The command journalctl -b -1 should show the previous boot’s journal, but on many systems it returns: Failed to look up boot -1: No such boot ID in journal This happens because persistent journal storage isn’t enabled by default. Without it, journald only keeps logs in volatile memory (/run/log/journal), which gets cleared on shutdown. Enable…
When you need to reverse-lookup an IP address against your local /etc/hosts file, several tools can help. This is different from a full DNS reverse lookup — you’re checking only against the static mappings on your local system. Why this matters By default, most hostname resolution tools check /etc/hosts first before querying DNS servers. If…
The LIMIT clause in MySQL lets you control how many rows a SELECT query returns. This is essential for pagination, performance tuning, and working with large datasets. Basic LIMIT Syntax To return only the first N rows from a table: SELECT * FROM qa_users LIMIT 10; This returns the first 10 rows from the qa_users…
Date comparison is one of the most common operations in SQL queries, whether you’re filtering orders, analyzing logs, or generating reports. The approach varies slightly across database systems, but the underlying principles remain consistent. Basic Date Comparison The simplest form uses standard comparison operators against a date string in YYYY-MM-DD format: SELECT * FROM orders…
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…
In C++, you have several ways to output to standard output and standard error streams. The choice depends on your project’s requirements and whether you’re working with older codebases or modern C++. Using std::cout and std::cerr The standard approach uses the C++ iostream library: #include <iostream> int main() { std::cout << “This goes to standard…
[md] In OCaml, the standard library provides straightforward functions for writing to standard output and standard error. ## Printing to STDOUT Use print_endline to write a string followed by a newline to standard output: print_endline “hello world!” This function is in the Stdlib module (formerly Pervasives in older OCaml versions) and automatically flushes the output…
Perl gives you straightforward ways to send output to both standard output and standard error. Understanding the difference matters — STDOUT handles normal program output, while STDERR carries diagnostics, warnings, and error messages. Separating them lets users redirect, log, or suppress errors independently. Basic Output Methods The simplest approach uses print with filehandles: print STDOUT…
Java provides straightforward ways to direct output to standard output and standard error streams. Understanding the difference between them is essential for proper logging and error handling. System.out vs System.err System.out and System.err are both PrintStream objects, but they serve different purposes: System.out: Standard output stream for normal program output System.err: Standard error stream for…
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 output\n”); fprintf(stderr, “This goes to standard error\n”);…
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 The most straightforward approach uses fwrite() with…
Understanding file descriptors is fundamental to shell scripting. By default, your shell has three standard streams: STDOUT (FD 1): Standard output, where commands print results STDERR (FD 2): Standard error, where commands print errors and diagnostics STDIN (FD 0): Standard input, where commands read data Basic Output Print to STDOUT: echo “This goes to stdout”…
By default, print() writes to STDOUT. Both STDOUT and STDERR go to your terminal unless you redirect them. Here’s how to send output to each stream explicitly. Printing to STDOUT The standard print() function writes to STDOUT and automatically adds a newline: print(“your message”) Printing to STDERR To print to STDERR, pass the file parameter:…
Go provides straightforward ways to write to standard output and standard error streams. Understanding when and how to use each is essential for building robust applications, especially in containerized and cloud environments where log separation matters. Using the fmt Package The fmt package is the most common approach for printing to STDOUT: package main import…
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 as well. Accessing Full Process Information For…
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” “os” ) func main() { ppid :=…
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; } Compile and run: gcc -o get_ppid get_ppid.c…
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, and others. Getting the Parent Process…
Every running process gets a unique identifier from the operating system called a PID (Process ID). You’ll need this when managing processes, logging, creating lock files, or coordinating between parent and child processes. The POSIX standard approach The simplest way is getpid() from unistd.h: #include <unistd.h> #include <stdio.h> int main() { pid_t pid = getpid();…
Every process running on a Unix-like system has a parent process. The parent process ID (PPID) identifies which process spawned the current one — critical information when debugging process hierarchies, managing child processes, or writing robust shell scripts. Built-in variable The simplest approach uses Bash’s $PPID variable: echo $PPID This prints the PPID of the…