File System

File system organization

The file system under Linux follows a hierarchical structure in the form of an inverted tree. Everything starts at the root represented by /.

Basic structure

Here are some important directories generally found at the root:

/bin: Contains essential programs accessible by all users.
/etc: Contains system configuration files.
/home: Contains users' personal folders.
/var: Contains variable files like system logs.
/tmp: Directory for temporary files.
/usr: Contains additional programs and files.

Each directory has a specific function and can contain subdirectories or files.

Hierarchy example

Here's a simplified representation:

/
|-- bin
|-- etc
|-- home
|   |-- user1
|   |-- user2
|-- var
|-- tmp
|-- usr

Paths in the file system

A path designates the location of a file or directory in the system.

Absolute path

An absolute path always starts from the root (/) and specifies the exact location.

Example:
- /home/user1/document.txt
- /etc/hosts

Relative path

A relative path is defined relative to the current directory (where you are in the system).

Example:
- If the current directory is /home/user1:
  - document.txt refers to /home/user1/document.txt
  - ../user2 refers to /home/user2

Important symbols

.: Represents the current directory.
..: Represents the parent directory.

Practical example

You are in /home/user1.
- Typing ls .. lists the contents of /home.
- Typing cd ../user2 places you in /home/user2.

Practice

Identifying absolute paths

Among the following paths, which ones are absolute?

/etc/passwd
document.txt
/var/log/syslog
../photos

/etc/passwd and /var/log/syslog are absolute paths.

Navigating the file system

From /home/user1, access /home/user2 using a relative path.
From /home, access /etc using an absolute path.

We'll refer to ../ to go up one level, to be in /home, which would give the following path: ../user2.
The absolute path doesn't need to know which folder we're in, so it will be enough to refer to /etc.

Summary

The Linux file system is organized hierarchically with a root /.
An absolute path always starts with /.
A relative path depends on the current directory and uses . or .. to navigate.