Java is a popular programming language used for building applications and software solutions. It runs on all major operating systems and devices.

This guide covers installing OpenJDK and Oracle JDK on Ubuntu 26.04.

Quick Reference #

Before You Begin #

There are several Java implementations available. OpenJDK and Oracle JDK are the two most common choices. OpenJDK is the default option in Ubuntu and the best fit for most systems.

Ubuntu 26.04 includes OpenJDK packages for both the Java Runtime Environment (JRE) and the Java Development Kit (JDK). The JRE includes the Java virtual machine (JVM) and the libraries needed to run Java programs. The JDK includes the JRE plus the tools needed to build Java applications.

If you are not sure which package to install, start with the default OpenJDK version. Some applications require a specific Java release, so check the application documentation before you install it.

Installing OpenJDK in Ubuntu #

Check if Java is already installed:

java -version

If Java is not installed, the output will tell you the command is not found. Otherwise, it shows the installed version.

Update the package index:

sudo apt update

The current long-term supported (LTS) versions of Java are: 11, 17, 21, and 25. The default Java in Ubuntu 26.04 is Java 25, which you get by installing the default-jdk package.

Install latest LTS Java 25:

sudo apt install openjdk-25-jdk

Verify the installation:

java -version

openjdk version "25.0.3-ea" 2026-04-21
OpenJDK Runtime Environment (build 25.0.3-ea+7-Ubuntu-2)
OpenJDK 64-Bit Server VM (build 25.0.3-ea+7-Ubuntu-2, mixed mode, sharing)

JRE is included in the JDK package. If you need only JRE, install the openjdk-25-jre package. For minimal Java runtime, install the openjdk-**25**-jre-headless package.

Installing Oracle Java in Ubuntu #

Oracle JDK is not available in the default Ubuntu repositories. You can install it by downloading the .deb package from Oracle.

At the time of writing, Oracle’s downloads page offers both JDK 26, the latest feature release, and JDK 25, the latest LTS release. Oracle JDK 25 is available under Oracle No-Fee Terms and Conditions (NFTC), which allows free production use and redistribution for that release. If you plan to standardize on Oracle JDK, review Oracle’s current licensing terms before deployment.

Visit the Oracle Java Downloads page and select the version you need.

In this example, we will download and install Java 25 because it is the current LTS release. If you want the newest feature release instead, download JDK 26 from the same page. Choose the Linux x64 Debian Package for the version you want and download the .deb file.

If you are installing on a server, use wget to download the file:

wget https://download.oracle.com/java/25/latest/jdk-25_linux-x64_bin.deb

Install the package:

sudo apt install ./jdk-25_linux-x64_bin.deb

Replace the filename if you downloaded a different version.

Setting the Default Java Version #

If you have multiple Java versions installed, check the current default:

java -version

Change the default version with update-alternatives:

sudo update-alternatives --config java

You will see a list of installed Java versions:

There are 2 choices for the alternative java (providing /usr/bin/java).
Selection Path Priority Status
------------------------------------------------------------
* 0 /usr/lib/jvm/jdk-25.0.3-oracle-x64/bin/java 419454976 auto mode
1 /usr/lib/jvm/java-25-openjdk-amd64/bin/java 2511 manual mode
2 /usr/lib/jvm/jdk-25.0.3-oracle-x64/bin/java 419454976 manual mode
Press <enter> to keep the current choice[*], or type selection number: 

Enter the number of the version you want as default and press Enter.

Verify the change:

java -version

Setting the JAVA_HOME Environment Variable #

Some Java applications use the JAVA_HOME environment variable to determine the JDK location.

First, find the Java installation path:

sudo update-alternatives --config java

The paths are:

• Oracle JDK 25 is located at /usr/lib/jvm/jdk-25-oracle-x64/bin/java
• OpenJDK 25 is located at /usr/lib/jvm/java-25-openjdk-amd64/bin/java

Open the /etc/environment file:

sudo nano /etc/environment

Add the following line (adjust the path for your preferred version):

JAVA_HOME="/usr/lib/jvm/java-25-openjdk-amd64"

Apply the changes:

source /etc/environment

Verify the variable is set:

echo $JAVA_HOME

/usr/lib/jvm/java-25-openjdk-amd64

Uninstalling Java #

Uninstall Java like any other package:

sudo apt remove openjdk-25-jdk

Replace the package name with the version you want to remove.

Conclusion #

We covered installing OpenJDK from the Ubuntu 26.04 repositories and downloading Oracle JDK manually. The default OpenJDK 25 works for most applications, but Java 26 is also available in the Oracle repositories for the latest features.

For more information, see the official OpenJDK documentation .

PHP is one of the most used server-side programming languages. Many popular CMS and frameworks such as WordPress, Magento, and Laravel are written in PHP.

This guide covers the steps necessary to install PHP on Ubuntu 26.04 and integrate it with Nginx and Apache. The default Ubuntu 26.04 repositories include PHP 8.5. We will also show you how to install other PHP versions.

Quick Reference #

Prerequisites #

To follow this guide, you need to be logged in as a user with sudo privileges .

Installing PHP 8.5 with Apache #

If you are using Apache as your web server, run the following commands to install PHP and the Apache PHP module:

sudo apt update
sudo apt install php libapache2-mod-php

Once the packages are installed, restart Apache for the PHP module to get loaded:

sudo systemctl restart apache2

Installing PHP 8.5 with Nginx #

Unlike Apache, Nginx does not have built-in support for processing PHP files. We will use PHP-FPM (FastCGI Process Manager) to handle PHP files.

Run the following commands to install PHP and the PHP-FPM package:

sudo apt update
sudo apt install php-fpm

Once the installation is completed, the FPM service starts automatically. To check the status of the service, run:

sudo systemctl status php8.4-fpm

● php8.4-fpm.service - The PHP 8.5 FastCGI Process Manager
Loaded: loaded (/usr/lib/systemd/system/php8.4-fpm.service; enabled; preset: enabled)
Active: active (running) since Sat 2026-04-26 09:15:22 UTC; 12s ago

You can now edit the Nginx server block and add the following lines so that Nginx can process PHP files:

server {

 # . . . other code

 location ~ \.php$ {
 include snippets/fastcgi-php.conf;
 fastcgi_pass unix:/run/php/php8.4-fpm.sock;
 }
}

Restart the Nginx service so that the new configuration takes effect:

sudo systemctl restart nginx

Installing PHP Extensions #

PHP extensions are compiled libraries that extend the core functionality of PHP. Extensions are available as packages and can be easily installed with apt :

sudo apt install php-[extname]

For example, to install the MySQL and GD extensions, run:

sudo apt install php-mysql php-gd

Here are some of the most commonly used PHP extensions:

To install all commonly needed extensions at once:

sudo apt install php-mysql php-curl php-gd php-mbstring php-xml php-zip php-intl php-opcache php-bcmath

After installing a new PHP extension, restart Apache or PHP-FPM depending on your setup:

sudo systemctl restart apache2

Or for Nginx with PHP-FPM:

sudo systemctl restart php8.4-fpm

To list all installed PHP modules:

php -m

Testing PHP Processing #

To confirm that the web server can process PHP files, create a new info.php file in /var/www/html:

echo '<?php phpinfo();' | sudo tee /var/www/html/info.php

Open http://your_server_ip/info.php in your browser. If PHP is configured correctly, you will see the PHP information page:

sudo rm /var/www/html/info.php

Installing Other PHP Versions #

Ondřej Surý, a Debian developer, maintains a repository that includes multiple PHP versions. This is a third-party source, so use it only if you need a different PHP version than what Ubuntu provides. To enable the repository , run:

sudo apt install software-properties-common
sudo add-apt-repository ppa:ondrej/php

You can now install any PHP version you need by appending the version number to the package name:

sudo apt install php[version]

For example, to install PHP 8.3 and a few common modules:

sudo apt install php8.3 php8.3-cli php8.3-common php8.3-opcache php8.3-gd php8.3-curl php8.3-mysql php8.3-mbstring php8.3-xml

Switching Between PHP Versions #

If you have multiple PHP versions installed, you can switch the default CLI version using update-alternatives:

sudo update-alternatives --set php /usr/bin/php8.3

To interactively choose the default version:

sudo update-alternatives --config php

For Apache, disable the current PHP module and enable the one you want:

sudo a2dismod php8.4
sudo a2enmod php8.3
sudo systemctl restart apache2

For Nginx, update the PHP-FPM socket path in your server block to point to the correct version, then restart Nginx:

sudo systemctl restart nginx

Checking the PHP Version #

To check which PHP version is installed on your system, run:

php -v

PHP 8.5.4 (cli) (built: Apr 1 2026 09:36:11) (NTS)
Copyright (c) The PHP Group
Built by Ubuntu
Zend Engine v4.5.4, Copyright (c) Zend Technologies
with Zend OPcache v8.5.4, Copyright (c), by Zend Technologies

PHP Configuration Files #

PHP configuration files are located at:

• Main config: /etc/php/8.5/cli/php.ini (CLI) and /etc/php/8.5/apache2/php.ini (Apache) or /etc/php/8.5/fpm/php.ini (FPM)
• FPM pool config: /etc/php/8.5/fpm/pool.d/www.conf
• Extension configs: /etc/php/8.5/mods-available/

After changing any configuration, restart the relevant service:

sudo systemctl restart php8.4-fpm

Uninstalling PHP #

To remove PHP and related packages, you can purge them and clean up dependencies:

sudo apt purge 'php*'
sudo apt autoremove

FAQ #

What PHP version does Ubuntu 26.04 include?
Ubuntu 26.04 ships with PHP 8.5 in its default repositories.

What is the difference between php and php-fpm?
The php package includes the CLI interpreter and the Apache module. The php-fpm package provides a FastCGI Process Manager used by Nginx and other web servers that do not have built-in PHP support.

Can I run multiple PHP versions at the same time?
Yes. You can install multiple PHP versions from the Ondřej Surý PPA and configure each virtual host or server block to use a different PHP version.

Do I need to restart Apache or Nginx after installing an extension?
Yes. After installing a PHP extension, restart Apache (sudo systemctl restart apache2) or PHP-FPM (sudo systemctl restart php8.4-fpm) for the extension to be loaded.

Where is the php.ini file located?
PHP uses separate php.ini files for each SAPI. The CLI config is at /etc/php/8.5/cli/php.ini, the Apache config at /etc/php/8.5/apache2/php.ini, and the FPM config at /etc/php/8.5/fpm/php.ini.

Conclusion #

We have shown you how to install PHP 8.5 on Ubuntu 26.04 with both Apache and Nginx. You can now install extensions, configure PHP, and start building your applications.

If you have any questions, feel free to leave a comment below.

Nginx (pronounced “engine x”) is an open-source, high-performance HTTP and reverse proxy server used by some of the largest sites on the Internet. It can act as a standalone web server, load balancer, content cache, and proxy for HTTP and non-HTTP services.

This guide explains how to install Nginx on Ubuntu 26.04, configure the firewall, and manage the service.

Prerequisites #

Before continuing, make sure you are logged in as a user with sudo privileges , and that no other service such as Apache is running on port 80 or 443.

Installing Nginx #

Nginx is available in the default Ubuntu repositories. To install it, run:

sudo apt update
sudo apt install nginx

Once the installation is completed, the Nginx service starts automatically. To verify it is running:

sudo systemctl status nginx

● nginx.service - A high performance web server and a reverse proxy server
Loaded: loaded (/usr/lib/systemd/system/nginx.service; enabled; preset: enabled)
Active: active (running) since Fri 2026-04-25 15:00:00 UTC; 10s ago
...

