Chapter 3

Now that you can run commands, let’s go sightseeing inside Linux. We’ll explore files, directories, and the weird but powerful concept of links.

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📂 Listing Files with ls

The ls command shows files and directories.

Basic usage:

ls

Useful options:

ls -l     # long listing (permissions, size, owner, date)
ls -a     # show hidden files (those starting with .)
ls -lh    # human-readable sizes
ls -lt    # sort by modification time (newest first)
ls -R     # list recursively into subdirectories

💡 Combine options → ls -lha shows everything in a readable way.

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🧾 What’s This File? (file)

Linux doesn’t rely on extensions like .txt or .exe. To know what something is:

file /bin/ls

Output example:

/bin/ls: ELF 64-bit LSB executable

It tells you if it’s a binary, script, image, text file, etc.

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📖 Viewing Files with less

Open a file to scroll through:

less /etc/passwd

Controls:

• ↑ ↓ → move line by line

• PgUp / PgDn → scroll pages

• /word → search forward

• ?word → search backward

• n → next match, N → previous

• q → quit

💡 less doesn’t load the whole file at once → perfect for giant logs.

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🗂️ Key Linux Directories

Linux follows the Filesystem Hierarchy Standard (FHS). Some key spots:

• / → root of everything

• /bin → essential binaries (like ls, cat, cp)

• /usr/bin → user applications (editors, compilers, etc.)

• /etc → system configuration files

• /home → user directories (/home/you)

• /var → variable data (logs, spool, caches)

• /tmp → temporary files

• /lib and /usr/lib → libraries programs depend on

• /dev → device files (disks, terminals, etc.)

• /proc → virtual system info (kernel, processes)

Run:

ls /bin /etc /usr /var

to see how different they look.

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🔗 Links: Hard vs Symbolic

Linux lets you make multiple names for the same file.

Hard Links

• A hard link is another directory entry pointing to the same file data.

• Both names are equal — delete one, the data still exists until all are gone.

ln original.txt hardlink.txt

Symbolic (Soft) Links

• A symlink is a shortcut that points to another file.

• If the target disappears, the symlink breaks.

ln -s /lib/libc-2.6.so libc.so.6

Example from a real system:

lrwxrwxrwx 1 root root 11 2007-08-11 07:34 libc.so.6 -> libc-2.6.so

Here:

• l at the start means “link”

• libc.so.6 is the symlink

• It points to → libc-2.6.so

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🏋️ Exercises

1. List everything in /etc with details:

   ls -lha /etc

2. Use file to check:

   file /bin/bash
   file /etc/passwd

3. Open /etc/passwd with less → search for your username.

4. Explore directories:

   ls /bin
   ls /usr/bin
   ls /var/log

5. Create a hard link and symbolic link to a file:

   echo "hello" > test.txt
   ln test.txt hard.txt
   ln -s test.txt soft.txt
   ls -l

   Now delete test.txt and see what happens to hard.txt vs soft.txt.

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Date Learned: 15 August 2025

Source: The Linux Command Line, Chapter 3