“Cleaning” history usually means rewriting it to remove large files, sensitive data, or to squash messy commits into logical units. This is destructive—it rewrites history and affects anyone who’s cloned the repo. Only do this on branches you control or coordinate with your team first. git filter-repo: The Standard Tool git filter-repo replaced the deprecated…
The Linux command readlink -m resolves a path to its absolute, canonical form, following all symlinks and resolving .. and . components. Python provides several ways to do this, depending on your needs and Python version. Using pathlib.Path.resolve() The modern standard approach uses pathlib: from pathlib import Path canonical_path = Path(“./../folder/./file.txt”).resolve() print(canonical_path) Path.resolve() returns an…
Thunderbird can leak your LAN IP address in SMTP email headers, even though the mail server itself only sees your public IP. This happens because Thunderbird sends its local IP during the HELO/EHLO handshake with the SMTP server, and that information gets recorded in the email header. For example, you might see: Received: from [192.168.1.2]…
GNOME Evolution’s email address auto-completion works by querying your local address books and, optionally, external sources. Here’s how to get it working properly. Check Your Address Books Evolution pulls auto-completion suggestions from multiple sources: Personal address book (local contacts you’ve added) On This Computer (system-wide contacts) Synced contact sources (Google, CalDAV, CardDAV, LDAP) To see…
If you’ve tried ssh root@my-server and got a “Permission denied” error, it’s not a bug—it’s a security feature. This behavior is standard across all modern distributions. Why Root SSH Login is Disabled By default, the PermitRootLogin directive in /etc/ssh/sshd_config is set to prohibit-password or no. This prevents direct root access over SSH regardless of whether…
Identifying which ports a specific process is using comes up regularly in debugging, security audits, and infrastructure management. Here are the practical methods. Using ss The ss command is the modern standard for socket inspection: ss -tlnp | grep <PID> This shows listening TCP sockets (-t for TCP, -l for listening). Add -u if you…
Retrieving hardware serial numbers is essential for inventory management, warranty tracking, and identifying physical servers across your infrastructure. The standard approach uses dmidecode, which reads the system’s DMI (Desktop Management Interface) data. Using dmidecode First, install the tool: sudo apt-get install dmidecode For Rocky Linux, RHEL, and derivatives: sudo dnf install dmidecode Then query the…
SMP (Symmetric Multiprocessing) and NUMA (Non-Uniform Memory Access) represent two fundamentally different approaches to multi-processor system architecture. Understanding the distinction matters because it affects how you tune applications, configure kernel parameters, and optimize workloads. Memory Access Latency In SMP, all processors have equal latency when accessing any memory location. Every CPU communicates with RAM through…
Password-less SSH login is faster, more secure, and essential for automation. Combining it with remote command execution lets you run tasks on servers from your local machine without interactive authentication. Setting Up SSH Key-Based Authentication Generate SSH Keys First, generate an ED25519 key pair on your local machine (A): ssh-keygen -t ed25519 -C “user@hostname” -f…
Accurate system time is critical for log timestamps, security operations, certificate validation, and coordinating across distributed systems. Modern Linux distributions handle time synchronization automatically, but you’ll occasionally need to set the time manually. Using timedatectl The standard tool for time management on systemd systems is timedatectl. Check your current time and synchronization status: timedatectl status…
The NameNode in HDFS maintains the filesystem namespace in memory. The Secondary NameNode (or Checkpoint Node in HA setups) periodically merges the namespace image (fsimage) with the edit logs to create a new checkpoint. Understanding how to force this process is essential for cluster maintenance and recovery operations. How Checkpointing Works The checkpoint process combines…
Interrupts are fundamental to how your Linux system handles hardware and software events. Monitoring them in real-time helps identify performance bottlenecks, device driver issues, and CPU load imbalances. Here’s how to check interrupts effectively. Quick Live Monitoring with /proc/interrupts The simplest approach is reading /proc/interrupts directly: cat /proc/interrupts This shows a snapshot of interrupt counts…
Achieving high performance in virtualized environments requires careful tuning of kernel parameters, CPU idle states, and hypervisor settings. The goal is to reduce context switching overhead, minimize latency, and keep vCPUs busy rather than cycling through low-power states. Kernel Boot Parameters Add these parameters to your kernel boot line in /etc/default/grub: intel_idle.max_cstate=0 processor.max_cstate=0 idle=poll intel_pstate=disable…
CPU affinity pins a process to specific CPU cores, reducing context switches and improving cache locality. This matters when you need consistent latency or want to isolate workloads on multi-core systems. Using taskset taskset is the standard tool for setting CPU affinity on running processes. The basic syntax: taskset -p -c 0,1,2 <pid> This binds…
SPF (Sender Policy Framework) is a DNS-based authentication mechanism that helps prevent email spoofing by specifying which mail servers are authorized to send emails on behalf of your domain. If your domain is hosted with DreamHost, you’ll need to add an SPF record to your DNS configuration. Understanding SPF Records An SPF record is a…
Limiting CPU resources for individual users is essential for preventing resource exhaustion, maintaining fair system performance, and isolating workloads. Whether you’re managing multi-user systems, shared hosting environments, or need to constrain specific applications, Linux provides several proven methods. Using cgroups (Control Groups) Modern cgroups v2 offer the most flexible and reliable approach. Most distributions use…
If you’re seeing PHP errors like Class ‘DOMDocument’ not found, your PHP installation is missing the XML extension. This is common after migrating sites or fresh installations where the base PHP package doesn’t include DOM support out of the box. Install php-xml The solution is straightforward — install the php-xml package: sudo dnf install php-xml…
The default data directory for MySQL and MariaDB installed from official repositories on modern distributions is: /var/lib/mysql This applies to CentOS 7, Rocky Linux 9, Fedora, and most RHEL-based systems. Finding the Data Directory Programmatically If you’ve customized your installation or need to verify the exact location, there are several reliable methods. Query MariaDB/MySQL Configuration…
The full URL is commonly needed for redirects, canonical link headers, or logging. While PHP superglobals provide the raw components, how you assemble them matters for security and reliability. Using $_SERVER Superglobals The most direct approach uses the $_SERVER array: $url = (isset($_SERVER[‘HTTPS’]) ? “https” : “http”) . “://$_SERVER[HTTP_HOST]$_SERVER[REQUEST_URI]”; This reconstructs the scheme, host, and…
Short open tags (<? ?>) create compatibility issues with XML declarations and are considered poor practice. While they’re disabled by default in modern PHP versions, you may need to manage this setting when working with legacy code or specific server configurations. Configuration Methods Via php.ini The primary way to control short open tags is through…