The sudo (superuser do) tool allows designated users to run commands with elevated privileges without sharing the root password. This is fundamental to the principle of least privilege: each administrator gets exactly the access they need for their role, no more. When access is misconfigured — for example with blanket ALL=(ALL) ALL entries or unsafe […]
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 (RHEL 9, codenamed “Plow”) is the most significant release of RHEL in years, built on Linux kernel 5.14, OpenSSL 3.0, and shipped with a hardened-by-default security posture including SELinux enforcing mode, nftables as the default firewall backend, and full support for the latest POWER, ARM, and x86_64 architectures. Whether you […]
User account management is one of the most fundamental administrative tasks on any Linux server. On Red Hat Enterprise Linux 9, every process, file, and network socket is owned by a user and group, making correct account hygiene essential for both security and auditability. Understanding the full lifecycle — creation, modification, and removal — and […]
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 — […]
SSH key-based authentication is the gold standard for remote server access. Unlike passwords, SSH keys cannot be guessed by brute-force attacks. An Ed25519 private key is a 256-bit secret that would take longer than the age of the universe to crack by exhaustive search. When combined with a key passphrase, you have two-factor authentication: something […]
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), […]
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