Home on arunsrin's notes

🔒 OpenSSL

Mon, 01 Jan 0001 00:00:00 +0000

🔒 OpenSSL

Some non-openssl security notes are in a sibling page.

Verify Public Cert, Private Key, CSR

Public Cert

openssl x509 -noout -text -in server.crt

Private Key

openssl rsa -noout -text -in server.key

openssl req -text -noout -verify -in server.csr

Verify if a cert and key are pairs

openssl x509 -noout -modulus -in server.pem | openssl md5 ;\
openssl rsa -noout -modulus -in server.key | openssl md5

Convert .cer to .pem

openssl x509 -inform der -in certificate.cer -out certificate.pem

Connect and verify

Connect to a remote host and see a whole lot of details:

 openssl s_client -connect remote-hostname.com:443 \
 -msg -showcerts -verify 1 \
-CAfile allca.cer -cert myhostname.cer -key myhostname.key

View a remote host’s certificate details:

echo | \
openssl s_client  -connect remote-hostname.com:443 2>/dev/null | \
openssl x509 -text

Generate a CSR

openssl req -newkey rsa:2048 -nodes -out myhostname.csr -config myopenssl.cnf

For this a config file is needed. Fill it up with details like this:

About

Mon, 01 Jan 0001 00:00:00 +0000

:material-penguin:{ .anim-heart }About

I’m a software engineer in Bangalore who is addicted to books . Classic Literature (Vladimir Nabokov ), Popular Science (Richard Dawkins ) and Science Fiction (Greg Egan) are the genres I prefer. The picture at the end of this page shows all the books I own, as of Feb 2015.

I seem to prefer breadth over depth, and enjoy playing games (mostly on my Xbox Series X these days), fiddling with GNU/Linux (Fedora or WSL2 on windows), Emacs and Python .

Accounting

Mon, 01 Jan 0001 00:00:00 +0000

:material-file-document-outline:{ .anim-heart } Accounting

Introduction

Apparently, the need to keep accounting was a key driver in the invention of writing and numbers.

Types of Accounting

Book keeping - raw data collection. Almost always double-entry bookkeeping
Financial accounting - Create reports about income statement, balance sheet, etc to see cash flows and profit and financial positiion of an entity.
Auditing - Independent checks
Management accounting - Internal use of accounting data to make decisions around prices, volumes of production, locations for expansion etc.

Deloitte, Ernst and Young, KPMG, PwC are apparently the big four.

Advertising

Mon, 01 Jan 0001 00:00:00 +0000

:material-file-document-outline:{ .anim-flip } Advertising

Introduction

I have a low impression of the advertising industry but it should be interesting to read an advocate’s perspective.

Lol the author blames policymakers for mandating content labels (this product is 90% sugar) over end result (it’s tasty and you’ll love eating it).

Types

Classifieds: ads which people look for; newspaper/internet
Display: ads which look for people; intrusive by nature; newspaper/tv/radio/internet

Advertising tripartite

Advertisers e.g. soda companies. The ones who pay money to reach an audience.
Media e.g. news channels, papers, radio stations. They have an ad arm that is hopefully independent of the content arm.
Advertising agencies e.g. the people who create the ads.

History and Ecosystem

Media and agency split is apparently about 90/10% these days.

AI

Mon, 01 Jan 0001 00:00:00 +0000

:material-brain:{ .anim-bounce } AI

Benefits

I’m enjoying playing with LLMs these days. Here are some ways they have improved my life:

In late 2024 I was using it for simple things like the random quotes at the bottom of this (and all other) pages: these are generated by a simple bit of JavaScript that ChatGPT helped create. It knew how to integrate this into MkDocs and generated a bunch of quotes too :)

Alexander the Great

Mon, 01 Jan 0001 00:00:00 +0000

:material-file-document-outline:{ .anim-bounce } Alexander the Great

Introduction

Born in 356 BCE, king of Macedon from 336 to his death in 323.

Sources

People used to maintain Astronomical Diaries to monitor positions of planets, and unusual phenomena like comets and eclipses. Some of them were seen as omens and used to decide how to protect the king. They are good texts that chronicle his deeds.

Later accounts lionize him as they were meant to serve as inspiration for their audience: the Roman elite. So they are not very reliable even if there are multiple accounts of the same story.

Anaesthesia

Mon, 01 Jan 0001 00:00:00 +0000

:material-file-document-outline:{ .anim-pulse } Anaesthesia

Suspended Animation: Concepts of Anaesthesia

In the mid-19th century, the term etherization was used to describe the state produced by the inhalation of ether vapour. They found chloroform and other agents were more effective. So the term anaesthesia, i.e. without sensation, came into being.

The ether/chloroform combo was not enough and intravenous agents, muscle relaxants and other adjuncts were introduced. Nowadays an anaesthetic agent, an analgesic, and a muscle relaxant are used together.

Ansible

Mon, 01 Jan 0001 00:00:00 +0000

:simple-ansible:{ .anim-heart } Ansible

These are mostly notes from reading Mastering Ansible, by James Freeman and Jesse Keating. I’ve used ansible quite a bit but wanted a structured understanding of it.

Setup

pip install ansible in a virtualenv is enough. Config is in ~/.ansible.cfg. Verify the critical paths with this:

~/code/learnansible via  v3.12.0 (.ans) ❯ ansible-inventory --version
ansible-inventory [core 2.16.x]
  config file = /home/arunsrin/.ansible.cfg
...

