Linux Café

The Flicker Problem

I bought a 2022 Dell XPS 13 a few months ago and, like most people, I wanted to use an external 4K monitor via the single USB‑C port. The laptop ships with a Thunderbolt 4 controller that should handle 60 Hz 4K output without issue. On my Fedora 38 machine the monitor flickers when I connect it, and the flicker is worse on Wayland than on Xorg. The screen stutters every 1–2 seconds because the refresh rate drops in a periodic fashion. I spent a week trying to pin down the cause before finding a reliable fix.

USB plug‑in spam is a classic annoyance on modern Linux boxes. Every time you drop a keyboard, a mouse, or even a USB‑SD card in, the kernel goes into a burst‑mode and writes a wall of messages to journalctl. On a busy server or a home‑lab machine that logs everything, those lines can quickly fill the journal, slow down log‑rotation, and make it hard to spot real problems.

Below is a hands‑on guide to quiet those messages without losing the useful diagnostics you need. The techniques work on recent systemd‑based distributions (Debian 12, Ubuntu 24.04, Arch 2026, etc.) and are safe for a security‑aware setup because they only suppress noise, not real alerts.

I was running a little home‑lab server on a 2 GB SSD. The board was an Orange Pi Zero‑like single‑board computer, and it was juggling a personal web server, a GitLab instance, and a handful of containerised apps. After a month of steady traffic, the SSD hit 100 % on /var. The culprit? systemd‑journald had quietly gobbled up the whole drive.

journald is the default logger on most modern distros. It keeps logs in binary form under /var/log/journal. By default it will keep everything until the filesystem is full, then start deleting the oldest entries. On a tiny SSD that can happen faster than you can say “disk full”.

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The mystery of the reboot crash

I had a single‑board server running Debian 12 in my living‑room. Every time I rebooted it, the Docker Compose stack that powers my home‑lab services would fail to start, and the machine would hang in a boot loop. The logs were a jumble of “failed to start” messages, but the root cause turned out to be a mis‑configured systemd unit. Below is the exact process I followed to diagnose and fix the issue, with a few trade‑offs and security notes that apply to any Docker‑based deployment on a small server.

When /var/log fills up

I’ve run a handful of services on my homelab box—Docker containers, an Nginx reverse proxy, a Samba share, and a few cron jobs that ping my home router. It’s a quiet machine most of the time, but every so often the disk starts choking on logs. When /var/log hits the filesystem limit, new log entries stop, services can silently die, and journalctl starts spitting out “no space left on device”. The fix is usually a quick vacuum of the journal and a tidy‑up of the plain‑text logs. Below is a step‑by‑step recipe that works on Debian, Ubuntu, Arch, and other systemd‑based distros.

Why I keep a weekly backup copy of my home directory on an external SSD using rsync

I’m not a “data‑hoarder” in the sense of storing every file I own. I keep a single, up‑to‑date snapshot of my ~/ on a 2 TB SSD that I plug into my workstation once a week. The copy is made with rsync, stored on a separate partition, and I run a quick restore test every month. The routine feels like a small ritual that gives me confidence without eating bandwidth or storage.

Why SSH keeps spawning new processes on every connect

Every time I run ssh host, the client forks a new process that talks to the remote sshd.
On the server side, sshd spawns a child for each accepted connection.
The model is simple and works fine for a handful of sessions, but it starts to feel like a drain when you:

• run a script that opens dozens of SSH connections in a row,
• use CI/CD pipelines that hit a remote host repeatedly, or
• have a home‑lab with many small services that need quick SSH access.

Each fork eats a few kilobytes of RAM and a handful of file descriptors.
If you hit the per‑user process limit (ulimit -u) or the system’s max_user_processes, you’ll see “Too many users” or “Connection refused” errors.
Even on a modest machine, the cumulative CPU cost of negotiating the SSH handshake over and over can add up.

A Raspberry Pi stuck in emergency mode after a kernel update?

I hit this one last week while upgrading to the 6.6‑raspi kernel. The Pi rebooted, the splash screen faded, and I was greeted with the dreaded “Emergency mode” prompt. I had no idea what was wrong until I dug into the initramfs. Below is a step‑by‑step guide I used to recover, plus a few lessons that apply to any Debian‑based system.

Nightly rsync and the heat problem

When I first set up a nightly cron job to copy my home directory to an external SSD, the laptop’s fan stayed at full blast all night. The CPU hit 90 °C, and the battery life dropped noticeably. I blamed the SSD’s sluggish write speed, but the real culprit turned out to be the I/O scheduler giving the backup process too much priority. Adding ionice -c3 (the idle class) to the rsync command brought the temperature back to sane levels without sacrificing backup reliability.