Linux on tplat

Distributions

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

Distributions

A Linux distribution is the Linux kernel bundled with userland tools, package management, and defaults.

Overview

Distros differ by package manager, default tools, desktop environment, and target use case
Common use cases include desktop, server, embedded, and security tooling
The same kernel can feel very different depending on the distribution

Reference

Common distributions

Category	Examples
General purpose	Ubuntu, Fedora, Debian
Enterprise	Red Hat Enterprise Linux, CentOS
Security tooling	Kali Linux, Parrot OS, BlackArch, Pentoo, BackBox
Specialized	Raspberry Pi OS

Debian focus

Known for stability, reliability, and conservative defaults
Common in servers, desktops, and embedded systems
Uses the APT ecosystem for installs, upgrades, and dependency resolution

Property	Notes
Stability	Conservative package updates
Release cycle	Long-term support style releases
Security	Dedicated security updates
Flexibility	Highly configurable
Learning curve	Higher than beginner-focused distros

Trade-offs

Pros: predictable behaviour, strong security track record, large package repository
Cons: older package versions, more manual configuration, less beginner-friendly UX

Mental Model

A distro is an opinionated bundle around the same kernel
The right choice depends on environment and workflow
Most trade-offs come down to stability versus freshness and control versus convenience

Permissions

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

Permissions

Linux permissions use an owner, group, and others model to control access to files and directories.

Overview

Permission bits define read, write, and execute access
Files and directories interpret those bits differently
chmod, chown, and special bits modify access rules

Reference

Permission types

Symbol	Meaning
`r`	Read
`w`	Write
`x`	Execute

Permission scope

Scope	Meaning
`u`	Owner
`g`	Group
`o`	Others

File vs directory semantics

Object	`r`	`w`	`x`
File	Read contents	Modify contents	Execute file
Directory	List entries	Create or remove entries	Traverse directory

Directory traversal requires x, even if r is set
x on a directory does not mean you can execute files inside it
Changing directory contents requires w on the directory itself

Representation

ls -l /etc/passwd
-rwxrw-r-- 1 root root 1641 May 4 23:42 /etc/passwd

Segment	Meaning
`-`	File type
`rwx`	Owner permissions
`rw-`	Group permissions
`r--`	Others permissions
`1`	Hard link count
`root root`	Owner and group
`1641`	File size
`May 4 23:42`	Last modified

Octal notation

Value	Permission
`4`	Read
`2`	Write
`1`	Execute

Example	Meaning
`7`	`rwx`
`6`	`rw-`
`5`	`r-x`
`4`	`r--`

rwxrw-r-- = 764

Modifying permissions

chmod a+r shell
chmod 754 shell
chown <user>:<group> <file-or-directory>

chmod adds or removes permissions with symbolic or numeric modes
chown changes the owner and optionally the group

Special bits

SUID and SGID run a program with the file owner’s or group’s privileges
The sticky bit prevents users from deleting files they do not own in shared directories
In ls -l, s replaces x for SUID or SGID, and t marks the sticky bit

Mental Model

Ownership sets the baseline
Groups extend access
Permission bits gate operations
Special bits change how execution and deletion behave

Core Linux Commands

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

Core Linux Commands

Common commands are easier to remember when grouped by discovery, inspection, navigation, and search.

Overview

man and apropos help you discover commands
which resolves the executable that will run
find is precise and real-time; locate is fast and indexed

Reference

Discovery

Command	Purpose
`man`	Read manual pages
`apropos`	Search manual page descriptions by keyword
`explainshell`	External reference for command syntax

System inspection

Command	Purpose
`whoami`	Print the current user
`id`	Show user and group IDs
`hostname`	Get or set the hostname
`uname`	Show kernel and system information
`pwd`	Print the current directory
`env`	Show or set environment variables
`ps`	Inspect processes
`who`	Show logged-in users
`lsof`	Show open files
`lsblk`	List block devices
`lsusb`	List USB devices
`lspci`	List PCI devices

Networking

Command	Purpose
`ifconfig`	Legacy network interface tool
`ip`	Modern network interface tool
`netstat`	Legacy network status tool
`ss`	Inspect sockets

File and path utilities

Command	Purpose
`ls`	List directory contents
`cd`	Change directory
`which`	Show the executable path for a command

ls -l /etc
which python

ls -a includes hidden files. cd - returns to the previous directory.

