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

If cannot connect to host, enusre no sudo problem: https://askubuntu.com/questions/477551/how-can-i-use-docker-without-sudo
For alma, ensure the env.sh is well loaded otherwise, docker-compose won’t be ble to work

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