craig-m-unsw

File Magic Numbers

Magic numbers are the first bits of a file which uniquely identify the type of file. This makes programming easier because complicated file structures need not be searched in order to identify the file type.

For example, a jpeg file starts with ffd8 ffe0 0010 4a46 4946 0001 0101 0047 ......JFIF.....G ffd8 shows that it's a JPEG file, and ffe0 identify a JFIF type structure. There is an ascii encoding of "JFIF" which comes after a length code, but that is not necessary in order to identify the file. The first 4 bytes do that uniquely.

This gives an ongoing list of file-type magic numbers.

Image Files

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readme

mkdir ollama_models

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Understanding the Memory Layout of Linux Executables

Required tools for playing around with memory:

• hexdump
• objdump
• readelf
• xxd
• gcore

craig-m-unsw

Setup a Local Only SMTP Email Server (Linux, Unix, Mac)

1 - Point localhost.com to your machine

Most of programs will not accept an email using just @localhost as domain. So, edit /etc/hosts file to make the domain localhost.com point to your machine, including this content to the file:

127.0.0.1 localhost.com

2 - Install Postfix

craig-m-unsw

Docker compose as a systemd unit

Create file /etc/systemd/system/[email protected]. SystemD calling binaries using an absolute path. In my case is prefixed by /usr/local/bin, you should use paths specific for your environment.

[Unit]
Description=%i service with docker compose
PartOf=docker.service
After=docker.service

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security and hardening options for systemd service units

A common and reliable pattern in service unit files is thus:

NoNewPrivileges=yes
PrivateTmp=yes
PrivateDevices=yes
DevicePolicy=closed
ProtectSystem=strict

craig-m-unsw

Multipass

It works both with VirtualBox and Hyper-V on Windows, it also support MacOS including M1

Install

Configure virtualization driver

If you want VirtualBox (works on Linux, Windows, and MacOS)

craig-m-unsw

1. remove grub

apt purge --allow-remove-essential grub2-common grub-pc-bin grub-pc grub-gfxpayload-lists grub-efi-amd64-bin grub-efi-amd64-signed grub-common os-prober shim-signed libfreetype6 
apt-get autoremove --purge
rm -rf /boot/grub/
rm -rf /boot/efi/EFI/ubuntu

2. make sure it's not installed back
   • edit /etc/apt/apt.conf.d/01autoremove

• add "grub*"; at the end of the Never-MarkAuto-Sections section

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Signing VirtualBox Kernel Modules

These are the steps I followed enable VirtualBox on my laptop without disabling UEFI Secure Boot. They're nearly identical to the process described on [Øyvind Stegard's blog][blog], save for a few key details. The images here are borrowed from the [Systemtap UEFI Secure Boot Wiki][systemtap].

1. Install the VirtualBox package (this might be different for your platform).

   src='https://download.virtualbox.org/virtualbox/rpm/fedora/virtualbox.repo'

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Install the virtualbox manually

sudo apt-get update  
sudo apt-get install virtualbox-6.1  

Sign the modules for secureboot

sudo -i  
mkdir /root/module-signing  
cd /root/module-signing