openssl s_client -connect localhost:6443 -showcerts < /dev/null 2>&1 | openssl x509 -noout -enddate

Beispiel:
root@kubepi03:~# openssl s_client -connect localhost:6443 -showcerts < /dev/null 2>&1 | openssl x509 -noout -enddate
notAfter=Oct  9 17:06:31 2022 GMT

for crt in /var/lib/rancher/k3s/server/tls/*.crt; 
do printf '%s: %s\n' "$(date --date="$(openssl x509 -enddate -noout -in "$crt"|cut -d= -f 2)" --iso-8601)" "$crt"; 
done | sort