Nginx is now installed and running. You can manage the Nginx service in the same way as any other systemd unit.

Configuring the Firewall #

Now that Nginx is running, you need to make sure the firewall allows traffic on HTTP (80) and HTTPS (443). If you are using ufw , enable the Nginx Full profile which covers both ports:

sudo ufw allow 'Nginx Full'

To verify the firewall status:

sudo ufw status

Status: active
To Action From
-- ------ ----
22/tcp ALLOW Anywhere
Nginx Full ALLOW Anywhere
22/tcp (v6) ALLOW Anywhere (v6)
Nginx Full (v6) ALLOW Anywhere (v6)

Testing the Installation #

To confirm Nginx is serving requests, open http://YOUR_IP in a browser. You should see the default Nginx welcome page. You can also test from the command line:

curl -I http://localhost

HTTP/1.1 200 OK
Server: nginx/1.28.3 (Ubuntu)
...

Nginx Configuration Structure #

• All Nginx configuration files are located in /etc/nginx/.
• The main configuration file is /etc/nginx/nginx.conf.
• Create a separate configuration file for each domain to keep things manageable. Server block files are stored in /etc/nginx/sites-available/ and must be symlinked to /etc/nginx/sites-enabled/ to be active.
• Follow the standard naming convention: if your domain is mydomain.com, name the file /etc/nginx/sites-available/mydomain.com.conf.
• The /etc/nginx/snippets/ directory holds reusable configuration fragments that can be included in server block files.
• Log files (access.log and error.log) are located in /var/log/nginx/. Use a separate log file per server block.
• Common document root locations: /var/www/<site_name>, /var/www/html/<site_name>, or /home/<user>/<site_name>.

Conclusion #

Nginx is now installed and ready to serve your applications on Ubuntu 26.04. To set up multiple sites on the same server, see the guide on Nginx server blocks .

PostgreSQL is an open-source, object-relational database management system known for its reliability, feature set, and standards compliance. It is widely used in production environments ranging from small applications to large-scale data warehouses.

This guide explains how to install PostgreSQL 18 on Ubuntu 26.04, set up roles and authentication, and configure remote access.

Prerequisites #

To follow this guide, you need to be logged in as a user with sudo privileges .

Installing PostgreSQL on Ubuntu 26.04 #

The default Ubuntu 26.04 repositories include PostgreSQL 18.

Start by updating the local package index:

sudo apt update

Install the PostgreSQL server and the contrib package, which provides several additional features:

sudo apt install postgresql postgresql-contrib

Once the installation is completed, the PostgreSQL service starts automatically. Use the psql tool to verify the installation by connecting to the PostgreSQL server and printing its version :

sudo -u postgres psql -c "SELECT version();"

 version
----------------------------------------------------------------------------------------------------------------------------------
PostgreSQL 18.3 (Ubuntu 18.3-1) on x86_64-pc-linux-gnu, compiled by gcc (Ubuntu 15.2.0-14ubuntu1) 15.2.0, 64-bit
(1 row)

PostgreSQL has been installed and is ready to use.

PostgreSQL Roles and Authentication #

Database access in PostgreSQL is managed through roles. A role can represent a database user or a group of database users.

PostgreSQL supports several authentication methods . The most commonly used are:

• Trust lets a role connect without a password, as long as the conditions in pg_hba.conf are met.
• Password lets a role connect by providing a password. Passwords can be stored as scram-sha-256 or md5.
• Ident is supported on TCP/IP connections. It obtains the client’s operating system username, with optional mapping.
• Peer works like Ident, but for local connections only.

PostgreSQL client authentication is defined in pg_hba.conf. By default, PostgreSQL uses the peer authentication method for local connections.

The postgres user is created automatically during installation. It is the superuser for the PostgreSQL instance, equivalent to the MySQL root user.

To log in to the PostgreSQL server as the postgres user, use the sudo command:

sudo -u postgres psql

You can also switch to the user first:

sudo su - postgres
psql

To exit the PostgreSQL shell, type:

\q

Creating a Role and Database #

Only superusers and roles with the CREATEROLE privilege can create new roles.

The following example creates a role named john, sets a password for the role, and creates a database named johndb owned by that role:

1. Create a new PostgreSQL role:

   Terminal

   sudo -u postgres createuser john

2. Set a password for the role:

   Terminal

   sudo -u postgres psql

   sql

   ALTER ROLE john WITH ENCRYPTED PASSWORD 'strong_password';

   Use a real password here. Do not store it in shell history, scripts, or version control.

3. Create a new database owned by that role:

   Terminal

   sudo -u postgres createdb johndb --owner=john

Because john owns the database, it can create objects in the default public schema without additional grants.

Enabling Remote Access #

By default, PostgreSQL only listens on localhost (127.0.0.1).

To allow remote connections, open the PostgreSQL configuration file:

sudo nano /etc/postgresql/18/main/postgresql.conf

Find the listen_addresses line in the CONNECTIONS AND AUTHENTICATION section and set it to '*' to listen on all interfaces:

listen_addresses = '*'

Save the file and restart the PostgreSQL service:

sudo systemctl restart postgresql

Verify that PostgreSQL is now listening on all interfaces:

ss -nlt | grep 5432

LISTEN 0 244 0.0.0.0:5432 0.0.0.0:*
LISTEN 0 244 [::]:5432 [::]:*

The next step is to configure which hosts are allowed to connect by editing pg_hba.conf:

sudo nano /etc/postgresql/18/main/pg_hba.conf

Add rules at the bottom of the file. Some examples:

# TYPE DATABASE USER ADDRESS METHOD
# Allow jane to connect to all databases from anywhere using a password
host all jane 0.0.0.0/0 scram-sha-256
# Allow jane to connect only to janedb from anywhere
host janedb jane 0.0.0.0/0 scram-sha-256
# Allow jane to connect from a trusted host without a password
host all jane 192.168.1.134 trust

Reload PostgreSQL to apply the changes:

sudo systemctl reload postgresql

Finally, open port 5432 in the firewall. To allow access from a specific subnet:

sudo ufw allow proto tcp from 192.168.1.0/24 to any port 5432

Conclusion #

We have shown you how to install PostgreSQL 18 on Ubuntu 26.04 and covered the basics of roles, authentication, and remote access. For more details, consult the PostgreSQL 18 documentation .

MySQL is one of the most popular open-source relational database management systems. It is fast, easy to manage, scalable, and an integral part of the popular LAMP and LEMP stacks.

This guide explains how to install and secure MySQL 8.4 on an Ubuntu 26.04 machine. Upon completion, you will have a fully functional database server that you can use for your projects.

Quick Reference #

Prerequisites #

To follow this guide, you need to be logged in as a user with sudo privileges .

Installing MySQL on Ubuntu 26.04 #

The default Ubuntu 26.04 repositories include MySQL 8.4.

Start by updating the local package index:

sudo apt update

Install the MySQL server package:

sudo apt install mysql-server

Once the installation is completed, the MySQL service starts automatically. To verify that the MySQL server is running, type:

sudo systemctl status mysql

The output should show that the service is enabled and running:

● mysql.service - MySQL Community Server
Loaded: loaded (/usr/lib/systemd/system/mysql.service; enabled; preset: enabled)
Active: active (running) since Fri 2026-04-25 09:14:23 UTC; 15s ago
Process: 1234 ExecStartPre=/usr/share/mysql/mysql-systemd-start pre (code=exited, status=0/SUCCESS)
Main PID: 1242 (mysqld)
Status: "Server is operational"
Tasks: 38 (limit: 4558)
Memory: 362.4M
CPU: 1.183s
CGroup: /system.slice/mysql.service
└─1242 /usr/sbin/mysqld

If the server fails to start, you can check the logs with journalctl :

sudo journalctl -u mysql

To check the installed version, run:

mysql --version

mysql Ver 8.4.8-0ubuntu1 for Linux on x86_64 ((Ubuntu))

Securing MySQL #

MySQL includes a script named mysql_secure_installation that helps you improve the database server security.

Run the script:

sudo mysql_secure_installation

You will be asked to configure the VALIDATE PASSWORD component, which tests the strength of MySQL users’ passwords:

Securing the MySQL server deployment.
Connecting to MySQL using a blank password.
VALIDATE PASSWORD COMPONENT can be used to test passwords
and improve security. It checks the strength of password
and allows the users to set only those passwords which are
secure enough. Would you like to setup VALIDATE PASSWORD component?
Press y|Y for Yes, any other key for No: y

There are three levels of password validation policy. Press y to enable the password validation plugin, or any other key to skip:

There are three levels of password validation policy:
LOW Length >= 8
MEDIUM Length >= 8, numeric, mixed case, and special characters
STRONG Length >= 8, numeric, mixed case, special characters and dictionary file
Please enter 0 = LOW, 1 = MEDIUM and 2 = STRONG: 1

Next, you will be asked to remove the anonymous user, restrict root user access to the local machine, remove the test database, and reload privilege tables. Answer y to all questions:

Remove anonymous users? (Press y|Y for Yes, any other key for No) : y
Success.
Disallow root login remotely? (Press y|Y for Yes, any other key for No) : y
Success.
Remove test database and access to it? (Press y|Y for Yes, any other key for No) : y
- Dropping test database...
Success.
Reloading the privilege tables will ensure that all changes
made so far will take effect immediately.
Reload privilege tables now? (Press y|Y for Yes, any other key for No) : y
Success.
All done!

Logging In as Root #

You can interact with the MySQL server from the command line using the MySQL client utility, which is installed as a dependency of the MySQL server package.

On Ubuntu 26.04, the MySQL root account uses the auth_socket plugin by default. This plugin authenticates users that connect from localhost through the Unix socket file, which means you cannot authenticate as root by providing a password.

To log in to the MySQL server as the root user, type:

sudo mysql

You will be presented with the MySQL shell:

Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 10
Server version: 8.4.8-0ubuntu1 (Ubuntu)
Copyright (c) 2000, 2024, Oracle and/or its affiliates.
Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
mysql>

To exit the MySQL shell, type exit or press Ctrl+D.

Changing Root Authentication #

If you want to log in to your MySQL server as root using an external program such as phpMyAdmin, you have two options.

Option 1: Change the Authentication Method #

Change the authentication method from auth_socket to caching_sha2_password:

ALTER USER 'root'@'localhost' IDENTIFIED WITH caching_sha2_password BY 'very_strong_password';
FLUSH PRIVILEGES;

Option 2: Create a Dedicated Administrative User #

The recommended approach is to create a new administrative user with access to all databases:

CREATE USER 'administrator'@'localhost' IDENTIFIED BY 'very_strong_password';
GRANT ALL PRIVILEGES ON *.* TO 'administrator'@'localhost' WITH GRANT OPTION;
FLUSH PRIVILEGES;

Creating a Database and User #

Once MySQL is secured, you can create databases and user accounts. For example, to create a database named myapp and a user that has access to it:

Log in to the MySQL shell:

sudo mysql

Create the database:

CREATE DATABASE myapp;

Create a user and grant privileges on the database:

CREATE USER 'myappuser'@'localhost' IDENTIFIED BY 'strong_password';
GRANT ALL PRIVILEGES ON myapp.* TO 'myappuser'@'localhost';
FLUSH PRIVILEGES;

To allow the user to connect from any host (for remote access), replace 'localhost' with '%'.

Enabling Remote Access #

By default, MySQL only listens on localhost (127.0.0.1). To allow remote connections, you need to change the bind address.

