CentOS

Scripting & Utilities

Converting JPG to EPS on Linux with ImageMagick and Ghostscript
ByEric Ma Jul 13, 2013Apr 12, 2026

Converting raster images to EPS format is necessary when working with LaTeX documents or professional publishing workflows that require PostScript compatibility. While online converters exist, command-line tools give you reproducibility, automation, and batch processing capabilities—essential for production work. Why EPS Still Matters EPS (Encapsulated PostScript) embeds images with precise positioning metadata and works reliably with…

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System Administration & Cloud

Configuring Custom Error Pages on Apache and Nginx
ByEric Ma Jul 13, 2013Apr 12, 2026

Apache’s default 404 error page is generic and often displays hosting provider branding. Customizing it gives you control over the user experience when they land on missing pages. The same applies to other HTTP error responses like 403 Forbidden or 500 Internal Server Error. Apache: Using ErrorDocument Directive The ErrorDocument directive in Apache accepts two…

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Linux & Systems Administration

Using DVDs as Local Package Repositories in DNF
ByEric Ma Jul 13, 2013Apr 12, 2026

Insert the installation media and create a mount point: sudo mkdir -p /media/dvd sudo mount /dev/sr0 /media/dvd For a DVD image file instead of physical media: sudo mount -o loop /path/to/image.iso /media/dvd Verify the mount and check that packages exist: ls /media/dvd/Packages/ | head On systems with automatic mounting (systemd-based), the DVD may already be…

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Linux & Systems Administration

Running Commands Across Multiple Servers with Bash and Ansible
ByEric Ma Jul 13, 2013Apr 12, 2026

Running the same command across dozens of servers is a routine task in infrastructure work. Whether you’re checking disk usage, deploying updates, or gathering system metrics, doing this manually wastes time and introduces errors. The straightforward approach: iterate through a list of hosts and execute commands via SSH on each one. Basic Shell Loop Approach…

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Linux & Systems Administration

Opening XPS Files on Linux
ByEric Ma Jul 13, 2013Apr 13, 2026

The mupdf package is available in most major Linux distributions. On RHEL/CentOS/Fedora: sudo dnf install mupdf mupdf-tools On Debian/Ubuntu: sudo apt install mupdf On Arch: sudo pacman -S mupdf mupdf is a lightweight, fast PDF and XPS viewer written in C. It’s significantly faster than heavier alternatives like Evince or Okular, making it ideal for…

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Linux & Systems Administration

Clearing iptables Rules on Fedora
ByEric Ma Jul 13, 2013Apr 13, 2026

Modern Fedora (29+) uses firewalld by default instead of the legacy iptables service. If you’re working with an older system or one configured for iptables, the concepts here still apply, but you should first check what’s actually managing your firewall: systemctl status firewalld systemctl status iptables If firewalld is active, use firewall-cmd instead. For iptables-based…

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Linux & Systems Administration

Formatting DVD+RW and DVD-RW Disks on Linux
ByEric Ma Jul 13, 2013Apr 13, 2026

Start by identifying your optical drive device. List your CD/DVD drives: ls -l /dev/cdrom This typically shows a symlink to your actual device: lrwxrwxrwx. 1 root root 3 Aug 1 17:00 /dev/cdrom -> sr0 You can also check active optical drives with lsblk: lsblk | grep -i rom Modern systems may use /dev/sr0, /dev/sr1, etc….

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Linux & Systems Administration

Converting JPG Images to EPS Format
ByEric Ma Jul 13, 2013Apr 13, 2026

If you’re working with LaTeX documents that need to include JPG or PNG images, converting them to EPS (Encapsulated PostScript) format is a straightforward approach. While modern LaTeX workflows often handle JPG directly, EPS conversion remains useful for compatibility with certain tools, print workflows, or when working with legacy build systems. Installation ImageMagick is the…

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Linux & Systems Administration

Convert Video Files for iPhone, iPad, and iPod
ByEric Ma Jul 13, 2013Apr 12, 2026

Modern iOS devices handle a wider range of video formats natively, but if you’re working with legacy formats or need specific encoding for compatibility, conversion is straightforward with ffmpeg. This guide covers converting common video formats (.wmv, .mpg, .mkv, .webm, etc.) to .mp4 format suitable for Apple devices. Installing ffmpeg On most modern Linux distributions,…

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Linux & Systems Administration

Installing NS-2 and NS-3 on Fedora
ByEric Ma Jul 13, 2013Apr 13, 2026

ns (Network Simulator) is a discrete-event simulator used primarily for research and educational purposes in networking. The two major versions—ns-2 and ns-3—are substantially different in architecture and usage patterns. This guide covers installation on current Fedora systems. Installing ns-2 on Fedora Note: ns-2 is legacy software and requires significant compatibility workarounds on modern systems. Consider…

