Articles
Security
Security errors explained: changed SSH host keys and SSL certificate chains, how to check them and fix them without turning the check off.
"Certificate has expired": check the dates, renew it, and find out why it didn't renew
Fix "certificate has expired" and NET::ERR_CERT_DATE_INVALID: check the dates with openssl, renew with Certbot, reload the server, and fix why renewal or clock failed.
Beginner · 4 min read
Certbot "failed to authenticate some domains": read the Type, then fix DNS, port 80 or the path
Fix Certbot "failed to authenticate some domains": read the error type, then fix DNS records, an IPv6 AAAA record, a closed port 80, the webroot, Cloudflare and CAA.
Intermediate · 5 min read
JWT "jwt expired" and "invalid signature": how to find out what is wrong with a token
Fix JWT "jwt expired" and "invalid signature": read the exp claim, check clock differences, the secret, HS256 vs RS256 and rotated keys, without turning verification off.
Intermediate · 5 min read
SSH "WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED!": check it, then fix known_hosts
Fix the SSH host key warning safely: find out why the key changed, verify the new fingerprint on the server, then remove the old key with ssh-keygen -R.
Beginner · 3 min read
"SSL certificate problem: unable to get local issuer certificate": fix the chain, not the check
Fix "unable to get local issuer certificate" in curl, git, pip, npm and Docker: find the broken link with openssl, then fix the server chain or add the missing CA.
Intermediate · 4 min read