After installing MariaDB on your Linux server, you must know some basic MariaDB commands.

Problem

How to manage a database and its table(s) in MariaDB?

Solution

Below are the basic commands of MariaDB to manage a database and its table(s):

1. Access to the MariaDB database

Use the format below to access MariaDB:

mariadb -h ip_address -u username -p

If you access MariaDB from the server using the root user directly, type the command below:

mariadb -u root -p

Enter the password for the root in MariaDB, and if the password is appropriate then you can access MariaDB as in the image below:

2. Creating a new database

Use the format below to create a new database:

CREATE DATABASE database_name;

You can see the options for this command on this page. For example, if you want to create a new database called db_office, use the command below;

CREATE DATABASE db_office;

3. See the entire database

Type the command below to see all the databases stored in MariaDB:

SHOW DATABASES;

4. Select a database

Use the format below to select the database you want to access:

USE db_name;

For example, if you want to access the db_office database, then type the command below:

USE db_office;

5. Create a table

Use the format below to create a new table:

CREATE TABLE table_name (name_of_column1 column_data_type1, name_of_column2 column_data_type2, ...);

You can see the options for this command on this page. Type the command below to create an employee table:

CREATE TABLE employee (name varchar (100), age int (3));

You can see data types that can be used on this page.

6. Display the entire table(s)

Use the command below to display the entire table in a database:

SHOW TABLES;

7. Display the table structure

Use the command below to display the table structure:

DESC table_name;

For example, if you want to see the employee table structure, then use the command below:

DESC employee;

8. Add a column

Use the format below to make a column in table:

ALTER TABLE db_name ADD COLUMN column_name type (nnn);

You can see the options for this command on this page. For example, if you want to add to the city column in the employee table, use the command below:

ALTER TABLE employee ADD COLUMN city VARCHAR (100);

9. Insert data into the table

Use the format below to enter data in a table:

INSERT INTO table_name (Column1, Column2,…, ColumnN) VALUES (Value1,…ValueN), (Value1,…ValueN);

You can see the options for this command on this page. Type the command below if you want to insert 2 data to the employee table:

INSERT INTO employee (name,age,city) VALUES ('bob',21,'New York'), ('John',22,'Chicago');

10. Displays data in a table

Use the format below to display all data in a table:

SELECT option1 FROM table_name option2;

You can see the options for this command on this page. For example, use the command below to display all data in the employee table:

SELECT * FROM employee;

Or, if you want to display the name of the user who lives in the city of Chicago then use the command below:

SELECT name FROM employee where city='Chicago';

11. Update data

Use the format below to update data in a table:

UPDATE table_name SET columnX=valueX WHERE columnY=valueY;

You can see the options for this command on this page. For example, if you want to update the age of the employee named Bob, use the command below:

UPDATE employee SET age=23 WHERE name='bob';

12. Delete Data

Use the format below to delete one or more rows of a table:

DELETE FROM table_name WHERE column=value;

You can see the options for this command on this page. For example, if you want to delete the data where the user is in Chicago, then use the command below:

DELETE FROM employee WHERE city='Chicago';

13. Delete the column

Use the format below to make changes in the table:

ALTER TABLE db_name DROP COLUMN column_name;

If you want to delete the column, for example, city, you can use the following command:

ALTER TABLE employee DROP COLUMN city;

14. Empty the table

You can delete all data in a table with the format as below:

TRUNCATE table_name;

You can see the options for this command on this page. For example, if you want to delete all the data in the employee table, then type the command below:

TRUNCATE employee;

15. Change a table name

You can change the name of the table using the format below:

RENAME TABLE old_table_name TO new_table_name;

You can see the options for this command on this page. Use the command below if, for example, you want to change the name of the employee table to employees:

RENAME TABLE employee to employees;

16. Delete a table

Use the format below to delete a table:

DROP TABLE table_name;

You can see the options for this command on this page. For example, if you want to delete the employee table, then use the command below:

DROP TABLE employees;

17. Delete a database

To delete a database, use the format below:

DROP DATABASE database_name;

You can see the options for this command on this page. For example, if you want to delete the db_office database, then type the command below:

DROP DATABASE db_office;

18. Quit from the database

To quit from the database, run the command below:

\q

Note

The next article will explain how to access a database using a user.

