docker_tricks.md

Docker Tricks and Commands

Container Logs and Debugging

Capture logs from crashing container Start Docker Container Locally

docker exec -it docker ps -aq | head -1 tail -f /app/logs/USER-user-service.txt

• don't quote command

Look at dead container's filesystems docker inspect | grep volume Locally on Mac, you won't be able to access /var/lib/docker. You need to use screens command:

screen ~/Library/Containers/com.docker.docker/Data/vms/0/tty cd /var/lib/docker/volumes ls -ltr | tail Use ctrl-a d to detach, 'screen -S -X quit' to stop screen process

Container Management

Running BusyBox Containers

BusyBox containers exit immediately because they don't have a long-running process by default.

Problem: Container exits even with -d flag

docker run -p 8080:8080 -d --name box-1 busybox  # This exits immediately

Solutions:

# Keep container running with sleep
docker run -p 8080:8080 -d --name box-1 busybox sleep infinity

# Interactive mode with pseudo-TTY
docker run -p 8080:8080 -d -it --name box-2 busybox

# Keep running with tail command
docker run -p 8080:8080 -d --name box-3 busybox tail -f /dev/null

Docker Exec Commands

Execute commands inside running containers:

# Interactive shell session
docker exec -it container_name /bin/sh

# For containers with bash
docker exec -it container_name /bin/bash

# Run single command
docker exec container_name ls -la

# Run command and see output
docker exec container_name ps aux

Flags explained:

• -i (interactive): Keep STDIN open
• -t (tty): Allocate a pseudo-TTY
• -it together: Interactive terminal session

Container Cleanup

TO delete the exited containers docker rm $(docker ps -aq --filter "name=box-1" --filter "status=exited")