Linux Basics & Fundamentals · Mark Thompson Portfolio

Linux Filesystem Hierarchy Overview

The Filesystem Hierarchy organizes everything as files under the root /. Knowing where things live helps with troubleshooting, backups, and automation.

Key Directories

/ – Root of the filesystem
/bin – Essential user binaries
/sbin – System binaries (admin)
/boot – Boot loader & kernel
/etc – System-wide configuration
/home – User home directories
/lib, /lib64 – Shared libraries
/usr – User-space apps & read-mostly data
/var – Variable data (logs, spool, DBs)
/tmp – Temporary files
/opt – Optional third-party software
/dev – Device files
/proc, /sys – Virtual kernel & device info
/mnt, /media – Mount points / removable media

Package Management on Debian-based Systems

Debian/Ubuntu use APT (Advanced Package Tool) to query, install, and update software from repositories defined in /etc/apt/sources.list (and files in /etc/apt/sources.list.d/).

Common APT Commands

sudo apt update            # Refresh package lists
sudo apt upgrade           # Upgrade installed packages
sudo apt install <pkg>    # Install a package
sudo apt remove <pkg>     # Remove (keep configs)
sudo apt purge <pkg>      # Remove incl. configs
apt search <term>         # Search available software

Low-Level: dpkg

dpkg works directly with .deb files and the local package database.

sudo dpkg -i package.deb   # Install a .deb
sudo dpkg -r <name>        # Remove (keep configs)
sudo dpkg -P <name>        # Purge (remove configs)
dpkg -l                    # List installed packages

Managing System Services (systemd)

systemd is the init system & service manager on most modern distros. You interact with it using systemctl and view logs via journalctl.

Common systemctl & journalctl Commands

systemctl status <service>               # Check status
sudo systemctl start|stop|restart <service>
sudo systemctl enable|disable <service>  # Manage autostart
journalctl -u <service>                  # Service logs

Process Management

Processes are running programs; each has a PID and consumes CPU/memory. Use these commands to inspect and control them.

Process Commands

ps aux                      # Snapshot of processes (BSD style)
top                         # Interactive live view
htop                        # Nicer top (if installed)
kill <PID>                  # Terminate by PID
pkill <name>                # Terminate by name
jobs; bg; fg                # Manage shell jobs

System Monitoring and Logging

System Info Commands

uname -a        # Kernel and OS info
hostnamectl     # Hostname and chassis info
lscpu           # CPU details
free -h         # Memory usage

Key Log Files

On Debian/Ubuntu, the most important logs are /var/log/syslog and /var/log/auth.log. The kernel ring buffer is accessible via dmesg.

Conclusion

These fundamentals — filesystem layout, packages, services, processes, and logs — form the day-to-day toolkit for Linux admins. Master them first, then layer on scripting, automation, and security hardening.