Skip to content

Linux introduction navigation

---
title: "Linux Introduction and Basic Navigation"
category: "linux-tutorials"
description: "Introduction to the Linux command line, shell prompt, basic commands like pwd, ls, cd, and understanding the directory structure."
---

# Linux Introduction and Basic Navigation

This tutorial introduces the basic Linux commands needed to use and run programs on the SCRC Linux computers, focusing on navigating the file system.

## The Command Line Interface (Shell)

The Linux machines use a command line interface called a Shell. The Shell is the interface where you enter Linux commands. There are many types of shells; by default, SCRC Linux machines use the BASH shell.

When you log in, the first thing you see is the shell's **command prompt**. This indicates the shell is ready to accept your commands. The prompt might look something like this:

```text
[your_netid@hostname ~ ]$

Your Home Directory

When you log in, you start in your home directory. Every user has a unique home directory, which is the primary location for storing your personal files and data.

Basic Navigation Commands

Here are some fundamental commands for navigating the Linux file system:

Show the present working directory (pwd)

To see the complete name and path of the directory you are currently in (the "present working directory"), use the pwd command:

pwd

Example Output:

/homedir/employees/c/ct27

This output shows the full path to the current directory. In this example, ct27 is the user's home directory, located inside c, inside employees, inside homedir.

Show contents of a directory (ls)

To see a list of the files and sub-directories within the current directory, use the ls command. Using the -l option provides a detailed "long format" listing:

ls -l

Example Output:

total 180
drwxr-xr-x 3 ct27 nobody 4096 Apr  5 2023 mywork
drwxr-xr-x 3 ct27 nobody 4096 Apr  3 2023 archived-work
-rw-r--r-- 1 ct27 nobody    0 Mar 18 2023 prog.sas7bdat
-rw-r--r-- 1 ct27 nobody 1421 Mar 18 2023 prog.sas7bdat.log
  • ls is the command, and -l is an option.
  • Lines starting with d indicate directories (mywork, archived-work).
  • Lines starting with - indicate regular files (prog.sas7bdat, prog.sas7bdat.log).
  • The long format shows permissions, owner (ct27), size (e.g., 1421 bytes), modification date, and name.
  • Using ls without options typically shows only the names of files and directories.

Create a sub-directory (mkdir)

To create a new directory (folder) inside your current directory, use the mkdir (make directory) command, followed by the desired directory name:

mkdir costProject

This creates a new sub-directory named costProject. You can verify its creation using ls -l.

Note: Linux file and directory names are case-sensitive. costProject is different from costproject.

Change Directory (cd)

To move into a different directory, use the cd (change directory) command, followed by the name of the directory you want to enter:

cd costProject

After running this command, your present working directory becomes /homedir/employees/c/ct27/costProject (in this example). You can verify this using pwd.

To move up one level in the directory structure (to the parent directory), use cd ..:

cd ..

The Linux File System Structure

Linux uses a hierarchical file structure, often visualized as an upside-down tree.

  • The top-level directory is called the root directory, represented by a forward slash (/).
  • All other files and directories are located within the root directory or its sub-directories.
  • A file can hold text, data, or a program.
  • A directory (or folder) contains files and other directories (sub-directories).
  • A sub-directory is simply a directory located inside another directory.

Understanding this structure is key to navigating using commands like pwd, ls, and cd.

Useful Tips and Tools

Auto Completion in the Shell

The BASH shell offers tab completion. Start typing a command or filename, and press the Tab key.

  • If the typed portion is unique, the shell will complete the rest of the name.
  • If there are multiple possibilities, pressing Tab a second time will often list them.

Create or Edit a File (nano)

nano is a simple, beginner-friendly text editor available on the command line. To create a new file or open an existing one for editing:

nano my_program.py

nano data_notes.txt

Inside nano, commands are listed at the bottom. The ^ symbol represents the Ctrl key.

  • Ctrl+O: Write Out (Save the file)
  • Ctrl+X: Exit nano

List the Contents of a File (more)

To view the contents of a text file one screen at a time, use the more command:

more my_data.txt
  • Press the Spacebar to advance to the next page.
  • Press q to quit viewing the file and return to the command prompt.

Breaking Out (Ctrl+C)

If a command seems stuck, unresponsive, or you want to cancel the current operation, press Ctrl+C. This usually interrupts the running process and returns you to the command prompt. ```