SysTutorials Posts

System Administration & Cloud

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

The conventional wisdom that smaller code is always better has been thoroughly invalidated on modern processors. A statement from kernel development circles captured this well: for performance-critical paths like interrupt handlers, large-but-correctly-aligned-and-optimized code consistently outperforms byte-packed alternatives. Consider this comparison: mov eax, [foo] add eax, 1 mov [foo], eax versus: inc [foo] The three-instruction sequence…

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Testing & DevOps

Efficiently Copy Large Sparse Files with SEEK_HOLE and SEEK_DATA
ByEric Ma Mar 24, 2018Apr 12, 2026

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…

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Linux System Configuration

Detecting Bad Blocks on Storage Devices
ByQ A Mar 24, 2018Apr 13, 2026

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…

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Linux System Configuration

Installing MATE Desktop on Fedora 17
ByQ A Mar 24, 2018Apr 13, 2026

MATE is a continuation of GNOME 2, maintained by the MATE Desktop Environment project. It’s included in Fedora’s official repositories and is a supported desktop option. Install MATE Desktop MATE is available as a desktop environment group in Fedora 41’s repositories. Install the base desktop with: sudo dnf install @mate-desktop The @mate-desktop group installs the…

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Linux & Systems Administration

Testing Network Connectivity Between Linux Servers
ByQ A Mar 24, 2018Apr 12, 2026

When you need to verify that two Linux systems can communicate over a specific protocol and port, you have several solid options. Let’s cover the most practical approaches. Using nc (netcat) The nc command remains a reliable choice for quick connectivity tests. It’s widely available and requires no special setup. TCP connection test To listen…

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Linux & Systems Administration

Managing LVM Logical Volumes on Linux
ByQ A Mar 24, 2018Apr 12, 2026

LVM (Logical Volume Management) abstracts physical storage into logical volumes, giving you flexibility to resize filesystems, snapshot data, and manage disk space without downtime. It sits between your physical disks and the filesystems you mount. The three core LVM concepts are: Physical Volumes (PVs): Physical disks or disk partitions Volume Groups (VGs): Collections of PVs…

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Linux & Systems Administration

Finding Hard Links to a File
ByQ A Mar 24, 2018Apr 13, 2026

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…

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Functional Programming

Memory-mapping Ranges Larger Than Available RAM and Swap
ByQ A Mar 24, 2018Apr 12, 2026

When you mmap() a range larger than your system’s total physical memory plus swap, the kernel normally reserves swap space to back the mapping. If that reservation would exceed available swap, mmap() fails with ENOMEM. The MAP_NORESERVE flag lets you bypass this reservation requirement. Understanding the Default Behavior By default, when you call mmap() with…

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Linux & Systems Administration

Where Linux Applications Store Configuration and Data Files
ByEric Ma Dec 31, 2017Apr 12, 2026

Evolution is a full-featured personal information management suite that handles email, contacts, calendars, and tasks. It includes enterprise features like native Microsoft Exchange support and integrates deeply with GNOME’s ecosystem. To troubleshoot issues, migrate data, back up configurations, or secure your setup, you need to know where Evolution stores everything. Evolution follows the XDG Base…

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Development Best Practices

Exporting NFSv4 Shares to External Networks
ByEric Ma Dec 16, 2017Apr 12, 2026

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….

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Development Best Practices

How to Add Custom Content to Receipts
Byjameswarner Dec 11, 2017Apr 12, 2026

When you need to display data on point-of-sale receipts that isn’t available in the standard receipt designer, you’ll need to create a custom field. This involves work in both Dynamics 365 (the backend) and the Retail SDK (the POS application layer). This walkthrough covers adding a custom field—using item barcodes as an example—though the pattern…

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Development Best Practices

.NET Core 2.1: What’s New in 2018
ByJohnnymorgan Nov 21, 2017Apr 13, 2026

This post covers .NET Core 2.1, which released in May 2018. Some of the predicted features below didn’t materialize as described; we’ll clarify what actually landed versus what was speculated. What is .NET Core? .NET Core is Microsoft’s open-source, cross-platform runtime for building applications in C#, F#, and Visual Basic. Unlike the monolithic .NET Framework…

