OpenSSL’s enc command supports passing passphrases programmatically rather than prompting interactively. This is essential for automation—cron jobs, CI/CD pipelines, backup scripts, and batch processing. Basic encryption with environment variables The safest approach is storing the passphrase in an environment variable, keeping it out of process listings and shell history: export PASS=examplepass openssl enc -aes-256-cbc -in…
By default, rsync connects as your standard user. When you need to write to protected directories like /etc, /var/www, or other root-owned locations, use the –rsync-path option to invoke rsync with sudo privileges on the remote side. Basic syntax rsync -avz –rsync-path=”sudo rsync” local-file user@remote:/protected/path This tells the remote server to execute rsync under sudo….
You opened a system config file in Vim without sudo, made changes, and hit :w to save. Permission denied. Retyping everything isn’t happening. The Solution: :w !sudo tee % From Vim’s normal mode, type: :w !sudo tee % This pipes your buffer through tee running as root: :w — write the current buffer ! —…
Before expanding your root partition and filesystem: Back up your data using cloud snapshots or external backup tools. Partition and filesystem resizing can cause data loss if misconfigured. Have root access to the VM. Ensure your cloud provider has already expanded the underlying block device (EBS volume for AWS, persistent disk for GCP, managed disk…
Use the -d flag to run a container in the background and return terminal control immediately: docker run -d –name my-service my-image The container starts as a daemon process. Verify it’s running and check output: docker ps docker logs my-service Essential Configuration for Production Daemons A single -d flag isn’t enough for real workloads. Here’s…
Zlib is a foundational open-source compression library implementing the DEFLATE algorithm. It powers gzip, PNG, HTTP compression, and countless applications. While Ubuntu’s package repositories provide pre-built binaries, compiling from source lets you use the latest version, customize the installation path, enable specific compile-time features, and maintain multiple versions simultaneously. This guide covers building zlib on…
Traditionally, tools like strace used ptrace to monitor system calls. While effective for development debugging, ptrace stops the entire process for every syscall, causing 2-10x slowdown. This makes it unsuitable for production workloads where you need real-time visibility without tanking performance. Modern Linux offers significantly faster alternatives through eBPF (Extended Berkeley Packet Filter), which runs…
When you need additional swap space but all partitions are allocated, creating a swap file lets you add capacity without repartitioning. This is especially useful on systems with fixed disk layouts or cloud instances where you can’t modify the underlying disk structure. Creating the Swap File Start by allocating space. fallocate is the fastest option…
Intercepting traffic before normal routing decisions requires understanding packet flow through iptables chains. If you need incoming packets to bypass the INPUT chain and process through FORWARD instead, you’ll use the PREROUTING chain with Destination NAT (DNAT). Packet Flow Through iptables When a packet arrives at your system, it traverses these chains in order: PREROUTING…
In XML, CDATA (Character Data) sections let you include text without worrying about XML special characters. Everything inside <![CDATA[ and ]]> is treated as literal text — no parsing, no entity references. This is useful for embedding code snippets, scripts, or any content with lots of <, >, or & characters. The catch: you can’t…
On Linux, block special files represent hardware devices like hard drives, SSDs, and other block devices. They’re typically found in /dev and can be identified using Python’s stat module combined with os.stat(). The Standard Approach import os import stat path = “/dev/sda” try: mode = os.stat(path).st_mode if stat.S_ISBLK(mode): print(f”{path} is a block device”) except FileNotFoundError:…
Vim’s default indentation can mangle C++11 lambdas, treating them like nested blocks instead of closures. The lambda body gets indented too far relative to the enclosing statement. The Problem Given this code: #include <iostream> #include <string> #include <vector> #include <algorithm> int main() { std::vector<std::string> strs({“one”, “two”}); std::vector<std::string> newstrs; std::transform(strs.begin(), strs.end(), std::back_inserter(newstrs), [](const std::string& s) ->…
If you’ve tried ssh root@my-server and got a “Permission denied” error, it’s not a bug—it’s a security feature. This behavior is standard across all modern distributions. Why Root SSH Login is Disabled By default, the PermitRootLogin directive in /etc/ssh/sshd_config is set to prohibit-password or no. This prevents direct root access over SSH regardless of whether…
Use ipcs to see all IPC resources on your system: ipcs -m This shows System V shared memory segments with details like: SHMID: The segment identifier OWNER: User who created it PERMS: Permissions (octal format) BYTES: Size in bytes NATTCH: Number of processes attached For a more compact view focused on just what you need:…
Identifying which ports a specific process is using comes up regularly in debugging, security audits, and infrastructure management. Here are the practical methods. Using ss The ss command is the modern standard for socket inspection: ss -tlnp | grep <PID> This shows listening TCP sockets (-t for TCP, -l for listening). Add -u if you…
Retrieving hardware serial numbers is essential for inventory management, warranty tracking, and identifying physical servers across your infrastructure. The standard approach uses dmidecode, which reads the system’s DMI (Desktop Management Interface) data. Using dmidecode First, install the tool: sudo apt-get install dmidecode For Rocky Linux, RHEL, and derivatives: sudo dnf install dmidecode Then query the…
If you’re getting this error when running bibtex on your auxiliary file, it typically means your document has no citations, even though BibTeX is being invoked: This is BibTeX, Version 0.99d (TeX Live 2015/Debian) The top-level auxiliary file: main.aux The style file: latex8.bst I found no citation commands—while reading file main.aux (There was 1 error…
Password-less SSH login is faster, more secure, and essential for automation. Combining it with remote command execution lets you run tasks on servers from your local machine without interactive authentication. Setting Up SSH Key-Based Authentication Generate SSH Keys First, generate an ED25519 key pair on your local machine (A): ssh-keygen -t ed25519 -C “user@hostname” -f…
Filesystem corruption occasionally happens. When it does, you need fsck to run before the system fully mounts its filesystems. Here’s how to force a filesystem check during the next boot. Using touch to Mark Filesystems The traditional method is to create /forcefsck: sudo touch /forcefsck sudo reboot On the next boot, the system will check…
SPF (Sender Policy Framework) is a DNS-based authentication mechanism that helps prevent email spoofing by specifying which mail servers are authorized to send emails on behalf of your domain. If your domain is hosted with DreamHost, you’ll need to add an SPF record to your DNS configuration. Understanding SPF Records An SPF record is a…