This guide focuses on the commands you will actually use, starting simple and gradually adding power — without edge cases or weird tricks.

You don’t need to memorize Docker.
You just need to understand why you run each command.

---

1️⃣ Listing containers: docker ps vs docker ps -a

docker ps
docker ps -a

What they do

• docker ps
  → Shows only running containers
• docker ps -a
  → Shows all containers
  (running, stopped, crashed, exited)

What does -a mean?

• -a = all
• Without -a, Docker hides containers that are not running

When do you use docker ps -a?

Use it when:

• A container stopped immediately
• Something failed to start
• You want to restart an old container
• You want to remove stopped containers

👉 Rule of thumb
If something “disappeared”, run:

docker ps -a

---

2️⃣ Running a container interactively: docker run -it

docker run -it ubuntu:24.04 bash

What this command does

• Starts a new Ubuntu container
• Opens a shell inside it
• Connects your keyboard and screen to the container

What does -it mean?

-it is actually two flags combined:

Flag	Meaning	Why it matters
-i	interactive	Keeps STDIN open
-t	terminal (TTY)	Gives you a proper shell

When do you use -it?

Use -it when you want to:

• Explore a container manually
• Debug something interactively
• Run shell commands yourself
• Use tools like bash, sh, python, psql

When do you not use -it?

Don’t use it when:

• Running servers (nginx, MySQL, APIs)
• Running background services
• Using -d (detached mode)

👉 Mental model

• -it = “I want to talk to the container”
• no -it = “Just run it, I don’t need a terminal”

---

3️⃣ Stopping, starting, restarting containers

docker stop CONTAINER
docker start CONTAINER
docker restart CONTAINER

Why would I stop a container?

You stop a container when:

• You want to free CPU / memory
• You’re changing configuration
• You don’t need it running right now
• You want a clean shutdown

Example:

docker stop mysql

This sends a graceful stop signal (like pressing Ctrl-C).

---

Why would I start a container?

You start a container when:

• It already exists
• You want to reuse the same container
• It has data you don’t want to lose

Example:

docker start mysql

👉 Starting is faster than re-creating.

---

Why restart?

You restart when:

• Config or environment changed
• The app is misbehaving
• You want a clean reboot

Example:

docker restart api

Equivalent to:

docker stop api
docker start api

---

Important concept (very important)

• Containers are not deleted when stopped
• Stopped containers still exist
• You can inspect, restart, or remove them later

To delete a container:

docker rm CONTAINER

---

4️⃣ Putting it together — real beginner workflow

Example: testing Ubuntu quickly

docker run -it ubuntu:24.04 bash

→ play around → exit with exit

Now check:

docker ps -a

Restart it:

docker start CONTAINER_ID
docker exec -it CONTAINER_ID bash

Clean up:

docker rm CONTAINER_ID

---

5️⃣ Quick flag reference (only common ones)

Flag	Meaning	Typical use
-a	all	show stopped containers
-it	interactive terminal	shells, debugging
-d	detached	servers
--name	readable name	sanity
-p	port mapping	web apps
-v	volume / mount	data & code

---

Final mental model (remember this)

• Images = templates
• Containers = running (or stopped) instances
• run = create + start
• stop/start = pause & resume
• rm = delete forever

If you want, next we can:

• Rewrite this as a printable one-page PDF
• Add a “Docker for Python devs” version
• Add a MySQL / Postgres focused section
• Or continue into Docker Compose, same style

The imagea are pretty big, compared to the text. Make them smaller! Also add some tips and tricks. For example, if a container needs to save something to a disk, it must attach a volume! Else the data disappears when the container stops! Also mention networks and ports but use common examples How can a container access the network for example And how can the container access MySQL And the host disk

Below is a revised WordPress-ready article with:

• ✅ Smaller, fewer images (one per major section, placed after headers)
• ✅ Clear explanations of flags (-a, -it)
• ✅ Practical tips & tricks beginners actually need
• ✅ Common examples for volumes, ports, networks
• ❌ No corner cases, no exotic flags

---

🐳 Docker Cheat Sheet — Beginner to Practical (Explained Clearly)

This guide teaches Docker the way you actually use it:

• Start simple
• Explain every flag
• Show why you’d do things
• Avoid clever-but-useless tricks

---

1️⃣ Listing containers: docker ps vs docker ps -a

docker ps
docker ps -a

What they do

• docker ps
  → Shows only running containers
• docker ps -a
  → Shows all containers
  (running, stopped, crashed, exited)

What does -a mean?