References

MariaDB.com
bertvv.github.io
zuar.com
educba.com
gist.github.com

Docker has a network system to regulate communication between one container and another container, your Docker host(server), and the outside world.

Problem

How to manage networking in Docker?

Solution

Docker provides six network drivers that you can use, as shown in the image below:

You can see from the image above that the bridge is a default network driver, so if you do not specify a driver, then this type of network is created. To see the types of network drivers on your server, use the command below:

docker network ls

To see the configuration details of each network driver, use the command below:

docker network inspect bridge host none

To see the type of driver network used in each container, use the command below:

docker ps -q | xargs docker inspect | jq '[.[] | {Name: .Name[1:], Networks: (.NetworkSettings.Networks | to_entries | map({(.key): .value.Driver}) | add)}]'

To see the IP of each container, for example, in the nginx container, use the command below:

docker inspect -f '{{range.NetworkSettings.Networks}}{{.IPAddress}}{{end}}' nginx

To communicate between one container with another container, both containers must have the same gateway. For example, you have made two containers, so by default, the two containers will use a network bridge driver so that it has the same gateway. Use the command below to see the two container IPs:

docker ps -q | xargs docker inspect | jq '[.[] | {Name: .Name[1:], IPAddress: .NetworkSettings.IPAddress, Gateway: .NetworkSettings.Gateway}]'

Then try to enter one of the containers and ping to another container using the command:

docker exec webapp1 ping -c2 172.17.0.2

And the containers should be able to communicate with each other like the image above.

A. Create a new network

You can create a new network on the server for your own needs using the format below:

docker network create network_name --driver driver_name

For example, you want to create an app-network network using a bridge driver, then use the command below:

docker network create app-network --driver bridge

After that, try to use the command below to see the detailed information of the app-network:

docker network inspect app-network

You can see from the picture above that the IP and Gateway from the app-network have been made automatically. You can make an IP and a Gateway according to what you want. For example, you want to create a new network with the name db-network, which has a range of IP 10.10.1.0/24 and Subnet 10.10.0.0/16 and Gateway 10.10.1.254, then use the command below:

docker network create -d bridge db-network \
--subnet=10.10.0.0/16 \
--ip-range=10.10.1.0/24 \
--gateway=10.10.1.254

Use the command below to display network information details easily:

docker network inspect db-network -f '{{json .IPAM}}' | python3 -m json.tool

From the image above, you can see that the IP, Subnet, and Gateway on the network are the same as what you want.

B. Connecting a network to a container

If you connect the current container to a network, use the format below:

docker network connect network-name container-name

For example, if you want to connect the webapp1 container to the app-network network, use the command below:

docker network connect app-network webapp1

If you want to create a new container by directly connecting to a network, use the format below:

docker container run --name container_name --network network_name image:tag

For example, if you want to create a db-mysql container on the db-network network, use the command below:

docker run -d --name db-mysql --network db-network -e MYSQL_ROOT_PASSWORD='q1w2e3r4' mysql

C. Disconnect a network in the container

To disconnect a network in the container, use the format below:

docker network disconnect network_name container_name

For example, if you want to break the app-network network from the webapp1 container, use the format below:

docker network disconnect network1 webapp1

D. Removing a network

To remove a network, use the format below:

docker network rm network_name

For example, I want to delete the app-network network, use the command below:

docker network rm app-network

Note

You must be careful when setting the network in Docker because if you set the wrong network, one or several containers will not be connected, which causes the application that runs on the Docker will be disturbed.

References

docs.docker.com
spacelift.io
youtube.dimas-maryanto.com
stackoverflow.com
youtube.com

The previous article explained how to access a container in Docker. Now, I need to move a file/folder from the server to the container and vice versa.

Problem

How to move a file/folder from the server to the container and vice versa?