Modern Ansible Tooling

While ansible-playbook is the classic way to run tasks, the modern ecosystem now prefers Ansible Navigator (ansible-navigator) for a more consistent, containerized execution environment and a rich TUI.

AWS

Mon, 01 Jan 0001 00:00:00 +0000

:material-cloud:{ .anim-fade } AWS

Most of this is from Amazon Web Services in Action, IInd edition.

CloudFormation

Use CloudFormation to create a wordpress infra using these services:

ELB - ALB specifically
EC2 - Let’s try 2 instances
RDS - For MySql
EFS - Using NFSv4.1 for User uploads
Security Groups - Firewall

Full yaml written by the authors is here .

Well that was fast. The template file externalizes the keypair so you can put your own from the drop down.

Browsers

Mon, 01 Jan 0001 00:00:00 +0000

:material-web:{ .anim-pulse } Browsers

I’ve settled on, surprisingly, MS Edge as my primary browser. The bits I like:

It allows me to have a separate instance signed in with my work profile, and another one with my personal profile. So I’m quite happy segregating bookmarks, extensions, etc across both those instances.
The chrome family of browsers have the best Print to PDF option. I use this once in a while to archive great pages (like LWN’s weekly news).

Great extensions

Bitwarden : This is my password manager so I can’t live without this one.

Capitalism

Mon, 01 Jan 0001 00:00:00 +0000

:material-cash-multiple:{ .anim-heart } Capitalism

Unfettered capitalism is the root of all evil.

‘There are now two Americas. My country is a horror show’ from The Wire creator, David Simon.
Pretty much all of the anti-work subreddit is a joy to lurk in.
Fuck the Plastic Industry
Nice overview of how the book industry compares with ebooks. Essentially amazon re-used the same model in both (where the publisher recommends a price but the seller decides it ultimately), and Apple colluded with the big publishers to switch it to another model: where the price can be determined by the publisher up front, and the seller just gets a flat 30% cut.

Carl Sagan

Mon, 01 Jan 0001 00:00:00 +0000

:material-weather-night:{ .anim-rotate } Carl Sagan

Why

Dawkins made me an atheist, but Sagan first had to make me a sceptic . In my childhood, I used to believe anything I read. I was obsessed with pseudo-scientific rubbish like ESP and Telepathy and Aliens in Roswell. It took kind-hearted Sagan’s thought-provoking books to guide me back to a more sensble path.

Carl Sagan was a great explainer and a passionate communicator. Who better to represent all of humanity, in the plaques that were sent out to space in the Voyager?

Climate Change

Mon, 01 Jan 0001 00:00:00 +0000

:material-thermometer:{ .anim-fade } Climate Change

10 charts by the Guardian
xkcd on temperature change
Australia’s 2019/2020 forest fires
My own notes from the book “The thinking person’s guide to Climate Change”

COVID-19 References

Mon, 01 Jan 0001 00:00:00 +0000

:material-virus:{ .anim-fade } COVID-19 References

I’m keeping a diary of interesting links to track the COVID-19 epidemic.

Global links

Archive of a good bunch of links on SSC .
A rationalist prepper . Articles like this helped me prepare about a month before shit hit the fan.
Why You Must Act Now - Nice comprehensive article that was doing the rounds in the early days.
Comprehensive arstechnica coverage .
Why the whole test kit availability thing was messed up in the early days: they were tainted .
Timeline of WHO’s response .
How New Zealand beat COVID-19 .
A nice summary of the Vaccine Protocols .

Scepticism

A paper that was doing the rounds on Whatsapp was retracted .
HCQ results after certain clowns made a big deal of it.
Lack of clarity on remdesivir’s effectiveness . It may be worse than doing nothing .
Social media scrambling as always, fighting misinformation .

India-specific links

Trying to predict the curve , way back in March.
Some more scenarios , from March.
Reasons for doubt: India under-reporting TB cases for years .
So cruel :( . Politicians and corporations put worker rights last.
India has an Integrated Disease Surveillance Program that is meant to handle epidemics like this. They had daily updates until COVID-19 hit, and ICMR stepped in instead.
How to make even a fucking epidemic about religion .
ICMR research that implies 7 lakh infected in a few districts, when the nation-wide count at that time was 3.4 lakhs (!!)

Bangalore-specific links

BBMP daily bulletins . Very nice charts.
Hospital beds allocated and available currently .

Crypto 101

Mon, 01 Jan 0001 00:00:00 +0000

:material-pencil:{ .anim-fade } Crypto 101

Notes from reading the excellent book at https://www.crypto101.io/

Other security notes.

Block ciphers

C = E(k, P)

k and P are the key and plain text.

The plain text is broken up into blocks of length equal to the key’s block size.

The same key is used to decrypt.

Most common one is AES. preceeded by DES.

AES was called Rijndael after its 2 developers. allows block sizes of 32, 128, 192 and 256.

Cryptocurrencies

Mon, 01 Jan 0001 00:00:00 +0000

:material-currency-btc:{ .anim-bounce } Cryptocurrencies

I find it telling that the loudest proponents of Crypto are VCs who extol the virtues of a decentralized system while building and profiting from centralized solutions. Here are some links that align well with how I perceive crypto.

