Launching Containers

# Basic syntax
docker run [OPTIONS] IMAGE [COMMAND]

# Lifecycle on first run
# 1. Local image lookup → download if missing
# 2. Container creation → default or supplied command
# 3. Container ID returned

docker run -d nginx

Frequently-used run flags

Flag examples

# Detached nginx
docker run -d nginx

# Fixed port mapping
docker run -d -p 8080:80 nginx

# Random port mapping
docker run -d -P nginx

# Interactive shell
docker run -it centos:7 bash

# Host volume mount
docker run -it -v /opt:/root centos:7 bash

# Ephemeral container
docker run -d --rm nginx

# Named container
docker run -d --name web nginx

# Custom network
docker network create demo
 docker run -d --net demo nginx

# Environment variable
docker run -it -e GREET=hello centos:7 bash

# Legacy link (still useful for quick tests)
docker run -d --name db postgres:13
 docker run -it --link db:pg centos:7 bash

# Custom hostname
docker run -it -h mybox centos:7 bash

# Full privileges
docker run -it --privileged ubuntu bash

Listing Containers

# Active containers
docker ps

# All containers (running & exited)
docker ps -a

# IDs only
docker ps -q
 docker ps -aq

Start / Stop Lifecylce

# Stop
docker stop web

# Start
docker start web

Removing Containers

# Single container
docker rm web

# Force removal
docker rm -f web

# Bulk cleanup
docker rm -f $(docker ps -aq)

Inspecting Containers

# Full JSON
docker inspect web

# Extract running state
docker inspect -f '{{.State.Running}}' web

File Transfer

# Host → container
docker cp ./data.csv web:/tmp

# Container → host
docker cp web:/var/log/nginx/access.log ./

Accessing a Running Container

1. Preferred: exec

docker exec -it web bash

2. Legacy: attach

docker attach web  # shares the main PID; exit kills container

3. Low-level: nsenter

PID=$(docker inspect -f '{{.State.Pid}}' web)
nsenter --target $PID --mount --uts --ipc --net --pid

4. SSH (when container runs sshd)

ssh root@$(docker inspect -f '{{.NetworkSettings.IPAddress}}' web)