Ssh on ads' corner

How installing nftables broke ssh-copy-id

Mon, 15 Jun 2026 00:00:00 +0200

While testing a new feature for WarehousePG in our Docker containers, I ran into an unexpected problem: I wanted to block certain network traffic between the Docker hosts, and therefore installed nftables. Suddenly very early in the startup process the ssh-copy-id ssh key exchange broke.

The error message:

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coordinator | Adding ssh keys for user gpadmin to host standby
coordinator | Attempt 1/5: Adding keys for user gpadmin to host standby ...
coordinator | Something went wrong adding ssh keys for user gpadmin to host standby.
coordinator | Here is the log output:
coordinator |
coordinator | /usr/bin/ssh-copy-id: INFO: Source of key(s) to be installed: "/home/gpadmin/.ssh/id_rsa.pub"
coordinator | /usr/bin/ssh-copy-id: INFO: attempting to log in with the new key(s), to filter out any that are already installed
coordinator | /usr/bin/ssh-copy-id: INFO: 1 key(s) remain to be installed -- if you are prompted now it is to install the new keys
coordinator | kex_exchange_identification: read: Connection reset by peer
coordinator | Connection reset by 169.254.2.66 port 22
coordinator |
coordinator | Attempt 1 failed with exit code 1.

The key question: why is simply installing a new package into the container breaking an unrelated tool?

Raspberry Pi OS - First Steps

Wed, 11 Jun 2025 00:00:00 +0200

A long time ago I wrote down the first steps I usually do when installing a new Raspberry Pi (or a Raspbian in that case). Now I’m installing a new system, with a 2025 Raspberry Pi OS. Time to update the notes.

Raspberry Pi 4B

Hardware requirements

The 64-bit Raspberry Pi OS “only” supports the “3B”, “3A+”, “3B+”, “4B”, “400”, “5”, “500”, “CM3”, “CM3+”, “CM4”, “CM4S”, “CM5” and the “Zero 2 W” hardware.

GitHub Actions: The `set-output` command is deprecated and will be disabled soon

Tue, 10 Jan 2023 13:42:00 +0100

If you use GitHub Actions to run Workflows and tests, you might have spotted this warning recently:

Run Ansible tasks as different remote user

Fri, 12 Aug 2022 00:40:00 +0200

Had a somewhat curious situation: need to run a task in Ansible in different user accounts, but I don’t have sudo or su access, only ssh access for every account. Took me a moment to figure out how to do that.

Delete directories recursive on Hetzner Storage Box

Fri, 09 Jul 2021 20:25:00 +0200

Among other external solutions, I store some data on Storage Boxes from Hetzner. The Storage Box allows you to have sub-accounts, so for every server and system storing data there, I use a separate account. For each sub-account, one can select a subdirectory where the data is stored, and the sub-account then can only see this data. The Admin account can see all data, and see all directories.

Raspberry Pi: take a screenshot from a display with no keyboard and mouse

Mon, 10 Feb 2020 00:58:00 +0100

The Raspberry Pi in the kitchen runs relatively stable, but recently the browser (which is showing the openHAB HABpanel) popped up a warning in the upper right corner. That’s annoying, because this area in HABpanel shows the outside temperature.

Before investigating what’s going on, I had to figure out a way to get a screenshot of the display - without running into the kitchen with my mobile phone. And without attaching a keyboard all the time (to press the Print button).

Raspberry - Raspbian - First steps

Tue, 26 Nov 2019 23:15:00 +0100

Installing a new Raspberry Pi is always the same few steps, and still I have to look them up almost every time. Here is the summary.

Ansible and LXC Containers

Sat, 13 Aug 2016 18:18:00 +0200

LXC is one of many available containerization solutions for Linux. Ansible has basic support for LXC integrated, which is fine if you do not intend to do much inside of the container (aka: fire & forget). My goal however is to start a full flavored container, and manage this container with Ansible as well. That’s where things get a bit tricky, and looking around I couldn’t find much documentation how to do this.

This posting describes my approach.

How I do backup of my mobile devices

Sat, 14 Sep 2013 21:44:00 +0200

Recently I was asked how I do backups of my mobile devices. The discussion started when I told that I “survived” a bricked device without data loss.

Disclaimer: I work (well, was working, before we got spinned of into a subsidiary) for EMC. Part of EMCs portfolio is “backup” and for sure I learned a lot from my employer. All my own devices and servers are backed up, some of them multiple times. Backups, devices and communication is encrypted. I’m not using public services (Dropbox, Google Drive, …) for the backups.

Start multiple ssh sessions with KDE konsole

Thu, 11 Sep 2008 00:52:00 +0200

I have shell accounts on different servers. Sometimes - especially if new Debian/Ubuntu/Redhat/Fedora updates are available - I have to open a ssh session to each server. That takes time and too many keyboard clicks and being a lazy admin I thought this job can be scripted.

f* MySQL

Sat, 03 Feb 2007 11:06:00 +0100

Today I woke up because the Nagios used by our ISP sent me a SMS: something does not work well on one of the association servers. According to the SMS, the webserver was not responding. Ok, the webserver is never the cause of the problem, something else is going wrong.