Usenix | The Web3 Fraud - Mostly from the perspective of how painfully slow and inefficient the compute is.
Web3? I have my DAOts - Nicely balances the FOMO that a self-respective engineer would have with a new technology with failings of crypto/NFTs.
look what you made me do: a lot of people have asked me to make NFT games and I won’t because i’m not a fucking dumbass. now let me tell you why only a dumbass would get into NFT games - A game developers perspective on NFTs.
Cryptocurrency is an abject disaster - From Drew DeVault, who is always worth reading.
Bitcoin: The Postmodern Ponzi - Comparison to a Ponzi scheme.
Blockchain and Trust - By Schneier.

Databases

Mon, 01 Jan 0001 00:00:00 +0000

:material-database:{ .anim-flip } Databases

Elastic notes are in a sibling page.

Notes from “SQL QuickStart Guide”

Author: Walter Shields

Basic operations

-- Single line comment
/* Multi 
Line
Comment */
SELECT FirstName, LastName, Email, City from customers;

Once more, using aliases:

SELECT FirstName AS "First Name", LastName AS "Surname", Email, City
from customers;

And again, with sorting:

SELECT FirstName AS "First Name", LastName AS "Surname", Email, City
from customers
ORDER BY Surname DESC;

Show only first 10 records: use the keyword LIMIT.

Despair, by Vladimir Nabokov

Mon, 01 Jan 0001 00:00:00 +0000

:material-pencil:{ .anim-heart } Despair, by Vladimir Nabokov

I reread this book this month. Nabokov’s protagonists are always fascinating. The one is Despair, Hermann, is almost tragic in how desperately he hides from reality. In this he is like that other great unreliable narrator, Charles Kinbote from Pale Fire. And when people in the real world laugh and point a finger at this naked emperor, he chooses to recede into a reality where his garments are the finest, his wit awes his friends, and his intellect outwits the police.

Docker

Mon, 01 Jan 0001 00:00:00 +0000

:simple-docker:{ .anim-fade } Docker

Once you get a bit of a rhythm with docker, it becomes pretty fun. Here are notes I took while reading some Docker books. Two good ones that I’d recommend are:

Using Docker
Docker in Action

Some kubernetes notes are here.

Useful commands

docker inspect <containerid> - Shows IPAddress among other things.
docker diff <containerid> - List of files changed in the container.
docker logs <containerid> - list of everything that happened in the container.

Eats, Shoots & Leaves

Mon, 01 Jan 0001 00:00:00 +0000

:material-pencil:{ .anim-pulse } Eats, Shoots & Leaves

Author: Lynne Truss

This one is for the pedants. Read this book if you’re the kind of person who grits your teeth every time you see a grammatical mistake in a hoarding. The title refers to a statement about a panda that eats (bamboo) shoots and leaves. But a misplaced comma makes it sound like a story about an evil panda that eats, shoots and leaves.

Editors

Mon, 01 Jan 0001 00:00:00 +0000

:material-keyboard-outline:{ .anim-bounce } Editors

My heart lies with GNU Emacs. It is probably my most used tool at work because I take a crapload of notes. The pages on this site are written in Emacs in markdown (because mkdocs supports it well). Some other notes are in org format. And the bulk of my work-related notes (dating back to 2007) are in one big fat plain text file that is, as of December 2017, 26252 lines long.

Elastic Stack

Mon, 01 Jan 0001 00:00:00 +0000

:material-magnify:{ .anim-fade } Elastic Stack

These are notes from Learning Elastic Stack 7.0, by Pranav Shukla and Sharath Kumar MN.

Using the Kibana Console

Some simple APIs to warm up.

GET / <- Prints version information
GET <index-name>/_mappings <- schema/mappings of this index
GET <index-name>/_doc/<id_of_document> <- Content of this document

Fundamentals

An Index is loosely analogous to a table, and a document to a record. One Index can have only one Type.

Flow

Mon, 01 Jan 0001 00:00:00 +0000

:material-pencil:{ .anim-rotate } Flow

I’ve long been interested in Active vs Passive hobbies, why one is better than the others, and so on. Here’s a nice reddit post that captures a similar mindset around gaming. So reading Flow gave a lot of clarity to these ideas.

Any programmer who’s been ‘in the zone’ and loses sense of time knows the feeling of ‘Flow’ and that is the subject of this book – Deep hobbies that improve one’s self.

Git

Mon, 01 Jan 0001 00:00:00 +0000

:material-database:{ .anim-fade } Git

Separate git configurations for work and play

Put something like this in your ~/.gitconfig:

[includeIf "gitdir:~/work/"]
    path = ~/.gitconfig.work

[includeIf "gitdir:~/code/"]
    path = ~/.gitconfig.personal

If your work repos are in ~/work, you can have a separate user/email etc for repos in that folder.

Delete a tag that’s already pushed

git tag -d <tag_name>
git push --delete origin <tag_name>

Signing commited commits

If you want to sign the last N commits that you have already pushed:

Go

Mon, 01 Jan 0001 00:00:00 +0000

:simple-go:{ .anim-pulse } Go

Notes from the book Learning Go, by Jon Bodner.

Setup, Environment

Difference between `go get` and `go install`:

See here . Basically go get downloads the source to $GOPATH/src along with the dependencies, and the latter compiles.

go install is recommended. Ignore go get.

Hey

hey for load testing http services. Install with:

go install github.com/rakyll/hey@latest

Vi

Install vim-go: it comes with a massive set of tools.

