This could be multiple issues why your not see logs. To start off troubleshooting this issue check the Graylog log file. Since your using RHEL it would be /var/log/graylog-server perhaps tail -f that file and watch what’s going on. Or restart GL service and watch how GL service is starting up , probably give you a better idea what’s going on.
Normally when logs are not shown this is a direct result of Elasticsearch. You could also check those logs which is located here /var/log/elasticsearch
If you see anything that could be a issue, post those logs here by using the markdown </> to format those logs and/or configuration files.
Which is my next suggestion, showing configuration files on this setup would be appreciated in helping us, helping you.
Since you have a cluster GL, ES and MongoDb. Checking the cluster health would be another way of finding out what’s going one. Insure Firewall and/or SELinux is not interfering.
To simplify troubleshooting tips, here is a list :
Check the following:
systemctl status graylog-server
systemctl status elasticsearch
systemctl status mongod
journalctl -xe
