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Lesson 03 - Finding Files and Links

Estimated time: 60–75 minutes

Module: Module 02 – Linux Filesystem Administration

Prerequisites: - Module 00 – Introduction to Linux - Module 01 – Command Line Fundamentals - Lesson 01 – Linux Filesystem Hierarchy - Lesson 02 – File Permissions and Ownership

Difficulty: Beginner to Intermediate

Overview

As Linux systems grow, they can contain thousands or even millions of files. System administrators need efficient ways to locate files, identify commands, and create links between files and directories.

In this lesson, you will learn how to search for files using a variety of tools, understand the differences between them, and use hard and symbolic links effectively.

Learning Objectives

By the end of this lesson you will be able to:

  • Find files using the find command.
  • Locate files quickly using locate.
  • Identify where commands are stored.
  • Understand hidden files.
  • Explain the difference between hard and symbolic links.
  • Create and remove links safely.

Finding Files with find

The find command searches the filesystem in real time.

Basic syntax:

find <location> <criteria>

Search for a file by name:

find /home -name "notes.txt"

Search for all text files:

find /home -name "*.txt"

Search for directories only:

find . -type d

Search for regular files:

find . -type f

Searching by Size

Find files larger than 100 MB:

find / -size +100M

Find files smaller than 10 KB:

find /home -size -10k

Searching by Modification Time

Find files modified within the last day:

find . -mtime -1

Find files older than 30 days:

find . -mtime +30

Using locate

The locate command searches a pre-built database instead of scanning the filesystem.

Example:

locate ssh_config

Because it uses a database, it is usually much faster than find.

If recently created files do not appear, update the database:

sudo updatedb

Note: locate may not be installed by default on all Linux distributions.

Finding Commands

Linux provides several commands for locating executables and identifying command types.

which

Displays the location of an executable in your PATH.

Example:

which ls

Output:

/usr/bin/ls

whereis

Displays the executable, source files and manual pages (where available).

Example:

whereis ssh

Example output:

ssh: /usr/bin/ssh /usr/share/man/man1/ssh.1.gz

type

Shows how the shell interprets a command.

Example:

type cd

Output:

cd is a shell builtin

Example:

type ls

Output:

ls is /usr/bin/ls

Hidden Files

Hidden files begin with a period (.).

Examples:

.bashrc
.profile
.gitconfig

To display hidden files:

ls -a

To include detailed information:

ls -la

Hidden files are commonly used to store configuration settings.

Understanding Links

Linux supports two types of links:

  • Hard links
  • Symbolic (soft) links

Both provide additional ways to reference files.

Hard Links

A hard link creates another directory entry for the same file.

Create a hard link:

ln notes.txt notes-hardlink.txt

Display the files:

ls -li

Example:

123456 notes.txt
123456 notes-hardlink.txt

Notice both files share the same inode number.

Changes made to either file affect the same underlying data.

  • Shares the same inode
  • Appears as another copy of the file
  • Continues to work if the original filename is deleted
  • Cannot normally link directories
  • Cannot span different filesystems

Symbolic Links

A symbolic link (or soft link) is a shortcut that points to another file or directory.

Create a symbolic link:

ln -s notes.txt notes-link.txt

Display the result:

ls -l

Example:

notes-link.txt -> notes.txt
  • Points to another file
  • Has its own inode
  • Can span filesystems
  • Can point to directories
  • Becomes broken if the original file is removed

Hard Links vs Symbolic Links

Feature Hard Link Symbolic Link
Shares inode ✅ Yes ❌ No
Can cross filesystems ❌ No ✅ Yes
Can link directories ❌ Normally no ✅ Yes
Works if original filename is removed ✅ Yes ❌ No

Removing Links

Remove a symbolic link:

rm notes-link.txt

This removes only the link, not the original file.

The same command removes hard links.

The original file remains until all hard links have been removed.

Best Practices

✔ Use find for accurate, real-time searches.

✔ Use locate when speed is important.

✔ Use which to locate executables.

✔ Use symbolic links for shortcuts.

✔ Verify links using:

ls -l

✔ Be careful when deleting linked files.

Practical Exercise

Task 1 – Find Files

Search your home directory for all Markdown files:

find ~ -name "*.md"

Task 2 – Search by File Type

List all directories in your current location:

find . -type d

Task 3 – Locate a Command

Find the location of the ls command:

which ls

Then run:

whereis ls

Compare the output.

Task 4 – Identify a Shell Built-in

Run:

type cd

Then:

type ls

Explain the difference.

Create a file:

touch original.txt

Create a hard link:

ln original.txt hardlink.txt

Display inode numbers:

ls -li

Create a symbolic link:

ln -s original.txt symlink.txt

Display the links:

ls -l

Task 7 – View Hidden Files

Display all files, including hidden files:

ls -la

Identify at least three hidden files in your home directory.

Knowledge Check

  1. What is the difference between find and locate?

  2. Which command locates an executable in your PATH?

  3. What does the type command show?

  4. How do hidden files differ from normal files?

  5. What is a hard link?

  6. What is a symbolic link?

  7. Which type of link continues to work if the original filename is deleted?

  8. Which type of link can point to directories?

Summary

In this lesson you learned:

  • How to locate files using find.
  • How locate performs fast database searches.
  • How to identify the location and type of commands.
  • How to display hidden files.
  • The differences between hard and symbolic links.
  • When to use each type of link.

These tools are used daily by Linux administrators to locate files, manage systems efficiently, and simplify access to commonly used resources.

Next Lesson

In Lesson 04 – Filesystem Practical Lab, you will apply everything you have learned in this module by exploring the Linux filesystem, managing permissions, locating files, and creating links in a series of hands-on exercises.