[md] Systemd’s coredump handler captures process crash dumps by default, which can consume significant disk space on development or test systems. Here’s how to disable or control coredump storage. ## Quick Solution Edit /etc/systemd/coredump.conf and set: [Coredump] Storage=none Then reload the systemd daemon: systemctl daemon-reload This prevents coredumps from being stored permanently while still logging…
When writing C programs on Linux that handle file paths, you need to allocate buffers safely. The kernel defines maximum path and filename lengths through standard macros in <linux/limits.h>. Getting the limits On Linux systems, <linux/limits.h> provides two key macros: NAME_MAX — maximum length of a single filename component (255 characters) PATH_MAX — maximum length…
The core problem here is legitimate: if you’re running multiple jobs on the same dataset where the mapper phase produces identical intermediate results, recomputing those results is wasteful. However, skipping the mapper phase entirely breaks MapReduce’s processing model. There are better approaches. Why You Can’t Just Skip the Mapper MapReduce assumes data flows through map…
The sed stream editor is the go-to tool for deleting lines from files in Linux. It’s fast, works on large files without loading everything into memory, and handles complex patterns easily. Delete a Single Line by Line Number To delete the 4th line from a file: sed -i ‘4d’ ./file The -i flag edits the…
[md] vbetool is a utility for executing real-mode x86 BIOS calls, commonly used for power management and display mode switching on legacy systems. Rocky Linux 9 doesn’t include it in standard repositories, so you’ll need to build it from source. ## What vbetool Does vbetool communicates with the video BIOS through the Video BIOS Extensions…
The default dd command can feel sluggish because it uses a small block size (512 bytes) by default. You can dramatically improve throughput by increasing the bs (block size) parameter. Basic optimization Instead of: dd if=/dev/sda2 of=./sda2.bak Use: dd if=/dev/sda2 of=./sda2.bak bs=1M The bs parameter controls how much data dd reads and writes in each…
Distributed systems need consensus — a way for multiple nodes to agree on state despite failures and network partitions. Understanding the key algorithms behind consensus is essential for anyone designing reliable systems. Paxos and Its Variants Paxos is the foundational consensus algorithm, proven to tolerate Byzantine failures. It works in three phases: prepare, accept, and…
Logging connections that hit rate-limit rules helps you identify brute force attempts and troubleshoot legitimate clients that are being blocked. The standard approach is to create a dedicated chain that logs packets before dropping them. Create a logging and drop chain First, create a custom chain to handle logging and dropping: iptables -N LOGNDROP iptables…
Rate-limiting SSH brute-force attempts is essential for any server exposed to the internet. Using iptables with the recent module, you can drop connections from IPs that exceed a threshold in a given time window—for example, blocking IPs that attempt more than 6 connections in 60 seconds. Using iptables The recent module tracks connection attempts by…
Making firewall rules persistent across system reboots is essential for any production Linux system. While the original iptables-persistent approach works, modern systems typically use ufw (Uncomplicated Firewall) or firewalld, but understanding the underlying iptables mechanism is still valuable for lower-level control. Using iptables-persistent The iptables-persistent package automatically saves and restores your firewall rules during boot….
When managing packages on Ubuntu or Debian systems, knowing what versions are available—and which one will be installed—is essential for dependency management and system stability. The aptitude command provides several ways to inspect package versions. Check all available versions of a package The most straightforward approach is to use the versions subcommand: aptitude versions package-name…
Database commands fall into distinct categories based on what they do. The two most fundamental are DDL (Data Definition Language) and DML (Data Manipulation Language). Understanding the difference is essential for anyone working with databases, from writing migrations to managing production systems. DDL: Data Definition Language DDL statements define and modify the structure of your…
Spark SQL doesn’t have a separate DDL/DML specification distinct from Hive QL — it inherits its SQL dialect directly from Hive. If you’re designing a SQL engine or looking to understand Spark SQL’s data definition and manipulation capabilities, you need to reference Hive’s DDL and DML documentation. Why Spark SQL Uses Hive QL Spark SQL…
A database schema is the blueprint that defines how data is organized and stored in a database. Think of it as the architectural plan for your database—it specifies tables, columns, data types, relationships, constraints, and rules that govern how data can be stored and accessed. Core Components of a Schema A schema encompasses several key…
When your iPhone completely freezes or becomes unresponsive, a force restart is usually the fastest way to get it working again. Unlike a regular restart, a force restart bypasses the normal shutdown process and forces the device to reboot immediately. Force Restart by iPhone Model The method depends on which iPhone you have. Apple changed…
[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…
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,…
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…
Understanding the difference between reliability, durability, and availability is critical when designing or operating distributed storage systems like HDFS, Ceph, or cloud object storage. These terms are often confused, but they address distinct concerns. Durability Durability answers: If the system fails completely, will my data survive? Durability is about persistence to non-volatile storage. Data is…
The .mbox format stores email messages as plain text in a single file, with each message separated by a “From ” line. If you have archived emails or need to work with mailbox exports, here are the practical ways to read and manipulate them on Linux. Using Thunderbird Thunderbird remains a solid option for viewing…