Docker Cheat Sheet for Sysadmins
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Docker Cheat Sheet for Sysadmins

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Docker Cheat Sheet will have most of the useful docker commands with all available options for sysadmins and developers in day to day activity.

If anyone would like to contribute in this docker cheat sheet sent me an email with contents to

Docker Cheat sheet
Docker Cheatsheet

Creating a dedicated mount point for docker

It’s good to start with a dedicated mount point for docker by creating a logical volume.

# fdisk /dev/sdb
# pvcreate /dev/sdb1
# vgcreate vg_docker /dev/sdb1
# lvcreate -n lv_docker -l 100%FREE vg_docker
# mkfs.xfs /dev/mapper/vg_docker/lv_docker
# mount /dev/mapper/vg_docker/lv_docker /var/lib/docker

Extending docker mount point

In case if we need more space under /var/lib/docker, add a new disk and extend the existing VG, LV, at last, grow the XFS mount point.

# fdisk /dev/sdc
# pvcreate /dev/sdc1
# vgextend vg_docker /dev/sdc1
# lvextend -l +100%FREE /dev/mapper/vg_docker/lv_docker
# xfs_growfs /var/lib/docker

Enabling Docker Repo, Installing and starting Docker

# cd /etc/yum.repos.d/; 
# curl -O
# yum repolist
# yum install yum-utils device-mapper-persistent-data lvm2 -y
# yum install docker-ce docker-ce-cli -y
# sudo systemctl start docker
# sudo systemctl enable docker

Granting Normal user to run docker commands

# sudo usermod -aG docker babinlonston

Verifying Docker Version

# docker -v
# docker info
# docker system info

Searching, Pulling, listing and Removing Docker images.

# docker search nginx
# docker pull nginx
# docker pull nginx:1.14
# docker images
# docker rmi nginx
# docker rmi nginx:1.14

Starting a container, with tag

# docker run nginx
# docker run -d nginx:1.14
# docker run -d --name web_server nginx
# docker run -d --name web_server1 nginx:1.14

Launching a container and login into it

# docker run --name web_server2 -it nginx /bin/bash

Listing all running and stopped containers

# docker ps
# docker ps -a

Accessing shell of a running Container after launch

# docker exec -it web_server /bin/bash

Executing a command on a running Container

# docker exec web_server cat /etc/hosts
# docker exec web_server env

Restarting, Stopping and Deleting

# docker restart web_server
# docker stop web_server1 nginx
# docker stop $(docker ps -aq)
# docker rm web_server1
# docker rm $(docker ps -aq)

Reference: How to manage Docker containers

Stop or kill by sending SIGKILL

# docker kill exec web_server2
# docker kill -s SIGKILL exec web_server2

Launch and expose the network.

# docker run --name web_server3 -p 8080:80 -d -it nginx
# docker run -d --name web_server4 -p nginx

Reference: How to connect Docker containers and expose the network

Running Inspect to Know the IP of a Container

# docker inspect web_server
# docker inspect web_server | grep -i -A 1 'IPAddress|ExposedPorts'
# docker inspect -f '{{ .NetworkSettings.IPAddress }}' web_server
# docker inspect -f '{{ .Config.ExposedPorts }}' web_server

Attaching a Volume

# mkdir /mysql_container 
# chown -R 27:27 /mysql_container 
# chcon -t svirt_sandbox_file_t /mysql_container  #temp
# semanage fcontext -a -t svirt_sandbox_file_t '/mysql_container(/.*)?'  #Persistent

# docker run --name mysql-pro-dbsrv -d -v /mysql_container:/var/lib/mysql/ -e MYSQL_ROOT_USER=root -e MYSQL_ROOT_PASSWORD=password123 mysql

Reference: Managing Docker data persistently by attaching a volume

Docker export, import, load and save

# docker export apache > linuxsysadins.local.tar
# docker import - website < linuxsysadins.local.tar 
# docker save -o website_backup.local.tar website
# docker load < website_backup.local.tar

Creating a Docker file and Building image with a Volume

# mkdir /root/linuxsysadmins
# vim /root/linuxsysadmins/Dockerfile

Replace with your required values.

 FROM centos
 MAINTAINER Babin Lonston
 RUN yum update -y && yum install httpd mod_ssl -y
 VOLUME /var/www/html
 ADD linuxsysadmins.local.conf /etc/httpd/conf.d/linuxsysadmins.local.conf
 ADD index.html /var/www/html/index.html
 CMD ["/usr/sbin/httpd", "-D", "FOREGROUND"]
 EXPOSE 80/tcp

Creating a virtual host configuration

# vim linuxsysadmins.local.conf
<VirtualHost *:80>
    ServerAdmin siteadmin@linuxsysadmins.local
    DocumentRoot /var/www/html
    ServerName linuxsysadmins.local
    ServerAlias nixsysadmins.local
    ErrorLog "/var/log/httpd/linuxsysadmins.local-error_log
    CustomLog "/var/log/httpd/linuxsysadmins.local-access_log common

Create an index.html file for Apache

# vim /root/linuxsysadmins/index.html

Append with your content.

