SysTutorials Posts

Scripting & Utilities

Resolving SSH “Remote Host Identification Has Changed” Errors
ByEric Ma Mar 24, 2018Apr 13, 2026

When you SSH to a server and see the warning below, your SSH client has detected that the server’s host key doesn’t match what’s stored locally: @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ @ WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED! @ @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY! Someone could be eavesdropping on you right now (man-in-the-middle attack)!…

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Linux & Systems Administration

Merge JPG Images into PDF on Linux
ByEric Ma Mar 24, 2018Apr 13, 2026

Converting a series of JPG images into a single PDF is useful for creating documents, presentations, or archiving scanned photos. Linux offers several tools for this task, each with different trade-offs between simplicity, quality preservation, and features. Using img2pdf (Recommended) For most cases, img2pdf is the best choice because it merges images without re-encoding or…

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Linux & Systems Administration

Extract Files from a .deb Package Without Installing
ByEric Ma Mar 24, 2018Apr 12, 2026

[md] When you need to inspect what files a .deb package contains or will install, dpkg is your primary tool. This is useful for understanding package contents before installation, checking what files a package added to your system, or troubleshooting file conflicts. ## Listing Files in an Installed Package If the package is already installed…

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Linux & Systems Administration

Checking HDFS File Replication Factor
ByEric Ma Mar 24, 2018Apr 13, 2026

When managing HDFS clusters, you often need to verify the replication factor of specific files to ensure data redundancy meets your requirements. Here are the practical methods to check this. Using hdfs dfs -ls The most straightforward way is to list the file with hdfs dfs -ls: hdfs dfs -ls /usr/GroupStorage/data1/out.txt Output: -rw-r–r– 3 hadoop…

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Linux & Systems Administration

Adjusting HDFS Replication Factor on Live Clusters
ByEric Ma Mar 24, 2018Apr 13, 2026

When you need to increase data redundancy or reduce storage overhead on a running HDFS cluster, you’ll often need to adjust the replication factor. Before making changes, understand that HDFS replication works differently than you might expect. How HDFS Replication Factor Works The replication factor in HDFS is determined at write time by the client,…

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Linux & Systems Administration

Capturing RTMP Streams on Linux: A Practical Guide
ByEric Ma Mar 24, 2018Apr 13, 2026

RTMP (Real Time Messaging Protocol) streams are still used for live broadcasts and on-demand video delivery, though less commonly than HLS or DASH. If you need to capture an RTMP stream, there are several solid tools available on Linux. Using ffmpeg (recommended) ffmpeg is the modern standard for working with RTMP streams. It’s widely available,…

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Linux & Systems Administration

Find and Delete Directories Recursively
ByWeiwei Jia Mar 24, 2018Apr 13, 2026

Removing version control or build artifact directories across a large directory tree is a common sysadmin task. SVN directories (.svn), Git metadata (.git), or node modules (node_modules) often need to be purged before deployment or archiving. Using find with xargs The most efficient approach combines find with xargs: find ./ -name “.svn” -type d |…

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Linux & Systems Administration

Installing Calibre on Linux
ByEric Ma Mar 24, 2018Apr 12, 2026

Distribution repositories often lag behind Calibre’s latest releases. If your package manager shows an older version and you need current features or bug fixes, installing directly from the official installer is straightforward. Official installer method Calibre provides a dedicated Linux installer that works across distributions. This is the recommended approach for staying current: sudo -v…

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Linux & Systems Administration

HDFS Snapshots: Architecture and Implementation Details
ByEric Ma Mar 24, 2018Apr 11, 2026

HDFS snapshots provide a way to create read-only point-in-time copies of the filesystem or specific directories without duplicating data. Understanding their design helps you implement efficient backup strategies and recover from accidental deletions in production clusters. How HDFS Snapshots Work Snapshots in HDFS use copy-on-write semantics to avoid duplicating data. When you create a snapshot,…

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Linux & Systems Administration

How to Find Which Package Provides a File
ByEric Ma Mar 24, 2018Apr 13, 2026

When you need a command or library file but don’t have the package installed, you need to search for which package provides it. On Red Hat/Fedora systems, yum provides or dnf provides does this. On Debian/Ubuntu, the equivalent is apt-file. Red Hat, Fedora, and CentOS (DNF/YUM) Use dnf provides (or yum provides on older systems):…

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Linux & Systems Administration