Good Math

Mon, 01 Jan 0001 00:00:00 +0000

:material-pencil:{ .anim-rotate } Good Math

Full Title: Good Math: A Geek’s Guide to the Beauty of Numbers, Logic, and Computation

Author: Mark C. Chu-Carroll

Here are some notes I took while reading this book. Overall I felt it was interesting, but there were large jumps in difficulty in some of the later chapters.

Continuous fractions

This was the most fascinating part of the book for me. I hadn’t heard of these before!

Grafana

Mon, 01 Jan 0001 00:00:00 +0000

:material-chart-bell-curve:{ .anim-flip } Grafana

Most of these notes are from the book Learn Grafana 7.0 by Eric Salituro.

Installation

docker volume create grafana-storage
docker run -d --name=grafana -p 3000:3000 \
  -v grafana-storage:/var/lib/grafana \
    grafana/grafana

Then in my virtualbox, I can access it at http://192.168.56.101:3000/login

admin/admin are the default credentials

Install plugins like this:

grafana-cli plugins install marcusolsson-csv-datasource

Then you can load csv data sources, and so on.

Prometheus

Time Series Basics

We launched its container in chapter04/docker-compose.yml and made it query itself and grafana.

Hate Inc.

Mon, 01 Jan 0001 00:00:00 +0000

:material-pencil:{ .anim-flip } Hate Inc.

Full Title: Hate Inc.: Why Today’s Media Makes Us Despise One Another

Author: Matt Taibbi

I’ve been reading Taibbi for a while now and this was a nice refreshing step back from his usual acerbic style. He covers the media industry’s complicity in creating a toxic political environment. Towards the end is where the book gets really interesting: as an inward-looking view into how the left-leaning media is as bad in creating filter bubbles as the usual suspects in the right.

How To Read A Book

Mon, 01 Jan 0001 00:00:00 +0000

:material-pencil:{ .anim-fade } How To Read A Book

By Mortimer J. Adler and Charles Van Doren

Reading this was a turning point for me. For a lifetime, I’d read anything that caught my interest: science fiction, evolutionary biology, classic literature and so on.

After reading far too many general science books, I started to realize that I’d hit a plateau, and was not learning anything new from them. I felt like I had to go deeper and analyze one of these subjects thoroughly, or wider, to learn something new.

Immune, by Phillip Dettmer

Mon, 01 Jan 0001 00:00:00 +0000

:material-pencil:{ .anim-fade } Immune, by Phillip Dettmer

This is an incredible book and the brief notes I took below do not do justice to how well it is written.

White blood cells is a too vague a term for the varied kinds of defenses we have.. Too simplistic.

Innate Immune System

First line of defense
Can differentiate Self vs other. Anything that is not Self is a threat
Simple blueprints for vast patterns of attacks (all bacteria for example)
Activates the 2nd line of defense if needed

Important players:

Java

Mon, 01 Jan 0001 00:00:00 +0000

:material-language-java:{ .anim-fade } Java

Most of these notes are from the book Java Projects by Peter Verhas.

Maven build lifecycle targets

validate - validate the project is correct and all necessary information is available
compile - compile the source code of the project
test - test the compiled source code using a suitable unit testing framework. These tests should not require the code be packaged or deployed
package - take the compiled code and package it in its distributable format, such as a JAR.
verify - run any checks on results of integration tests to ensure quality criteria are met
install - install the package into the local repository, for use as a dependency in other projects locally
deploy - done in the build environment, copies the final package to the remote repository for sharing with other developers and projects.

From the official documentation .

Kafka

Mon, 01 Jan 0001 00:00:00 +0000

:material-ladybug:{ .anim-heart } Kafka

These notes are based on a series of posts I read, starting with this one .

The Basics

Basically it lets you pub/sub to Events.

And store them.

And process and analyze them.

An Event is something that has a key, value and timestamp.

And a Table represents the state at that particular point in time. This is mutable.

A Stream provides immutable data. You can insert stuff into it.

Kubernetes

Mon, 01 Jan 0001 00:00:00 +0000

:material-kubernetes:{ .anim-flip } Kubernetes

Some kubernetes overview links, with a focus on networking.

Terminal Enhancements

k9s

Get it here . My go-to cluster navigator of choice. Very vim-like in behavior.

k3s / kind / minikube

For local development:

k3s: Lightweight Kubernetes, great for IoT and Edge but also amazing for local labs.
kind: Run Kubernetes inside Docker. Fast and reliable for CI/CD.

Cilium and eBPF

Modern Kubernetes networking is moving towards eBPF for performance and security. Cilium is the leading CNI in this space, replacing traditional iptables-based kube-proxy in many environments.

Learnings/Notes

Mon, 01 Jan 0001 00:00:00 +0000

:material-penguin:{ .anim-bounce } Learnings/Notes

Linux’s CFS: Completely Fair Scheduler

On a single cpu, the available cpu cycles are divided among all the threads in proportion to their weights.
The weight = priority = niceness.
Threads are organized in a runqueue (implemented as a red-black tree).
A thread exceeding its timeslice is pre-empted and the next one is given a slice.
In multicore systems, each core has its own runqueue.
But this may not always be fair (since one core may run one low-priority thread while the other may run several high-priority threads, inefficiently)
So linux has a load balancer that periodically keeps the queus in balance.
Load balancing is a costly operation (both computation and commuication operations are expensive) so it is kept at a minimum if possible.