Open the MySQL configuration file:

sudo nano /etc/mysql/mysql.conf.d/mysqld.cnf

Find the line that starts with bind-address and change it to 0.0.0.0 to listen on all interfaces, or to a specific IP address:

bind-address = 0.0.0.0

Restart the MySQL service for the changes to take effect:

sudo systemctl restart mysql

For production, consider enabling TLS so remote connections are encrypted. This protects credentials and data in transit when connecting over untrusted networks.

Configuring the Firewall #

If you have a firewall enabled and want to allow connections to MySQL from remote machines, you need to open port 3306.

To allow access from a specific IP address:

sudo ufw allow from 192.168.1.100 to any port 3306

To allow access from any IP address (not recommended for production):

sudo ufw allow 3306/tcp

FAQ #

What version of MySQL does Ubuntu 26.04 include?
Ubuntu 26.04 ships with MySQL 8.4 in its default repositories. To check the exact version installed on your system, run mysql --version.

What is the difference between auth_socket and caching_sha2_password?
auth_socket authenticates users based on the operating system user connecting through the Unix socket. No password is needed, but you must use sudo. caching_sha2_password uses traditional password-based authentication.

How do I reset the MySQL root password?
Stop the MySQL service with sudo systemctl stop mysql, start it with --skip-grant-tables, log in without a password, run ALTER USER 'root'@'localhost' IDENTIFIED WITH caching_sha2_password BY 'new_password';, then restart the service normally.

Is mysql_native_password still supported?
It is still available, but it is deprecated and disabled by default in MySQL 8.4. Use caching_sha2_password for new installations unless you have a specific compatibility requirement.

Can I install a newer MySQL release on Ubuntu 26.04?
Yes. If you need a newer release than the one in the Ubuntu repositories, you can use the official MySQL APT repository . For most setups, the Ubuntu package is the simplest choice.

Conclusion #

We have shown you how to install and secure MySQL 8.4 on Ubuntu 26.04. Now that your database server is up and running, your next step could be to learn how to manage MySQL user accounts and databases .

Docker is an open-source container platform that lets you build, test, and run applications as portable containers. Containers package the application code together with its dependencies, which makes it easier to run the same workload across development machines, test environments, and servers.

Docker is widely used in development workflows and DevOps pipelines because it keeps application environments predictable.

This tutorial explains how to install Docker on Ubuntu 26.04.

Supported Ubuntu Versions #

Docker is available from the standard Ubuntu repositories, but those packages are often outdated. To ensure you get the latest stable version, we will install Docker from the official Docker repository.

At the time of writing, the Docker repository provides packages for current supported Ubuntu releases, including Ubuntu 26.04 LTS, Ubuntu 25.10, Ubuntu 24.04 LTS, and Ubuntu 22.04 LTS.

Prerequisites #

Before you begin, make sure that:

• You are running a 64-bit supported Ubuntu version
• You have a user account with sudo privileges
• Your system is connected to the internet and up to date

Uninstall any old or conflicting Docker packages first to avoid potential issues:

sudo apt remove docker.io docker-doc docker-compose docker-compose-v2 podman-docker containerd runc

Installing Docker on Ubuntu 26.04 #

Installing Docker on Ubuntu is relatively straightforward. We will enable the Docker repository, import the repository GPG key, and install the Docker packages.

Step 1: Update the Package Index and Install Dependencies #

First, update the package index and install packages required to use repositories over HTTPS :

sudo apt update
sudo apt install ca-certificates curl

Step 2: Import Docker’s Official GPG Key #

Add Docker’s official GPG key so your system can verify package authenticity:

sudo install -m 0755 -d /etc/apt/keyrings
sudo curl -fsSL https://download.docker.com/linux/ubuntu/gpg -o /etc/apt/keyrings/docker.asc
sudo chmod a+r /etc/apt/keyrings/docker.asc

Step 3: Add the Docker APT Repository #

Add the Docker repository to your system:

sudo tee /etc/apt/sources.list.d/docker.sources <<EOF
Types: deb
URIs: https://download.docker.com/linux/ubuntu
Suites: $(. /etc/os-release && echo "${UBUNTU_CODENAME:-$VERSION_CODENAME}")
Components: stable
Architectures: $(dpkg --print-architecture)
Signed-By: /etc/apt/keyrings/docker.asc
EOF

$(. /etc/os-release && echo "${UBUNTU_CODENAME:-$VERSION_CODENAME}") reads your Ubuntu codename from the OS release file. On Ubuntu 26.04 it returns resolute.

Step 4: Install Docker Engine #

Now that the Docker repository is enabled, update the package index and install Docker:

sudo apt update
sudo apt install docker-ce docker-ce-cli containerd.io docker-buildx-plugin docker-compose-plugin

Installing a Specific Docker Version (Optional) #

If you want to install a specific Docker version instead of the latest one, first list the available versions:

sudo apt update
apt list --all-versions docker-ce

The available Docker versions are printed in the second column:

docker-ce/resolute 5:29.4.0-1~ubuntu.26.04~resolute amd64
docker-ce/resolute 5:29.3.1-1~ubuntu.26.04~resolute amd64
docker-ce/resolute 5:29.3.0-1~ubuntu.26.04~resolute amd64
...

Install a specific version by adding =<VERSION> after the package name:

DOCKER_VERSION="<VERSION>"
sudo apt install docker-ce=$DOCKER_VERSION docker-ce-cli=$DOCKER_VERSION containerd.io docker-buildx-plugin docker-compose-plugin

Replace <VERSION> with the exact version string returned by apt list --all-versions docker-ce.

Verify the Docker Installation #

On most Ubuntu systems, the Docker service starts automatically after installation. If it does not, start it manually:

sudo systemctl start docker

Check the service status:

sudo systemctl status docker

The output will look something like this:

● docker.service - Docker Application Container Engine
Loaded: loaded (/usr/lib/systemd/system/docker.service; enabled)
Active: active (running)
...

You can also confirm that the client and daemon are responding:

sudo docker version

To verify that Docker can pull and run containers correctly, run the test image:

sudo docker run hello-world

If the image is not found locally, Docker will download it from Docker Hub, run the container, print a “Hello from Docker” message, and exit.

The container stops after printing the message because it has no long-running process.

Run Docker Commands Without sudo (Highly Recommended) #

By default, only root and a user with sudo privileges can run Docker commands.

To allow a non-root user to execute Docker commands, add the user to the docker group:

sudo usermod -aG docker $USER

$USER is an environment variable that holds the currently logged-in username. If you want to execute commands with another user, replace $USER with that username.

Run newgrp docker or log out and log back in for the group membership changes to take effect.

After that, you can rerun the test container without sudo :

docker run hello-world

Updating Docker #

When a new Docker version is released, update it using standard system commands:

sudo apt update
sudo apt upgrade

To prevent Docker from being updated automatically, mark it as held:

sudo apt-mark hold docker-ce

Uninstalling Docker #

Before uninstalling Docker, it is recommended to remove all containers, images, volumes, and networks :

Run the following commands to stop all running containers and remove all Docker objects:

docker container stop $(docker container ls -aq)
docker system prune -a --volumes -f

Remove Docker packages:

sudo apt purge docker-ce docker-ce-cli containerd.io \
docker-buildx-plugin docker-compose-plugin docker-ce-rootless-extras
sudo apt autoremove

To completely remove Docker data from your system, delete the directories that were created during the installation process:

sudo rm -rf /var/lib/{docker,containerd}

Troubleshooting #

Permission denied while trying to connect to the Docker daemon socket
Your user is not yet in the docker group, or the group membership has not taken effect. Run sudo usermod -aG docker $USER, then log out and back in (or run newgrp docker).

Cannot connect to the Docker daemon. Is the daemon running?
The Docker service is not running. Start it with sudo systemctl start docker and check its status with sudo systemctl status docker.

Package ‘docker-ce’ has no installation candidate
The Docker repository was not added correctly. Re-run Steps 2 and 3, then run sudo apt update before installing.

Containers fail to start after an OS or Docker upgrade
Check the Docker daemon status, the installed Docker version, and your container runtime configuration. If the host or Docker Engine was upgraded recently, review the Docker release notes and verify that your workloads are using a supported configuration before restarting them.

Conclusion #

Installing Docker from the official repository ensures you always have access to the latest stable releases and security updates. For post-install steps such as configuring log drivers or setting up rootless mode, see the official post-install guide .

Node.js is an open-source JavaScript runtime built on Chrome’s V8 engine. It lets you run JavaScript outside the browser and is commonly used for APIs, command-line tools, and server-side applications. npm is the default package manager for Node.js.

This guide covers three ways to install Node.js and npm on Ubuntu 26.04:

• NodeSource repository - Install a specific Node.js version. NodeSource supports Node.js v25.x, v24.x, and v22.x.
• nvm (Node Version Manager) - Manage multiple Node.js versions on the same machine. This is the preferred method for developers.
• Ubuntu repository - The easiest way. Ubuntu 26.04 includes Node.js v22.x, which is suitable for many applications.

Choose the method that fits your needs. If you are not sure which version to install, check the documentation of the application you are deploying.

Quick Reference #

Installing Node.js and npm from NodeSource #

NodeSource maintains an APT repository with multiple Node.js versions. Use this method when you need a specific version.

Install the required dependencies:

sudo apt update
sudo apt install ca-certificates curl gnupg

Import the NodeSource GPG key:

sudo mkdir -p /etc/apt/keyrings
curl -fsSL https://deb.nodesource.com/gpgkey/nodesource-repo.gpg.key | sudo gpg --dearmor -o /etc/apt/keyrings/nodesource.gpg

NodeSource provides the following versions:

• v25.x - The current release.
• v24.x - The latest LTS version (Krypton).
• v22.x - Maintenance LTS version (Jod).

We will install Node.js version 24.x. Change NODE_MAJOR=24 to your preferred version if needed:

NODE_MAJOR=24
echo "deb [signed-by=/etc/apt/keyrings/nodesource.gpg] https://deb.nodesource.com/node_$NODE_MAJOR.x nodistro main" | sudo tee /etc/apt/sources.list.d/nodesource.list

Install Node.js and npm:

sudo apt update
sudo apt install nodejs

The nodejs package includes both node and npm binaries.

Verify the installation:

node --version

You should see output similar to this:

v24.x

npm --version

The output will show the npm version bundled with the installed Node.js release:

11.x

To compile native addons from npm, install the development tools:

sudo apt install build-essential

Installing Node.js and npm using NVM #

NVM (Node Version Manager) is a bash script that lets you manage multiple Node.js versions per user. This is the preferred method for developers who need to switch between versions.

Download and install nvm:

wget -qO- https://raw.githubusercontent.com/nvm-sh/nvm/v0.40.3/install.sh | bash

Do not use sudo , as it will enable nvm for the root user only.

The script clones the repository to ~/.nvm and adds the required lines to your shell profile:

=> Close and reopen your terminal to start using nvm or run the following to use it now:
export NVM_DIR="$HOME/.nvm"
[ -s "$NVM_DIR/nvm.sh" ] && \. "$NVM_DIR/nvm.sh" # This loads nvm
[ -s "$NVM_DIR/bash_completion" ] && \. "$NVM_DIR/bash_completion" # This loads nvm bash_completion

Either close and reopen your terminal or run the commands above to load nvm in the current session.