Solution

These are how to move a file/folder from the server to the container and vice versa:

A. Move from the server to the container

To move a file from the server to the container, use the format below:

docker cp src_path container:dest_path

For example, I want to move the nginx.tgz file from the server to the webapp1 container in the folder /home, so I use the command below:

docker cp nginx.tgz webapp1:/home

And the file will move to the /home folder in the container, like in the image below:

B. Move from the container to the server

To move a file from the server to the container, use the format below:

docker cp container:src_path dest_path

For example, you want to move the docker-entrypoint.sh file in the container to the server in the folder /tmp, use the command below to move the file:

docker cp webapp1:docker-entrypoint.sh /tmp

And the file should be transferred to the folder /tmp on the server as shown below:

Note

You can move the folder and its contents from the server to the container and vice versa by using the format above without the need to add the -r option, as shown in the image below:

References

youtube.dimas-maryanto.com
docs.docker.com
mkyong.com

The previous article explained how to shut down Windows OS in one click. This article will explain how to reboot Windows OS in one click.

Problem

How to reboot Windows OS in one click?

Solution

The following steps to reboot the Windows OS in one click:

1. Create a shortcut

Go to the desktop, then right click and select New – Shortcut as shown below:

2. Write a script

Write the script below:

shutdown.exe /r /t 0

In the section as shown below:

Then press the Next button, and then there will be a display as below:

You can change the name for the shortcut, and after that, press the Finish button, then there will be a display as below:

3. Change the icon

Right-click on the icon, select Properties as shown below:

Then click the Change Icon button, and there will be a display as below:

There will be a display as below:

Click the OK button, and after that, you can choose the icon you like, but I chose the icon like in the red box, press OK, then there will be a display as below:

The shortcut icon will change to what you chose in the previous section. After that, press OK, the shortcut icon will change the image according to what you choose.

4. Move the icon

Move the icon to the taskbar by dragging it as shown below:

After the icon has been moved to the taskbar, you can delete the icon from the desktop.

5. Test the result

After that, try clicking the icon in the taskbar, and your Windows OS should do the shutdown process.

Note

In this article, the time used is 0, so there is no time lag after you click the icon with the shutdown process. You can change it to the time you want, for example, to 5 seconds, so that the script becomes like below:

shutdown.exe /r /t 5

Then there will be a break of 5 seconds after you finish clicking the icon and the shutdown process.

References

boostitco.com
isumsoft.com
wikihow.com

Besides providing application images, Docker also provides database images such as PostgreSQL, MySQL, MariaDB, MongoDB, and so on for its users. As with databases installed on a physical server, which requires entering a username and password to access it, Docker also requires you to enter a username and password to use the database, commonly known as an environment variable.

Problem

How to run environment variables in Docker?

Solution

An environment variable is a dynamically named value that can affect how running processes behave on a computer. They are part of the environment in which a process runs. For example, a running process can query the value of the TEMP environment variable to discover a suitable location to store temporary files, or the HOME or USERPROFILE variable to find the directory structure owned by the user running the process. To find out whether a Docker image can use environment variables, you must check the documentation of the Docker image. Still, in general, Docker images in the form of databases such as MySQL, PostgreSQL, or MongoDB use environment variables.

Please note that if you install an image container that uses an environment variable, for example, installing a MySQL database in a container, but you don’t include an environment variable like in the command below:

docker container run -d \
--name db_mysql \
mysql

The container will not run as shown in the image below:

Docker has parameters that we can use to send environment variables to the application contained in the container by adding the ‐-env or -e option when we create the container, following the format below:

docker container run -d --name container_name --env KEY1="value" --env KEY2="value" image:tag

This article will use the MySQL Docker image as a case example. In the documentation, several variables are provided, such as MYSQL_ROOT_PASSWORD, MYSQL_DATABASE, and so on. So, if you want to install MySQL in the container, you have to insert the environment variable. So, if you want to create a MySQL container with root password q1w2e3r4, then run the command below:

docker container run -d \
--name mysql_db \
-e MYSQL_ROOT_PASSWORD=q1w2e3r4 \
mysql

After that, try to access the MySQL database by running the command below:

docker container exec -it db_mysql mysql -pq1w2e3r4

You will enter the database in the container, like in the image below:

And you can use database commands as usual, like in the image above.

