Linux Tutorials and Command Line Guides - Page 6

Add a user to a supplementary group in Linux with usermod -aG, gpasswd -a, or adduser on Debian. Verify with id, apply changes with newgrp or re-login, and avoid the missing -a mistake.

Configure BIND primary and secondary DNS on RHEL-family Linux with allow-transfer, slave zones, named-chroot on Rocky Linux 8, and dig verification after AXFR zone replication.

Important Linux sysctl parameters for performance — what each knob controls, what to check on your host, and the impact when you raise or lower it, without copying paste-and-go sysctl.conf lists.

Learn Linux setgid on directories and executables: chmod g+s, 2775 group inheritance, write and plocate examples, s vs S, find, and when to use setgid on shared folders.

Learn Linux setuid on executables: what chmod u+s and 4755 do, why passwd uses setuid, lowercase s vs uppercase S, how to find setuid files, and when not to add your own.

Learn the Linux sticky bit on directories: what chmod +t and 1777 do, why /tmp uses them, lowercase t vs uppercase T, how to remove the bit, and how to find sticky directories.

Suppress sysctl stable_secret read errors when piping sysctl -a to grep, understand why net.ipv6.conf.*.stable_secret returns I/O error, and check IPv6 settings without disabling IPv6.

List systemd services with systemctl list-units and list-unit-files — filter running, enabled, disabled, failed, and inactive units, compare loaded vs installed unit files, and check one service with is-active and …

Extract tar.gz and tgz archives with GNU tar, decompress plain .gz files with gunzip, list members without unpacking, and avoid mixing up gzip streams with tar archives.

Check and change ulimit resource limits in Linux, including open files, soft vs hard limits, persistent limits.conf settings, systemd LimitNOFILE, and prlimit for running processes.

Learn how to exclude selected users from pam_faillock account lockout on RHEL, Rocky Linux, AlmaLinux, and Oracle Linux using authselect and PAM rules.

Extract one file, multiple files, directories, wildcards, or symlinks from a tar.gz archive with tar, including custom destinations and --strip-components.

Find where OpenSSL keeps openssl.cnf, trust-store certificates, libssl libraries, and the openssl binary on Linux and Windows. Use openssl version -d, which openssl, ldconfig, and OPENSSL_CONF when paths differ between …

Create, copy, move, rename, and delete files and directories in Linux with touch, mkdir, cp, mv, rm, and rmdir—plus wildcards, brace expansion, and safe verification with ls, stat, and du.

Exclude one or multiple users from an OpenSSH Match Group with negated User patterns, validate sshd_config safely, and verify the effective SSH settings.

Create ext4, XFS and VFAT filesystems in Linux with mkfs: identify the right block device, add labels, mount and unmount, read capacity correctly, and check or repair each filesystem type.

Schedule one-time tasks in Linux with the at command: start atd, write relative and absolute time specs, list jobs with atq, inspect with at -c, cancel with atrm, capture job output, and control access with at.allow and …

Update 389 Directory Server safely with dnf, pre-upgrade health checks, verified backups, standalone and rolling replica updates, post-upgrade validation, and recovery when a package update fails.

Understand kernel-core on RHEL, the difference between kernel, kernel-modules-core and kernel-modules, which packages you need, and how DNF updates them safely.

Update the kernel safely on RHEL with DNF. Check available versions, install the latest kernel, verify the default boot entry, reboot, and confirm the new kernel.

Learn RHEL patch management with DNF: identify security advisories and CVEs, apply security-only updates, patch specific RHSA or CVEs, and verify remediation.

Fix "There are no enabled repositories" on RHEL by checking DNF repositories, system registration, BaseOS/AppStream, Subscription Manager, and offline repository configuration.

Remove old Linux kernels safely on RHEL, Rocky Linux and AlmaLinux with dnf remove --oldinstallonly, protecting the running kernel and a bootable fallback.

Downgrade an installed RPM package on RHEL-family systems with dnf downgrade, install an exact older build, handle common errors, and lock the version with versionlock.

To exit full screen in virt-manager, move the pointer to the top-center edge and click the hidden restore button. Learn why Ctrl+Alt+F may not work.

Learn how to check open and listening ports in Linux with ss, lsof, nmap, and nc. Find the process using a port and test remote port access.

Learn how to list running processes in Linux with ps, top, pgrep, and pstree. Filter processes by user, PID, name, CPU, memory, and state.

Automate RHEL installation with Kickstart on RHEL 10: file structure, ksvalidator, anaconda-ks.cfg templates, inst.ks boot options, rhsm registration, lab harness kickstart, and post-install verification.

Fix kickstart clearpart not working on RHEL 10: scope disks with ignoredisk and clearpart --drives, wipe old LVM with a %pre script, and validate storage before autopart.

Kickstart %pre and %pre-install script examples on RHEL 10: --log, --interpreter, disk wipe before clearpart, NIC inventory, and copying logs with %post --nochroot.