File Descriptors and Redirection

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

File Descriptors and Redirection

File descriptors provide a uniform way for processes to read and write streams.

Overview

0 is stdin, 1 is stdout, and 2 is stderr
Redirection rewires those streams to files or /dev/null
Pipes connect the output of one command to the input of another

Reference

Standard file descriptors

FD	Name	Purpose
`0`	STDIN	Standard input
`1`	STDOUT	Standard output
`2`	STDERR	Standard error

Redirection

Operator	Meaning
`>`	Overwrite a file with stdout
`>>`	Append stdout to a file
`<`	Use a file as stdin
`2>`	Redirect stderr
`1>`	Redirect stdout explicitly

find /etc/ -name networks 2>/dev/null
find /etc/ -name networks > results.txt
find /etc/ -name networks 2>/dev/null 1>stdout.txt
cat < stdout.txt

Here documents

cat << EOF >> stream.txt
My
Input
Stream
EOF

Pipes

find /etc/ -name "*.conf" 2>/dev/null | grep systemd | wc -l

Mental Model

Each process reads from FD 0 and writes to FD 1 or 2
Redirection changes where those streams go
Pipes build dataflow pipelines between commands
/dev/null is a sink for discarded output

SSH

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

SSH

SSH is the standard protocol for secure remote command execution and administration on Unix-like systems.

Overview

Provides encrypted remote access without a GUI
Is widely installed and efficient on low-resource systems
Commonly used for administration, automation, and file transfer workflows

Reference

ssh user@host

Mental Model

SSH replaces insecure remote login methods with an encrypted channel
It is the default way to manage many remote Linux systems

Regular Expressions (Regex)

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

Regular Expressions (Regex)

Regex patterns match and filter text. In Linux they are commonly used with grep, sed, and awk.

Overview

Regex is compact and composable
Start with simple patterns and add anchors or grouping only when needed
Most mistakes come from precedence, escaping, or incorrect anchoring

Reference

Core constructs

Pattern	Meaning
`.`	Any character
`*`	Zero or more of the previous token
`+`	One or more of the previous token
`?`	Zero or one of the previous token
`^`	Start of line
`$`	End of line
`\b`	Word boundary
`\w`	Word character
`[]`	Character class
`()`	Grouping
`\|`	OR operator

`grep` modes

Option	Meaning
`grep`	Basic regex
`grep -E`	Extended regex; usually preferred
`grep -v`	Invert the match

Common patterns

Use case	Pattern
Starts with a word	`^word`
Ends with a word	`word$`
Contains a word	`word`
Word boundary	`\bword\b`
Starts with A, ends with B	`^A.*B$`
A or B	`A\|B`

Examples

Task	Command
Exclude comment lines	`grep -v '#' /etc/ssh/sshd_config`
Match words starting with `Permit`	`grep -E '\bPermit\w*' /etc/ssh/sshd_config`
Match words ending with `Authentication`	`grep -E '\w*Authentication\b' /etc/ssh/sshd_config`
Match lines containing `Key`	`grep 'Key' /etc/ssh/sshd_config`
Match lines starting with `Password` and containing `yes`	`grep -E '^Password.*yes' /etc/ssh/sshd_config`
Match lines ending with `yes`	`grep -E 'yes$' /etc/ssh/sshd_config`

Best practices

Prefer grep -E for extended regex
Avoid unnecessary cat; pipe the file directly into the command
Build patterns incrementally and verify anchors and grouping

Mental Model

Regex matches text by combining anchors, quantifiers, and grouping
^ and $ constrain position
* and + control repetition
Parentheses and | change matching logic

Linux on tplat

Distributions

Distributions

Overview

Reference

Common distributions

Debian focus

Trade-offs

Mental Model

Permissions

Permissions

Overview

Reference

Permission types

Permission scope

File vs directory semantics

Representation

Octal notation

Modifying permissions

Special bits

Mental Model

Core Linux Commands

Core Linux Commands

Overview

Reference

Discovery

System inspection

Networking

File and path utilities

File Descriptors and Redirection

File Descriptors and Redirection

Overview

Reference

Standard file descriptors

Redirection

Here documents

Pipes

Mental Model

SSH

SSH

Overview

Reference

Mental Model

Regular Expressions (Regex)

Regular Expressions (Regex)

Overview

Reference

Core constructs

grep modes

Common patterns

Examples

Best practices

Mental Model

`grep` modes