Once again I missed the expiry date of one of the SSL certificates on my server. Therefore I am now using a cronjob to warn me early enough that a certificate is about to expire.

This is the script /usr/local/bin/ssl-cert-check which checks the expiry date of the certificate files passed as arguments:

#!/bin/bash
 
DAYS=30
 
for file in "$@"; do
    openssl x509 -checkend $(( 86400 * $DAYS )) -in "$file" > /dev/null
    if [ $? != 0 ]; then
        echo "==> Certificate $file is about to expire soon:"
        openssl x509 -enddate -in "$file" -noout
    fi
done

And the corresponding cronjob entry checking SSL certificates once a day:

MAILTO=root
6       6    * * *  nobody  /usr/local/bin/ssl-cert-check /etc/apache2/ssl/*.crt /etc/ssl/certs/dovecot.pem