Chapter - 1: Basics of linux on 0x-s0M3n4th's Blog

Linux Directories

Mon, 06 Jul 2026 12:10:10 +0530

The default display manager in RHEL 9 is called GDM(GNOME Display Manager)

Linux Directory Structure:

Linux files are organized logically in a hierarchy for ease of administration and recognition. This organization is maintained in hundreds of directories located in larger containers called file systems. Red Hat Enterprise Linux follows the Filesystem Hierarchy Standard (FHS) for file organization, which describes names, locations, and permissions for many file types and directories.
The Linux directory structure is analogous to an inverted tree, where the top of the tree is the root of the directory, tree branches are subdirectories, and leaves are files.
Path example: /etc/rc.d/init.d/README
- The etc directory is located under / -> here / is the parent and etc is the child.
- rc.d(child) is located under etc(parent) .
- init.d(child) is located under rc.d(parent) .
- README(leaf) is located under init.d(parent) .
==SUB-DIRECTORY:== A directory that has a parent directory.

Note

The root directory has no parent, and the lowest level subdirectory has no child.

Listing files and directories

Mon, 06 Jul 2026 12:11:10 +0530

One of the most rudimentary command in linux is ls.

Some options of ls:

Options	Description
-a	Shows hidden files and directories. A file or directory name that begins with the period character.
-l	Displays long listing with detailed file information like file type, permissions, link count, owner etc.
-ld	Displays long listing of the specified directory but hides its contents.
-lh	Displays long listing with file sizes shown in human-friendly format.
-lt	Lists all files sorted by date and time with the newest file first.
-ltr	Lists all files sorted by date and time with the oldest file first (reverse).
-R	Lists contents of the specified directory and all its subdirectories (recursive listing).

ls -l:

Long listing of the files.

ls -al:

List all the hidden files in the current working directory.

Debriefing the columns:

Columns 1: The first character (hyphen or d) divulges the file type, and the next nine characters (rw-rw-r–) indicate permissions.
Column 2: Displays the number of link.
Column 3: Shows the owner name.
Column 4: Exhibits the owning group name.
Column 5: Identifies the file size in bytes. For directories, this number reflects the number of blocks being used by the directory to hold information about its contents.
Column 6,7,8: Displays the month, day, and time of creation or last modification.
Column 9: Indicates the name of the file or directory.

ls -ll:

Alternative of ls -l , does the same thing.

ls -ld {directory_name}:

Shows long listing of the specified directory.
- For example: ls -ld /usr

ls -alh:

To show all the files in the current directory with their sizes in human readable format.

ls -lt:

Shows the output in a sorted order by date and time with the newest file first.

ls -R directory_name/by default the cwd is selected:

Shows content of any specified directory recursively, if directory is not specified it will take the current working directory as a default argument.

Directory Basics

Mon, 06 Jul 2026 12:12:10 +0530

pwd(Present working Directory):

It shows the a user’s current working directory.
pwd always returns the absolute path.

Navigating directories:

Absolute path: It is the full path starting from the top level path which is / to my current working directory. The absolute path will always start with / at the beginning.
Relative path: It is not a full path but rather a path which depicts the location relative to our own current working directory.
For example: we are in /home/user1 directory. To move upwards either we can write using the relative path like this → cd Desktop/ , or we can write using absolute path like this → cd /home/user1/Desktop/

Identifying terminal devices

Mon, 06 Jul 2026 12:13:10 +0530

Linux allocates unique pseudo (or virtual) numbered device files to represent terminal sessions opened by users on the system. It uses these files to communicate with individual sessions. By default, these files are stored in the /dev/pts (pseudo terminal session) directory. These files are created by the system when a user opens a new terminal session and they are removed on its closure.
We can see it via the command tty(teletype)

System uptime

Mon, 06 Jul 2026 12:14:10 +0530

The uptime command is used to display the system’s current time, length of time it has been up for, number of users currently logged in, and the average CPU (processing) load over the past 1, 5, and 15 minutes.
The output shows the current system time (18:28:09), up duration (49 minutes), number of logged-in users (2), and the CPU load averages over the past 1, 5, and 15 minutes (0.00, 0.00, and 0.00), respectively.
The load average numbers correspond to the percentage of CPU load with 0.00 and 1.00 represent no load and full load, and a number greater than 1.00 signifies excess load (over 100%).

