System Administration & Cloud

Server configuration, cloud infrastructure (AWS, KVM, VirtualBox), virtualization, performance tuning, and system administration tools.

System Administration & Cloud

Managing VirtualBox VMs from the Linux Command Line
ByDavid Yang Feb 29, 2020Apr 12, 2026

View all virtual machines registered with VirtualBox: vboxmanage list vms Output example: “ubuntu-server” {a1b2c3d4-e5f6-7890-abcd-ef1234567890} “debian-test” {b2c3d4e5-f6a7-8901-bcde-f12345678901} “centos-prod” {d6c938d8-0bec-57f0-9fd3-8e395ba3d218} Each VM appears with its name and UUID. The UUID uniquely identifies the VM in VirtualBox’s database. List running VMs only See only active virtual machines: vboxmanage list runningvms This is useful when you have many VMs…

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System Administration & Cloud

iPhone Performance Tuning: Disabling Unnecessary Battery-Draining Features
ByEric Ma Oct 1, 2019Apr 12, 2026

If your iPhone feels sluggish after a major iOS update, you’re running into resource contention. Newer iOS versions add features that demand CPU, GPU, and memory cycles. You can’t strip down iOS itself, but you can selectively disable features that drain resources without matching your actual workflow. Disable Haptic Feedback Haptic feedback—the vibrations on every…

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System Administration & Cloud

How Cloud Infrastructure Transforms Remote Work and Reduces Costs
ByEthan Millar Sep 4, 2019Apr 12, 2026

Cloud computing has fundamentally reshaped how organizations operate, shifting from on-premises infrastructure to distributed, internet-accessible systems. Rather than maintaining physical servers and data centers, companies now leverage cloud platforms where data storage, processing, and management occur across networked server clusters accessible via the internet. This shift has concrete implications for how work gets done, where…

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System Administration & Cloud

EC2 Instance Control with IAM Tags: Allowing Developers to Start Only Dev Instances
ByEric Ma Mar 10, 2019Apr 12, 2026

Shared AWS accounts across multiple teams require careful access controls to prevent costly mistakes. A common requirement is allowing developers to view and start all instances, but restrict stopping to only non-production resources. IAM policies with resource tags give you fine-grained control over who can do what. The Problem You have 50 production VMs and…

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System Administration & Cloud

Resizing a KVM Virtual Disk: A Step-by-Step Guide
ByWeiwei Jia Mar 24, 2018Apr 12, 2026

Expanding a VM’s storage is a routine operation in KVM environments. The process has two distinct phases: expanding the raw disk capacity and then growing the partitions and filesystems to use that space. Resizing the Disk Image The first step is to increase the virtual disk size using qemu-img: qemu-img resize disk.qcow2 +10G This adds…

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System Administration & Cloud

Retrieve a Server’s Serial Number Remotely
ByWeiwei Jia Mar 24, 2018Apr 12, 2026

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…

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System Administration & Cloud

Optimizing Virtual Machine Performance: A Tuning Guide
ByWeiwei Jia Mar 24, 2018Apr 12, 2026

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…

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System Administration & Cloud

Getting vCPU Thread IDs in QEMU/KVM
ByWeiwei Jia Mar 24, 2018Apr 12, 2026

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…

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System Administration & Cloud

Sharing Data Between QEMU/KVM Host and Guest
ByWeiwei Jia Mar 24, 2018Apr 12, 2026

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….

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System Administration & Cloud

How to Fix `/var/run/screen/S-apache` Permission Denied Error
ByEric Ma Mar 24, 2018Apr 12, 2026

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…

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System Administration & Cloud

How to Enable PHP DOM Extension in Apache on CentOS 7
ByEric Ma Mar 24, 2018Apr 12, 2026

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…

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System Administration & Cloud

MySQL and MariaDB Default Data Directories on CentOS 7
ByEric Ma Mar 24, 2018Apr 12, 2026

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…

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System Administration & Cloud

Configuring PHP Upload Size Limits on Linux Apache
ByQ A Mar 24, 2018Apr 12, 2026

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 -v php -i | grep “Loaded Configuration File” Modifying Upload Limits Open…

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System Administration & Cloud

Updating String Values in MySQL with REPLACE()
ByEric Ma Mar 24, 2018Apr 12, 2026

The REPLACE() function is your primary tool for modifying string values within a column. It scans for a substring and replaces all occurrences with a new value. Basic syntax UPDATE table_name SET column_name = REPLACE(column_name, ‘old_string’, ‘new_string’) WHERE condition; Simple example Replace all instances of “old_domain” with “new_domain” in the email column: UPDATE users SET…

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System Administration & Cloud

Connecting to MySQL: Client Libraries and Best Practices
ByWeiwei Jia Mar 24, 2018Apr 12, 2026

Connecting your application to a MySQL database is fundamental to most backend systems. Rather than shelling out to the mysql command-line client, you’ll use language-specific connectors that provide proper connection pooling, error handling, and prepared statements. Language-Specific MySQL Drivers The best approach depends on your tech stack: Python Use mysql-connector-python for straightforward connections or PyMySQL…

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System Administration & Cloud

Custom Headers and Footers in Apache Directory Listings
ByEric Ma Mar 24, 2018Apr 12, 2026

Custom headers and footers in Apache directory listings let you add branding, instructions, or navigation without modifying the core file listing. This is useful for public file archives, download directories, or any indexed directory you want to customize. Basic Setup with .htaccess Add these directives to .htaccess in the directory where you want custom listings:…

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System Administration & Cloud

Managing LVM Storage with libvirt
ByQ A Mar 24, 2018Apr 12, 2026

By default, libvirt stores VM images as files in /var/lib/libvirt/images/. While functional, this approach limits flexibility. LVM (Logical Volume Management) provides better control over disk space, snapshots, and performance tuning. Using LVM volumes as libvirt storage pools lets you manage VM storage like block devices rather than files, giving you faster provisioning, atomic snapshots, and…

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System Administration & Cloud

Windows 7 64-bit Installation Fails with Error 0xc0000225 on VirtualBox
ByQ A Mar 24, 2018Apr 12, 2026

Continue Learning Explore the Programming Academy

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System Administration & Cloud

Code alignment matters more than code size for performance
ByQ A Mar 24, 2018Apr 12, 2026

Continue Learning Explore the Programming Academy

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System Administration & Cloud

Installing a Paravirtualized DomU on Xen with Rocky Linux 9
ByEric Ma Apr 15, 2017Apr 12, 2026

Xen remains a solid hypervisor choice for specific workloads, though KVM dominates most Linux distributions today. This guide covers installing a paravirtualized DomU on Xen using modern tooling and Rocky Linux 9, which requires specific kernel parameters during installation. Why Paravirtualization Matters Paravirtualized guests communicate directly with the hypervisor rather than emulating hardware, resulting in…

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