Verify the installation:

nvm -v

0.40.3

List all available Node.js versions:

nvm list-remote

...
v22.x (LTS: Jod)
...
v24.x (LTS: Krypton)
...
v25.x

Install the latest Node.js version:

nvm install node

...
Now using node v25.x (npm v11.x)
Creating default alias: default -> node (-> v25.x)

Verify the installation:

node -v

v25.x

Install additional versions:

nvm install --lts
nvm install 22

List installed versions:

nvm ls

-> v22.x
v24.x
v25.x
default -> node (-> v25.x)
iojs -> N/A (default)
unstable -> N/A (default)
node -> stable (-> v25.x) (default)
stable -> 25 (-> v25.x) (default)
lts/* -> lts/krypton (-> v24.x)
lts/jod -> v22.x
lts/krypton -> v24.x

The arrow (-> v22.x) indicates the active version. The default version activates when opening new shells.

Switch to a different version:

nvm use 24

Now using node v24.x (npm v11.x)

Change the default version:

nvm alias default 24

Installing Node.js and npm from the Ubuntu repository #

Ubuntu 26.04 includes Node.js v22.x in its default repositories. This version works well for many applications and receives security updates through Ubuntu.

Install Node.js and npm:

sudo apt update
sudo apt install nodejs npm

This installs Node.js along with the tools needed to compile native addons from npm.

Verify the installation:

node -v

v22.x

npm -v

10.x

Uninstalling Node.js #

The uninstall method depends on how you installed Node.js.

NodeSource or Ubuntu repository:

sudo apt remove nodejs
sudo apt autoremove

nvm:

nvm uninstall 24

To completely remove nvm, delete the ~/.nvm directory and remove the nvm lines from your ~/.bashrc or ~/.zshrc file.

Conclusion #

We covered three ways to install Node.js and npm on Ubuntu 26.04. NodeSource provides specific versions, nvm offers flexibility for managing multiple versions, and the Ubuntu repository includes a stable LTS version out of the box.

For more information, see the official Node.js documentation .

Ubuntu 26.04 LTS (Resolute Raccoon) was released on April 23, 2026. It ships with Linux kernel 7.0, GNOME 50, Python 3.14, PHP 8.5, Java 25, TPM-backed full-disk encryption, post-quantum cryptography support in OpenSSL, and a Wayland-only GNOME session. As an LTS release, it receives standard security updates for five years, with expanded coverage available through Ubuntu Pro.

This guide shows how to upgrade to Ubuntu 26.04 LTS from the command line. Ubuntu 25.10 systems can upgrade now, while Ubuntu 24.04 LTS systems will be offered the standard upgrade path after Ubuntu 26.04.1 is released.

Prerequisites #

You need to be logged in as root or a user with sudo privileges to perform the upgrade.

You can upgrade to Ubuntu 26.04 from Ubuntu 25.10 today. Ubuntu 24.04 LTS systems will be offered the standard upgrade path after Ubuntu 26.04.1 is released. If you are running an older release, you must first upgrade to Ubuntu 22.04 and then to 24.04 before continuing.

Make sure you have a working internet connection before starting.

Back Up Your Data #

Before starting a major version upgrade, make sure you have a complete backup of your data. If you are running Ubuntu on a virtual machine, take a full system snapshot so you can restore quickly if anything goes wrong.

Update Currently Installed Packages #

Before starting the release upgrade, bring your existing system fully up to date.

Check whether any packages are marked as held back, as they can interfere with the upgrade:

sudo apt-mark showhold

An empty output means there are no held packages. If there are held packages, unhold them with:

sudo apt-mark unhold package_name

Refresh the package index and upgrade all installed packages:

sudo apt update
sudo apt upgrade

Perform a full distribution upgrade to resolve any remaining dependency changes:

sudo apt full-upgrade

Remove automatically installed dependencies that are no longer needed:

sudo apt --purge autoremove

Upgrade to Ubuntu 26.04 LTS #

You can upgrade from the command line using do-release-upgrade, which works for both desktop and server installations.

do-release-upgrade is part of the update-manager-core package, which is installed by default on most Ubuntu systems. If it is not present, install it first:

sudo apt install update-manager-core

If you are upgrading over SSH, do-release-upgrade may start an additional SSH daemon on port 1022 so you can reconnect if the main session drops. If you use a firewall, you may need to open that port temporarily:

sudo ufw allow 1022/tcp

To begin the release upgrade, run:

sudo do-release-upgrade

If Ubuntu does not offer the new release yet, follow the standard supported rollout for your current version. This guide covers the normal upgrade path.

The tool will disable third-party repositories, update the apt sources to point to the Ubuntu 26.04 repositories, and begin downloading the required packages.

You will be prompted several times during the process. When asked whether services should be automatically restarted, type y. When asked about configuration files, type Y to accept the package maintainer’s version if you have not made custom changes; otherwise keep your current version to avoid losing your customizations.

The upgrade runs inside a GNU screen session and will automatically re-attach if the connection drops.

The process may take some time depending on the number of packages, your hardware, and your internet speed.

Once the new packages are installed, the tool will ask whether to remove obsolete software. Type d to review the list first, or y to proceed with removal.

When the upgrade finishes, you will be prompted to restart the system. Type y to reboot and complete the upgrade.

Verify the Upgrade #

After the system boots, log in and check the Ubuntu version :

lsb_release -a

No LSB modules are available.
Distributor ID: Ubuntu
Description: Ubuntu 26.04 LTS
Release: 26.04
Codename: resolute

You can also confirm the kernel version:

uname -r

The output should show a 7.0.x kernel.

Troubleshooting #

Third-party repository errors during apt update
The upgrade tool disables third-party repositories automatically. If you see errors before running do-release-upgrade, disable the affected sources under /etc/apt/sources.list.d/ and re-enable them one by one after the upgrade completes.

“Packages have been kept back”
Run sudo apt full-upgrade to resolve held-back packages before starting the upgrade. Do not proceed with do-release-upgrade until there are no held packages.

SSH connection drops mid-upgrade
The upgrade runs inside a GNU screen session. Reconnect over SSH and run sudo screen -r to re-attach to the running session.

A service or container does not work after the reboot
If something that worked before the upgrade fails afterward, check its status and logs first. Run systemctl status service_name and journalctl -xe for services, and review your container runtime logs and configuration for Docker or containerd workloads. Third-party packages and older configurations sometimes need updates after a major release upgrade.

GNOME desktop shows only Wayland sessions
Ubuntu 26.04 drops the X11 GNOME session. If you relied on an X11 desktop session, applications that do not support Wayland natively will run through XWayland automatically. For most applications this is transparent, but some older tools may behave differently.

Conclusion #

Your system is now running Ubuntu 26.04 LTS Resolute Raccoon. Re-enable any third-party repositories you disabled before the upgrade and verify that your critical services are running. For a full list of known issues and changes, see the official Ubuntu 26.04 release notes .

Branches are how Git keeps your work separated from the main line of development. A new branch lets you experiment, fix a bug, or build a feature without touching what is already shipped, and a merge brings the work back together when it is ready. The tool that creates, lists, and removes those branches is git branch.

This guide explains how to use git branch to manage local and remote branches, filter by merged or upstream state, rename branches, and clean up stale ones.

git branch Syntax #

The general form of the command is:

git branch [OPTIONS] [BRANCH] [START_POINT]

With no arguments, git branch lists your local branches and marks the currently checked-out one with an asterisk. With a branch name, it creates a new branch pointing at the current commit. With additional flags, it can list remote branches, delete branches, rename them, or set upstream tracking.

Listing Branches #

To list the local branches in the current repository, run git branch with no arguments:

git branch

 develop
* main
feature/login

The asterisk marks the branch you are currently on. The branches are sorted alphabetically.

To include remote-tracking branches, add -a (all):

git branch -a

 develop
* main
feature/login
remotes/origin/HEAD -> origin/main
remotes/origin/develop
remotes/origin/main

Anything prefixed with remotes/ is a local reference to a branch on a remote, not a branch you can commit to directly. Check it out to create a local tracking branch.

To list only remote-tracking branches, use -r:

git branch -r

To see the latest commit on each branch, add -v:

git branch -v

 develop a1b2c3d Add release notes
* main 7e8f9a0 Merge pull request #42
feature/login 3d4e5f6 Stub login form

For even more detail, -vv also prints the upstream branch each local branch tracks and whether it is ahead, behind, or in sync:

git branch -vv

 develop a1b2c3d [origin/develop] Add release notes
* main 7e8f9a0 [origin/main] Merge pull request #42
feature/login 3d4e5f6 [origin/feature/login: ahead 2] Stub login form

Creating a Branch #

To create a new branch, pass the name as an argument. This creates the branch at the current HEAD but does not switch to it:

git branch feature/login

To start the branch from a specific commit, tag, or another branch, pass it as the second argument:

git branch hotfix v1.4.0

git branch hotfix 3d4e5f6

Creating a branch without switching to it is useful when you want to mark a commit for later work. Most of the time, though, you create a branch and switch to it in one step. The modern command for that is git switch -c:

git switch -c feature/login

The older equivalent is git checkout -b feature/login. Both create the branch at the current commit and check it out immediately. See the create and list Git branches guide for a fuller walkthrough.

Renaming a Branch #

To rename the branch you are currently on, use -m with the new name:

git branch -m new-name

To rename any branch, pass both the old and the new name:

git branch -m old-name new-name

If a branch with the target name already exists, this form fails to protect you from overwriting it. To force the rename and overwrite the existing branch, use the capital -M instead. Use -M with care: it discards the destination branch.

After renaming a branch that is already pushed, push the new name to the remote and delete the old one so collaborators see the change. The rename a Git branch guide walks through the full local-and-remote flow.

Deleting a Branch #

To delete a local branch that has been merged into the current branch, use -d:

git branch -d feature/login

Deleted branch feature/login (was 3d4e5f6).

Git refuses to delete a branch that has unmerged work, to protect you from losing commits:

error: The branch 'feature/wip' is not fully merged.
If you are sure you want to delete it, run 'git branch -D feature/wip'.

If you are sure the work is no longer needed, force the deletion with -D:

git branch -D feature/wip

You cannot delete the branch you are currently on. Switch to another branch first, then delete it. For remote branch deletion, see the delete local and remote Git branch guide.

Filtering by Merged State #

git branch can filter branches by whether they are fully merged into the current branch. List branches that have been merged:

git branch --merged

This is the safest way to find branches that can be deleted without losing history. Before deleting anything, preview the filtered list:

git branch --merged | grep -vE '^\*|^[[:space:]]*(main|develop)$'

The grep filter keeps the current branch and the protected main and develop branches out of the list. If the output looks correct, pipe the same list to git branch -d:

git branch --merged | grep -vE '^\*|^[[:space:]]*(main|develop)$' | xargs -r git branch -d

To list branches that still have unmerged work, use --no-merged:

git branch --no-merged

These are the branches you should review before deleting, because they contain commits that are not on your current branch.

Filtering Remote Branches Too #

--merged and --no-merged accept a reference argument. To check against main from the remote:

git branch --merged origin/main

This is useful in CI or cleanup scripts where you want to see which local branches are safely merged into the shipped code, regardless of which branch you are currently on.

Setting an Upstream Branch #

An upstream branch tells Git which remote branch your local branch tracks for git pull and git push. To set it on an existing branch, use --set-upstream-to (or -u):

git branch --set-upstream-to=origin/main main

Branch 'main' set up to track remote branch 'main' from 'origin'.

To remove tracking information from a branch, use --unset-upstream:

git branch --unset-upstream main

When you push a new branch to a remote for the first time, pass -u to git push to create the remote branch and set it as the upstream in one step:

git push -u origin feature/login

Showing the Current Branch #

To print just the name of the branch you are on, use --show-current:

git branch --show-current

main

This is the right command for shell prompts and scripts. It prints nothing if you are in a detached HEAD state, which scripts can detect and handle.