You know this alrady ;)

Mon, 06 Jul 2026 12:10:10 +0530

You can clear the terminal screen using the command clear .

Determining path of commands

Mon, 06 Jul 2026 12:10:10 +0530

RHEL provides a set of tools that can be used to identify the absolute path of the command that will be executed when you run it without specifying its full path. These tools are the which, whereis, and type commands.

which:

whereis:

type:

Viewing system information

Mon, 06 Jul 2026 12:10:10 +0530

The uname command identifies elementary information about the system including its hostname.
- uname → shows only the kernel name.
- uname -a → showing all information
- - Kernel name(1), hostname(2), kernel release(3), date and time of the kernel built(4), machine and hardware name(5), processor type(6), hardware platform(7), operating system name(8).
- More separate commands to try on uname

Viewing CPU information

Mon, 06 Jul 2026 12:10:10 +0530

We can see all cpu info using the command lscpu

How to get help when you are stuck in any command?

Mon, 06 Jul 2026 12:10:10 +0530

man pages:

Press h to get help on navigation, press q to quit and return to the command prompt, use the Up and Down arrow keys to scroll up and down, and the PgUp and PgDn keys to scroll one page at a time.
KEYS WHICH CAN HELP IN NAVIGATION:

apropos command:

It is alias of the command man -k {half_remembered_cmd_name} → This command allows us to perform keyword search on manual pages incase we have forgot what the command name is.

Note

Before we run the keyword search we need to run the command mandb

Practice lab scenarios

Mon, 06 Jul 2026 12:20:10 +0530

Navigate Linux Directory Tree - Practice questions:

Note

Do it yourself, try to use the existing knowledeg you had learned from the chapter 1. If you get stuck , you can look into AI tools but don’t overuse them.

Chapter 1 cheatsheet

Mon, 06 Jul 2026 12:21:10 +0530

Main commands:

Commands	Short description
ls -l	Lists files in a long format showing permissions, owner, and size.
ls -a	Lists all files, including hidden ones (those starting with a dot).
ls -ld	Lists details of the directory itself rather than its contents.
ls -lh	Lists files in long format with file sizes in human-readable format (KB, MB).
ls -lt	Lists files sorted by modification time, newest first.
ls -ltr	Lists files sorted by modification time in reverse order (oldest first).
ls -R	Lists all files in the current directory and all subdirectories recursively.
pwd	Prints the full path of the current working directory.
cd ..	Moves one level up into the parent directory
cd `dir_name`	Changes the current directory to the specified folder
cd ~	Moves directly to the current user’s home directory.
cd -	Switches back to the previous directory you were in.
cd	Shortcut to return to the home directory.
tree -a	Displays all files and directories in a tree structure, including hidden ones.
tree -d	Displays only directories in the tree structure.
tree -h	Displays the tree structure along with human-readable file sizes.
tree -f	Displays the full path prefix for each file in the tree.
tree -p	Displays the tree structure along with file permissions.
tty	Prints the file name of the terminal connected to standard input.
uptime	Shows how long the system has been running and the current load.
clear	Clears the terminal screen for a fresh workspace.
which `command_name`	Shows the full path of the executable for a command.
whereis `command_name`	Locates the binary, source, and manual page files for a command.
type `command_name`	Explains how a command name would be interpreted (alias, builtin, or file).
uname	Prints the name of the operating system kernel.
uname -a	Prints all available system information in one line.
uname -s	Displays the kernel name.
uname -n	Displays the network node hostname.
uname -r	Displays the kernel release version.
uname -v	Displays the kernel version date and build info.
uname -m	Displays the machine hardware architecture (e.g., x86_64).
uname -p	Displays the processor type or “unknown”.
uname -i	Displays the hardware platform or “unknown”.
uname -o	Displays the operating system name (e.g., GNU/Linux).
lscpu	Displays detailed information about the CPU architecture.
man `cmd_name`	Opens the official manual page for a specific command.
man -k `cmd_name`	Searches the manual descriptions for a specific keyword.
appropos `cmd_name`	Searches the manual pages for a keyword (same as man -k).
`cmd_name --help`	Displays a brief summary of a command’s options and usage.
`cmd_name` -?	An alternative flag used by some programs to show help.
ls -l /usr/share/doc/`cmd_name`	Checks for additional offline documentation files for a program.