Useful commands for Docker

• Docker is mainly used for run programs on server side.
• Companies customize their OS before use. They don’t require many things like GUI.
• Less program means less RAM used and more security.
  • More features means more chances to hack, more vulnerabilities.
• We use OS to run program. Docker gives us an environment to run our program.

Installing docker-engine

For Redhat OS

• First, setup yum repo

    [docker]
    baseurl = https://yum.dockerproject.org/repo/main/centos/7
    gpgcheck=0 
  

• Then, install docker-engine $ yum install docker-engine

### Start the services of docker $ systemctl restart docker It starts the docker server.

See all the images available in docker

$ docker images The default docker images will show all top level images, their repository and tags, and their size.

Load an image in docker

$ docker load -i ubuntu-14.04.tar

• i - Read from tar archive file, instead of STDIN

It loads an image or repository from a tar archive (even if compressed with gzip, bzip2, or xz) from a file or STDIN. It restores both images and tags.

Docker run reference

• Docker runs processes in isolated containers.
• A container is a process which runs on a host. The host may be local or remote.
• When an operator executes docker run, the container process that runs is isolated in that it has its own file system, its own networking, and its own isolated process tree separate from the host.

Run or start a new OS

$ docker run -it ubuntu:14.04

• The docker run command first creates a writeable container layer over the specified image, and then starts it using the specified command.
• The above example runs a container using the ubuntu:14.04 image. The -it instructs Docker to allocate a pseudo-TTY connected to the container’s stdin; creating an interactive bash shell in the container.

See all the running OSs

$ docker ps

• The docker ps command only shows running containers by default.
• To see all containers, use the -a (or --all) flag:

$ docker ps -a

Come out from docker OS console

exit

From shell of docker OS, for coming out without exiting container

press ctrl + p + q

From terminal of base system, to run a command in docker OS

$ docker exec mycontainer ifconfig

• mycontainer is the name of container.
• The docker exec command runs a new command in a running container.

Usually run docker using this command

$ docker run –dit ubuntu:14.04

• i - interactive
• t - terminal
• d - detach

Stop all running OSs

$ docker ps -q //shows id of every running OS 
$ docker stop  $(docker ps -q) 

Permanently remove a container

$ docker rm id

Permanently Remove all the stopped containers

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

• This command will delete all stopped containers.
• The command docker ps -a -q will return all existing container IDs and pass them to the rm command which will delete them.
• Any running containers will not be deleted.

Remove containers while running (forcefully)

$ docker rm -f $(docker ps -a -q)

Giving docker OS a name when starting

• By default, docker gives unique name to every container with a unique id.
• We can also give a name to container using following command - $ docker run -it --name adarsh centos:latest

Copy a file in container

$ docker cp /root/form.txt myconatiner:/ This command will copy a file form.txt from the base system to the specified container.

Download docker images

docker hub - All the available docker images can be downloaded from this URL.

Check different versions of OS that are available

$ docker search ubuntu //search
$ docker pull ubuntu:17.10 //downlaod required version 

Docker Storage

Basic Storage types

1. Empheral disk (temporary) – OS removal will remove data (like windows C drive)
2. Persistent disk (permanent) - OS removal will not erase data (like windows D drive)
   • -v gives persistent storage. OS removal will not remove data.

Docker volume manager

Docker by default takes space from / drive of host system to store data. Overall / drive amount of storage docker can use.

Give separate space to a docker container

• Make a partition, format it and mount in base system. Let the partition created is mypart
• Then, run following command $ docker run –it -v /mypart:/data centos
  • mypart is a partition in base system and data is the folder where docker will store it’s data.
  • v - volume

Attaching dvd to a container

$ docker run –it –v /run/media/root/RHEL-7.3\ Server.. centos This command will attach a RHEL to the container.

Copy content from a folder of base system to /data in docker centos

$ docker run –it -v /folder_name:/data centos