Copying a Branch #

git branch -c copies a branch, including its reflog and configuration, to a new name:

git branch -c old-branch new-branch

The original branch is kept. Use the capital -C to force the copy and overwrite an existing target branch. Copying is less common than creating a fresh branch, but it is useful when you want to preserve the history and config of a branch under a new name.

Sorting the Branch List #

By default, branches are listed alphabetically. The --sort option changes the order. To sort by the date of the most recent commit:

git branch --sort=-committerdate

The minus sign reverses the order, so the most recently updated branch appears first. This is handy when you return to a project after a break and want to see what you were working on last.

Quick Reference #

FAQ #

What is the difference between git branch and git checkout?
git branch manages branches: creating, listing, renaming, and deleting. git checkout (and its modern replacement git switch) changes which branch you are on. Creating and switching in one step uses git switch -c or git checkout -b.

How do I delete a remote branch?
git branch -d only deletes local branches. To delete a branch on the remote, run git push origin --delete BRANCH_NAME. The delete local and remote Git branch guide covers the full flow, including cleanup of stale tracking references.

Why does Git say “branch is not fully merged”?
The branch has commits that are not reachable from your current branch. Git is protecting you from losing work. Review the commits with git log BRANCH_NAME, merge them if needed, and then use -d again. If you are certain the commits are not needed, force the delete with -D.

How do I see which branch a remote branch tracks locally?
Run git branch -vv. The output includes each local branch’s upstream in brackets along with its ahead and behind counts relative to that upstream.

Can I list branches sorted by who committed most recently?
Yes. Use git branch --sort=-committerdate to sort branches by the timestamp of their most recent commit, with the freshest branch first. This is a fast way to see what is actively being worked on.

Conclusion #

git branch covers the full lifecycle of a branch: creating it, renaming it, keeping track of what it points at, and deleting it when the work is done. Combined with git switch for moving between branches and git merge for integrating changes, it is the foundation of any Git workflow.

For related Git commands, see the git diff guide for reviewing changes and the git log guide for inspecting branch history.

By default, a Bash script will keep running after a command fails, treat unset variables as empty strings, and hide errors inside pipelines. That is convenient for one-off commands in an interactive shell, but inside a script it is a recipe for silent corruption: a failed backup step that still reports success, an unset path that expands to rm -rf /, a curl | sh pipeline that swallows a 500 error.

Bash strict mode is a short set of flags you put at the top of a script to make the shell fail loudly instead. This guide explains each flag in set -euo pipefail, shows what it changes with real examples, and covers the cases where you need to turn it off.

The Strict Mode Line #

You will see this line at the top of many modern shell scripts:

#!/usr/bin/env bash
set -euo pipefail
IFS=$'\n\t'

Each flag addresses a different class of silent failure:

• set -e exits immediately when a command returns a non-zero status.
• set -u treats references to unset variables as an error.
• set -o pipefail makes a pipeline fail if any command in it fails, not just the last.
• IFS=$'\n\t' narrows word splitting so unquoted expansions do not split on spaces.

You can enable the options separately, but in practice they are almost always used together.

set -e: Exit on Error #

Without set -e, a failing command in a script does not stop execution. The script happily continues to the next line:

#!/usr/bin/env bash
cp /does/not/exist /tmp/dest
echo "Backup complete"

Running it prints both the error and the success message:

./no-strict.sh

cp: cannot stat '/does/not/exist': No such file or directory
Backup complete

The script exits with status 0, so any caller thinks the backup worked. Adding set -e changes the behavior:

#!/usr/bin/env bash
set -e
cp /does/not/exist /tmp/dest
echo "Backup complete"

./strict.sh
echo $?

cp: cannot stat '/does/not/exist': No such file or directory
1

The script stops at the failing cp, never prints “Backup complete”, and exits with a non-zero status. Anyone scheduling this through cron or a CI pipeline now gets a real failure signal.

Opting Out for a Single Command #

Sometimes you expect a command to fail and want to handle the result yourself. Append || true to tell set -e to ignore the exit status of that one command:

grep "pattern" config.txt || true

You can also use if or &&, which set -e treats as deliberate checks:

if ! grep -q "pattern" config.txt; then
 echo "pattern missing"
fi

This is the canonical way to check for something without exiting the script when it is not there.

set -u: Fail on Unset Variables #

A classic shell footgun is a typo in a variable name. Without strict mode, Bash silently expands the misspelled variable to an empty string:

#!/usr/bin/env bash
TARGET_DIR="/var/backups"
rm -rf "$TARGE_DIR/old"

The script deletes /old because $TARGE_DIR is empty. With set -u, the same script exits before the rm runs:

#!/usr/bin/env bash
set -u
TARGET_DIR="/var/backups"
rm -rf "$TARGE_DIR/old"

./unset-strict.sh: line 4: TARGE_DIR: unbound variable

Handling Optional Variables #

Environment variables that may or may not be set need a default to play nicely with set -u. The ${VAR:-default} syntax provides one without touching the original:

PORT="${PORT:-8080}"
echo "Listening on $PORT"

If $PORT is unset or empty, the script uses 8080. If it is set, the original value is kept.

set -o pipefail: Catch Failures Inside Pipelines #

By default, the exit status of a pipeline is the exit status of the last command. Everything to the left can fail silently:

curl https://bad.example.com/data | tee data.txt

If curl fails with a 404, the pipeline still exits 0 because tee wrote its (empty) input successfully. With set -o pipefail, the pipeline adopts the first non-zero exit status from any command in it:

#!/usr/bin/env bash
set -o pipefail
curl https://bad.example.com/data | tee data.txt
echo "Exit: $?"

curl: (6) Could not resolve host: bad.example.com
Exit: 6

This is the one flag that fixes the most “my script said it succeeded but clearly did not” bugs, and it is the one most often forgotten when people add just set -e.

IFS: Safer Word Splitting #

The Internal Field Separator (IFS) controls how Bash splits unquoted expansions into words. The default is space, tab, and newline, which means a filename with a space in it gets split into two arguments:

files="one two.txt three.txt"
for f in $files; do
 echo "$f"
done

one
two.txt
three.txt

Setting IFS=$'\n\t' removes the space from the separator list. You still get clean splitting on newlines (useful for reading find or ls output) and on tabs (useful for TSV data), but spaces inside values are preserved.

Even with a narrower IFS, always quote your expansions ("$var", "${array[@]}"). IFS tightening is a safety net, not a replacement for quoting.

When Strict Mode Gets in the Way #

Strict mode is opinionated, and a few situations push back. The most common one is reading a file line by line with a while loop and a counter:

count=0
while read -r line; do
 count=$((count + 1))
done < input.txt

That works fine, but if you increment with ((count++)) inside set -e, the script exits on the first iteration because ((count++)) returns the pre-increment value (0), which Bash treats as a failure. Use count=$((count + 1)) or ((count++)) || true to stay compatible.

Another common case is probing for a command:

if ! command -v jq >/dev/null; then
 echo "jq is not installed"
 exit 1
fi

Using command -v inside an if is safe even under set -e, because set -e does not trigger on commands in conditional contexts.

If you need to temporarily disable a flag for a specific block, turn it off and back on:

set +e
some_flaky_command
result=$?
set -e

This is cleaner than sprinkling || true everywhere when you have a block of commands that need softer error handling.

A Minimal Strict Script Template #

Use this as a starting point for new scripts:

#!/usr/bin/env bash
set -euo pipefail
IFS=$'\n\t'

# Script body goes here.

It is four lines, and it catches the majority of silent failures that cause shell scripts to misbehave in production.

Quick Reference #

Troubleshooting #

Script exits silently with no error message
A command is failing under set -e without printing anything. Run the script with bash -x script.sh to trace execution and see which line aborts.

unbound variable on a variable that sometimes is set
Replace the reference with ${VAR:-} to provide an empty default, or ${VAR:-fallback} to provide a meaningful one.

Pipeline fails on a command that is supposed to stop early
Commands like head can cause the producer to receive SIGPIPE, which pipefail treats as a failure. Either redesign the pipeline or wrap the producer in || true when the early exit is expected.

Strict mode breaks a sourced script
The set flags apply to the current shell. If you source a script that expects the old behavior, either fix the sourced script or wrap the source call between set +e and set -e.

FAQ #

Should every Bash script use strict mode?
For scripts that run unattended (cron jobs, CI steps, deployment scripts), yes. For short interactive helpers, the flags are still useful, but the cost of a missed edge case is lower.

Does strict mode work in sh or dash?
set -e and set -u are POSIX, so they work in any compliant shell. set -o pipefail is a Bash extension that also works in Zsh and Ksh, but not in pure POSIX sh or dash.

Is set -e really that unreliable?
set -e has well-known edge cases, especially around functions and subshells. It is not a replacement for explicit error handling in critical paths, but combined with pipefail and -u it catches far more bugs than it causes.

How do I pass set -euo pipefail to a one-liner?
Use bash -euo pipefail -c 'your command' when invoking Bash from another program such as ssh or a Makefile.

Conclusion #

set -euo pipefail and a tighter IFS catch many of the silent failures that make shell scripts hard to trust. Pair strict mode with clear error handling using Bash functions and a proper shebang line when you want scripts to fail early and predictably.

Sooner or later, every Git user runs into the same question: should you use git fetch or git pull to get the latest changes from the remote? The two commands look similar, and both talk to the remote repository, but they do very different things to your working branch.

This guide explains the difference between git fetch and git pull, how each command works, and when to use one over the other.

Quick Reference #

What git fetch Does #

git fetch downloads commits, branches, and tags from a remote repository and stores them locally under remote-tracking references such as origin/main or origin/feature-x. It does not touch your working directory, your current branch, or the index.

git fetch origin

remote: Enumerating objects: 12, done.
remote: Counting objects: 100% (12/12), done.
From github.com:example/project
4a1c2e3..9f7b8d1 main -> origin/main
a6d4c02..1e2f3a4 feature-x -> origin/feature-x

The output shows which remote branches were updated. After the fetch, the local branch main is still pointing to whatever commit it was on before. Only the remote-tracking branch origin/main has moved.

You can then inspect what changed before doing anything with it:

git log main..origin/main

This is the safe way to look at new work without merging or rebasing yet. It gives you a preview of what the remote has that your branch does not.

What git pull Does #

git pull is a convenience command. Under the hood, it runs git fetch followed by an integration step (a merge by default, or a rebase if configured). In other words:

git pull origin main

is roughly equivalent to:

git fetch origin
git merge origin/main

After git pull, your current branch has moved forward, and your working directory may contain new files, updated files, or merge conflicts that need resolving. The change is immediate and affects your checked-out branch.

Side-By-Side Comparison #

The difference between the two commands comes down to what they change in your repository.

git fetch is read-only from your branch’s perspective. git pull actively changes your branch.

When to Use git fetch #

Use git fetch when you want to see what changed on the remote without integrating anything yet. This is useful before you start new work, before rebasing a feature branch, or when you want to inspect a teammate’s branch safely.

For example, after fetching, you can compare your branch with the remote like this:

git log HEAD..origin/main --oneline

This shows commits that exist on the remote but not in your current branch. Running git fetch often is cheap and has no side effects on your work, which is why many developers do it regularly throughout the day.

When to Use git pull #

Use git pull when you are ready to bring remote changes into your current branch and keep working on top of them. The common flow looks like this:

git checkout main
git pull origin main

This is the quickest way to sync a branch with its upstream when you know the integration will be straightforward, such as on a shared main branch where you rarely have local commits. git pull always updates the branch you currently have checked out, so it is worth confirming where you are before you run it.

