Andrew Potts: 2023

Saturday, 25 February 2023

FreeBSD discretionary ACLs

As well as the normal user,group,all file permissions, my FreeBSD server had additional ACLs that were preventing the NFS client from accessing files.

To solve this, use setfacl:

setfacl -bn *

Friday, 24 February 2023

Docker bind mount assumes ownership of container user

I had a mosquitto image running in Docker, with a bind mount:

docker run -it --name mosquitto -p 1883:1883  -v /home/pi/mosquitto/mosquitto:/mosquitto/ -v ~/mosquitto/mosquitto/log:/mosquitto/log -v ~/mosquitto/mosquitto/data:/mosquitto/data  eclipse-mosquitto

Before I ran the container: I created the source folder and set the owner to pi:

sudo chown -R pi /home/pi/mosquitto/

Yielding the following permissions

drwxr-xr-x 5 pi 1883 4096 Feb 19 20:14 mosquitto

On running the container the folder changes permissions:

drwxr-xr-x 5 1883 1883 4096 Feb 19 20:14 mosquitto

Debugging the container:

docker exec -it mosquitto /bin/sh

and checking the users:

sudo nano /etc/passwd

It can be seen that UID 1883 is the mosquitto user:

mosquitto:x:1883:1883:mosquitto:/var/empty:/sbin/nologin

Linux utilities

The strace program prints all the system calls made by a program.

strace ls -lhn $(which sleep) 2>&1 | grep passwd
What you are trying to see is whether ls command is trying to read the /etc/passwd file or not.
Networking tools:
Performance tools:

Pe

Monday, 20 February 2023

Setting a password remotely when you can't login to RDP

How to change your own expired password when you can't login to RDP - Evotec

Sunday, 5 February 2023

Fine Offset WH1080 Weather Station and a Raspberry Pi

To receive the weather readings from a WH1080 by radio, you can use a SDR USB with a Raspberry Pi 3/4, however it will not work with a Raspberry Pi as it is's power requirements are too high. The SDR USBs draw considerable current from the USB port as they are powering the amplifier.

The appeal of using a Pi Zero is it's low power usage - it is approximately 0.7W (120mA) compare to a Pi 4's 5.1W (1010mA).

So we need another radio receiver. The RFM01 and RFM12b are candidates, and this article describes using them with a Raspberry Pi.

My weather station transmits data on 868Mhz, using Frequency Shift Keying (FSK). This is where a digital '1' is transmitted at one frequency and the '0' at another.

Video: 433Mhz with the Pi

Code for controlling the RFM01 with SPI on the Pi.

Wednesday, 11 January 2023

z80 ZX Spectrum assembler

Download tools

Visual Studio Code – Editor, with the following extensions:
- Z80 Assembly 0.0.3 by Imanolea
- DeZog 2.2.3 by Maziac (this is a renamed update to Z80 Debugger 0.9.1, also by Maziac)
ZEsarUX 10.1 – Emulator
sjasmplus 1.18,2 – Z80 compiler

A comparison of the debugger compatibilities are here.

Add launch.json to your workspace's .vscode folder:

{
    // Use IntelliSense to learn about possible attributes.
    // Hover to view descriptions of existing attributes.
    // For more information, visit: https://go.microsoft.com/fwlink/?linkid=830387
    "version": "0.2.0",
    "configurations": [
        {
            "type": "dezog",
            "request": "launch",
            "name": "Z80 Debugger",
            "remoteType": "zrcp",
            "zrcp": {
                "hostname": "localhost",
                "port": 10000,
                "skipInterrupt": false
            },
//          "topOfStack": "Stack_Top",
            "rootFolder": "${fileDirname}",
            "sjasmplus": [
              {
                  "path": "${fileDirname}/${fileBasenameNoExtension}.sld",
                  "useFiles": true,
                  "asm": "sjasmplus",
                  "mainFile": "${fileDirname}/${fileBasenameNoExtension}.z80"
              }
            ],
            "disassemblerArgs": {
                "esxdosRst": true
            },
            "load": "${fileDirname}/${fileBasenameNoExtension}.sna",
            "startAutomatically": false,
            "preLaunchTask": "sjasmplus"
        }
    ]
}

Add tasks.json to the same folder:

  {
    // See https://go.microsoft.com/fwlink/?LinkId=733558
    // for the documentation about the tasks.json format
    "version": "2.0.0",
    "tasks": [
                {
            "label": "sjasmplus",
            "type": "shell",
            "command": "sjasmplus", 
            "args": [
                "--fullpath",
                "--sld=${fileDirname}/${fileBasenameNoExtension}.sld",
                "${file}"
            ],
            "group": {
                "kind": "build",
                "isDefault": true
            }
        }
    ]
}

Compilation instructions

Download zesarux for Windows (or it's Linux alternative - remember to include lib-spectrum). The source code is here.

Start zesarux
Set up zesarux remote debugging