Memory layout in Linux

32-bit: 3:1 ratio: out of 4gb, 3gb is for users and 1gb for kernel
64-bit: 1:1: out of 128TB, 64TB is for users and 64 for kernel.
So the kernel memory starts at 0xffff80000000000 in 64-bit, and 0xc000000 in 32-bit.
For a user process, Stack size is 8mb by default (see ulimit -s).
Stack occupies top of the address space and grows down.
The botttom of the stack contains env variables, prog name and **args
Below the stack is memmap which has stuff linked dynamically and mapped by the kernel at runtime.
Then is the heap.
Then there’s bss/data/program text.
text is usually read-only.
stack and data are non-executable (to prevent (partially) overflows).

Docker Notes:

apache mesos: get a lot of compute clusters looking like a single system.
Docker Trusted Registry: on-prem repository service
Machine: configures docker on cloud instances
Swarm: deploys containers in clusters. (Docker’s version of Kubernetes)
Compose: use YAML templates ofr multiple application deployments.
Tutum - like compose for cloud deployment. New acquisition.
OpenStack Havana supports docker as a hypervisor.
docker run -d (detaches and runs as a daemon)
use docker start -i asdasdas123 bash to connect to an existing instance. (or actually attach).
use docker exec if you want another process in an existing container. better than attach since attach just reattaches to the original pid1 process.
docker rename renames an existing container. otherwise --name while starting.
docker ps -a shows non-running containers.
names are auto-generated if you don’t specify them :)
=docker run –name loopdate -d centos /bin/sh -c “while true; do date; sleep 3; done”=
(daemonize example)
docker logs --tail 0 -f loopdate
(to see the live logs for the example above)
docker cp /etc/hostname asdasd123132:/tmp
docker run --restart <etc>: sets a policy to restart if it stops. doesn’t start a new container, just restarts the same id.
NUMA - Non-Uniform Memory Access.
/var/lib/docker/containers/<id>
/var/lib/docker/aufs/diff/<id>: see the CopyOnWrite diffs between this instance and the base layers.
docker diff <id>: shows files changed in a container.
docker inspect loopdate|less : json metadata, e.g. ipaddress.
docker history <image> shows the history of commands used to build that image.
’latest’ is a convention but need not be latest.. e.g. ubuntu sets ’latest’ to their LTS release 14.04, and not to bleeding edge.
creating images: either ‘commit’ an existing container, or specify a dockerfile.
you can save and package to tar file instead of pushing to a registry.
docker images -a: show intermediate images (these don’t have tags)
docker rm `docker ps --no-trunc -aq` (remove everything)
sample commit command: docker commit --change 'CMD ["/usr/sbin/httpd","-D","FOREGROUND"]' --change 'ENV APACHE_RUN_USER www-data' --change 'ENV APACHE_RUN_GROUP www-data' 26cb lab/websvr:v0.2
do a docker pull <image> before use if you want to speed up your boxes.
docker registry is opensource, and v1.6+ is in go and supports parallel downloads.
registry:latest is 0.9, and is a python app. deprecated.
docker run -p 5000:5000 -d registry:2 –gives a web interface for registry v2.
docker tag arun/myapache localhost:5000/myapache, followed by a push: pushes myapache to the local registry.
docker save/load: tar a repo (i.e. image), including parent layers and tags and versions, for local circulation.
docker export is like save, but flattens the filesystem.
build a docker image from a dockerfile: docker build some/path
use --link to link two containers together (adds to each container’s hosts file). newer versions have advanced networking: put associated containers in a single subnet , and allow them to talk to each other.

Vagrant notes:

setup:

vagrant init
vagrant box add centos/7
mention the same box in the vagrantfile

start:

vagrant up
vagrant ssh

stop:

vagrant suspend # save state and stop
vagrant halt # graceful shutdown
vagrant destroy # wipe out hd etc

Ansible notes

Modules are wrappers for administration commands (like ping, apt, yum, copy, etc).
Always use these instead of shell exec since modules are idempotent: you specify the state you want to be in, and the commands are run appropriately.
A task contains a module to be run, along with Facts or conditions or anything else.
Handlers can do everything tasks can, and are triggered by tasks when conditions are met. e.g. ‘start nginx’ would be a handler called in ‘install nginx’.
Roles organize multiple tasks in one coherent whole (e.g. installing nginx may require adding a repo, copying certs, installing the rpm and starting the server).
Roles are organized like this: files, handlers, meta, templates, tasks, vars.
Except files and templates, a main.yml file present in all other folders will be executed automatically.
Files have static files, e.g. httpd.conf, certs etc.
Handlers have triggers obviously
Meta has dependencies and other metadata. e.g. run the ssl role before starting the nginx role.
Templates are based on jinja2.
Variables have vars that are used to fill the templates.
Tasks have the main logic.
To run the whole role, just call the main yaml: ansible-playbook -s main.yml
Facts are metadata gathered by ansible on init: num_processors, cores, interfaces, mounts etc. you can use these vars in your templates.
ansible-vault can be used to encrypt vars and files in a role.