Note

Besides using the -e or ‐-env parameter arguments, you can use a file to save the environment variables, commonly known as Env-File, using the VAR=VALUE format. Use the format below to run the container that uses Env-File like in the format below:

docker container run -d --name container_name --env-file=filename container_name

First, you create the file, which usually ends with .env or .env.prod or .env.dev, and I create mysql.env. After that, you add to the file the script below:

MYSQL_ROOT_PASSWORD=q1w2e3r4

Run the command below to create a new container for MySQL using the environment file:

docker run -d --name db_mysql_file --env-file=mysql.env mysql

The MySQL container will be created, and you can access the database in the container like in the command below:

References

youtube.dimas-maryanto.com
youtube.com
stackoverflow.com

After you install Docker and learn some basic Docker commands to set up a container, this article will explain how to access a container in Docker.

Problem

How to access a container in Docker?

Solution

There are 2 ways to access a container in Docker:

A. Via CLI

If you want to access a container in Docker, use the format below:

docker exec -it container_id/container_name shell

where the -i option is interactive to keep the input active, the -t option is an argument for pseudo -tty (terminal access) allocation, and shell is the program contained in the container and it can be different to be different to the code used in the container likes bash or sh shell, but for more details, please look at the documentation of each image). For example, there is an nginx container that is running, and if you want to access the nginx container, you can use the command below:

docker exec -it nginx bash

After that, you should be able to access the container as shown below:

If you want the results of the command in the container to be shown on the server, then use the format below:

docker exec container_name/container_id bash -c "your-linux-commands"

For example, use the command below:

docker exec webapp1 bash -c "ls -al /bin/sync; echo; ls -al /usr"

Or you can also use the format below if you only run a command in the container:

docker exec container_name/container_id linux-command

For example, use the command below:

docker exec nginx ls -al /usr

B. Via website

You can access a container through the website, but this method only produces applications that run in the container on the website and do not run commands in the container. Usually, these containers use a web server image such as Apache or Nginx, or applications made by developers. If you want to run these applications and access the application in the browser, use the format below:

docker container run -d --name container_name -p port_server:port_container image_name:tag

For example, you want to run an nginx container whose application can be seen by using port 8080 on the server, then use the command below:

docker container run -d --name webapp1 -p 8080:80 nginx

Open your browser and type the url below:

http://your_ip_server:8080

There should be a display as below:

If you stop the container, then the application cannot be accessed through a browser as below:

Note

You can also access a database installed in a container using the commands in this article.

References

docs.docker.com
spacelift.io
youtube.com

The previous article explained how to monitor an entire container in Docker. In addition to monitoring, you should also limit the resource usage of each container so that server performance remains in good condition.

Problem

How to limit resources in Docker?

Solution

If you run the docker stats command, the command will display the resource container as shown in the image below:

As you can see in the image above, there are 2 containers running, and both containers have a memory limit of 941 MB, where the memory size is the size of the memory of the server. This is dangerous because the application in the container can use all the memory or CPU on the server, causing the server to run abnormally. Therefore, you should limit the use of resources in the container.

A. RAM limitation

There are 2 types of memory limitations in Docker:

• The hard limit is a maximum value that cannot be exceeded. When a container exceeds a hard memory limit, Docker takes aggressive actions such as terminating the container so that there will be an OOM or Out Of Memory error in the container. The options used in Docker are ‐‐memory or -m.
• The soft limit is a limit that can be temporarily exceeded. When a soft limit is reached, Docker warns the user but does not take immediate action. The option used is ‐‐memory-reservation.

If you use swap on the server, you can use the ‐‐memory-swap option to allocate available swap memory to the container. This swap memory must be larger than the hard limit, usually twice larger than the hard limit. If you want to use a percentage for memory swap, use the ‐‐memory-swappiness option.

