SSL Certificate Expiry Checker Shell Script for Linux

Never miss an SSL renewal — this certificate expiry checker monitors domains and alerts you before they expire.

What this script does

• Checks SSL expiry for multiple domains
• Warns when cert expires within N days
• Uses openssl s_client — no extra tools needed
• Optional email alert summary
• Ideal for cron on monitoring servers

Prerequisites

• openssl installed
• Outbound HTTPS from server
• Optional: mail command for alerts

Step 1: Save the script

sudo nano /usr/local/bin/ssl-expiry-check.sh
sudo chmod +x /usr/local/bin/ssl-expiry-check.sh

Step 2: Full script (scroll to read)

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

DOMAINS=("blog.example.com" "shop.example.com")
WARN_DAYS=14
ALERT_EMAIL="[email protected]"
LOG="/var/log/ssl-check.log"

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

check_domain(){
  local domain="$1"
  local end date_left days
  end=$(echo | openssl s_client -connect "${domain}:443" -servername "$domain" 2>/dev/null | openssl x509 -noout -enddate | cut -d= -f2)
  date_left=$(date -d "$end" +%s)
  days=$(( (date_left - $(date +%s)) / 86400 ))
  log "$domain expires in $days days ($end)"
  if (( days <= WARN_DAYS )); then ALERTS+="WARNING: $domain expires in $days days\n"; fi
}

for d in "${DOMAINS[@]}"; do check_domain "$d"; done

if [[ -n "$ALERTS" && -n "$ALERT_EMAIL" ]] && command -v mail >/dev/null; then
  echo -e "$ALERTS" | mail -s "SSL expiry alert on $(hostname -s)" "$ALERT_EMAIL"
fi

Scroll inside the box to read the full script.

Step 3: Configure settings

• DOMAINS — space-separated list of hostnames
• WARN_DAYS — alert threshold (default 14)
• ALERT_EMAIL — notification address

Step 4: Test manually

sudo /usr/local/bin/ssl-expiry-check.sh

openssl s_client -connect google.com:443 -servername google.com </dev/null 2>/dev/null | openssl x509 -noout -dates

Schedule with cron

sudo crontab -e

Add:

0 8 * * * /usr/local/bin/ssl-expiry-check.sh >> /var/log/ssl-check.log 2>&1

Related tutorials

• Linux Disk Monitor Shell Script
• Linux Backup Shell Script: Files & Database to Remote Server
• Cron Jobs in Linux: Schedule Tasks with crontab
• SSH Key Authentication on Linux Servers

Terminal screenshot is an original illustration created for Gnome IT Solutions (blog.gnomeitsolutions.com).