On systemd-based RHEL, almost every log message from the kernel, systemd itself, and every managed service goes into the journal — a structured, indexed binary store managed by systemd-journald. journalctl is the single CLI for reading it. It replaces a decade of tail -f /var/log/messages | grep httpd — you get filters for unit, time range, priority, boot ID, and a structured follow mode in one tool.
Cert