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Linux & Systems Administration

Setting Up NFS Server and Client Configuration
ByEric Ma Jul 13, 2013Apr 12, 2026

Package Installation Install the required packages: dnf install nfs-utils nfs-utils includes both server and client tools. The separate rpcbind package is no longer needed on modern systems — it’s handled as a dependency and runs as part of the NFS service. Configure /etc/exports Edit /etc/exports to define which directories clients can mount and with what…

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Linux & Systems Administration

Connecting Multiple Clusters with iptables NAT
ByEric Ma Jul 13, 2013Apr 12, 2026

Connecting servers with internal IPs across multiple clusters over the internet is a common infrastructure requirement. While a traditional VPN is the standard approach, you can implement similar functionality using iptables and Network Address Translation (NAT) rules, often with lower overhead than VPN solutions. This method works by forwarding traffic between clusters at the IP…

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Object-Oriented Programming

An Introduction to Xen’s paravirt_ops Interface
ByEric Ma Jul 13, 2013Apr 12, 2026

paravirt_ops is an abstraction layer in the Linux kernel that allows the same binary to run efficiently on both bare metal and various hypervisors through runtime patching. Rather than compiling separate kernels for each platform, paravirt_ops lets the kernel detect its environment at boot and optimize itself accordingly. The Core Problem paravirt_ops Solves Traditional virtualization…

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Linux & Systems Administration

Cloning LVM-Backed Xen Domains
ByEric Ma Jul 13, 2013Apr 12, 2026

LVM snapshots provide an efficient way to duplicate virtual machines in seconds rather than minutes. Instead of copying an entire filesystem, snapshots leverage copy-on-write semantics—physical blocks are only duplicated when the source or snapshot is modified. This approach works well for any LVM-backed virtualization platform, though Xen is used here as an example. Note: Xen…

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Linux & Systems Administration

Checking Your Linux Firmware Version
ByEric Ma Jul 13, 2013Apr 13, 2026

The firmware (BIOS/UEFI) on your system contains critical hardware settings and boot information. Knowing your firmware version is essential for updates, compatibility checks, and troubleshooting. Here’s how to find it. Using dmidecode dmidecode is the standard tool for reading the Desktop Management Interface (DMI) table, which stores hardware and firmware metadata. Most distributions include it,…

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Linux & Systems Administration

GNOME’s Hidden Easter Eggs: Free the Fish and Gegl from Outer Space
ByEric Ma Jul 13, 2013Apr 12, 2026

GNOME has hidden a few playful easter eggs in its desktop environment over the years. Two of the most well-known are “Free the Fish” and “Wanda the Fish” — small animated features that surprise unsuspecting users. Free the Fish (GNOME 2) In GNOME 2, pressing Alt+F2 and running this command: free the fish releases a…

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Linux & Systems Administration

Installing Specific Package Versions with Yum
ByEric Ma Jul 13, 2013Apr 12, 2026

To find all available versions of a package in your repository, use the –showduplicates flag: dnf list –showduplicates kernel Or for other packages: dnf list –showduplicates <package-name> The output shows both installed and available versions with their release tags. For example: Installed Packages kernel.x86_64 6.8.1-1.fc39 @updates Available Packages kernel.x86_64 6.7.12-200.fc39 updates kernel.x86_64 6.6.25-1.fc39 updates kernel.x86_64…

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Linux & Systems Administration

Setting Date, Time, and Timezone in Linux
ByEric Ma Jul 13, 2013Apr 12, 2026

Understanding and managing system time is crucial for logging, cron jobs, SSL certificates, and system synchronization. Here’s how to handle it properly on modern Linux systems. Unix Time (POSIX Time) Unix time represents seconds elapsed since 00:00:00 UTC on January 1, 1970, excluding leap seconds. Get the current Unix timestamp: $ date +%s 1735689600 This…

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Linux & Systems Administration

Preventing dnf/yum from Updating Specific Packages
ByEric Ma Jul 13, 2013Apr 13, 2026

You may need to prevent certain packages from being updated during system maintenance—the kernel on production servers, or specific library versions you’ve carefully tuned. When you run dnf update or yum update, you want those packages skipped entirely. The solution is straightforward: add an exclusion to DNF or YUM’s configuration file. Configuration Syntax Add this…

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Linux & Systems Administration

NFS Server on tmpfs: Setup and Caveats
ByEric Ma Jul 13, 2013Apr 12, 2026

tmpfs delivers exceptional I/O performance since it lives entirely in RAM. Exporting it via NFS can be useful for temporary caches, build artifacts, or high-speed data sharing between systems on a trusted network. The catch: NFS needs additional configuration to export pseudo-filesystems like /dev/shm. Without the right settings, you’ll hit access denied errors or fsid…

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