Welcome to Linux Developer’s documentation!

I will be documenting here tools I used during my software engineering career, as well as tips and tricks on how to get up and running with everything Fedora related.

Note

This project is under active development.

Contents

• Bash - variables, arrays & eval
  • How the shell processes a command
  • Variables (strings)
  • The word splitting problem
  • eval - the nuclear option
  • Arrays - the proper solution
    • [@] vs [*] - the critical difference
    • Arrays as command arguments
  • Quick reference
  • When to use what
• CKA preparation
  • Exam setup (do this first)
  • Cluster architecture & RBAC
  • etcd backup and restore
  • Cluster upgrade (kubeadm)
  • Workloads & scheduling
  • Services & networking
  • Storage
  • Troubleshooting
  • Exam tips
• CoreOS
  • building rhcos
  • cosa func
  • Running the iscisi
  • cosa shell
  • cosa spawn and zincati
  • Format of the credentials file:
  • Checking zincati logs
• CoreOS pipeline
  • Jenkins Error message
    • Debugging steps
• Forgotten bash commands
  • pushd / popd - the directory stack
  • curl cheat.sh
  • progress
  • watch
  • history shortcuts
  • brace expansion
  • process substitution
  • text wrangling
  • xargs
  • tee
  • small but handy
  • trap - clean up on exit
  • watching progress
  • timers and stopwatches
  • terminal toys
• Git
  • commit
  • rebase workflow
  • useful commands
  • comparing branches: .. vs ...
  • editing an earlier commit
  • force-push safety
• GPG & SSH keys
  • Managing multiple identities
  • Backing up GPG keys
  • YubiKey architecture
  • Key storage options
• Groovy - concepts
  • Types and variables
  • Strings - GString vs String
  • Closures
    • Delegation
  • Operators
  • Collections
  • Control flow
  • Methods and classes
  • Groovy vs Java - quick reference
  • Common gotchas
• Java - concepts
  • Annotations - metadata on classes and methods
  • Interfaces, inheritance, generics
  • Access modifiers
  • Reading Java plugin source - what to look for
• Jenkins - concepts
  • What is Jenkins?
  • Core concepts
    • Jobs
    • Pipelines, agents, plugins
  • Jenkinsfiles
  • Jenkins configuration - XML under the hood
  • Job DSL plugin
    • Static vs Dynamic DSL
  • Constructors and setters (Java basics)
  • Stapler annotations
  • How the dynamic DSL generates methods
  • DSL calls are nested closures, not dot-chains
  • The configure block (raw XML)
  • Multibranch pipeline - key concepts
  • Migrating a configure block to native DSL
• jq & yq - JSON and YAML on the CLI
  • jq basics
  • Selecting and filtering
  • Transforming
  • Building JSON from the shell
  • yq (YAML)
• junitparser - JUnit XML in Python
  • The model
  • Test case details
  • Pass / fail / skip
  • Full example
  • Quick reference
  • vs the older python-junit-xml
• Podman
  • Quadlets
  • Working with images
    • Pull, run, inspect
    • List and clean up
    • Build and push
  • skopeo - inspect & copy without pulling
  • oc adm release info
• Python essentials
  • Data structures
  • Strings
  • Control flow
  • Functions
  • Classes
  • Error handling
  • File I/O, YAML, JSON
  • Common algorithm patterns
  • Useful stdlib
  • argparse
  • subprocess
  • pathlib
  • Version-string parsing
  • Complexity quick reference
• Python exercises
  • Lists
    • Rotate a list k places to the right
    • Remove duplicates preserving order
    • Flatten a list of lists (one level)
  • Dicts
    • Group by first letter
    • Invert a dict
    • Merge keeping the larger value
  • Strings
    • Palindrome (ignoring case and punctuation)
    • Most frequent character
  • Functions
    • A @timer decorator
    • Call a function with only the kwargs it accepts
  • Classes
    • A simple stack
    • __eq__ and __hash__
  • Error handling
    • Retry with exponential backoff
  • Interview algorithms
    • Two sum (hash map, O(n))
    • Valid parentheses (stack)
    • Merge intervals (sort + linear scan)
    • BFS shortest path in a grid
    • Binary search for a boundary (first >= target)
  • File I/O
    • Top words in a file
    • Parse a key=value config
• Regular expressions - Python re + bash grep/sed
  • Literal matching & metacharacters
  • Character classes
  • Quantifiers
  • Groups and capturing
  • Alternation and anchors
  • Substitution
  • Lookahead and lookbehind
  • Multiline and flags
  • Common patterns
  • Quick reference
• Regex exercises
  • Character classes & anchors
    • Filter RPMs by prefix
    • Extract individual digits
  • Quantifiers
    • Extract version numbers (X.Y or X.Y.Z)
    • Extract quoted strings (greedy vs lazy)
  • Groups and capturing
    • Parse an RPM NVR
    • Parse os-release (quoted and unquoted)
  • Alternation and anchors
    • Filter by OS variant
    • Whole-word match
  • Substitution
    • Mask IP addresses
    • Strip the minor version from repo names
  • Lookahead and lookbehind
    • Extract a value after a label
    • Match a version only before a suffix
  • Multiline and flags
    • Parse ARG definitions from a Containerfile
  • Real-world combined
    • Parse kola test results
    • Validate and normalize image references
    • Extract failed tests from a CI log
• RHCSA preparation
  • Networking
  • Users and groups
  • Permissions and ACLs
  • SELinux
  • Storage and LVM
  • Scheduling tasks
  • Containers (podman)
  • Troubleshooting boot
  • systemd services and boot targets
  • Managing software
  • Processes and tuning
  • firewalld
  • Network file systems (NFS / autofs)
  • Time and chrony
  • Finding and archiving files
  • Exam tips
• How this site is built
  • Project layout
  • Adding a page
  • Enabling an extension
• Fedora Silverblue
  • Status and updates
  • Layering packages
  • Rolling back and pinning
  • Rebasing to a new release
  • toolbox - a mutable dev container
• SSH
  • Config (~/.ssh/config)
  • Keys and the agent
  • ProxyJump (bastion hosts)
  • Port forwarding and tunnels
  • Running commands and copying files
  • Debugging
• systemd
  • Managing services
  • Listing and inspecting units
  • Overriding a unit (drop-ins)
  • Writing a unit
  • journalctl
  • Timers (a cron replacement)
  • Targets (runlevels)
  • Boot analysis
  • User units
• TMT (Test Management Tool)
  • What TMT is and why it exists
  • The three building blocks
    • .fmf/version - the root marker
    • Tests - what to run
    • Plans - how to find and run tests
  • Plan phases
  • Running TMT locally
  • Verbosity - --debug -vvvv
  • GitHub Actions workflow for TMT
  • GitHub Actions vs Testing Farm vs Konflux
  • The two-layer pattern - upstream + dist-git
  • gating.yaml - skip it
  • Useful commands
  • Docs
• tmux
  • Sessions
  • Windows (tabs)
  • Panes (splits)
  • Copy mode and scrolling
  • Config (~/.tmux.conf)
  • Scripting a layout
• Training your own models
  • Why fine-tune?
  • Core concepts
  • Choosing a base model
  • Gathering training data
  • Fine-tuning with QLoRA
  • Hardware and cost
  • Fine-tuning vs RAG
  • Glossary
• YAML config as nested maps (Python + Groovy)
  • Python
  • Groovy
  • Python vs Groovy side-by-side
• .zshrc & .bashrc modifications
  • aliases