<h1>This is Test page for linuxsysadmins.local</h1>

Build an image using docker file. Make sure to use “.” as shown below to build from the current directory.

# docker build  -t linuxsysadmins.local .
# docker images

Pushing images to Docker Hub

Log in to Docker hub using “docker login“, tag the image and push to your repository.

# docker login
# docker tag linuxsysadmins.local babinlonston/linuxsysadmins.local:0.1
# docker images
# docker push babinlonston/linuxsysadmins.local:0.1

Find the changes with an image and running Container

To list out the changed files on a container by comparing with its image

# docker run -d --name webserver nginx
# docker diff webserver
[root@docker ~]# docker diff webserver 
 C /var
 C /var/cache
 C /var/cache/nginx
 A /var/cache/nginx/client_temp
 A /var/cache/nginx/fastcgi_temp
 A /var/cache/nginx/proxy_temp
 A /var/cache/nginx/scgi_temp
 A /var/cache/nginx/uwsgi_temp
 C /run
 A /run/

Creating and mounting Volumes

Creating a Volume on Container

# docker run -d -v /var/www/html --name websrv linuxsysadmins.local

Mounting a local directory inside a Container

# docker run -d --name webserver_hosted -v /var/www/html:/var/www/html linuxsysadmins.local

Creating, Inspecting, Removing unused and Deleting a Volume

To create a volume for different applications, inspecting a volume, remove a local unused volume.

# docker volume ls
# docker volume create web_apps
# docker volume inspect web_apps
# docker volume prune
# docker volume rm web_apps1
[root@docker ~]# docker volume inspect web_apps
         "CreatedAt": "2019-07-03T00:47:33+05:30",
         "Driver": "local",
         "Labels": {},
         "Mountpoint": "/var/lib/docker/volumes/web_apps/_data",
         "Name": "web_apps",
         "Options": {},
         "Scope": "local"

Create Docker Network

Creating a network for communicating between container and host, this will be a bridge by default. Use Inspect to know more information about the network.

# docker network create --subnet --gateway web_apps_net
# docker network inspect web_apps_net
# docker network ls
[root@docker ~]# docker network inspect web_apps_net 
         "Name": "web_apps_net",
         "Id": "f2cca056137040b8e05d6e70cd4287a056356642e49ee9f264ef06b6b637f35e",
         "Created": "2019-07-03T21:54:30.35434543+05:30",
         "Scope": "local",
         "Driver": "bridge",
         "EnableIPv6": false,
         "IPAM": {
             "Driver": "default",
             "Options": {},
             "Config": [
                     "Subnet": "",
                     "Gateway": ""
         "Internal": false,
         "Attachable": false,
         "Ingress": false,
         "ConfigFrom": {
             "Network": ""
         "ConfigOnly": false,
         "Containers": {},
         "Options": {},
         "Labels": {}
 [root@docker ~]#

Assigning a static IP address to a Container

Start a container from nginx image by assigning a static IP address and verify the same.

# docker run -d --name web_apps_srv1 --network web_apps_net --ip nginx
# docker inspect web_apps_srv1
# docker inspect -f '{{ .NetworkSettings.IPAddress }}' web_apps_srv1
# curl

Verify using curl by pointing to Nginx server’s static IP.

[root@docker ~]# curl
<!DOCTYPE html>
<title>Welcome to nginx!</title>
    body {
        width: 35em;
        margin: 0 auto;
        font-family: Tahoma, Verdana, Arial, sans-serif;
<h1>Welcome to nginx!</h1>
<p>If you see this page, the nginx web server is successfully installed and
working. Further configuration is required.</p>

<p>For online documentation and support please refer to
<a href=""></a>.<br/>
Commercial support is available at
<a href=""></a>.</p>

<p><em>Thank you for using nginx.</em></p>
[root@docker ~]#

Disconnecting and Reconnecting Network from a Container

To disconnect a network from a container use “disconnect network container“. Once disconnected, we need to specify the IP again while reconnecting the network to the Container. Finally, inspect the IP once connected.

# docker network disconnect web_apps_net web_apps_srv1
# docker inspect web_apps_srv1
# docker network connect web_apps_net web_apps_srv1 --ip
# docker inspect web_apps_srv1

Removing a Network and Prune

To remove a network using “network rm“. To remove all unused network those are not attached to any container will be removed while we run “network prune“.

# docker inspect web_apps_net
# docker network rm web_apps_net
# docker network ls
# docker network prune

Click Next to continue reading

Docker Cheat Sheet for Sysadmins 1

About Post Author

Babin Lonston

Overall 14+ Years of experience in the IT field, currently working as a Senior Linux administration with Virtualization & Cloud. Being numismatist for a long time.
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