When you’re managing KVM virtual machines on a Linux host, you often need to identify which OS threads correspond to vCPU threads. This is essential for CPU pinning, performance analysis, and troubleshooting resource contention. Using virsh to List vCPU Thread IDs The most straightforward approach is through virsh, libvirt’s command-line tool: virsh vcpuinfo <domain-name> This…
The error “Cannot make directory ‘/var/run/screen/S-apache’: Permission denied” typically means the screen session directory can’t be created under /var/run/screen/. This happens when screen lacks proper permissions or when security policies block the operation. Verify screen installation and permissions First, confirm screen is installed with correct permissions: $ ls -la $(which screen) -rwxr-sr-x 1 root screen…
When running virtual machines with QEMU/KVM, you’ll frequently need to transfer files or share directories between the host and guest systems. Several methods work well depending on your use case and performance requirements. 9p (Virtio) Filesystem The 9p protocol is the most straightforward approach for sharing directories. It’s lightweight and doesn’t require additional guest agents….
Getting accurate I/O metrics per process is critical for troubleshooting performance issues, identifying storage bottlenecks, and capacity planning. Linux provides several tools for this task, each with different trade-offs between accuracy and overhead. Using /proc/[pid]/io The simplest approach is reading directly from the proc filesystem. Each process has an io file containing I/O statistics: cat…
Rocky Linux 9 and later distributions use FirewallD as the default firewall management tool. However, if you need direct control over iptables and ip6tables rules, you can disable FirewallD and use the iptables-services package to restore your rules at boot. Install and Configure iptables-services Start by installing the iptables-services package: dnf install iptables-services Create the…
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…
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…
When truncating strings, you often need to avoid cutting off in the middle of a word. The naive substr() approach will break words, so you need logic to backtrack to the previous word boundary. The problem Given a string like “ab cc dde ffg ff”, if you want a substring of maximum 7 characters starting…
HTML to plain text conversion is a common task in PHP applications — whether you’re sanitizing user input, preparing content for email, generating text previews, or creating searchable indexes. Here are the practical approaches. Using strip_tags() The simplest method is PHP’s built-in strip_tags() function: $html = ‘<p>Hello <strong>world</strong>!</p>’; $text = strip_tags($html); echo $text; // Output:…
You can pause and resume any process on Linux using signals without stopping it completely. This is useful for managing resource-heavy jobs, debugging, or controlling execution flow without losing process state. Using SIGSTOP and SIGCONT The standard approach uses two signals: SIGSTOP: Pauses a process (cannot be caught or ignored) SIGCONT: Resumes a paused process…
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…
If you’re running an older CentOS or RHEL system with Vim 7.4, upgrading to Vim 8 or later gives you modern features like async I/O, jobs API, terminal emulator support, and better plugin performance. Here are the practical approaches. Check Your Current Version $ vim –version VIM – Vi IMproved 7.4 (2013 Aug 10, compiled…
Files with replication factor 1 are a liability in production HDFS clusters. They have no redundancy, meaning a single node failure results in data loss. Identifying and fixing these files should be part of your regular cluster maintenance. Using the HDFS CLI The most straightforward approach is using hdfs fsck with output parsing: hdfs fsck…
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…
When processing text data, you often need to extract everything from a certain field onward. awk makes this straightforward once you understand the mechanics. Basic Syntax The fundamental approach uses awk’s field variables and looping: awk ‘{for(i=N;i<=NF;i++) printf “%s “, $i; print “”}’ file.txt Replace N with the field number you want to start from….
[md] PHP upload limits are controlled through the php.ini configuration file. On Ubuntu/Debian systems, the file location depends on your PHP version: /etc/php/8.3/apache2/php.ini # PHP 8.3 /etc/php/8.2/apache2/php.ini # PHP 8.2 /etc/php/8.1/apache2/php.ini # PHP 8.1 To find your actual PHP version and configuration path: php -i | grep “Loaded Configuration File” ## Key Configuration Directives Three…
Go’s net/http package provides straightforward methods for sending POST requests. The two main approaches are Post() for raw body content and PostForm() for URL-encoded form data. Using PostForm for Form Data PostForm() handles URL-encoded form submissions automatically, setting the Content-Type header to application/x-www-form-urlencoded: package main import ( “io” “net/http” “net/url” ) func main() { data…
Several methods exist to prepend a prefix string to each line of text. The right approach depends on your input source and performance requirements. Using sed The sed stream editor is the most portable and efficient approach: sed ‘s/^/PREFIX/’ file.txt This uses a substitution command where ^ matches the start of each line and PREFIX…
Monitoring server temperatures is essential for preventing hardware damage and maintaining system stability. Linux provides several tools to query thermal sensors and identify which components are running hot. Using lm-sensors The most reliable approach is lm-sensors, a userspace tool that reads temperature data from kernel drivers: # Install lm-sensors sudo apt install lm-sensors # Debian/Ubuntu…
To load a kernel module automatically at system startup, create a configuration file in /etc/modules-load.d/ with a .conf extension. The systemd-modules-load.service daemon reads these files during early boot and loads the specified modules. Basic method Create a new configuration file. For the ixgbe driver example: echo “ixgbe” | sudo tee /etc/modules-load.d/ixgbe.conf Or use your editor…