If you want a cleaner history without merge commits, configure pull to rebase:

git config --global pull.rebase true

From that point on, git pull runs git fetch followed by git rebase instead of git merge. Your local commits are replayed on top of the fetched changes, producing a linear history.

Avoiding Merge Surprises #

The biggest reason to prefer git fetch over git pull in day-to-day work is control. A bare git pull on a branch where you have local commits can create a merge commit, introduce conflicts, or rewrite history during a rebase, all in one step.

A safer pattern is:

git fetch origin
git log HEAD..origin/main --oneline
git merge origin/main

You fetch first, review what is coming, then decide whether to merge, rebase, or defer the integration. For active feature branches, this workflow avoids most of the “what just happened to my branch” moments.

If you already ran git pull and need to inspect what happened, start with:

git log --oneline --decorate -n 5

This helps you confirm whether Git created a merge commit, fast-forwarded the branch, or rebased your local work.

If the pull created a merge commit that you do not want, ORIG_HEAD often points to the commit your branch was on before the pull. In that case, you can reset back to it:

git reset --hard ORIG_HEAD

Useful Flags #

A few flags make both commands more predictable in real workflows.

• git fetch --all - Fetch from every configured remote, not only origin.
• git fetch --prune - Remove remote-tracking branches that no longer exist on the remote.
• git fetch --tags - Download tags in addition to branches.
• git pull --rebase - Rebase your local commits on top of the fetched changes instead of merging.
• git pull --ff-only - Update the branch only if Git can fast-forward it; prevents unexpected merge commits.

--ff-only is especially useful on shared branches. If your branch cannot move forward by simply advancing the pointer, the pull fails and you decide what to do next.

FAQ #

Does git fetch modify any local files?
No. It only updates remote-tracking references such as origin/main. Your branches, working directory, and staging area stay the same.

Is git pull the same as git fetch plus git merge?
By default, yes. With pull.rebase set to true (or --rebase on the command line), it runs git fetch followed by git rebase instead.

Which one should I use daily?
Prefer git fetch for visibility and git pull --ff-only (or git pull --rebase) for the integration step. A bare git pull works, but it hides two operations behind one command.

How do I see what git fetch downloaded?
Use git log main..origin/main to see commits on the remote that are not yet in your local branch, or git diff main origin/main to compare the content directly.

Can git fetch cause conflicts?
No. Conflicts only happen when you merge or rebase the fetched commits into your branch. Fetching itself is conflict-free.

Conclusion #

git fetch lets you inspect remote changes without touching your branch, while git pull fetches and integrates those changes in one step. If you want more control and fewer surprises, fetch first, review the incoming commits, and then merge or rebase on your own terms. For more Git workflow details, see the git log command and git diff command guides.

When you download an ISO image, a backup archive, or a large release tarball, there is no easy way to tell by looking whether the file arrived intact. A single flipped bit can break a boot image or turn a compressed archive into junk, and a compromised mirror can serve a tampered file that looks legitimate. The fix is to compare a cryptographic fingerprint of the file against a value the publisher has signed or posted somewhere you trust.

This guide shows how to use sha256sum and md5sum to generate, compare, and verify checksums on Linux, and when to use each one.

sha256sum and md5sum Syntax #

Both commands follow the same form:

sha256sum [OPTIONS] [FILE]...
md5sum [OPTIONS] [FILE]...

Without options, each command prints a hex digest followed by two spaces and the file name. Pass -c to verify files against a list of previously generated checksums.

sha256sum vs md5sum #

The two tools do the same job: they read a file and print a fixed-length fingerprint. The difference is the algorithm and, by extension, how safe the result is against intentional tampering.

md5sum uses the MD5 algorithm and produces a 128-bit digest. MD5 is fast but has been broken for years: it is possible to construct two different files that share the same MD5 hash. Treat it as a checksum for accidental corruption only, not for authenticity or security.

sha256sum uses SHA-256 from the SHA-2 family and produces a 256-bit digest. It is the default choice for verifying downloads, release artifacts, and anything where the threat model includes a malicious middle party. Most Linux distributions publish SHA256SUMS files next to their ISO images for exactly this reason.

When in doubt, use sha256sum. Reach for md5sum only when a publisher provides MD5 values and nothing stronger, or when you need quick parity checks between known-good files.

Generating a Checksum for a File #

To produce a SHA-256 digest for a single file, pass it as an argument:

sha256sum ubuntu-24.04.2-desktop-amd64.iso

5e38b55d57d94ff029719342357325ed3bda38fa80054f9330dc789cd2d43931 ubuntu-24.04.2-desktop-amd64.iso

The output is one line: the hex digest, two spaces, and the file name. The same file always produces the same digest, so you can run the command again after a copy or a download and compare the values by eye.

md5sum behaves the same way:

md5sum ubuntu-24.04.2-desktop-amd64.iso

2e3720b76b2f9f96edc43ec4d87d7d52 ubuntu-24.04.2-desktop-amd64.iso

Notice that the MD5 digest is shorter. That is the 128-bit hash encoded in 32 hex characters, compared with 64 hex characters for SHA-256.

Generating Checksums for Multiple Files #

Both commands accept any number of file arguments and print one line per file:

sha256sum *.tar.gz

b2b09c1e04b2a3a4c5d6e7f890123456789abcdef0123456789abcdef01234567 backup-2026-04-01.tar.gz
c3d4e5f6a7b8c9d0e1f2a3b4c5d6e7f8091a2b3c4d5e6f708192a3b4c5d6e7f8 backup-2026-04-08.tar.gz

To save the output to a checksum file that you can share or verify later, redirect it:

sha256sum *.tar.gz > SHA256SUMS

The resulting SHA256SUMS file can be published alongside the archives, and anyone who downloads them can run a single command to confirm that their copy matches.

Verifying a File Against a Known Checksum #

The most common task is to check that a download matches the digest the publisher posted. Distributions usually ship a SHA256SUMS file that lists every release file and its digest. Change into the directory that holds both the archive and the checksum file, then pass -c:

sha256sum -c SHA256SUMS

ubuntu-24.04.2-desktop-amd64.iso: OK
ubuntu-24.04.2-live-server-amd64.iso: OK

sha256sum reads each line of SHA256SUMS, recomputes the digest for the named file, and prints OK when they match. Any line whose file is missing or whose digest differs prints a clear error and causes the command to exit with a non-zero status, which is convenient in scripts.

When you only care about one file out of many, grep the relevant line into the check:

grep "ubuntu-24.04.2-desktop-amd64.iso" SHA256SUMS | sha256sum -c -

The trailing - tells sha256sum to read the checksum list from standard input. This keeps the verification scoped to a single file without creating a second checksum file.

Comparing a File to a Published Digest #

Sometimes the publisher does not provide a full SHA256SUMS file but instead shows a single digest on a release page. You can compare it directly without creating a file:

echo "5e38b55d57d94ff029719342357325ed3bda38fa80054f9330dc789cd2d43931 ubuntu-24.04.2-desktop-amd64.iso" | sha256sum -c -

ubuntu-24.04.2-desktop-amd64.iso: OK

The key detail is the double space between the digest and the file name. That is the exact format sha256sum produces and expects, and a single space will cause the check to fail.

Quiet and Warn Modes #

During an automated check, the per-file OK lines can be noisy. The --quiet option suppresses successful lines so only failures appear:

sha256sum -c --quiet SHA256SUMS

If every file passes, the command prints nothing and exits with status 0. If a file fails, you see a single failure line and a non-zero exit status, which fits well in a CI job or a backup script.

To flag lines in a checksum file that are not formatted correctly, add --warn. This is helpful when the file was assembled by hand and you want to be sure every entry parses.

Common Options #

The flags below are the ones you are likely to use day to day:

• -c, --check - Read digests from a file and verify each one.
• -b, --binary - Mark files as binary in the output (default on Linux).
• -t, --text - Read files in text mode (rare on Linux, kept for portability).
• --quiet - Suppress OK lines when checking.
• --status - Print nothing; rely on the exit status alone.
• --ignore-missing - Skip files listed in the digest file that are not present.
• --tag - Output BSD-style tagged format, useful when mixing hash algorithms.

md5sum accepts the same flags, which makes it easy to swap one command for the other when the algorithm changes.

Quick Reference #

Verifying a Download End to End #

Putting the pieces together, a typical download check looks like this:

wget https://releases.ubuntu.com/24.04/ubuntu-24.04.2-desktop-amd64.iso
wget https://releases.ubuntu.com/24.04/SHA256SUMS
sha256sum -c --ignore-missing SHA256SUMS

The --ignore-missing flag keeps the check focused on the file you actually downloaded instead of failing on every other release listed in SHA256SUMS.

For full confidence, also verify the signature on SHA256SUMS itself using the publisher’s GPG key. A digest is only as trustworthy as the source you got it from, so a signed checksum file closes the loop.

Troubleshooting #

Checksum mismatch on a freshly downloaded file
Re-download the file, ideally from a different mirror. The most common cause is a truncated transfer or a network error. If the second download still fails, the file on the mirror may be stale or tampered with, and you should report it to the project.

No such file or directory when running with -c
The names in the checksum file are resolved relative to the current directory. Change into the directory that holds the files, or edit the checksum file to use paths that match where the files live.

improperly formatted checksum line warnings
A single space between the digest and the file name instead of two, trailing whitespace, or Windows line endings will all trip the parser. Run dos2unix on the file or recreate it with sha256sum > SHA256SUMS to reset the format.

The MD5 digest matches but you still do not trust the file
You are right to be cautious. MD5 collisions are practical, so match an MD5 against accidental corruption only. Ask the publisher for a SHA-256 digest or a signed checksum file.

FAQ #

Which is faster, sha256sum or md5sum?
md5sum is faster, sometimes noticeably so on large files. The speed difference rarely matters on modern hardware, and it is not a good reason to pick MD5 over SHA-256 for security-sensitive checks.

Can I use sha256sum on a directory?
Not directly. Hash tools operate on files. To produce a digest that represents an entire directory, pipe a deterministic listing such as find ... -type f -print0 | sort -z | xargs -0 sha256sum through another sha256sum.

Where do I find the expected digest for a Linux distro ISO?
Every major distribution publishes a SHA256SUMS or SHA512SUMS file on its download page, usually along with a detached GPG signature. Prefer those files over digests shown in third-party blog posts.

Is sha256sum available by default on Linux?
Yes. Both sha256sum and md5sum ship with the GNU coreutils package, which is installed on every mainstream Linux distribution.

Conclusion #

sha256sum should be the default for verifying downloads and backups, with md5sum reserved for quick corruption checks when the publisher provides nothing stronger. When you pair a SHA-256 digest with a signed checksum file and a trusted key, you can answer the question that matters most: did I get the file the publisher actually shipped?

When you run a PostgreSQL database in production, you rarely want every application and every developer to connect as the postgres superuser. A clean setup gives each service its own login role with a scoped set of privileges, so a bug or a leaked password cannot touch unrelated data.

PostgreSQL handles this with roles. A role can represent a single user, a group, or both at the same time, and privileges are granted to roles rather than to raw login accounts. This guide explains how to create roles, set passwords, grant and revoke privileges, and clean up roles you no longer need.

Roles vs Users in PostgreSQL #

Historically, PostgreSQL had separate CREATE USER and CREATE GROUP statements. Modern versions replaced both with a single concept: the role. A role with the LOGIN attribute can connect to the server, which makes it a user. A role without LOGIN is typically used as a group that other roles inherit privileges from.

In practice, CREATE USER is still valid and is treated as a shortcut for CREATE ROLE ... LOGIN. We will use both forms in this guide.

