In previous article I had written about the Linux Container archtecture and hereby, I am letting you know on how docker as a management interface could be used as a command line.
Ensure that the docker package is installed on your system else install.
#yum install docker
After you successfully installed the application, use the usual system ctl commands to start docker and to make it run automatically at boot time.
# systemctl start docker.service
# systemctl enable docker.service
Search for an existing image which you are looking for, the command searches the Docker.io Index which is currently the main public registry for sharing repository images where few of them are marked as trusted which means officially checked.
# docker search centos
NAME DESCRIPTION STARS OFFICIAL TRUSTED
centos The official build of CentOS. 463 [OK]
#
To download a selected image from the remote registry to your local machine pull repository_name/image_name
# docker pull centos
Pulling repository centos
70214e5d0a90: Download complete
5a1ebaa356ff: Download complete
68eb857ffb51: Download complete
511136ea3c5a: Download complete
34e94e67e63a: Download complete
#
Listing the images
# docker images
REPOSITORY TAG IMAGE ID CREATED VIRTUAL SIZE
centos centos5 5a1ebaa356ff 2 weeks ago 484 MB
centos centos7 70214e5d0a90 2 weeks ago 224 MB
centos latest 70214e5d0a90 2 weeks ago 224 MB
centos centos6 68eb857ffb51 2 weeks ago 212.7 MB
#
To remove one or more images from your system,
#docker rmi image_name
Managing Containers
To creating a new container, replace the given container name and specify the image on top of which will the container run. The docker run command lets you say which command to run in a container. Once the container is running, you can manage [ start/stop/restart] accordingly. you could also remove if no longer needed.
The command that you pass on the docker run will see to it that the command runs inside the container as its running environment, hence very little can be seen from the host system.
# docker run --rm --name=dockertest centos ip addr show
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 1500 qdisc noqueue state UNKNOWN
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
inet 127.0.0.1/8 scope host lo
valid_lft forever preferred_lft forever
inet6 ::1/128 scope host
valid_lft forever preferred_lft forever
7: eth0: <NO-CARRIER,BROADCAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state DOWN qlen 1000
link/ether 4a:69:d0:e6:b7:2e brd ff:ff:ff:ff:ff:ff
inet 172.17.0.3/16 scope global eth0
valid_lft forever preferred_lft forever
inet6 fe80::4869:d0ff:fee6:b72e/64 scope link tentative
valid_lft forever preferred_lft forever
#
If you want to make a directory from the host available to the container, map network ports from the container to the host which can be done by docker run command line.
# mkdir -p /docker/centos7
# echo "Docker testing" >/docker/centos7/dockertest.txt
#
# docker run -d -p 8080:6000 --name="dockerwebserver" -w /docker -v /docker/centos7:/docker centos /bin/python -m SimpleHTTPServer 6000
acbc99f8b64b8f3472a6740a2d22ba10ab42ff2615c6adda08ca52236293e136
#
where,
Detach (-d) the container so it runs in the background
Map (-p) TCP port 6000 on the container to port 8080 on the host
Map Working directory(-w /docker) in the container when the command runs.
Map directory from the host (-v /docker/centos7) to the container
HTTPserver module(-m) with /bin/python command.
# netstat -tupln | grep 8080
tcp6 0 0 :::8080 :::* LISTEN 2006/docker
#
To execute commands inside of a running container, you need to connect to it through a command-line interface. T he docker attach command is not suitable for this, since it only lets you observe the standard output of the application currently running in the container. Instead, use the nsenter command to enter the container namespace. T his command requires the ID of the container as it appears on the host system.
