Docker is a software platform that allows you to build, test, and deploy applications quickly. Docker is an operating system for containers. Containers have everything the software needs to run including libraries, system tools, code, and runtime.

What is Docker Privileged Mode?

Docker privileged mode grants a docker container to have all of the root capabilities of a host machine which are not accessible in ordinary containers.

What does the privileged do?

Executing container engines with the — privileged flag tells the engine to launch the container process without any further “security” lockdown.

What are yum-utils?

yum-utils is a collection of tools and programs for managing yum repositories, installing debug packages, source packages, extended information from repositories, and administration.

yum-config-manager --add-repo repository_url

See Docker-in-Docker in action

1. Launch a container and execute it in privileged mode.

docker run -it --name container1 --privileged lwimage:v1

2. Install yum-utils

yum install -y yum-utils

3. Install glibc-all-langpacks package.

dnf install langpacks-en glibc-all-langpacks -y

4. Add repository file

    yum-config-manager \
    --add-repo \
    https://download.docker.com/linux/centos/docker-ce.repo

5. Install docker

yum install docker-ce

dockerd &

docker info

docker ps
docker ps -a

6. Launch a container in containerized docker

docker run -it --name container2 centos:latest

New container “container2” is launched inside the “container1”

Can I Run Docker-in-Docker-in-Docker?

Yes. When you are inside a privileged container, you can always nest one more level:

Description :

The date command writes the current date and time to standard output if called with no flags or with a flag list that begins with a + (plus sign). Otherwise, it sets the current date. Only a root user can change the date and time. The date command prints the usage message on any unrecognized flags or input.

If you follow the date command with a + (plus sign) and a field descriptor, you can control the output of the command. You must precede each field descriptor with a % (percent sign). The system replaces the field descriptor with the specified value. Enter a literal % as %% (two percent signs). The date command copies any other characters to the output without change. The date command always ends the string with a new-line character.

The Linux date command displays or set the system date and time.

Custom Formatting :

-d date arithmetic

Display the time described by the user friendly string.

Date String :

The -s option allows you to operate on a specific date. You can specify the date as a human-readable date string.

Date Formatting :

The output of date can be formatted with a format string that is preceeded by a + sign.

Using date with Other Commands :

Timeout

Print the date, run sleep for 10 seconds but with a timeout of 1 second and than run date again :

Common formats :

ISO 8601 format

-I or — iso-8601 prints the date in ISO 8601 format.

RFC 3339 format

Similarly, — rfc-3339=x prints a date in RFC 3339 format, x being date, sec or ns.

Email format

Then, there is also the so called email format.

UTC format

zenity — progress

Zenity is an open source and a cross-platform application which displays GTK+ Dialog Boxes in command-line.

Description :

Zenity is a Linux command that uses dialog boxes to make shell script more graphical to end-users.

Basic Usage :

When you write scripts, you can use Zenity to create simple dialogs that interact graphically with the user, as follows:

You can create a dialog to obtain information from the user. For example, you can prompt the user to select a date from a calendar dialog, or to select a file from a file selection dialog.

You can create a dialog to provide the user with information. For example, you can use a progress dialog to indicate the current status of an operation, or use a warning message dialog to alert the user.

When the user closes the dialog, Zenity prints the text produced by the dialog to standard output.

Options of Zenity :

1) Message Box :

In its simplest form, zenity can be used to create a message box with a info, warning or error.

Zenity can create four types of message dialog :

Error : Display Error Dialog

Information : Display Info Dialog

Warning : Display Warning Dialog

Question : Display Question Dialog

Questions that can be answered with either yes or no can be asked with the

--question.

2) Entry Dialog :

The text entry dialog supports the following options:

–text=text
Specifies the text that is displayed in the text entry dialog.

–entry-text=text
Specifies the text that is displayed in the entry field of the text entry dialog.

–hide-text

Hides the text in the entry field of the text entry dialog. For sensitive data, such as passwords, the — hide-text option can be used.

3) Progress Dialog :

Progress dialog is to track a progression of a routine.

The progress dialog supports the following options :

–text=text
Specifies the text that is displayed in the progress dialog.

–percentage=percentage
Specifies the initial percentage that is set in the progress dialog.

–auto-close
Closes the progress dialog when 100% has been reached.

–pulsate
Specifies that the progress bar pulsates until an EOF character is read from standard input.

4) Choosing :

Use the calendar to choose a date :

Use the file selector to choose a file :

File selection dialog is one of the a very useful zenity dialog, it support open file or save file dialog.