When renewing an SSL certificate, your CA will request a Certificate Signing Request (CSR). If you have the private key but need to generate a fresh CSR, OpenSSL handles this straightforwardly. Basic CSR Generation Generate a CSR from your existing private key: openssl req -new -key ssl.key -out req.pem This creates req.pem containing your CSR,…
LevelDB allows key ranges to overlap across SSTables in Level 0, unlike higher levels where overlaps are eliminated through compaction. This design choice is fundamental to LevelDB’s write performance and is worth understanding in detail. Why Level 0 Allows Overlaps The reason comes down to write efficiency. When you write data to LevelDB, it follows…
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 you open a new window with window.open(), you often need to communicate between the parent (opener) window and the child (opened) window. The most straightforward approach is to access the opener window directly through the opener property. Basic Two-Way Communication In the parent window, define a variable: let exchangeVar = ”; From the child…
Automating keyboard input on Linux is useful for testing, accessibility workflows, and automation scripts. If you need to simulate pressing multiple keys simultaneously and holding them, xdotool is the standard tool for this job. Basic approach with xdotool The keydown and keyup commands let you press and release individual keys without triggering the other. To…
When you need to traverse a directory tree in Python, you have several options. The choice depends on whether you want recursive traversal, how you want to handle the results, and your Python version. Using os.walk() The os.walk() function is the classic approach for recursively iterating through directories. It yields tuples of (dirpath, dirnames, filenames)…
When you have SSH key-based authentication set up, the client will prefer it by default. This can make it difficult to test whether password authentication is working—especially after changing a password or troubleshooting login issues. Force password-only authentication Use the -o PreferredAuthentications=password flag: ssh -o PreferredAuthentications=password username@host This tells SSH to use password authentication exclusively,…
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…
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…
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…
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 you SSH to a server and see the warning below, your SSH client has detected that the server’s host key doesn’t match what’s stored locally: @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ @ WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED! @ @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY! Someone could be eavesdropping on you right now (man-in-the-middle attack)!…
When you need to extract a value from a list that should contain exactly one element, pattern matching is the idiomatic way to handle it in functional languages. The error “unbound value c” typically occurs when you try to use a variable that wasn’t properly bound through pattern matching. OCaml Pattern Matching In OCaml, use…
If you’ve accidentally frozen your SSH terminal with Ctrl+S, you’re experiencing flow control lock — a terminal feature that dates back to the era of slow serial connections. Your session isn’t actually hung; it’s just paused. The Quick Fix Press Ctrl+Q to unfreeze the terminal immediately. That’s it. Your session will resume and you can…
The fclose theme is a lightweight Question2Answer theme distributed as a set of PHP and CSS files. It provides a clean base layout that you can extend with custom styling and icon sets. Getting the Theme Files You need two core files to run fclose: qa-theme.php — The theme class that extends qa_html_theme_base and controls…
Thunderbird wraps lines at a fixed character width by default during composition, which interferes with code snippets, preformatted text, and any content where line breaks matter. Here’s how to turn it off. Via Preferences The quickest method through the GUI: Open Thunderbird and go to Edit → Preferences (or Thunderbird → Settings on macOS) Navigate…
The most straightforward approach is whitespace-mode, which provides built-in visual feedback for lines exceeding a specified column width. Add this to your Emacs configuration: (require ‘whitespace) (setq whitespace-style ‘(face empty tabs lines-tail trailing)) (setq whitespace-line-column 80) (global-whitespace-mode t) The lines-tail style highlights only the portion of the line exceeding whitespace-line-column, which is less visually intrusive…
To see the current file path immediately, use the Elisp evaluation prompt: M-: buffer-file-name This displays the full path in the echo area. Alternatively, press M-x, type eval-expression, and enter buffer-file-name. In Elisp code Reference buffer-file-name directly in your configuration or custom commands: (message “Editing: %s” buffer-file-name) This prints to the echo area and logs…
To toggle between Simplified Chinese and Traditional Chinese input modes in ibus-libpinyin, press Ctrl+Shift+F. This shortcut has been the standard method since ibus-pinyin 1.3.7 and works across modern versions. Common ibus-libpinyin Shortcuts Beyond script conversion, these shortcuts handle daily input tasks: Shortcut Function Ctrl+Shift+F Toggle Simplified/Traditional Chinese Ctrl+. Toggle full-width/half-width punctuation Ctrl+, Toggle English/Chinese punctuation…
The Windows (Super) key can be remapped to function as an additional Ctrl key, useful if you work across multiple systems or prefer the extra modifier. The approach varies significantly by display server and desktop environment. GNOME (Wayland and X11) GNOME 3.38 and later have built-in remapping through Settings: Open Settings → Keyboard → Special…