Even with SSH key authentication enabled, a badly configured or temporarily accessible server with password auth still faces a constant barrage of brute-force login attempts. Fail2ban monitors log files for authentication failures, counts them per source IP, and when a configured threshold is crossed it issues a temporary ban by injecting a drop rule via […]
A server’s hostname is its identity on the network. The fully qualified domain name (FQDN) combines the short hostname with the DNS domain, forming an address like web01.example.com. Many services depend on a correctly configured hostname and FQDN to function properly: email servers use the FQDN in SMTP HELO greetings (incorrect values cause delivery rejections), […]
Accurate time synchronization is not optional on a server — it is a hard requirement. TLS certificate validation fails when the clock is wrong by more than a few minutes. Kerberos authentication rejects tickets with a clock skew over 5 minutes. Cron jobs fire at the wrong time. Log correlation across multiple servers becomes impossible […]
Unpatched software is the leading cause of server compromise. The majority of publicly disclosed vulnerabilities already have patches available by the time attackers start actively exploiting them — the window between patch availability and active exploitation has shrunk from months to days. Manually patching servers is error-prone and inconsistent at scale. Automatic security updates ensure […]
Systemd is the init system and service manager for RHEL 9 — it is PID 1, the parent of every other process on the system. Understanding how to manage systemd services is foundational to every other administrative task: installing Nginx means enabling the nginx service; configuring a database means understanding its unit file; debugging a […]
Every time you open a terminal on RHEL 9, Bash reads one or more startup files before presenting you with a prompt. Which files are read depends on whether the shell is a login shell (started by SSH, a console login, or su -) or an interactive non-login shell (a new terminal window in a […]
Terminal multiplexing solves one of the most common problems in server administration: when your SSH connection drops mid-task, any running process in that session is killed. With tmux, your terminal sessions run inside a server-side process that persists independently of your SSH connection. You can detach from a session, disconnect, reconnect hours later from a […]
Log files are the primary diagnostic tool for server administrators — but without rotation they become a problem in their own right. An unrotated /var/log/nginx/access.log on a busy server can grow to tens of gigabytes within weeks, filling the filesystem, crashing the logging application, and making the log itself unusable because no tool can efficiently […]
Red Hat Enterprise Linux 9 uses firewalld as its default firewall management daemon, backed by nftables as the kernel netfilter framework (replacing iptables which was the default in RHEL 7 and earlier). firewalld provides a zone-based model where each network interface is assigned to a trust zone — public, internal, dmz, trusted, and more — […]
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