Suddenly, started getting "ERROR 2026 (HY000): Unknown SSL error"

MariaDB instance has been running well for ages, and suddenly, starting about 30 minutes ago, my apps get this error trying to connect: # mysql ERROR 2026 (HY000): Unknown SSL error My certs have been always under "/etc/my.cnf.d/certs/", generated by LetsEncrypt. They expire on 2021-11-04, last modified date 2021-08-06. my.cnf: ssl_cert = "/etc/my.cnf.d/certs/fullchain.pem" ssl_key = "/etc/my.cnf.d/certs/privkey.pem" Looking at the logs, there's nothing that hints anything. The latest log there is about "InnoDB: Online DDL", long ago. No recent yum system updates. **How can I investigate the cause of this problem?** From the research I made, the questions are due to setup issues, while in my case it's been working since always, but **"suddenly" failed, and I can't see what changed**. -- UPDATE: I wonder if this related, https://letsencrypt.org/docs/dst-root-ca-x3-expiration-september-2021/ https://community.letsencrypt.org/t/help-thread-for-dst-root-ca-x3-expiration-september-2021/149190 > On September 30 2021, there will be a small change in how older browsers and devices trust Let’s Encrypt certificates. > (...) > DST Root CA X3 will expire on September 30, 2021. I wonder how can I make MariaDB trust ISRG Root X1!