# docker ps -a
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
acbc99f8b64b centos:centos7 /bin/python -m Simpl 11 minutes ago Up 11 minutes 0.0.0.0:8080->6000/tcp dockerwebserver
#
# docker inspect -f {{.State.Pid}} acbc99f8b64b
4526
#
# nsenter -m -u -n -i -p -t 4526 /bin/sh
sh-4.2# cat /etc/centos-release
CentOS Linux release 7.0.1406 (Core)
sh-4.2#
sh-4.2# ps -ef
UID PID PPID C STIME TTY TIME CMD
root 1 0 0 13:35 ? 00:00:00 /bin/python -m SimpleHTTPServer 6000
root 6 0 0 13:49 ? 00:00:00 /bin/sh
root 9 6 0 13:50 ? 00:00:00 ps -ef
sh-4.2#
sh-4.2# uptime
13:50:33 up 2:16, 0 users, load average: 0.00, 0.01, 0.05
sh-4.2#
sh-4.2#
sh-4.2# free -m
total used free shared buffers cached
Mem: 994 318 676 6 2 123
-/+ buffers/cache: 192 802
Swap: 1023 0 1023
sh-4.2#
sh-4.2# df -h
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/docker-253:3-3148627-acbc99f8b64b8f3472a6740a2d22ba10ab42ff2615c6adda08ca52236293e136 9.8G 280M 9.0G 3% /
tmpfs 498M 0 498M 0% /dev
shm 64M 0 64M 0% /dev/shm
/dev/mapper/VolGroup-varlv 6.0G 1.5G 4.6G 25% /etc/hosts
/dev/mapper/VolGroup-rootlv 4.9G 102M 4.8G 3% /docker
tmpfs 498M 0 498M 0% /proc/kcore
sh-4.2#
sh-4.2#
sh-4.2#exit
List/stop/start/restart/Monitoring the containers
# docker ps
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
acbc99f8b64b centos:centos7 /bin/python -m Simpl 20 minutes ago Up 20 minutes 0.0.0.0:8080->6000/tcp dockerwebserver
#
# docker stop dockerwebserver
dockerwebserver
#
# docker ps
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
#
# docker start dockerwebserver
dockerwebserver
#
# docker ps
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
acbc99f8b64b centos:centos7 /bin/python -m Simpl 22 minutes ago Up 2 seconds 0.0.0.0:8080->6000/tcp dockerwebserver
#
# docker restart dockerwebserver
dockerwebserver
#
# docker ps
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
acbc99f8b64b centos:centos7 /bin/python -m Simpl 22 minutes ago Up 3 seconds 0.0.0.0:8080->6000/tcp dockerwebserver
#
Commit containers
To create a new image from changes made in the running container,syntax as below
docker commit container_name [repository_name:tag]
# docker commit dockerwebserver centos:dockerwebserver_V1.0
f7c53eac787979bccc347e08c1f7a6da96daf6a829c5f35165b2675763943cbc
#
# docker images
REPOSITORY TAG IMAGE ID CREATED VIRTUAL SIZE
centos dockerwebserver_V1.0 f7c53eac7879 10 seconds ago 224 MB
centos centos5 5a1ebaa356ff 2 weeks ago 484 MB
centos centos7 70214e5d0a90 2 weeks ago 224 MB
centos latest 70214e5d0a90 2 weeks ago 224 MB
centos centos6 68eb857ffb51 2 weeks ago 212.7 MB
#
View containers
To view an overall information on how Docker is configured on your system
# docker info
Containers: 1
Images: 6
Storage Driver: devicemapper
Pool Name: docker-253:3-3148627-pool
Data file: /var/lib/docker/devicemapper/devicemapper/data
Metadata file: /var/lib/docker/devicemapper/devicemapper/metadata
Data Space Used: 1365.8 Mb
Data Space Total: 102400.0 Mb
Metadata Space Used: 1.4 Mb
Metadata Space Total: 2048.0 Mb
Execution Driver: native-0.2
Kernel Version: 3.10.0-123.el7.x86_64
#
To display a detailed information about an image or a container,
# docker inspect acbc99f8b64b
[{
"ID": "acbc99f8b64b8f3472a6740a2d22ba10ab42ff2615c6adda08ca52236293e136",
"Created": "2014-09-25T12:35:20.804560542Z",
"Path": "/bin/python",
Archive containers/images
Archive files are useful for backing up or restoring containers and images. Note that you can not backup
data volumes this way since they are external to containers.
To export the contents of a container file system as an archive in tar compress format.
# docker ps
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
acbc99f8b64b centos:centos7 /bin/python -m Simpl 46 minutes ago Up 23 minutes 0.0.0.0:8080->6000/tcp dockerwebserver
#
# docker export dockerwebserver > centos-webserver-docker-7.0-x86_68
# tar -cvf centos-webserver-docker-7.0-x86_68.tar centos-webserver-docker-7.0-x86_68
# gzip centos-webserver-docker-7.0-x86_68.tar
# du -sh rhel-server-docker-7.0-21.4-x86_64.tar.gz
Conversely, you can import an content from an URL or an tar archive as below
#docker import <source>
On conclusion, summarizing the docker command reference.
| Docker commands | Descriptions |
| docker version | Find the version number currently installed |
| docker search <name> | Search for existing images |
| docker pull repository_name/image_name | Download a selected image from remote to your local machine |
| docker images | Lists all locally installed image |
| docker push | Copy image or repository to a remote location |
| docker rmi image_name | Remove one or more images from your system |
| docker commit container_name | create a new image from changes made in the running container |
| docker stop container_name | stop the running container gracefully |
| docker kill container_name | stop a container that is not responding |
| docker start container_name | start a previously stopped container |
| docker restart container_name | Restart a running container |
| docker rm container_name | remove a container |
| docker ps | Listing containers |
| docker info | overall information on how Docker is configured on your system |
| docker top container_name | dynamic view of processes currently running inside of a certain container |
| docker export container_name | export the contents of a container file system as an archive in tar compress format |
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