Author: Cloudkid

A small cheatsheet to handle and manage local docker images (Import/Export).

docker pull <image_name>:<tag>

Download or Pull the Docker Image

docker save -o <output_file>.tar <image_name>:<tag>

Save a Docker Image as a Tarball

docker load -i <image_file>.tar

Load a Docker Image from a Tarball

Here’s a MySQL Cheatsheet with commonly used commands for managing users, passwords, privileges, and checking permissions.

---

User Management

Create a User

CREATE USER 'username'@'host' IDENTIFIED BY 'password';

• Replace username with the desired username.
• Replace host with localhost, % (all hosts), or a specific IP/hostname.
• Replace password with the desired password.

Change Password

ALTER USER 'username'@'host' IDENTIFIED BY 'new_password';

Delete a User

DROP USER 'username'@'host';

---

Grant and Revoke Privileges

Grant Privileges to a User

GRANT ALL PRIVILEGES ON database_name.* TO 'username'@'host';

• Grants all privileges on database_name.

Grant Specific Privileges

GRANT SELECT, INSERT ON database_name.* TO 'username'@'host';

• Grants only SELECT and INSERT privileges.

Revoke Privileges

REVOKE ALL PRIVILEGES ON database_name.* FROM 'username'@'host';

Apply Changes to Privileges

FLUSH PRIVILEGES;

---

Checking Permissions

Show Privileges for a Specific User

SHOW GRANTS FOR 'username'@'host';

Show All Users and Their Hosts

SELECT user, host FROM mysql.user;

Check Database Privileges

SELECT User, Host, Db, Select_priv, Insert_priv, Update_priv, Delete_priv
FROM mysql.db
WHERE Db = 'database_name';

Check Table Privileges

SELECT * FROM mysql.tables_priv WHERE Db = 'database_name';

---

Password and Authentication

View Stored Password Hashes

SELECT user, host, authentication_string FROM mysql.user;

• Displays hashed passwords; plain-text passwords are not retrievable.

Reset Password (If Forgotten)

ALTER USER 'username'@'host' IDENTIFIED BY 'new_password';
FLUSH PRIVILEGES;

---

Backup and Restore

Backup a Database

mysqldump -u root -p database_name > backup_file.sql

Restore a Database

mysql -u root -p database_name < backup_file.sql

---

Host Management

Change a User’s Host

Replace the old host (host1) with a new host (host2):

UPDATE mysql.user
SET Host = 'host2'
WHERE Host = 'host1' AND User = 'username';
FLUSH PRIVILEGES;

Duplicate User for a New Host

INSERT INTO mysql.user (Host, User, authentication_string, plugin)
SELECT 'host2', User, authentication_string, plugin
FROM mysql.user
WHERE Host = 'host1';
FLUSH PRIVILEGES;

---

Troubleshooting

Access Denied Error

Check if the user exists:

SELECT User, Host FROM mysql.user WHERE User = 'username';

If the user doesn’t exist, create it:

CREATE USER 'username'@'host' IDENTIFIED BY 'password';

Check MySQL Version

SELECT VERSION();

Show Current User

SELECT USER();

---

Security Tips

• Avoid Plain-Text Passwords: Store credentials securely using a secrets manager.
• Restrict Hosts: Use specific IP addresses or localhost instead of % for better security.
• Backup Regularly: Always back up user data (mysql.user) before making changes.

---

This cheatsheet covers essential commands for managing users, privileges, and permissions in MySQL.

Ubuntu

Editing the DNS servers on Ubuntu is an easy task, here is a little documentation to how to do it.

Check your current configuration

To view the current DNS servers that are being used per interface, you can use this command :

resolvectl status

Or this one for Ubuntu 20.04 or newer :

systemd-resolve --status

These commands will show you the DNS server(s) being used by each network interface.

Edit DNS servers temporarily

To temporarily edit the DNS server, edit the /etc/resolv.conf file.

In /etc/resolv.conf, the line which starts with the keyword nameserver deals with DNS Servers.

Do not remove the line that says nameserver 127.0.0.53. Comment it out by putting a pound/hash symbol at the beginning of that line.

Add a line for every DNS server you’d like to add, here an example with Cloudflare DNS servers :

nameserver 1.1.1.2
nameserver 1.0.0.2

Here we add two DNS servers one main and one as a fallback;

You can then verify if the DNS server changed with the help of dig command.

$ dig google.com | grep SERVER
;; SERVER: 1.1.1.2#53(1.1.1.2) (UDP)

Grep-ing the output, we see that Cloudflare’s DNS servers are being used. That confirms that the temporary change in DNS server was in effect immediately.

Permanently change DNS

If you want to permanently change your DNS server (Persists after a reboot) you will have to edit the YAML network config file that resides in the /etc/netplan/ directory.

Before that, note down the name of your network interface beforehand. You can do so using the ip command:

ip add

Usually, there is only one file in /etc/netplan/ directory, but the name is mostly different. If there are multiple files, grep all files for your interface name. That should narrow down the candidate file to one.

grep -H INTERFACE_NAME *.*

Once you know the filename, open it for editing. You should see something similar to this output :

network:
  ethernets:
    enp1s0:
      dhcp4: true
  version: 2

My network interface is called ‘enp1s0‘, yours might be different.

Under my interface, I will add the nameservers field (below, not under dhcp), and another filed called addresses under it as well. I will specify the address in a bracket, separated by commas, like so :

network:
  ethernets:
    enp1s0:
      dhcp4: true
      nameservers:
        addresses: [1.1.1.2, 1.0.0.2]
  version: 2

Once the file is edited, save modifications and exit.

Then, run the following command to make changes effective:

sudo netplan apply

Your DNS servers are now edited.