Omer Cakmak

Fix Linux errno 99 (EADDRNOTAVAIL): when bind() fails because the IP is not local, when Docker publishes to a missing host address, when services start before the interface is ready, and when connect() exhausts ephemeral …

Batch resize images in Linux with ImageMagick mogrify and magick, including aspect-ratio control, non-destructive output directories, mixed JPG and PNG folders, recursive trees, and optional format conversion.

Fix bash: curl: command not found by installing the curl package with apt, dnf, pacman, zypper, or apk, or by restoring /usr/bin and /bin in PATH when curl is already installed.

Learn what systemd is in Linux, how units and targets fit together, and which systemctl commands to run first. This beginner tutorial focuses on concepts and points to dedicated guides for listing services, targets, …

Back up and restore GPT or MBR partition tables in Linux with sfdisk --dump, clone a layout to another disk, and save raw partition-table sectors with --backup-pt-sectors without touching filesystem data.

Automate SFTP file transfers in Linux shell scripts using sftp batch mode with SSH keys, or password authentication with sshpass or expect when keys are not available.

Install ARPACK runtime and development packages on Ubuntu, Debian, and RHEL-family Linux from distribution repositories, verify libraries with dpkg or rpm and pkg-config, and link a sample Fortran program against …

Fix “another app is currently holding the yum lock” and modern DNF lock messages on RHEL and Fedora. Find the holding PID, wait safely, and clear stale metadata or RPMDB locks on DNF4 and DNF5.

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.

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.

The OpenSSH client reads ~/.ssh/config for host aliases, keys, ports, ProxyJump bastions, and connection reuse—this guide walks through examples and how to verify them with ssh -G.

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.

Extend or resize a non-LVM root partition in Linux with parted or fdisk when unallocated space exists after the target partition, then grow ext4 with resize2fs without reformatting.

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

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.

Rebuild the initramfs image with dracut for one kernel or every installed kernel, add storage and network drivers, and inspect the result with lsinitrd.

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.