"The following command runs an ubuntu container, attaches interactively to your local command-line session, and runs /bin/bash," reads the official Docker starter guide.

docker run -it ubuntu /bin/bash

Inspecting the Linux virtual machine

docker run -it ubuntu /bin/bash

# List files inside of the Docker container
root@642064598df6:/ ls
# bin   dev  home  lib32  libx32  mnt  proc  run   srv  tmp  var
# boot  etc  lib   lib64  media   opt  root  sbin  sys  usr

# Print the current directory
root@642064598df6:/ pwd
# /

# Exit the instance
root@642064598df6:/ exit
# exit

Behind the scenes

Here's a summary from Docker's docs.

When you run this command, the following happens (assuming you are using the default registry configuration):

• If you don't have the ubuntu image locally, Docker pulls it from your configured registry (as if you had run docker pull ubuntu).
• Docker creates a new container (as if you had run a docker container create command manually).
• Docker allocates a read-write filesystem to the container as its final layer. This allows a running container to create or modify files and directories in its local filesystem.
• Docker creates a network interface to connect the container to the default network, since you did not specify any networking options. This includes assigning an IP address to the container. By default, containers can connect to external networks using the host machine's network connection.
• Docker starts the container and executes /bin/bash. Because the container is running interactively and attached to your terminal (due to the -i and -t flags), you can provide input using your keyboard while the output is logged to your terminal.

When you type exit to terminate the /bin/bash command, the container stops but is not removed. You can start it again or remove it.

Read the Docker overview guide.

Remove the container on exit

If you don't want your container to persist after you exit, you should use the --rm flag.

docker run -it --rm ubuntu /bin/bash

Today I've automated the backup of the configuration, database, and static files of all the websites I manage. Two hours and a half that will save me a lot of time in the coming future, and remove stress when weird things happen. The backup—of six websites in three different servers running Laravel—downloads a copy of the database, the .env files, and the static files (a zip with the contents of the public folder) of each site.

I'll probably open source these scripts in the near future.

One new thing I learned was creating bash functions, like this one.

# create a variable with current date, formatted as yymmdd_HHMMSS
DATE_NOW=$(date '+%y%m%d_%H%M%S') 

# function that zips something and removes it
zip_and_remove() { cd $1 && zip "$2.zip" $2 && rm $2 && cd .. }

# function that downloads a file via ssh then calls the previous one
download_zip_remove() { scp $1 $2/$3 && zip_and_remove $2 $3  }

# a function call
download_zip_remove root@192.168.1.2:/var/www/site.com/folio/.env $DESTINATION $(echo $DATE_NOW)_$SITENAME.env