• -a = all
• Without it, Docker hides stopped containers

When do you need docker ps -a?

Use it when:

• A container stopped immediately
• Something crashed
• You want to restart or remove an old container

👉 Beginner rule

If something “vanished”, always run:

docker ps -a

---

2️⃣ Interactive containers: docker run -it

docker run -it ubuntu:24.04 bash

What this does

• Starts a new Ubuntu container
• Opens a shell inside it
• Connects your keyboard & screen

What does -it mean?

It’s two flags combined:

Flag	Meaning	Why
-i	interactive	Keep input open
-t	terminal	Proper shell (TTY)

When should I use -it?

Use -it when you want to:

• Explore a container
• Debug manually
• Run commands interactively
• Use bash, sh, python, psql

When should I NOT use it?

Don’t use -it for:

• Web servers
• Databases
• Background services

👉 Mental shortcut

• -it = “I want to talk to the container”
• no -it = “Just run it”

---

3️⃣ Starting, stopping, restarting containers

docker stop CONTAINER
docker start CONTAINER
docker restart CONTAINER

Why stop a container?

You stop a container to:

• Free CPU / RAM
• Shut down cleanly
• Pause something you don’t need right now

docker stop mysql

Docker sends a graceful stop signal (like Ctrl-C).

---

Why start a container?

You start a container when:

• It already exists
• You want to reuse its state
• You don’t want to reconfigure it

docker start mysql

👉 Starting is faster than re-creating.

---

Why restart?

Restart when:

• Config changed
• App misbehaves
• You want a clean reboot

docker restart api

Equivalent to:

docker stop api
docker start api

---

4️⃣ ⚠️ VERY IMPORTANT: Containers do NOT keep data by default

The rule

If a container needs to save data, you MUST attach a volume.

If you don’t:

• Data disappears when the container stops
• Or when it’s removed
• Or when the image is rebuilt

---

Example: database WITHOUT a volume (bad)

docker run -d --name mysql \
  -e MYSQL_ROOT_PASSWORD=secret \
  mysql:8

❌ Database files are lost when container is removed.

---

Example: database WITH a volume (correct)

docker run -d --name mysql \
  -e MYSQL_ROOT_PASSWORD=secret \
  -v mysql_data:/var/lib/mysql \
  mysql:8

✅ Data survives restarts and upgrades.

What is a volume?

• Managed by Docker
• Stored on the host
• Safe place for persistent data

---

5️⃣ Accessing the host disk (bind mounts)

Share a host directory with a container

docker run -it --rm \
  -v "$PWD":/work \
  -w /work \
  python:3.12 bash

What this means

• Your current folder appears inside container as /work
• Changes are reflected both ways

When to use this

• Local development
• Editing code with your editor
• Running tools inside Docker

---

6️⃣ Ports: accessing services from the host

docker run -d --name web \
  -p 8080:80 \
  nginx

What does -p 8080:80 mean?

• Port 8080 on your computer
• Is forwarded to port 80 inside the container

Now visit:

http://localhost:8080

Common ports

Service	Container port
Nginx	80
FastAPI	8000
Flask	5000
MySQL	3306
Postgres	5432

---

7️⃣ Networking: containers talking to each other

Create a network

docker network create appnet

Run MySQL on that network

docker run -d --name mysql \
  --network appnet \
  -e MYSQL_ROOT_PASSWORD=secret \
  -v mysql_data:/var/lib/mysql \
  mysql:8

Run an app that connects to MySQL

docker run -d --name api \
  --network appnet \
  -e DB_HOST=mysql \
  myapi

Key concept

• Containers on the same network can reach each other by name
• No IP addresses needed
• mysql becomes a hostname

---

8️⃣ Quick tips & tricks (gold for beginners)

🧠 Tip 1: Name your containers

--name mysql

Names beat random IDs. Always.

---

🧠 Tip 2: If it stores data → volume

• Databases
• Uploaded files
• Caches you care about

No volume = data loss.

---

🧠 Tip 3: run vs start

• run = create + start (new container)
• start = start existing container

---

🧠 Tip 4: Look before deleting

docker ps -a
docker logs CONTAINER

---

🧠 Tip 5: Clean up safely

docker container prune
docker image prune

---

Final mental model (keep this)

• Images → templates
• Containers → running or stopped instances
• Volumes → persistent data
• Networks → container communication
• Ports → host ↔ container access