Cryptographic Hash Functions A cryptographic hash function is a mathematical algorithm that takes any input—a file, password, transaction, or string of any length—and produces a fixed-length output called a “hash” or “digest.” The output is always the same size regardless of input size. SHA-256, for example, always produces a 256-bit (64 hexadecimal character) output. Core…
Converting Hex to ASCII Using xxd Hex-encoded strings are common in system administration, debugging, and network packet analysis. Whether you’re examining binary data, decoding network protocols, or troubleshooting data encoding issues, you’ll often need to convert between hex and ASCII representations. xxd is the standard tool for this task on Unix-like systems. It creates hexdumps…
This document preserves the original release notes for Linux kernel v0.97, an early milestone in kernel development that demonstrates the rapid evolution of core subsystems in the 1990s. The content below has been reformatted from the original ASCII release notes for readability while maintaining historical accuracy. Changes in 0.97 Display and graphics support VESA support…
Linux v0.95a Release Notes This document covers the Linux v0.95a root diskette release from March 17, 1992. It documents the changes between v0.95/0.12 and v0.95a. For context on the base 0.95 release, read RELNOTES-0.95 first — this only covers the delta. Changes to the Root Diskette Shell replacement: bash → ash Bash was replaced with…
Release Notes for Linux v0.95 This document preserves the historical release notes for Linux v0.95 (March 7, 1992), one of the earliest public kernel versions. These notes provide valuable insight into early Linux development decisions and technical challenges. The original notes are presented here with minor formatting improvements for readability. Copyright Linux 0.95 is copyrighted…
Overview This document preserves the original release notes for Linux kernel version 0.01, the first public release by Linus Torvalds in 1991. These notes provide historical context on the early design decisions and limitations of what would become the world’s most widely used operating system kernel. Contents The 0.01 distribution included: linux-0.01.tar.Z — kernel source…
Generating RSA Key Pairs in Go Go’s standard library provides everything needed to generate RSA key pairs and save them in PEM format. Here are the essential packages: crypto/rsa — Implements RSA encryption per PKCS #1 and RFC 8017. The GenerateKey() function creates a keypair of specified bit size. crypto/rand — Provides Reader, a cryptographically…
Bash Learning Materials Bash (GNU Bourne-Again SHell) is the default shell for most Linux distributions and the standard for shell scripting across Unix-like systems. It’s straightforward for writing small utilities and larger automation frameworks, but its syntax and scoping rules can introduce subtle bugs without careful attention. This guide covers essential learning resources for both…
Static Linking OCaml Programs Static linking is useful when you need to distribute binaries across systems without managing runtime dependencies. OCaml supports static linking through two primary approaches: glibc-based static linking (which still requires glibc at runtime in some cases) and musl-based static linking (which produces truly static binaries). Static Linking with glibc The simplest…
Sparse files are common in Linux/Unix and are also supported by Windows (e.g. NTFS) and macOSes (e.g. HFS+). Sparse files uses storage efficiently when the files have a lot of holes (contiguous ranges of bytes having the value of zero) by storing only metadata for the holes instead of using real disk blocks. They are…
Generate strong passwords from the command line Generating secure, random passwords is a fundamental task for sysadmins. You have several reliable options depending on your use case and environment. openssl (most portable) The simplest and most widely available method: openssl rand -base64 12 This generates a 12-character base64-encoded string. Adjust the number to change length…
Checking if STDERR is redirected in Bash You need to detect whether STDERR (file descriptor 2) is connected to a terminal or redirected to a file or pipe. This is useful for conditional logging, color output, or error handling that depends on the output destination. Using file descriptor tests The primary method is the -t…
Finding Differences Between Files on Windows The diff command on Linux is standard, but Windows doesn’t ship with an equivalent by default. You have several solid options depending on whether you prefer command-line or GUI tools. Command-Line Alternatives If you want a command-line experience similar to Linux diff: Windows PowerShell (built-in, Windows 10+): Compare-Object (Get-Content…
Getting File Modification Time on Linux The modification time (mtime) indicates when a file’s content was last changed. This is critical for scripting, backups, logging, and dependency tracking in builds. Using stat The stat command is the most reliable tool for retrieving mtime programmatically: stat -c %Y filename This outputs the Unix timestamp (seconds since…
Outputting to STDOUT and STDERR in PHP In PHP, STDOUT and STDERR are standard output streams that handle different types of output. STDOUT carries normal program output, while STDERR carries error messages and diagnostic information. Properly directing output to the correct stream is essential for building reliable scripts and applications. Using fwrite() with Stream Handles…
Printing to STDOUT and STDERR in C The fundamental distinction between standard output and standard error matters for proper program behavior, logging, and stream redirection. Here’s how to handle both correctly. Basic Approach with fprintf() The simplest method uses fprintf() to write to specific streams: #include <stdio.h> int main() { fprintf(stdout, “This goes to standard…
Getting the Parent Process ID in Python To get the parent process ID (PPID) of the running process, use the os.getppid() function: import os ppid = os.getppid() print(f”Parent Process ID: {ppid}”) This returns the process ID of the parent process as an integer. On Unix-like systems, this is straightforward. On Windows, the behavior is consistent…
Getting the Parent Process ID in Go Getting a process’s parent process ID (PPID) is useful for monitoring, debugging, and process management tasks. Go provides straightforward ways to access this information across different platforms. Using the os Package The simplest approach is the os package, which works on Unix-like systems: package main import ( “fmt”…
Getting the parent process ID in C/C++ To retrieve the parent process ID (PPID) of the current running process, use the getppid() system call. This is the standard and portable approach on Unix-like systems including Linux. #include <stdio.h> #include <unistd.h> int main() { pid_t ppid = getppid(); printf(“Parent process ID: %d\n”, ppid); return 0; }…
Getting the Process ID in Go The standard way to get your running process’s PID in Go is through the os package: package main import ( “fmt” “os” ) func main() { pid := os.Getpid() fmt.Println(“Current PID:”, pid) } os.Getpid() returns an int representing the current process’s ID. This works across all platforms—Linux, macOS, Windows,…