Connecting to PostgreSQL #

All the commands below run inside the psql shell. On most systems you can open it as the postgres system user:

sudo -u postgres psql

You will see a prompt like this:

postgres=#

Every SQL statement ends with a semicolon. If you forget it, psql keeps waiting for more input.

Creating a Role #

The simplest form of CREATE ROLE takes just a name:

CREATE ROLE linuxize;

This role exists but cannot log in yet and has no password.

To create a login role with a password, use LOGIN:

CREATE ROLE linuxize_login WITH LOGIN PASSWORD 'strong_password_here';

The equivalent shortcut is:

CREATE USER linuxize_user WITH PASSWORD 'strong_password_here';

Both statements produce the same result. Use whichever form reads more clearly in your scripts.

Useful Role Attributes #

You can combine several attributes in a single CREATE ROLE statement. These are the ones you will reach for most often:

• LOGIN - The role can connect to the server.
• PASSWORD 'secret' - Sets the login password.
• SUPERUSER - Grants full access, equivalent to the postgres role. Use sparingly.
• CREATEDB - The role may create new databases.
• CREATEROLE - The role may create and modify other roles.
• INHERIT - The role automatically inherits privileges of roles it is a member of. This is the default.
• VALID UNTIL 'timestamp' - Expires the password at the given time.
• CONNECTION LIMIT n - Caps the number of concurrent connections for this role.

For example, to create a login role that can also create databases and is limited to ten concurrent connections:

CREATE ROLE app_owner WITH LOGIN PASSWORD 'strong_password_here' CREATEDB CONNECTION LIMIT 10;

Listing Existing Roles #

To see every role on the server, use the \du meta-command:

\du

 List of roles
Role name | Attributes
-----------+------------------------------------------------------------
app_owner | Create DB, 10 connections
linuxize |
postgres | Superuser, Create role, Create DB, Replication, Bypass RLS

The Attributes column tells you what each role can do. A blank column means the role has no special attributes beyond the defaults, such as NOLOGIN and INHERIT.

Changing a Role #

Use ALTER ROLE to change attributes, rename a role, or reset a password. To change the password:

ALTER ROLE linuxize WITH PASSWORD 'new_password_here';

To grant an additional attribute:

ALTER ROLE linuxize CREATEDB;

To remove one, prefix it with NO:

ALTER ROLE linuxize NOCREATEDB;

Creating a Database for the Role #

It is common to give each application its own database owned by its login role. Create the database and assign ownership in one statement:

CREATE DATABASE linuxize_app OWNER linuxize;

The owner of a database has full control over it, so the role can create tables, schemas, and other objects without any further grants.

Granting Privileges #

Privileges in PostgreSQL are granted at several levels: database, schema, table, column, sequence, and function. The syntax is consistent across levels:

GRANT privilege_list ON object_type object_name TO role_name;

Database-level Privileges #

To let a role connect to a database and create objects in it:

GRANT CONNECT ON DATABASE linuxize_app TO linuxize;
GRANT CREATE ON DATABASE linuxize_app TO linuxize;

CONNECT controls whether the role can open a session to the database. CREATE controls whether it can create schemas.

Schema-level Privileges #

To let a role create and use objects inside a schema:

GRANT USAGE ON SCHEMA public TO linuxize;
GRANT CREATE ON SCHEMA public TO linuxize;

USAGE is required for almost every operation inside the schema. CREATE lets the role add new tables, views, or functions.

Table-level Privileges #

Table privileges match the common SQL operations:

GRANT SELECT, INSERT, UPDATE, DELETE ON TABLE orders TO linuxize;

To grant every available table privilege at once:

GRANT ALL PRIVILEGES ON TABLE orders TO linuxize;

To grant the same privileges on every existing table in a schema:

GRANT SELECT, INSERT, UPDATE, DELETE ON ALL TABLES IN SCHEMA public TO linuxize;

This only affects tables that exist at the moment you run the command. Tables created later are not covered.

Default Privileges for Future Objects #

To cover tables created in the future, set default privileges:

ALTER DEFAULT PRIVILEGES IN SCHEMA public
 GRANT SELECT, INSERT, UPDATE, DELETE ON TABLES TO linuxize;

From this point on, any new table created in public by the current role inherits the listed privileges for linuxize.

Revoking Privileges #

REVOKE is the mirror of GRANT and uses the same structure:

REVOKE INSERT, UPDATE, DELETE ON TABLE orders FROM linuxize;

To strip every privilege on a table:

REVOKE ALL PRIVILEGES ON TABLE orders FROM linuxize;

Revoking a privilege only affects the privileges you previously granted. Ownership is a separate concept: the owner of an object always keeps full control over it, regardless of grants.

Group Roles #

To manage privileges for a team, create a role without LOGIN and add members to it:

CREATE ROLE readonly;
GRANT CONNECT ON DATABASE linuxize_app TO readonly;
GRANT USAGE ON SCHEMA public TO readonly;
GRANT SELECT ON ALL TABLES IN SCHEMA public TO readonly;

GRANT readonly TO linuxize;

linuxize now inherits every privilege granted to readonly. To remove the membership later:

REVOKE readonly FROM linuxize;

This pattern scales better than granting privileges role by role, because you change permissions in one place.

Deleting a Role #

To drop a role, use DROP ROLE:

DROP ROLE linuxize;

PostgreSQL refuses the command if the role still owns any objects or holds any privileges. To clean these up first, reassign the objects and drop dependent privileges in each database where the role owns objects:

REASSIGN OWNED BY linuxize TO postgres;
DROP OWNED BY linuxize;
DROP ROLE linuxize;

REASSIGN OWNED transfers ownership of objects owned by the role in the current database, and DROP OWNED removes any remaining privileges there. If the role owns objects in other databases, repeat the cleanup in each one before dropping the role.

Quick Reference #

Troubleshooting #

ERROR: permission denied for schema public
Grant USAGE on the schema: GRANT USAGE ON SCHEMA public TO role_name;. On PostgreSQL 15 and later, the public schema is no longer writable by default, so you may also need GRANT CREATE ON SCHEMA public.

ERROR: role "name" cannot be dropped because some objects depend on it
Reassign and drop the role’s objects first: REASSIGN OWNED BY name TO postgres; DROP OWNED BY name;, then run DROP ROLE name; again.

FATAL: password authentication failed for user
Check that the role has LOGIN and that the authentication method in pg_hba.conf matches the client (for example, md5 or scram-sha-256). Reload the configuration with SELECT pg_reload_conf(); after editing pg_hba.conf.

New tables are not visible to a read-only user
Grants on ALL TABLES IN SCHEMA only cover tables that exist at grant time. Set ALTER DEFAULT PRIVILEGES for the owning role so new tables inherit the read permissions automatically.

FAQ #

What is the difference between CREATE USER and CREATE ROLE?
CREATE USER is a shortcut for CREATE ROLE ... LOGIN. Both create the same kind of object. Use CREATE USER when you want a login account and CREATE ROLE when you are creating a group role without login.

Can a single role be both a user and a group?
Yes. A role with LOGIN can still be granted to other roles. Members inherit its privileges as long as INHERIT is set, which is the default.

How do I change the owner of an existing database?
Use ALTER DATABASE db_name OWNER TO new_owner;. The new owner gains full control over the database and its objects.

Do I need to restart PostgreSQL after creating a role?
No. Role changes take effect immediately. Only changes to pg_hba.conf or the main server configuration require a reload or restart.

Conclusion #

Roles are the single unit of access control in PostgreSQL. Give each application its own login role, group shared privileges into group roles, and use ALTER DEFAULT PRIVILEGES so future objects stay consistent with your current policy.

For related reading, see how to check the PostgreSQL version and the installation guide for your distribution under the PostgreSQL tag .

Sometimes the change you need is already written, just on the wrong branch. A hotfix may land on main when it also needs to go to a maintenance branch, or a useful commit may be buried in a feature branch that you do not want to merge wholesale. In that situation, git cherry-pick lets you copy the effect of a specific commit onto your current branch.

This guide explains how git cherry-pick works, how to apply one or more commits safely, and how to handle the conflicts that can appear along the way.

Syntax #

The general syntax for git cherry-pick is:

git cherry-pick [OPTIONS] COMMIT...

• OPTIONS - Flags that change how Git applies the commit.
• COMMIT - One or more commit hashes, branch references, or commit ranges.

git cherry-pick replays the changes introduced by the selected commit on top of your current branch. Git creates a new commit, so the result has a different commit hash even when the file changes are the same.

Cherry-Picking a Single Commit #

Start by finding the commit you want to copy. This example lists the recent commits on a feature branch:

git log --oneline feature/auth

a3f1c92 Fix null pointer in auth handler
d8b22e1 Add login form validation
7c4e003 Refactor session logic

The output gives you the abbreviated commit hashes. In this case, a3f1c92 is the fix we want to move.

Switch to the target branch before running git cherry-pick:

git switch main
git cherry-pick a3f1c92

[main 9b2d4f1] Fix null pointer in auth handler
Date: Tue Apr 14 10:42:00 2026 +0200
1 file changed, 2 insertions(+)

Git applies the change from a3f1c92 to main and creates a new commit, 9b2d4f1. The subject line is the same, but the commit hash is different because the parent commit is different.

Cherry-Picking Multiple Commits #

If you need more than one non-consecutive commit, pass each hash in the order you want Git to apply them:

git cherry-pick a3f1c92 d8b22e1

Git creates a separate new commit for each one. This works well when you need a few targeted fixes but do not want the rest of the source branch.

For a range of consecutive commits, use the range notation:

git cherry-pick a3f1c92^..7c4e003

This tells Git to include a3f1c92 and every commit after it up to 7c4e003. If you omit the caret, the starting commit itself is excluded:

git cherry-pick a3f1c92..7c4e003

That form applies every commit after a3f1c92 through 7c4e003.

Applying Changes Without Committing #

Sometimes you want the changes from a commit, but not an automatic commit for each one. Use --no-commit (or -n) to apply the changes to your working tree and staging area without creating the commit yet:

git cherry-pick --no-commit a3f1c92

This is useful when you want to combine several small fixes into one commit on the target branch, or when you need to edit the files before committing.

After reviewing the result, create the commit yourself:

git status
git commit -m "Backport auth null-check fix"

This gives you more control over the final commit message and lets you group related backports together.

Recording Where the Commit Came From #

For maintenance branches and backports, it is often helpful to keep a reference to the original commit. Use -x to append the source commit hash to the new commit message:

git cherry-pick -x a3f1c92

Git adds a line like this to the new commit message:

(cherry picked from commit a3f1c92...)

That extra line makes future audits easier, especially when you need to prove that a fix on a release branch came from a reviewed change on another branch.

Cherry-Picking a Merge Commit #

Cherry-picking a regular commit is straightforward, but merge commits need one extra option. Git must know which parent to treat as the main line:

git cherry-pick -m 1 MERGE_COMMIT_HASH

• -m 1 - Use the first parent as the base, which is usually the branch that received the merge.
• -m 2 - Use the second parent instead.

If you are not sure which parent is which, inspect the history first:

git log --oneline --graph

Cherry-picking merge commits is more advanced and easier to get wrong. If the goal is to bring over an entire merged feature, a normal merge is often clearer than cherry-picking the merge commit itself.

Resolving Conflicts #

If the target branch has changed in the same area of code, Git may stop and ask you to resolve a conflict:

error: could not apply a3f1c92... Fix null pointer in auth handler
hint: After resolving the conflicts, mark them with
hint: "git add/rm <pathspec>", then run
hint: "git cherry-pick --continue".