To limit the memory on the new container, use the format below:

docker run -d --memory='hard_limit_value' --name docker_name docker-image

For example, if you want to limit the memory on a container of 512 MB with a soft limit of 256 MB, then I run the command below:

docker run -d --memory='512m' --name nginx nginx

You can immediately change the container memory when the container is running using the format below:

docker update docker_name --memory='hard_limit_value'

For example, I want to change the Redis container memory from 971 MB to 256 MB using the command below:

But when running the command, there is an error as below:

Error Response from Daemon: Cannot Update Container 94DD458F891C08D8E0A15EB00878FC83E5C6660D6AF8Beb0815A3A9040C57F7: Memory Limit Should Be Smaller Than Already Set Time

To overcome the error, update the memory container swap, whose value must be greater than the memory value. Therefore, use the command below to increase the memory of a container:

docker update redis --memory='256m' --memory-swap='512mb'

And the container memory value should have changed as shown below:

B. CPU limitation

Before you limit the CPU in the container, you need to know how many CPU cores there are on your server by using the command below:

nproc

To limit the CPU used in the container, use the ‐‐cpus option to determine how many CPU cores can be used in a container. If your server has two CPUs and you set ‐‐cpus=’1.5′, the container is guaranteed at most one and a half of the CPUs and this is the equivalent of setting ‐‐cpu-period=’100000′ and ‐‐cpu-quota=’150000′ (cpu-period is used with cpu-quota to configure the CPU scheduler with defaults to 100000 microseconds and cpu-quota is used with cpu-period to configure the CPU scheduler). Use the format below to limit the CPU in the container:

docker run -d --cpus='cpu_value' --name docker_name docker_image:tag

You can see the details of the CPU used by a container by using the format below:

docker inspect nginx | grep -e Cpu -e cpu

For example, I want to limit the CPU to 1, so I run the command below:

docker run -d --cpus='1' --name nginx nginx

You can use the ‐‐cpu-shares option for a container to control the share of CPU cycles available, whose default value is 1024. This option is like a soft limit option on memory, so if you run the command below:

docker run -d --cpu-shares='2048' --name webapp1 nginx

If there is more than 1 container on a host and CPU cycles are constrained, then the webapp1 container will receive 2x more CPU than the other containers. You can update the CPU in a running container using the format:

docker update docker_name --cpus='cpu_value'

For example, I have 2 CPUs on the server, and initially, I use all the CPUs in the webapp1 container. Then, I wanted to update the CPU on the container to 1.5, so I ran the command below:

docker update webapp1 --cpus='1.5' nginx

C. HDD limitation

As of this writing (April 2025), the HDD limitation can only be used for btrfs, overlay2, windowsfilter, and zfs storage drivers. For the overlay2 storage driver, the size option is only available if the backing filesystem is xfs and mounted with the pquota mount option. Type the command below to see the Docker settings on the server:

docker info | grep -e 'Filesystem' -e 'Support' -e 'Storage'

Run the command above, and here is the result:

To limit the hard disk in a container, follow the format below:

docker run -d --name nginx --storage-opt size=1g nginx

If I want to limit my hard disk in a container, I run the command below:

docker run -d --name nginx --storage-opt size=1g nginx

But, I have an error like the image below:

docker: Error response from daemon: –storage-opt is supported only for overlay pver xfs with ‘pquota’ mount option

From the image above,  I can’t limit the HDD to the container because my Backing Filesystem in my server still uses extfs, not xfs. So, if I want to limit my HDD in my containers, I have to change my Backing Filesystem in my server. So I made an experiment by turning off Docker and deleting the Docker folder using the command below:

sudo systemctl stop docker
sudo rm -rf /var/lib/docker && sudo mkdir /var/lib/docker

Then I inserted an additional hard disk into the existing server, and then I converted the file system to xfs using the commands below:

sudo mkfs.xfs /dev/sdb1
sudo mount /dev/sdb1 /var/lib/docker

And I added to the /etc/fstab file the script below:

echo '/dev/sdb1 /var/lib/docker xfs defaults,quota,prjquota,pquota,gquota 0 0' | sudo tee -a /etc/fstab

I rebooted the server to test whether the fstab file settings were correct. After that, I tried to create a container by limiting the container’s hard disk to 1GB using the command below:

docker run -d --name nginx --storage-opt size=1g nginx

Note

You can combine more than one restriction above by using one command. For example, if you want to limit memory, CPU, and HDD in a container, then you can run the command below:

docker run -d --name webapp1 -m 512m --cpus=1.5 --storage-opt size=1g nginx

As far as I know, Sysadmin only limits the use of RAM and CPU in Docker, but rarely limits HDD in Docker. If you want to limit resources in Docker, you must discuss it with the developers so that there are no problems with the application in the future.

References