Linux ad-hoc daemonization

If a script is running in a terminal and you want to daemonize it, do this:
Ctrl-Z to suspend it
bg to make it a background job
disown -h %job-id where job-id is what bg returned. This removes the command from the shell’s job list, so it won’t get a SIGHUP when the terminal closes.

linux ctime vs mtime

ctime is for inode, mtime is for contents
e.g. chmod changes ctime. echo "asd">>file changes mtime.

soft vs hard links

Hard links:

Two filenames in a folder pointing to the exact same inode.
There is no distinction between the link and the original.
This means you can delete one file and the other will still exist!
Cannot traverse filesystems. cannot hard link directories

Soft links:

A new kind of file that has its own inode entry. the OS knows how to traverse from it to the parent.

Movies

Mon, 01 Jan 0001 00:00:00 +0000

:material-television-classic:{ .anim-flip }Movies

I’m a bit of a movie snob and prefer ones where the director’s love shines through. Commercially-focused movies are quite boring. I like to second-guess what happens next, and thoroughly enjoy movies that ‘surprise’ me.

Favourite Directors

Alex Garland - The Beach, Ex Machina, 28 Days Later
Denis Villenueve - Arrival, Bladerunner 2049
Joel and Ethan Coen - Fargo, No Country For Old Men, O Brother Where Art Thou
Guillerma del Toro - Pan’s Labyrinth, Hellboy

The best of the best

My all-time favourite movies are:

Networking

Mon, 01 Jan 0001 00:00:00 +0000

:material-lan:{ .anim-heart } Networking

iperf

This link is quite nice: https://www.golinuxcloud.com/linux-monitor-network-traffic/

How to use iperf:

Whitelist port 5201 on your security group and firewall.

Then start the server first:

iperf3 -i 5 -s

Then the client:

iperf3 -i 5 -t 60 -c <IP/hostname of the server>

It gives a nice report but apparently isn’t good for latency checks, only bandwidth.

UDP Client (Python 3)

import socket
import sys

# Create a UDP socket
sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)

server_address = ('127.0.0.1', 10000)
message = b'This is the message. It will be repeated.'

try:
    # Send data
    print(f'sending "{message!r}"', file=sys.stderr)
    sent = sock.sendto(message, server_address)

    # Receive response
    print('waiting to receive', file=sys.stderr)
    data, server = sock.recvfrom(4096)
    print(f'received "{data!r}"', file=sys.stderr)

finally:
    print('closing socket', file=sys.stderr)
    sock.close()

UDP Server (Python 3)

import socket
import sys

# Create a UDP socket
sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)

# Bind the socket to the port
server_address = ('localhost', 10000)
print(f'starting up on {server_address[0]} port {server_address[1]}', file=sys.stderr)
sock.bind(server_address)

while True:
    print('\nwaiting to receive message', file=sys.stderr)
    data, address = sock.recvfrom(4096)

    print(f'received {len(data)} bytes from {address}', file=sys.stderr)
    print(data, file=sys.stderr)

    if data:
        sent = sock.sendto(data, address)
        print(f'sent {sent} bytes back to {address}', file=sys.stderr)

…

Noam Chomsky

Mon, 01 Jan 0001 00:00:00 +0000

:material-thought-bubble:{ .anim-bounce } Noam Chomsky

Why

I read Chomsky through this article by Aaron Swartz on the book that changed his life. So I did what Aaron did, and picked up Understanding Power. Everything about that book is as crushingly world-changing as he describes.

Considering his subject material and how challenging it must be to communicate his world-view to others, he does a phenomenal job of it. He never raises his voice, resorts to ad-hominems, or loses his calm.

Online Privacy and the Internet

Mon, 01 Jan 0001 00:00:00 +0000

:material-lock-check:{ .anim-bounce } Online Privacy and the Internet

On blocking ads, filter bubbles, fake news and the like.

Ads and Ad blocking

Ads don’t work that way
A slightly different and interesting perspective on how advertising works.
Total advertising denial - This guy blocks everything.
Advertising is a cancer on society
Ad networks

Fake news

India had its first Whatsapp election

Package management

Mon, 01 Jan 0001 00:00:00 +0000

:material-penguin:{ .anim-heart } Package management

Sort RPMs by size

rpm -qa --queryformat '%{size} %{name}\n' | sort -rn | more

Extract rpm into current folder instead of installing:

rpm2cpio boost-system-1.53.0-23.el7.x86_64.rpm | cpio -idmv

Trace a binary or file to the RPM that installed it:

yum whatprovides /usr/lib64/libdbus-c++-1.so.0

or this:

rpm -qf /usr/lib64/libdbus-c++-1.so.0

Yum/dnf revert

If a yum remove wiped out several packages, do this:

dnf history # note the id of the bad removal here
dnf history undo 96

yum/dnf will reinstall all the packages that were removed in that id.

Pale Fire, by Vladimir Nabokov

Mon, 01 Jan 0001 00:00:00 +0000

:material-pencil:{ .anim-heart } Pale Fire, by Vladimir Nabokov

I bought this at a used book store a few weeks back. It is a worn down, old edition from the 1960’s. This is my third Nabokov book, and ever since my first, I seem to have lost interest in the ‘normal’ fiction books I used to read. There is a cadence to his choice of words that shines through in all his works.

Philosophy / Morality

Mon, 01 Jan 0001 00:00:00 +0000

:material-thought-bubble:{ .anim-rotate } Philosophy / Morality

Personal stance

I find myself leaning towards Stoicism quite a bit. It’s core principles are around the Dichotomy of Control , i.e. understand the things that are outside your control and those that are within, and focus on the latter.

