🌿💻 The Packets Garden

Linux Upskill Challenge: Day 4 - Installing software, exploring the file structure

🌱 🪴 ⏱️ 9 min read

Introduction

This is the Day 4 Journal on my Linux Upskill Challenge , yes, this is the lesson when you get in deep with the Linux File System, I also learned about how to install packages in Ubuntu Linux with APT.

Table of Contents

Installing packages in Ubuntu Linux

  • Think of packages like programs or applications (apps) that you install on your phone.
  • Like the “App Store” or the “Market” on your phone, in Linux we call them Package Managers.
  • One of the most popular (if not the most used) package managers in Ubuntu (and other Linux distributions based on Debian) is apt.
  • APT stands for “Advanced Package Tool” and is used to install, update, and manage software packages.
  • For example, to install a package, you can use the command: 
    sudo apt install <package-name>
  • To update the list of available packages and their versions, run: 
    sudo apt update
  • And to upgrade all installed packages to their latest versions: 
    sudo apt upgrade
  • If you know a keyword or part of the description of a package, you can search for it using the apt search command. For example:
apt search "midnight commander"
  • This will display a list of packages matching the search term along with a brief description of each:
mc/noble-updates,now 3:4.8.30-1ubuntu0.1 arm64 [installed]
  Midnight Commander - a powerful file manager
  • Here we can see mc is the package name for the Midnight Commander package (application).
  • To install the package with apt you need to use sudo, unless you’re already logged in as root.
sudo apt install mc
  • Package managers like apt make it easy to handle dependencies and ensure your system stays up-to-date.
  • There are other package managers available for Debian-based Linux distributions.
  • For Red Hat-based Linux distributions, the equivalent of apt is yum. (but that’s a completely different story! 🙂)

Now that we’ve installed Midnight Commander, we can use its retro interface to easily navigate the Linux file system.

The Linux File System

  • The Linux operating system has a standard file system structure. At first, it might seem a bit intimidating—especially if you’re only familiar with Windows, where you have the C: drive, D: drive, and various folders within each. With Linux, it’s a totally different beast.
  • The Filesystem Hierarchy Standard (FHS) defines the structure of file systems on Linux and other UNIX-like operating systems. However, Linux file systems also contain some directories that aren’t yet defined by the standard.
  • If you want to read the official manual of the file system hierarchy, type man hier

/ ⇒ (La Raiz 🫚) The Root Directory

  • Everything on your Linux system is located under the / directory, also called the root directory. (Don’t confuse it with the /root directory.)
  • In Linux you don’t have drive letters like C: or D:. Everything is under /, even if you have different physical drives and partitions— all of them will be under /.

/boot ⇒ 🥾 Boot files

  • Contains all the files needed to boot the system, including the currently installed Linux kernels and their supporting files.
  • The GRUB bootloader’s files are stored here as well.
  • It is better not to mess with this directory!

/etc ⇒ ⚙️ Configuration Files

  • Key configuration files are stored here, and in subdirectories inside.
  • Most of the files here are simple text files.
  • Some interesting files under /etc:
    • /etc/passwd: contains basic information about each user account (like username, UID, default shell, etc.). Passwords are stored in another file.
    • /etc/ssh/sshd_config: this is the configuration file for the SSH daemon (sshd), which acts as the server for the SSH connection. (The client is on your computer! 💻)

/home ⇒ 🏠 User Home Folders

  • Each user in the system will have a folder inside /home (for example /home/carlos, /home/ubuntu).
  • Inside each folder we have user data files, user-specific configuration files, and folders. Many of them are hidden (use ls -la to list them).
  • Each user can only write in their own home folder.
  • Example files and folders found in a home folder: .bashrc, .profile, .ssh/, .config

/root ⇒ ⛪ The root home directory

  • Instead of being inside /home, the root user has their own home directory in /root.

/bin ⇒ Essential binaries 🧱

  • The /bin directory contains all the essential system binaries that Linux needs to function — even when it boots into a special recovery state called single-user mode (you can think of it like Safe Mode in Windows).
  • It contains important core command-line tools that must be available even if no other filesystems are mounted yet — such as ls, cp, mv, and the bash shell.
  • It traditionally has two sibling directories: /sbin (for essential system binaries for administrators) and /usr/bin (for general user binaries that are not critical for boot).

/sbin ⇒ System administration binaries 💾

  • The /sbin directory contains essential system administration binaries used for system booting, repairing, or managing services — like fsck, reboot, and ifconfig.
  • These tools are generally intended for the root user or administrators, and may not be in a regular user’s $PATH.

