When you run journalctl without options on a system with years of log history, it can take seconds or even minutes to parse everything. The slowness comes from journalctl loading and deserializing potentially gigabytes of journal data. The solution is targeted querying — you almost never need the entire journal, so restrict what journalctl reads…
[md] The dd command doesn’t evaluate arithmetic expressions in its parameters. If you try this: $ dd if=/dev/zero of=./4Ktest100M bs=4KB count=25000*9 dd: invalid number ‘25000*9′ You’ll get an error because dd expects literal numeric values, not expressions. The shell doesn’t expand 25000*9 as arithmetic — it’s passed to dd as a literal string. ## Using…
When you run a command like this in Bash: ssh host1 hostname &; ssh host2 hostname & You get an error: bash: syntax error near unexpected token `;’ The issue stems from how Bash interprets command separators. The & and ; characters are both command terminators, but they serve different purposes, and Bash has strict…
When a process mmaps and mprotects many memory ranges, you’ll eventually hit the kernel limit and start seeing ENOMEM errors from mprotect() calls. This happens because Linux maintains internal kernel structures for each mapped range, and there’s a hard ceiling on how many the kernel will track per process. The culprit is the vm.max_map_count sysctl…
When pushing to GitHub over HTTPS, you’ll see: error: The requested URL returned error: 403 Forbidden while accessing https://github.com/username/repo.git fatal: HTTP request failed This means Git connected to GitHub successfully, but your credentials were rejected. Common causes: Expired or revoked Personal Access Token (PAT) Using a password instead of a PAT (GitHub disabled password auth…
When you open a popup window with window.open(), you’ll often need to detect when the user closes it so you can update your UI, refresh data, or clean up resources. Here are the practical approaches, from polling to event-driven methods. Polling the closed property The simplest method is to periodically check the popup’s closed property:…
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);…
Sending POST requests from client-side JavaScript is a common task, and you have several modern options. The approach you choose depends on your project’s dependencies and browser support requirements. Fetch API (Recommended for Modern Projects) The Fetch API is the modern standard and requires no external library. It’s built into all current browsers and handles…
Getting a file’s size is a common task in Python. There are several ways to do it, depending on what you need and how much detail you want about the file. Using os.path.getsize() The simplest approach is os.path.getsize(): import os file_path = ‘/path/to/your/file.txt’ size_bytes = os.path.getsize(file_path) print(f”File size: {size_bytes} bytes”) This returns the size in…
When handling POST requests in Node.js, you need to read the incoming data stream and parse it. The approach varies depending on whether you’re using raw Node.js http module, Express, or another framework. Using Express (Recommended) Express handles POST parsing automatically with built-in middleware. This is the standard approach for most modern Node.js applications: const…
When your Node.js application encounters a fatal error or needs to terminate, you need a reliable way to shut it down. Understanding how to exit gracefully—or forcefully when necessary—is essential for production applications. Using process.exit() The most direct method is process.exit(), which immediately terminates the Node.js process: process.exit(); This is a global method that doesn’t…
The git status command shows repository state visually, but when you need to detect it programmatically in bash — say, to fail a CI pipeline or prevent deployments — you need a different approach. Quick Method: Check Unstaged Changes The most reliable way to detect uncommitted changes is with git diff: if [[ -n $(git…
When working with file I/O in C on Linux, you’ll often need to convert between low-level file descriptors (returned by open(), socket(), etc.) and higher-level FILE pointers (returned by fopen()). This is common when integrating different libraries or mixing POSIX I/O with standard C I/O. Getting a FILE Pointer from a File Descriptor Use fdopen()…
By default, Apache2 ignores .htaccess files. The AllowOverride directive controls which directives in .htaccess Apache will process. To enable .htaccess, you need to configure Apache to allow overrides. Enable AllowOverride Edit your Apache configuration file. On Ubuntu/Debian, this is typically: sudo nano /etc/apache2/apache2.conf Find the <Directory /var/www/> block and change AllowOverride None to AllowOverride All:…
A 403 Forbidden error when running git push means your credentials aren’t valid or you lack permission to access the repository. This is one of the most common Git frustrations, but it’s usually fixable once you understand what’s actually happening. Why 403 Errors Happen Your authentication method has expired or been revoked Your GitHub Personal…
You may need to deactivate a LVM volume group to make it unknown to the kernel — typically before removing disks, migrating storage, or performing maintenance. The vgchange command handles this with the -a (or –activate) flag. Basic deactivation To deactivate a volume group named vg, use: vgchange -a n vg The -a n flag…
When you try to create a filesystem on a disk with mkfs, you may see this error: # mkfs -t ext4 /dev/sdd1 mke2fs 1.42.8 (20-Jun-2013) /dev/sdd1 is apparently in use by the system; will not make a filesystem here! Even though the device isn’t mounted, mkfs refuses to proceed. This safety mechanism prevents accidental data…
These kernel messages from the libata driver indicate SATA link-layer errors between your drive and controller. They look alarming, but they’re usually fixable — and the fix is typically hardware-related, not a software or drive firmware issue. What These Error Messages Mean When you see messages like this in dmesg: ata4.00: exception Emask 0x10 SAct…
When you run a curl GET request with spaces in the query string, the shell interprets the space as a separator and truncates the URL: curl “http://example.com/send?msg=hello world” The space causes the shell to treat world as a separate argument, so only hello gets sent. You need to properly URL-encode the space (and other special…
When sending POST requests through a Squid proxy with curl, you may encounter a proxy error that blocks the request, even though the same request works fine with GET. The issue typically appears as: ERROR The requested URL could not be retrieved The root cause is the Expect: 100-continue header that curl automatically adds to…