A virtuous life - according to Stoics - is one where we live in accordance with nature and cultivate our mind and character - the only things that we really have control over.

Powershell

Mon, 01 Jan 0001 00:00:00 +0000

:material-powershell:{ .anim-bounce } Powershell

These notes are from Mastering PowerShell Scripting - Fourth Edition, by Chris Dent.

Discovery, Basics

Update-Help to get the latest docs.

Get-help Get-Process gets you help about the Get-Process command.

Very cool, you can also add a -Examples to specifically see a bunch of examples :)

Get-Command shows all available commands, and you can use a regex like this to filter the output:

Get-Command Get-*ip*

Get-Alias prints all the aliases, as always use regexes to filter, e.g. Get-Alias s*. Some linux equivalents:

Productivity

Mon, 01 Jan 0001 00:00:00 +0000

:material-check-circle:{ .anim-flip } Productivity

Summary

I’ve tried a crapload of tools for tasks, notes, bookmarking, scheduling and what not. I realize I was more interested in trying new things than in really ‘maximizing’ my ‘productivity’.

These days I’m in a high-stress job involving a lot of churn and unpredictability, and I’ve found that checklists are /very/ useful and MS ToDo is a decent enough app to settle down with.

Bookmarks are overrated.

Prometheus

Mon, 01 Jan 0001 00:00:00 +0000

:material-fire:{ .anim-fade }Prometheus

I’m familiar with the architecture etc, and am currently interested in the querying side of things. So here are my notes from reading Prometheus: Up & Running by Brian Brazil.

Basic queries

Use rate for counters, e.g. rate(prometheus_blah[1m])

Curly braces for labels i.e. tags, e.g. process_resident_memory_bytes{job="node"}

Basic alerting

up == 0 returns only results where the condition matches. You can set this as an alert if it happens over a particular duration, e.g 1m.

Python

Mon, 01 Jan 0001 00:00:00 +0000

:material-language-python:{ .anim-heart } Python

pip: upgrade all packages in a virtual env

pip list --outdated --format=freeze | grep -v '^\-e' | cut -d = -f 1  | xargs -n1 pip install -U

Modern Python (2026 edition)

I use Python heavily and keep up with the evolving ecosystem. Here are the current standard tools and libraries.

ruff

The “new hotness” in the Python world. It’s an extremely fast linter and formatter written in Rust that replaces flake8, black, isort, and more.

Richard Dawkins

Mon, 01 Jan 0001 00:00:00 +0000

:material-dna:{ .anim-heart } Richard Dawkins

Why

Dawkins is my role model because his books played a major role in forming my understanding of the world. His writing is crisp and clear: he knows his stuff and can defend it well, so he doesn’t need to obfuscate or confuse. He has strong opinions on religion and is not afraid to share them.

This was my first brush with a Dawkins box was probably the single most influential, mind-changing experience I’ve ever had with a book. Until I’d read him, I didn’t have well-formed mental models of scepticism, religion, or evolutionary biology.

Richard Stallman

Mon, 01 Jan 0001 00:00:00 +0000

:material-penguin:{ .anim-rotate } Richard Stallman

Why

Stallman is the heart of the Free Software Foundation and the reason for the GNU in GNU/Linux . He represents a certain purity and conviction that is hard to get in our industry these days.

I sit strongly on the GPL side of the GPL vs MIT license debate. Software that use GPL licenses are like life forms that contain genes, in the sense that the license carries the promise that the software can evolve and take new forms, while continuing to be open and accessible. MIT-based Licenses don’t ensure their own survival in the same way.

Scepticism

Mon, 01 Jan 0001 00:00:00 +0000

:material-thought-bubble:{ .anim-heart } Scepticism

I feel lucky to have grown up as the internet was starting out. I honed my debating skills in forums (talk.origins, James Randi’s forum, and so on) and feel I have a pretty good bullshit detector thanks to that training.

Sometimes I get into arguments with people about some fairly interesting topics. Other times it’s on stupid things they read on social media and swallow without a second thought. Here are some well written articles on interesting topics.

Security

Mon, 01 Jan 0001 00:00:00 +0000

:material-lock:{ .anim-flip } Security

Query list of ciphers supported by a server

nmap --script ssl-enum-ciphers -p 443 example.com

Things that go in a certificate

Subject: CN     the certificate owner's common name
Subject: E      the certificate owner's email address
Subject: T      the certificate owner's locality
Subject: ST     the certificate owner's state of residence
Subject: O      the organization to which the certificate owner belongs
Subject: OU     the name of the organizational unit to which the certificate owner belongs
Subject: C      the certificate owner's country of residence
Subject: STREET the certificate owner's street address
Subject: ALL    the certificate owner's complete distinguished name
Serial  the certificate's serial number
SignatureAlg    the algorithm used by the Certificate Authority to sign the certificate
BeginDate       the date at which the certificate becomes valid
EndDate the date at which the certificate becomes invalid
PublicKey       the certificate's public key
FriendlyName    the certificate's friendly name

selinux example:

ls -Z file1
-rwxrw-r-- user1 group1 unconfined_u:object_r:user_home_t:s0 file1

SELinux contexts follow the SELinux user:role:type:level syntax.
Use the ps -eZ command to view the SELinux context for processes
and id -Z for users
seinfo -r (part of setools-console): shows all available user roles: such as guest, unconfined, webadm, sysadm, dbadm, etc.

also see /etc/selinux/targeted/context/users

Systemd

Mon, 01 Jan 0001 00:00:00 +0000

:material-penguin:{ .anim-heart }Systemd

Socket activation

Systemd has a neat little feature where a daemon can turn on whenever a connection is made to it. Works with Unix and network sockets. More details here . Essentially you create a socket file alongside your service file. The advantage is that you don’t need to start your services in a specific order.

