Use usermod to add a user to supplementary groups. The -a (append) flag is critical — without it, you’ll remove the user from all groups not explicitly listed. usermod -a -G group_name user_name To add a user to multiple groups at once: usermod -a -G group1,group2,group3 user_name Options explained -a, –append Append the user to…
Working in an SVN repository often leaves behind temporary build artifacts, compiled outputs, and editor cache files. Unlike Git’s git clean command, SVN has no built-in cleanup mechanism for untracked files. Using svn st to Identify Untracked Files The svn status command (or svn st) marks untracked files with a ? prefix. You can leverage…
When you modify /etc/sysctl.conf, the changes take effect on the next reboot. To apply them immediately without rebooting, use the sysctl -p command: sudo sysctl -p This reads the configuration file and applies all settings to the running kernel. Reloading Specific Configuration Files By default, sysctl -p reads from /etc/sysctl.conf. You can specify a different…
Directory listing exposes your file structure to visitors and can be a security concern. Apache’s .htaccess file provides a straightforward way to disable this behavior while still allowing direct file access. Basic Implementation Create a .htaccess file in the directory where you want to disable listing: Options -Indexes Place this file in the root directory…
If you’ve made changes to your working copy but haven’t committed them yet, you can discard them using svn revert. This is useful when you want to abandon edits and go back to the last committed version. Basic Revert To revert all changes in your working copy, run this from the repository root: svn revert…
MySQL Cluster uses NDB (Network Database) storage engine to provide high availability and data redundancy across multiple nodes. This guide covers installation and configuration on modern RHEL-compatible systems. Prerequisites Three or more servers (minimum: one management node, two data nodes, one SQL node) Rocky Linux 9 or AlmaLinux 9 Root or sudo access Static IP…
To disable all active swap spaces on Linux, run: swapoff -a The -a flag targets all currently enabled swap devices and files. This forces the kernel and applications to rely entirely on physical RAM. When You’d Do This Disabling swap is useful for: Performance testing: Eliminating swap I/O variance to get consistent benchmarks Latency-sensitive workloads:…
To enable debugging, configure your CMake build with CMAKE_BUILD_TYPE set to Debug. This tells CMake to invoke the compiler with the -g flag, generating debug symbols that tools like gdb and lldb need. From your project’s root directory: cmake -DCMAKE_BUILD_TYPE=Debug -B build cd build make The -B build flag creates a separate build directory, which…
LaTeX is a document preparation system widely used for scientific and technical documents. Most modern workflows use pdflatex or xelatex to compile directly to PDF, avoiding the outdated DVI → PostScript → PDF pipeline. Debian/Ubuntu sudo apt-get update sudo apt-get install texlive-latex-base texlive-latex-extra texlive-fonts-recommended For a complete installation with all packages: sudo apt-get install texlive-full…
No-IP provides dynamic DNS service for systems that don’t have static IP addresses. The noip2 client daemon monitors your system’s IP and automatically updates your No-IP domain when changes occur. Here’s how to set it up properly. Prerequisites You’ll need: A No-IP account with at least one hostname configured Root or sudo access A Linux…
When you first use git on a machine, you’ll need to configure your identity. Git uses these credentials to author your commits: git config –global user.name “Your Name” git config –global user.email you@example.com These settings are stored in ~/.gitconfig and apply to all repositories on your system. Verifying your configuration Check what you’ve set: git…
Archiving or copying a 1TB sparse file containing only 32MB of actual data is impractical with naive approaches—you’ll waste time and I/O bandwidth copying zeros. The solution is using SEEK_HOLE and SEEK_DATA flags with lseek(), which allow tools to skip over hole regions entirely. How SEEK_HOLE and SEEK_DATA work The Linux kernel provides two additional…
If you suspect a disk has bad blocks, use the badblocks utility to scan for them. This tool probes a device (usually a disk partition) and reports which blocks are unreliable or unreadable. Basic Usage badblocks /dev/sda1 This scans /dev/sda1 from the first block to the last block on the device. Common Options -s: Show…
A hard link is an additional directory entry pointing to the same inode as the original file. Unlike symbolic links, hard links share the same inode number and have identical permissions, ownership, and content. To find all hard links to a file, you need to locate every directory entry with the same inode. Using find…
NFSv4 significantly simplifies network exposure compared to NFSv3. Where NFSv3 requires managing multiple dynamic ports (mountd, statd, lockd), NFSv4 uses only port 111 (rpcbind) and port 2049 (NFS). This makes firewall configuration and port forwarding straightforward. For production environments, consider implementing Kerberos authentication (krb5, krb5i, or krb5p) instead of relying solely on network-based access control….
When you need to debug kernel behavior without full instrumentation frameworks, module parameters offer a pragmatic shortcut. Rather than immediately reaching for perf, kprobes, or eBPF, you can add simple toggles and state tracking directly in the code you’re investigating, then control them at runtime through sysfs. Frameworks like perf, kprobes, and eBPF are powerful…
HTML entities represent characters that either have special meaning in HTML or benefit from explicit encoding. You have three syntax options: Named entity: &name; (e.g., ©) Decimal numeric: &#number; (e.g., ©) Hexadecimal numeric: &#xhexcode; (e.g., ©) With UTF-8 encoding (the only sensible choice in 2026), most special characters can be typed directly. However, certain characters…
Data visualization transforms raw metrics into actionable insights. When you’re managing infrastructure metrics, application logs, business KPIs, or system performance data, visualization is how you extract signal from noise. The human brain processes visual information faster and more reliably than log files or spreadsheet rows—which is why dashboards have become essential infrastructure in modern operations….
The Linux kernel provides the taskstats API to monitor detailed per-task statistics, including I/O wait time, CPU scheduling delays, and memory reclamation waits. Understanding how these metrics are collected at the kernel level is essential for diagnosing performance issues and understanding process behavior. How the Kernel Records I/O Delays The kernel records I/O wait delays…
In computer systems, resources must be balanced across available hardware to maximize performance. The Linux kernel runs migration threads as per-CPU daemons to handle this work. These threads manage task migration between CPUs, CPU hotplug operations, and stop-machine synchronization. You can observe migration threads on any modern system: $ ps aux | grep migration root…