Balancing HDFS DataNode Storage
ByEric Ma Mar 24, 2018Apr 13, 2026

As nodes are added or removed from a Hadoop cluster, storage utilization becomes uneven across DataNodes. Some fill up while others remain mostly empty, leading to inefficient resource use and potential storage bottlenecks. HDFS provides the Balancer tool to redistribute blocks across DataNodes and even out disk usage. Understanding the Balancer The HDFS Balancer is…

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Linux & Systems Administration

Installing GitBook on Linux
ByEric Ma Mar 24, 2018Apr 13, 2026

GitBook is a tool for building documentation and ebooks from Markdown content. Here’s how to set it up on a Linux system. Prerequisites You’ll need Node.js installed first. On Ubuntu/Debian: curl -fsSL https://deb.nodesource.com/setup_20.x | sudo -E bash – sudo apt-get install -y nodejs On Fedora/RHEL: sudo dnf install nodejs Verify the installation: node –version npm…

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Linux & Systems Administration

Installing Node.js on Fedora: DNF and Alternative Methods
ByEric Ma Mar 24, 2018Apr 12, 2026

Node.js is available on Fedora through the DNF package manager and several alternative methods. Here’s how to install it using each approach. Method 1: DNF (System Package Manager) The simplest method — install Node.js directly from Fedora’s repositories: sudo dnf install nodejs npm Check the installed version: node –version npm –version Fedora’s repositories typically include…

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Linux & Systems Administration

Running Calibre’s ebook-convert on Headless Servers with Xvfb
ByEric Ma Mar 24, 2018Apr 13, 2026

When GitBook or other tools call Calibre’s ebook-convert command on a headless server, you’ll hit this error: RuntimeError: X server required. If you are running on a headless machine, use xvfb This happens because Calibre needs an X11 display server, even though you’re just converting files. The solution is to wrap ebook-convert with xvfb-run, which…

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Linux & Systems Administration

Installing Node.js on Ubuntu and Linux Mint
ByEric Ma Mar 24, 2018Apr 13, 2026

Node.js installation on Ubuntu and Linux Mint has evolved significantly. The approach depends on your use case — whether you need the latest stable version, multiple Node versions for different projects, or just a quick setup. Using the NodeSource Repository (Recommended) The NodeSource repository provides current, well-maintained Node.js packages. This is the best approach for…

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Linux & Systems Administration

Locating Which DataNodes Store a Specific HDFS File
ByEric Ma Mar 24, 2018Apr 13, 2026

In HDFS, files are split into blocks and replicated across multiple DataNodes for fault tolerance and parallelism. When you need to know exactly which DataNodes hold a specific file’s blocks, use hdfs fsck with the -locations and -blocks flags. Basic command hdfs fsck /path/to/file -files -locations -blocks This queries the NameNode and returns the block…

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Linux & Systems Administration

Configuring QEMU Guest Network Access Over Wireless
ByWeiwei Jia Mar 24, 2018Apr 11, 2026

When your host machine connects to the network via WiFi, giving QEMU guests network access requires a different approach than traditional bridged networking. Since wireless interfaces typically don’t support bridge mode, you’ll need to use NAT (Network Address Translation) or a tap device with masquerading. Understanding your options NAT mode is the simplest approach—the host…

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Linux & Systems Administration

Increase the Maximum Open Files Limit on Linux
ByEric Ma Mar 24, 2018Apr 13, 2026

When you hit the open files limit on Linux, you’ll see errors like “Too many open files” — typically when running applications that create many temporary file handles. The default limit is often 1024, which isn’t enough for resource-heavy workloads. Check your current limit: ulimit -n Understanding soft and hard limits Linux maintains two types…

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Linux & Systems Administration

Resolving “Too many frags” and “skb rides the rocket” Errors in Xen
ByEric Ma Mar 24, 2018Apr 13, 2026

Xen VMs sometimes log cryptic kernel messages about fragmentation that indicate a mismatch between the VM’s network driver and the host’s virtual interface settings: kernel netfront: Too many frags skb rides the rocket These errors occur when the guest kernel’s netfront driver tries to send packets with more fragments than the backend can handle, or…

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Linux & Systems Administration

Adding Bind Mounts to /etc/fstab
ByEric Ma Mar 24, 2018Apr 13, 2026

Bind mounts let you mount a directory or file at another location in your filesystem hierarchy without duplicating the underlying data. They’re useful for directory reorganization, containerization, and working around path constraints. Here’s how to configure them in /etc/fstab. Basic Syntax The /etc/fstab syntax for bind mounts is straightforward: /source/path /mount/point none bind 0 0…

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