/usr ⇒ 🧰 user-space programs and tools

  • It contains applications and files used by users, as opposed to the system itself.
  • These files and folders are meant to be read-only for regular users, unless you’re installing something manually into /usr/local.
  • These files are installed and managed by the package manager (apt, dnf, yum, etc.).
  • In some distros (especially immutable or container-focused ones like Fedora Silverblue, Alpine, or embedded systems), /usr is even mounted read-only at the filesystem level to improve security and stability.
  • /usr/bin, /usr/lib, /usr/share, and /usr/local are examples of directories inside /usr.

/usr/bin ⇒ 🛠️ main executables for users and apps

  • The /usr/bin directory contains most user-level commands and applications that are not essential for booting or single-user mode.
  • It’s often much larger than /bin and includes tools like git, nano, python, gcc, etc.

NOTE

⚠️ Modern Linux systems often merge /bin and /usr/bin using symbolic links. So the physical separation may no longer exist — but conceptually, this is still true.

/usr/lib ⇒ 📚 shared libraries for installed programs

  • Contains the libraries for the non-essential user-level binaries located in /usr/bin.

/usr/local ⇒ 🧪 custom software installed manually

  • Locally compiled programs not managed by the package manager.

/var ⇒ 📝 logs and variables

  • /var stands for “variable” — it contains files that change frequently, like logs and temporary data.
  • It is the writable counterpart to the /usr directory, which must be read-only in normal operation.
  • It stores system logs, like authentication attempts and errors, usually inside /var/log.
  • It also holds spools and queues — like for print jobs, mail, or cron jobs.
  • If a system is acting weird or you’re running out of disk space, /var is often the first place to check.

/var/log ⇒ 📂 system and service logs

  • This is the folder where Linux keeps log files from the system and various services.
  • Most of the files here are simple text files.
  • Some interesting files under /var/log are:
    • /var/log/auth.log: Captures all authentication events — like login attempts, sudo usage, and SSH access.
    • /var/log/syslog: General system activity log, useful for debugging services and applications.
    • /var/log/kern.log: Messages from the Linux kernel, helpful when troubleshooting hardware or low-level issues.
    • /var/log/dpkg.log: Logs of all package installations and updates (on Debian/Ubuntu systems).
    • /var/log/boot.log: Records messages during the system boot process, helpful for startup issues.

/tmp ⇒ 🧊 temporary files for programs

  • /tmp is used to store temporary files created by programs, scripts, or the system itself.
  • The data here is not meant to be permanent — it’s usually deleted on reboot or after a certain time.
  • Applications use it for things like installers, locks, or temp caches while they run.
  • You can manually delete files here to free up space, but be careful not to remove in-use files.

/dev ⇒ 🔌 devices as files

  • /dev contains device files that represent your hardware (like disks, USBs, and terminals).
  • Linux treats devices like files, so you can interact with them via commands (e.g., /dev/sda, /dev/null).
  • It includes both physical devices and virtual ones (like /dev/random, /dev/tty).
  • Device files are managed by the udev system and updated automatically as devices are added or removed.

/proc ⇒ 🧠 system and process info

  • /proc is a virtual filesystem that shows real-time information about running processes and the kernel. Similarly to /dev, it doesn’t contain regular files but virtual representations of system internals.
  • Each process has a folder like /proc/1234 containing its memory, open files, and status.
  • It includes files like /proc/cpuinfo, /proc/meminfo, and /proc/uptime — great for monitoring.
  • These files aren’t stored on disk — they’re generated live by the kernel when you access them.

/sys ⇒ 🛠️ kernel interface to hardware

  • /sys is another virtual filesystem, used to expose and control kernel data structures.
  • It provides detailed info about hardware devices, drivers, and kernel modules.
  • It’s commonly used by tools like udevadm, systemd, or udev to detect and manage hardware.
  • You can even tweak some kernel parameters from here (with caution), usually under /sys/class or /sys/block.

/lib ⇒ 📚 Essential common libraries

  • This folder contains libraries needed by the binaries found in /bin and /sbin.
  • Linux libraries are shared collections of precompiled code that programs can use to perform common tasks.

/media & /mnt ⇒ 💽 mount points for external and manual storage

  • Both /media and /mnt are used as mount points — places where external or additional filesystems are attached to the main system.
  • /media is typically used by the desktop environment or automount system to mount USB drives, SD cards, and external disks automatically (e.g. /media/carlos/USB).
  • /mnt is usually reserved for manual or temporary mounts done by system administrators (e.g. mounting a backup disk or ISO).
  • You can mount a filesystem to either, but by convention: automated → /media, manual → /mnt.

Questions I asked myself 🤔

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