The stat() system call is the standard way to retrieve file metadata on Linux, including modification time (mtime). It’s fast, portable, and gives you access to nanosecond-precision timestamps. Basic Approach with stat() #include <sys/stat.h> #include <stdio.h> struct stat st; if (stat(“path/to/file”, &st) == -1) { perror(“stat failed”); return 1; } printf(“Mtime (seconds): %ld\n”, st.st_mtime); printf(“Mtime…
Determining whether a path points to a directory or regular file is a common task in system programming. You need to stat the path and inspect the file mode. Using lstat() and stat macros The lstat() system call retrieves file metadata into a struct stat. For a given path, you can use the standard macros…
CPU affinity pins a process to specific CPU cores, reducing context switches and improving cache locality. This matters when you need consistent latency or want to isolate workloads on multi-core systems. Using taskset taskset is the standard tool for setting CPU affinity on running processes. The basic syntax: taskset -p -c 0,1,2 <pid> This binds…
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…
Limiting CPU resources for individual users is essential for preventing resource exhaustion, maintaining fair system performance, and isolating workloads. Whether you’re managing multi-user systems, shared hosting environments, or need to constrain specific applications, Linux provides several proven methods. Using cgroups (Control Groups) Modern cgroups v2 offer the most flexible and reliable approach. Most distributions use…
Getting accurate I/O metrics per process is critical for troubleshooting performance issues, identifying storage bottlenecks, and capacity planning. Linux provides several tools for this task, each with different trade-offs between accuracy and overhead. Using /proc/[pid]/io The simplest approach is reading directly from the proc filesystem. Each process has an io file containing I/O statistics: cat…
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….
When you modify /etc/fstab, systemd doesn’t automatically pick up the changes. You need to explicitly tell systemd to reload its configuration and apply the new mount points. The Basic Reload To force systemd to recognize changes in /etc/fstab, run: sudo systemctl daemon-reload This tells systemd to re-read all unit files and configuration, including the mounts…
Atomicity is fundamental to distributed filesystems. When multiple processes across a cluster access the same files, operations must either complete fully or not at all—no partial states. HDFS provides specific atomic guarantees that applications can rely on for implementing distributed locks and coordinating access patterns. What HDFS Guarantees as Atomic As of Hadoop 3.2.1 (and…
The traditional Node.js approach uses require(). Create a module that exports functions, then import them where needed. exporting functions (math.js): function add(a, b) { return a + b; } function subtract(a, b) { return a – b; } module.exports = { add, subtract }; importing in another file (app.js): const { add, subtract } =…
Processing files line by line is a common task in Go. Here are the practical approaches, from simplest to most flexible. Using bufio.Scanner The most straightforward method uses bufio.Scanner, which handles line splitting automatically: package main import ( “bufio” “fmt” “log” “os” ) func main() { file, err := os.Open(“input.txt”) if err != nil {…
mpv is a powerful media player for Linux that supports looping videos with minimal configuration. Here’s how to loop videos in fullscreen mode using mpv. Loop a Single Video The simplest way — use the –loop flag: mpv –fullscreen –loop video.mp4 –loop replays the video infinitely. To loop a specific number of times: # Loop…
Serializing objects to JSON is a fundamental task in Node.js for APIs, databases, and file storage. The approach depends on your object complexity and performance requirements. Basic Conversion with JSON.stringify The standard approach uses the built-in JSON.stringify() method: const myObject = { name: ‘John’, age: 30, email: ‘john@example.com’ }; const jsonString = JSON.stringify(myObject, null, 2);…
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…
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…
When you start a QEMU guest without explicitly configuring VNC, the display server may not bind to an address your VNC client can reach. You’ll see an error like: vncviewer: ConnectToTcpAddr: connect: Connection refused Unable to connect to VNC server This happens because QEMU defaults to SDL display output and doesn’t automatically expose VNC to…
When you need to completely wipe a USB drive on Windows, you have several reliable options. Choose based on your security requirements: Disk Management for quick reformatting, DiskPart for automation, or secure erasure tools if the drive contained sensitive data. Using Windows Disk Management The simplest built-in approach: Connect the USB drive Open Disk Management…
MPlayer is largely obsolete, but if you’re maintaining legacy systems, you’ll need to know how to position windows. For new work, use mpv (MPlayer’s maintained fork) instead. Centering with MPlayer Add this to ~/.mplayer/config: geometry=50%:50% This centers the window by setting both X and Y to 50% of screen dimensions. Override at runtime: mplayer -geometry…
The cut command is designed for simple field splitting, but it has a hard limitation: the delimiter must be a single character. cut –delimiter=”delim” -f 1,3 # Error: cut: the delimiter must be a single character This is a deliberate design choice. cut prioritizes speed and simplicity for common use cases like splitting on tabs,…
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…