
  log "ALERT sent to $ALERT_TO"
fi

exit "$ec"

Scroll inside the box to read the full script.

Step 3: Configure settings

ALERT_TO — destination email
On cloud VPS without MTA, use msmtp or an API webhook instead
Different from uptime monitors — see uptime script

Shell script sending email alert after command failure

Step 4: Test manually

sudo alert-on-fail.sh /bin/false

sudo alert-on-fail.sh /bin/true

Schedule with cron

sudo crontab -e

Add:

0 3 * * * /usr/local/bin/alert-on-fail.sh /usr/local/bin/mysql-backup.sh

Email Alert on Script Failure Shell Script (mail, Logging for Cron)