OpenWrt runs Dropbear as its SSH server instead of OpenSSH. While Dropbear supports RSA and modern key types, the authorized_keys file lives in a different location, which causes ssh-copy-id to fail silently. Here’s how to set up key-based authentication properly. Why ssh-copy-id doesn’t work ssh-copy-id looks for ~/.ssh/authorized_keys on the remote system, which is OpenSSH’s…
systemd uses targets instead of the old sysvinit runlevels. Runlevel 3 (console mode) maps to multi-user.target. Here’s how to boot directly to console on Fedora, RHEL, Debian, Ubuntu, and other systemd-based distributions. Switch to Console Mode Immediately To switch from graphical mode to console without rebooting: sudo systemctl isolate multi-user.target This immediately stops the display…
Vim supports Xterm 256-color codes on Linux and modern terminals. Understanding the color palette and how to use it in your configuration is essential for building readable syntax highlighting schemes and custom colorschemes. The 256-Color Palette Xterm’s 256-color mode consists of: Colors 0-15: Standard ANSI colors (black, red, green, yellow, blue, magenta, cyan, white, and…
SSH performs reverse DNS lookups on connecting clients by default. If your DNS infrastructure is slow or misconfigured, this can add several seconds to every login attempt. Disabling this lookup is a straightforward performance optimization, especially in cloud environments where internal IPs often lack valid PTR records. Disable the UseDNS Setting Edit /etc/ssh/sshd_config: sudo nano…
When transferring large files over a shared network, you may need to throttle scp to avoid consuming all available bandwidth. The -l flag lets you set a hard limit on the transfer rate. Basic Usage The -l option limits bandwidth in Kbit/s (kilobits per second): scp -l 1000 file user@remote:/path/to/dest/ This caps the transfer at…
When you need to browse the web over SSH or in a headless environment, graphical browsers aren’t an option. Several terminal-based browsers exist that actually handle modern websites reasonably well, though with limitations around JavaScript and CSS. Lynx Lynx is the oldest and most established terminal browser, first released in 1992. It’s still actively maintained…
When you’re managing a Linux server remotely over SSH, determining whether a USB drive has been connected requires checking kernel messages and device listings since you can’t visually inspect the hardware. Check dmesg for USB Detection Events The most reliable method is examining kernel logs with dmesg. When a USB device is detected, the kernel…
Managing a cluster of servers, you’ll want to be notified when they come back online after restarts or unexpected reboots. Email notifications on boot let you track infrastructure changes and catch potential issues early. Using crontab @reboot The simplest approach is a crontab @reboot entry that runs once at startup. This executes before most services…
When a kernel panic occurs on a remote Linux server, manual intervention via SSH becomes impossible. The kernel can be configured to automatically reboot after a panic, allowing the system to recover without human intervention. Enable Kernel Panic Auto-Reboot The kernel.panic parameter controls this behavior. A value of 0 disables auto-reboot; any positive integer specifies…
iptables remains the standard firewall configuration tool on Linux systems, though many distributions now layer it with ufw or firewalld. Understanding the basics helps you troubleshoot, migrate, or work on systems without those abstractions. Understanding iptables Fundamentals iptables operates on three main chains: INPUT: rules for incoming traffic FORWARD: rules for traffic passing through the…
Logging connections that hit rate-limit rules helps you identify brute force attempts and troubleshoot legitimate clients that are being blocked. The standard approach is to create a dedicated chain that logs packets before dropping them. Create a logging and drop chain First, create a custom chain to handle logging and dropping: iptables -N LOGNDROP iptables…
Rate-limiting SSH brute-force attempts is essential for any server exposed to the internet. Using iptables with the recent module, you can drop connections from IPs that exceed a threshold in a given time window—for example, blocking IPs that attempt more than 6 connections in 60 seconds. Using iptables The recent module tracks connection attempts by…
Making firewall rules persistent across system reboots is essential for any production Linux system. While the original iptables-persistent approach works, modern systems typically use ufw (Uncomplicated Firewall) or firewalld, but understanding the underlying iptables mechanism is still valuable for lower-level control. Using iptables-persistent The iptables-persistent package automatically saves and restores your firewall rules during boot….
When managing a Linux system remotely, you sometimes need to terminate all sessions for a specific user—whether they’re logged in locally at the console, via SSH, through X11 forwarding, VNC, or any other method. Here’s how to do it. Quick Answer To terminate all processes for a user named bob: killall -u bob This kills…
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)!…
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…
A user’s UID (User ID) is a unique numerical identifier in Linux. You’ll need to check or modify UIDs when migrating systems, fixing permission issues, or managing user accounts across multiple machines. Finding a user’s UID To check a user’s UID, use the id command: id -u username This returns just the numeric UID. For…
When you start a QEMU guest without explicitly configuring VNC, the display server may not bind to an address your VNC client can reach. You’ll see an error like: vncviewer: ConnectToTcpAddr: connect: Connection refused Unable to connect to VNC server This happens because QEMU defaults to SDL display output and doesn’t automatically expose VNC to…
The hostname identifies your system on the network. On Linux Mint, you can change it through the GUI or command line depending on your preference and situation. Using the GUI (Easiest Method) Open Settings from the application menu Go to Details or About Click the hostname field (you may need to click a pencil icon…
Google Code was shut down in 2016, but you might still need to migrate legacy projects that were hosted there. If you have a local Git repository from Google Code or an archived mirror, here’s how to push it to GitHub while preserving all history. Prerequisites A GitHub account and a new empty repository created…