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Scripting & Utilities

SSH, File Transfer, and Remote Access: Linux from Windows
ByEric Ma Nov 14, 2017Apr 12, 2026

If you’re working on Windows but need to interact with Linux systems, you’ll need reliable remote access tools. SSH is the standard—it’s secure, scriptable, and works everywhere. Here’s what actually matters. SSH Clients Windows Terminal + OpenSSH is the baseline for Windows 11. It’s built-in, integrates native SSH without extra installation, and handles key authentication…

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Development Best Practices

Implementing Hibernate Envers for Entity Auditing
ByJoseph Macwan Sep 21, 2017Apr 12, 2026

Hibernate Envers is a proven auditing framework that automatically tracks changes to JPA entities without cluttering your domain model with logging code. It stores historical data in separate audit tables and lets you query entity states at any point in time. Why Use Hibernate Envers Envers handles the mechanics of change tracking transparently: Audits all…

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Testing & DevOps

Deploy ASP.NET Core MVC Apps to Azure App Service
ByJohnnymorgan Sep 18, 2017Apr 12, 2026

ASP.NET Core remains one of the most efficient frameworks for building scalable web applications. This guide walks through deploying an ASP.NET Core MVC application to Azure App Service using Visual Studio — the quickest path from local development to production. Prerequisites You’ll need: An active Azure subscription (free tier accounts work fine for testing) Visual…

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Linux & Systems Administration

x86-64 Instruction Encoding: From Assembly to Machine Code
ByEric Ma Sep 9, 2017Apr 12, 2026

Before encoding instructions, you need to understand the two assembly syntaxes you’ll encounter—they differ fundamentally in operand order and addressing format. Intel syntax (Intel/AMD manuals): Operand order: destination, source Memory addressing: [base+offset] Example: add r8, [rdi+0xa] AT&T syntax (GNU toolchains on Linux): Operand order: source, destination Memory addressing: offset(%base) Example: addq 0xa(%rdi), %r8 For most…

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Systems & Architecture

HDFS NameNode Metadata Checkpointing: Resolving Sync Issues
ByEric Ma Sep 9, 2017Apr 12, 2026

The Secondary NameNode periodically merges the fsimage and edits log files to keep the edits log manageable and consolidate metadata. When this checkpointing fails, you’ll see errors like: ERROR org.apache.hadoop.hdfs.server.namenode.SecondaryNameNode: Exception in doCheckpoint java.io.IOException: Inconsistent checkpoint fields. This typically indicates a mismatch between the NameNode and Secondary NameNode metadata states, often from unclean shutdowns or…

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Linux & Systems Administration

Debugging Kernel Modules with Runtime Parameters
ByWeiwei Jia Aug 28, 2017Apr 12, 2026

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…

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Systems & Architecture

QEMU/KVM Networking: TAP, virtio, and vhost Explained
ByWeiwei Jia Aug 26, 2017Apr 12, 2026

QEMU/KVM networking operates across multiple layers — TAP devices, QEMU’s packet queuing, virtio descriptors, and kernel bypass mechanisms. Understanding this stack is essential for debugging connectivity issues and tuning performance in production environments. TAP Device Fundamentals TAP (TUN/TAP) devices create a bridge between the guest and host network stack. A typical QEMU/KVM configuration looks like:…

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Systems & Architecture

Measuring Task I/O with eBPF: Microsecond Precision
ByWeiwei Jia Aug 20, 2017Apr 12, 2026

Most popular task monitoring tools (top, iotop, procfs) sample disk I/O information at granularity limited by kernel timer frequency—typically once per second. This sampling rate misses short-lived I/O bursts and makes it difficult to accurately measure which tasks are truly I/O bound. eBPF and kernel tracepoints let you capture microsecond-level accuracy without heavy overhead. Why…

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