OP5 Monitor - Why is Apache/httpd not starting?

General troubleshooting

The issues mentioned in this article are to some extent OP5 Monitor specific. For a more general troubleshooting of Apache issues, we can recommend How To Troubleshoot Common Site Issues on a Linux Server.

Issue with the SSL certificate private key

If you see the following error message in /var/log/httpd/ssl_error_log

[error] Unable to configure RSA server private key
[error] SSL Library Error: 185073780 error:0B080074:x509 certificate routines:X509_check_private_key:key values mismatch

Verify that the checksum of the private key and the certificate matches:

# openssl pkey -in /etc/pki/tls/private/localhost.key -pubout -outform pem | sha256sum
# openssl x509 -in /etc/pki/tls/certs/localhost.crt -pubkey -noout -outform pem | sha256sum

Sample:

[root@mnpc-mon9 ~]# openssl pkey -in /etc/pki/tls/private/localhost.key -pubout -outform pem | sha256sum
844abbe8004d631243343fcec8c341beed6653ac4e2b17f3af9e826774a1dde8 -
[root@mnpc-mon9 ~]# openssl x509 -in /etc/pki/tls/certs/localhost.crt -pubkey -noout -outform pem | sha256sum
844abbe8004d631243343fcec8c341beed6653ac4e2b17f3af9e826774a1dde8 -

If they do not match you have to issue a new certificate. Please see Add or renew an SSL certificate for op5 Monitor.