Flush old logs in journalctl

By date or by size:

    sudo journalctl --vacuum-time=2d
    sudo journalctl --vacuum-size=500M

Tail journalctl

journalctl -f

For a specific service:

The Art of the Infinite

Mon, 01 Jan 0001 00:00:00 +0000

:material-pencil:{ .anim-heart } The Art of the Infinite

This is the kind of book I wish I’d read 20 years back.

The Kaplans cover a lot of ground, so the book is densely packed with remarkable insights. Although most of the topics (algebra, geometry) were covered in my school syllabus in my younger days, the difference is in how it bridges vast areas of mathematics together.

A seemingly insurmountable problem is shown first. Then some remarkable piece of magic happens. And the clouds clear and light shines through.

The Happiness Hypothesis

Mon, 01 Jan 0001 00:00:00 +0000

:material-pencil:{ .anim-flip } The Happiness Hypothesis

This book is written by Jonathan Haidt. I’d read his other book, The Righteous Mind, and enjoyed it. I liked this one as well. What follows is not really a review. These are just notes I took from the book that I found interesting.

Not a metaphor: there’s literally a Gut brain , connected by vagus nerve with main one. Runs independently to manage the intestine. Huge lining of neurons in the lining. Triggers anxiety when infections are present.

The Thinking Person's Guide to Climate Change

Mon, 01 Jan 0001 00:00:00 +0000

:material-pencil:{ .anim-heart } The Thinking Person’s Guide to Climate Change

Author: Robert Henson

Part 1 - The Basics - Global Warming in a nutshell

Chapter 1 - Climate Change: A Primer

Check out the IPCC organization and it’s reports.
Detection and attribution i.e. is the climate Changing, and is it changing because of humans.
Eg temperature warming at poles is not expected from natural causes.

The spectrum extends anywhere from 0.4° to 2.6°C (0.7°–4.7°F) by 2046–2065 and from 0.3° to 4.8°C (0.5°–8.6°F) by 2081–2100. Importantly, this would be on top of the warming of about 0.6°C (1.1°F) that occurred from the 1850–1900 period to the 1986–2005 comparison period.

Think Like A Stoic, by Massimo Pigliucci

Mon, 01 Jan 0001 00:00:00 +0000

:material-pencil:{ .anim-bounce }Think Like A Stoic, by Massimo Pigliucci

These are just some random thoughts I jotted during my listen, so I’m not sure that it will be very useful for someone else. Don’t take it to be a comprehensive review or summary.

Basics

Live according to nature

i.e. we have the capacity for reason plus we are social animals.. that is our nature so anything that stays true to it is virtuous.

We Are Our Brains

Mon, 01 Jan 0001 00:00:00 +0000

:material-pencil:{ .anim-flip } We Are Our Brains

Notes taken while reading the excellent We are our brains by Dick Shwaab.

Hormones

Oxytocin - comfort , bonding
Prolactin - in expectant fathers. Nesting behaviour in moms.
Vasopressin - marital difficulties and aggression in men, but trust of strangers in women. Hormone created and released by the brain. Also inhibits excretion of water.
Both vasopressin and oxytocin levels are unbalanced in autists

Other

Anencephaly linked to pesticide use
Thalidomide taken during pregnancy led to birth defects (missing limbs)

Pain in a fetus

Pain sensors on skin - 7th week onwards
BUT wiring to cerebral cortex - 26 weeks onwards
So the fetus can react locally after 7 weeks but it is doubtful that pain is actually transmitted until about 25-29 weeks
Finally it must be perceived by the brain. Only at 35-37 weeks is there slight difference in reaction to a touch vs a pin prick

Puberty

Young people have a poor PFC i.e. pre frontal cortex , which limits their planning and organisational skills
Puberty kicks in annoying behaviour within the family to limit incest, at the same time increasing risk taking and exploration.
The kiss1 gene starts the whole process. Fat reserves are ensured by monitoring leptin. Melatonin inhibits puberty.

Miscellaneous

Narcolepsy - sleep disorder. Tiredness in day, uneasy sleep at night.
Cataplexy - too much emotion leads to patient seemingly becoming unconscious. They lose muscle tension and collapse but are fully aware otherwise.

Windows

Mon, 01 Jan 0001 00:00:00 +0000

:material-microsoft-windows:{ .anim-bounce } Windows

Change a wireless network to Private

  Get-NetConnectionProfile
  # Note the InterfaceIndex here
  Set-NetConnectionProfile -InterfaceIndex <id>  -NetworkCategory Private

Xbox Series X

Mon, 01 Jan 0001 00:00:00 +0000

:material-controller-classic:{ .anim-heart } Xbox Series X

I love my Xbox because this is the console where I have formed memories of:

playing co-op games with my kids (like Rayman Legends),
playing through an entire series (like Gears and Halo),
discovering games through Game Pass that I’d’ve never otherwise tried (like Immortality)