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Docker.md

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Quickstart

# Alpine (fast)
docker pull alpine
docker run -it --name=alpine_container alpine

# Ubuntu
echo "from ubuntu:latest" > dockerfile_bash
docker build -t bash_image -f dockerfile_bash .
docker run -it --name=bash_container bash_image
docker restart bash_container
docker exec -it bash_container bash 
docker cp bash_test.sh bash_container:bash_test.sh

docker container ls -a
docker ps -a

su - www-data -s /bin/bash

Tips

docker rm $(docker ps -a -q)
docker rmi $(docker images -q)

Tip: Keep alive

From: https://stackoverflow.com/questions/29599632/container-is-not-running

docker pull debian

docker run -t -d --name my_debian debian
e7672d54b0c2

docker ps -a
CONTAINER ID        IMAGE               COMMAND             CREATED             STATUS              PORTS               NAMES
e7672d54b0c2        debian              "bash"              3 minutes ago       Up 3 minutes                            my_debian

#now you can execute command on the container
docker exec -it my_debian bash
root@e7672d54b0c2:/#

Docker vs chroot

  • mnt namespace provides a root filesystem (this one can be compared to chroot I guess)
  • pid namespace so the process only sees itself and its children
  • network namespace which allows the container to have its dedicated network stack
  • user namespace (quite new) which allows a non root user on a host to be mapped with the root user within the container
  • uts provides dedicated hostname
  • ipc provides dedicated shared memory
  • There are also cgroups (for cpu and memory limits), reduced capabilities, seccomp, selinux/apparmor, and ulimits. The filesystem is also layered, potentially read only, and allowed to be overlaid with volume mounts.

Tips

Check is running

docker inspect returns a JSON object with a lot of info about the container, and in particular whether the container is currently running or not. The -f flag lets you easily extract the bits needed:

  • docker inspect -f "{{.State.Running}}" $CONTAINER_ID
  • docker top

Command

  • Copy: docker cp foo.txt mycontainer:/foo.txt
  • List: docker ps -a

Stop

docker stop $(docker ps -a -q)

Run

From: https://docs.docker.com/engine/reference/commandline/run/

  • -i : read from stdin
  • -t : prompt to terminal
  • -e VAR=value : set an environment variable before invoking the command
  • -d : run in detached mode
  • --name=toto : set the name of container to toto
  • --rm : clean up directory at leave
  • --user , -u Username or UID (format: <name|uid>[:<group|gid>])
  • -v [host_src:]docker_dest : volume mount bind
  • -w [pwd] : set working directory

Location

  • var/lib/docker
    • containers
    • image
    • volume