Linux – Practical guide

This page is intended as a compact but useful Linux reference.
All examples are generic and applicable to most Linux distributions
(Debian/Ubuntu, RHEL/Fedora, Arch, Alpine), unless otherwise stated.

1. File structure and navigation

Linux works with a single central tree structure (/), not with drive letters like in Windows.

Important folders:

• / – root of the system
• /home – personal user folders
• /etc – configuration files
• /var – variable data (logs, mail, cache)
• /usr – programs and libraries
• /tmp – temporary files
• /srv – data for services (web, applications)

Navigation is done entirely through the terminal. You always work from a "current directory."

View the current path:

pwd

Show files and folders in the current directory:

ls
ls -lah

Options:

• -l shows a list view
• -a also shows hidden files
• -h makes sizes readable

Navigating through the folder structure:

cd /path/to/folder
cd ..
cd ~

2. Managing files and folders

Files and folders are created, moved, and deleted entirely via commands.

Create a folder:

mkdir folder
mkdir -p a/b/c

-p ensures that missing intermediate directories are also created.

Create an empty file or update the timestamp:

touch file.txt

Copying files or folders:

cp source dest
cp -a source dest

-a (archive) preserves permissions, ownership, and symlinks and is almost always recommended.

Move or rename files or folders:

mv old new

Delete files and folders:

rm file
rm -r folder
rm -rf folder

• -r = recursive
• -f = forced, without confirmation

Use rm -rf only if you know what you are doing.

Create a symbolic link:

ln -s target link

3. Viewing and Reading Files

Various tools are available for viewing files, depending on size and usage.

Show full content:

cat file

Suitable for small files.

Interactive viewing (scrolling and searching):

less file

View the first or last lines:

head -n 20 file
tail -n 20 file

Follow a file live (for example logs):

tail -f /var/log/syslog

4. Searching and filtering text

Linux offers powerful tools for searching and filtering text, especially in logs and configuration files.

Searching for text:

grep "text" file
grep -R "text" folder
grep -Rni "tekst" folder

Options:

• -R = recursive
• -n = line number
• -i = case insensitive

Searching for files by name:

find . -name "*.log"

Search files by modification date:

find . -type f -mtime -7

Extracting columns or fields from text:

awk '{print $1}' file
cut -d: -f1 file

5. Rights and ownership

Linux works with users, groups, and permissions per file.

View rights:

ls -l

Adjust rights:

chmod 644 file
chmod 755 script.sh

Meaning:

• 644 = read/write for owner, read for others
• 755 = executable by everyone

Adjust owner and group:

chown user:group file

View current user and groups:

id
groups

6. Processes and system status

Linux provides extensive insights into active processes and system usage.

Show all processes:

ps aux

Live overview of CPU and memory:

top
htop

View memory usage:

free -h

Disk space per filesystem:

df -h

Size of a folder:

du -sh folder

Terminate a process:

kill PID
kill -9 PID

-9 forces shutdown and should only be used as a last resort.

7. Network and connectivity

Network status and connectivity are essential for servers and applications.

Network interfaces and routes:

ip a
ip r

Listening ports and processes:

ss -tulpn

Test network connection:

ping domain.tld

Executing HTTP requests:

curl https://site.tld
curl -I https://site.tld

Requesting DNS information:

dig domain.tld

Checking if a port is reachable:

nc -vz host 443

8. Services and logs (systemd)

Most modern Linux systems use systemd for service management.

Status and management of services:

systemctl status service
systemctl start service
systemctl stop service
systemctl restart service
systemctl reload service

Services start automatically at boot:

systemctl enable service
systemctl disable service

View logs:

journalctl -u service
journalctl -u service -f
journalctl -p err

9. Package managers

Software is installed via the package manager of the distribution.

Debian / Ubuntu (apt)

apt update
apt install package
apt remove package
apt purge package
apt autoremove

RHEL / Fedora (dnf)

dnf install package
dnf remove package
dnf search package

Arch (pacman)

pacman -S package
pacman -Rns package
pacman -Syu

Alpine (apk)

apk add package
apk del package

10. Git – version control

Git is used for version control of code and configuration.

Base commands:

git init
git clone url
git status
git add .
git commit -m "description"

Synchronizing with a remote:

git pull --rebase
git push

Insight into changes:

git log --oneline --graph
git diff

11. Docker – containers

Docker makes it possible to run applications in isolation.

Managing images in containers:

docker pull image
docker images
docker ps
docker ps -a

Starting and managing a container:

docker run -d -p 8080:80 image
docker logs container
docker exec -it container sh

Docker Compose:

docker compose up -d
docker compose down

12. Basic security

A minimal security baseline is essential, especially on servers.

Firewall (Ubuntu):

ufw status
ufw allow 22
ufw enable

Nftables (low-level firewall):

nft list ruleset

Protection against brute-force attacks:

fail2ban-client status

Automatic security updates:

apt install unattended-upgrades

13. Frequently Used Utilities

• curl, wget – HTTP requests
• jq – Process JSON
• rsync – efficient file synchronization
• tmux – multiple shells in one session
• ncdu – analyze disk space
• lsof – open files and ports
• tcpdump – inspect network traffic