Open the conflicted file and look for the conflict markers:

<<<<<<< HEAD
return session.getUser();
=======
if (session == null) return null;
return session.getUser();
>>>>>>> a3f1c92 (Fix null pointer in auth handler)

Edit the file to keep the final version you want, then stage it and continue:

git add src/auth.js
git cherry-pick --continue

If you decide the commit is not worth applying after all, abort the operation:

git cherry-pick --abort

git cherry-pick --abort puts the branch back where it was before the cherry-pick started.

A Safe Backport Workflow #

When you cherry-pick onto a release or maintenance branch, slow down and make the source obvious. A simple workflow looks like this:

git switch release/1.4
git pull --ff-only
git cherry-pick -x a3f1c92
git status

The important part is the sequence. Start from the branch that needs the fix, make sure it is up to date, cherry-pick with -x, then review and test the branch before pushing it. This avoids the common mistake of copying a fix into an outdated branch and shipping an untested backport.

If the picked commit depends on earlier refactors or new APIs that are not present on the target branch, stop there. In that case, either copy the prerequisite commits too or recreate the fix manually.

When to Use git cherry-pick #

git cherry-pick is a good fit when you need a precise change without the rest of the branch:

• Backporting a bug fix from main to a release branch
• Recovering one useful commit from an abandoned feature branch
• Moving a small fix that was committed on the wrong branch
• Pulling a reviewed change into a hotfix branch without merging unrelated work

Avoid it when the target branch needs the full context of the source branch. If the commit depends on earlier commits, shared refactors, or schema changes, a merge or rebase is usually the cleaner option.

Troubleshooting #

error: could not apply ... during cherry-pick
The target branch has conflicting changes. Resolve the files Git marks as conflicted, stage them with git add, then run git cherry-pick --continue.

Cherry-pick created duplicate-looking history
That is normal. Cherry-pick copies the effect of a commit, not the original object. The new commit has a different hash because it has a different parent.

The picked commit does not build on the target branch
The commit likely depends on earlier work that is missing from the target branch. Inspect the source branch history with git log and either cherry-pick the prerequisites too or reimplement the change manually.

You picked the wrong commit
If the cherry-pick already completed, use git revert on the new commit. If the operation is still in progress, use git cherry-pick --abort.

Quick Reference #

For a printable quick reference, see the Git cheatsheet .

FAQ #

What is the difference between git cherry-pick and git merge?
git cherry-pick copies the effect of selected commits onto your current branch. git merge joins two branch histories and brings over all commits that are missing from the target branch.

Does cherry-pick change the original commit?
No. The source commit stays exactly where it is. Git creates a new commit on your current branch with the same file changes.

Should I use -x every time?
Not always, but it is a good habit for backports and maintenance branches. It gives you a clear link back to the original commit.

Can I cherry-pick commits from another remote branch?
Yes. Fetch the remote branch first, then cherry-pick the commit hash you want. You can inspect the incoming history with git log or review the file changes with git diff before applying anything.

Conclusion #

git cherry-pick is the tool to reach for when one commit matters more than the branch it came from. Use it for targeted fixes, keep -x in mind for backports, and fall back to merge or rebase when the change depends on broader branch context.

If your server is open to the public network, it needs a firewall. On Ubuntu and Debian, the easiest way to set one up is with ufw. This tool sits on top of iptables (or nftables on newer systems) and replaces complex rules with simple, easy-to-read commands.

This guide walks through the ufw command, from enabling the firewall and setting default policies to writing rules for ports, services, and specific addresses.

ufw Syntax #

The general form of the command is:

sudo ufw [OPTIONS] COMMAND [ARGS]

• OPTIONS - Flags such as --dry-run to preview what a rule would do.
• COMMAND - The action, for example enable, allow, deny, delete, or status.
• ARGS - The rule body, such as a port number, a service name, or a full rule specification.

ufw changes firewall rules, so almost every invocation needs sudo.

Checking the Firewall Status #

Before you touch the rules, check whether the firewall is running and what is already in place:

sudo ufw status

If ufw is inactive, you will see:

Status: inactive

This confirms that ufw is installed but not currently enforcing any firewall rules.

Once active, the same command lists the rules:

Status: active
To Action From
-- ------ ----
22/tcp ALLOW Anywhere
80/tcp ALLOW Anywhere
22/tcp (v6) ALLOW Anywhere (v6)
80/tcp (v6) ALLOW Anywhere (v6)

For a numbered view that is easier to reference when deleting rules, use:

sudo ufw status numbered

And for a more detailed output that shows default policies and logging level:

sudo ufw status verbose

Enabling and Disabling the Firewall #

The first time you enable ufw, make sure you have already allowed SSH. Enabling the firewall over an SSH session without an allow ssh rule will lock you out of the server.

Allow SSH first:

sudo ufw allow ssh

Then turn the firewall on:

sudo ufw enable

Firewall is active and enabled on system startup

At this point, ufw starts enforcing the rules immediately and will come back automatically after a reboot.

To stop the firewall and clear it from the startup sequence:

sudo ufw disable

A disabled ufw keeps the rules you defined. When you re-enable it, the same rules come back.

Default Policies #

Default policies decide what happens to traffic that does not match any rule. The usual hardening is to deny incoming traffic and allow outgoing traffic:

sudo ufw default deny incoming
sudo ufw default allow outgoing

After running these two commands, you only need to open the specific inbound ports your server should expose. Outbound traffic still flows freely, which is what most servers need.

You can also set the default for forwarded traffic, which matters if the host acts as a router or runs containers:

sudo ufw default deny routed

Allowing Connections #

The allow command is the one you will use most often. It accepts a service name, a port, a protocol, or a full rule.

Allow a Service by Name #

ufw reads /etc/services and understands common service names:

sudo ufw allow ssh
sudo ufw allow http
sudo ufw allow https

Each command opens the matching port (22, 80, and 443) for both TCP and UDP where applicable.

Allow a Specific Port #

To open a port directly, pass the port number:

sudo ufw allow 8080

By default, this opens the port for both TCP and UDP. To limit it to one protocol, add /tcp or /udp:

sudo ufw allow 8080/tcp
sudo ufw allow 53/udp

Allow a Port Range #

Port ranges require an explicit protocol:

sudo ufw allow 6000:6007/tcp
sudo ufw allow 6000:6007/udp

The colon separates the start and the end of the range, both inclusive.

Allow Traffic From a Specific Address #

To accept connections from a single IP address, use from:

sudo ufw allow from 203.0.113.25

To restrict that to a single service, add to any port:

sudo ufw allow from 203.0.113.25 to any port 22

Allow Traffic From a Subnet #

CIDR notation works the same way for whole networks:

sudo ufw allow from 192.168.1.0/24 to any port 3306

This is a common pattern for databases: the port stays closed to the internet and is only reachable from your internal network.

Allow Traffic on a Specific Interface #

To tie a rule to a network interface, add on INTERFACE:

sudo ufw allow in on eth1 to any port 3306

The in keyword applies the rule to inbound traffic on eth1. Use out for outbound traffic.

Denying Connections #

The deny command is the mirror of allow and takes the same arguments:

sudo ufw deny 23
sudo ufw deny from 198.51.100.77

When the default incoming policy is already deny, you usually do not need to write explicit deny rules for closed ports. Explicit denies are useful when you want to block a specific address while keeping a port open to everyone else.

To log the denied packets instead of silently dropping them, use reject:

sudo ufw reject 23

A reject sends an ICMP message back to the sender, while a deny drops the packet with no response.

Rate Limiting SSH #

ufw can throttle repeated connections from the same IP, which is handy for SSH brute-force protection:

sudo ufw limit ssh

The limit rule denies a connection if the source address attempts six or more connections in 30 seconds. This is a quick way to slow down password-guessing bots without installing a full intrusion-prevention tool.

Deleting Rules #

There are two common ways to remove a rule. The first is to repeat the rule with delete in front:

sudo ufw delete allow 8080/tcp

The second is to delete by rule number:

sudo ufw status numbered

 To Action From
-- ------ ----
[ 1] 22/tcp ALLOW IN Anywhere
[ 2] 80/tcp ALLOW IN Anywhere
[ 3] 8080/tcp ALLOW IN Anywhere

sudo ufw delete 3

ufw asks for confirmation before removing the rule. Keep in mind that after a deletion, the numbering shifts for the remaining rules, so always check the numbered status again before deleting another rule.

For a deeper walkthrough, see how to list and delete UFW firewall rules .

Application Profiles #

Services that come with their own ufw profile can be referenced by name. List them with:

sudo ufw app list

Available applications:
Nginx Full
Nginx HTTP
Nginx HTTPS
OpenSSH

To open the ports that a profile covers, pass its name to allow:

sudo ufw allow 'Nginx Full'

Quote profile names that contain spaces. To see what ports a profile includes, use:

sudo ufw app info 'Nginx Full'

Dry Run #

Before you commit to a change, you can preview the iptables rules ufw would add with --dry-run:

sudo ufw --dry-run allow 8080/tcp

No rule is created. The output shows the exact lines ufw would write, which is useful when you are writing rules over SSH and want to double-check them first.

Logging #

ufw can log packets that match rules, which helps when troubleshooting. The log level can be adjusted:

sudo ufw logging on
sudo ufw logging medium

Valid levels are off, low, medium, high, and full. ufw logs through the kernel log facility, so the exact destination depends on your system logging setup. On many Ubuntu systems with rsyslog, you will see entries in /var/log/ufw.log, and you can often inspect them with journalctl as well.

Reset the Firewall #

To clear every rule and set ufw back to its fresh state, run:

sudo ufw reset

IPv6 Support #

On most modern systems, ufw can manage IPv6 rules as well as IPv4 rules. Check the setting in /etc/default/ufw:

IPV6=yes

When IPV6=yes, generic rules such as sudo ufw allow 22/tcp are created for both IPv4 and IPv6. Rules that include an explicit address stay specific to that address family. In the status output, the IPv6 rules appear with (v6) next to them.

Quick Reference #

For a printable quick reference, see the ufw cheatsheet .

Troubleshooting #

ufw: command not found
Install the ufw package with sudo apt install ufw on Ubuntu or Debian. On Fedora, RHEL, and derivatives, firewalld is the default and ufw is rarely used.

Locked out after enabling the firewall over SSH
The default deny policy blocked your SSH session. You will need console access to the server. Once in, run sudo ufw allow ssh and sudo ufw reload to restore access. The usual safeguard is to allow SSH before the first enable.

Rule added but traffic still blocked
Confirm the rule is in the right direction (inbound vs outbound) and on the right interface. Check with sudo ufw status verbose. If Docker is running, it writes its own iptables rules that can bypass ufw.

Changes do not take effect
After manual edits to /etc/ufw/ files, reload the firewall with sudo ufw reload. Commands issued through ufw apply immediately and do not need a reload.

FAQ #

Is ufw the same as iptables?
No. ufw is a front end that generates iptables (or nftables) rules for you. The kernel still enforces the rules through its packet filter, but you do not need to edit the raw tables yourself.

Does ufw start automatically after reboot?
Yes, once you run sudo ufw enable, the service is registered with systemd and starts on boot. You can confirm with systemctl status ufw.

How do I allow a port for a single IP address?
Use the from and to any port form: sudo ufw allow from 203.0.113.25 to any port 22. This keeps the port closed to the rest of the internet and only opens it for that one address.

What is the difference between deny and reject?
deny drops the packet without any reply. reject sends an ICMP message back to the sender telling them the connection was refused. Reject is slightly friendlier to well-behaved clients but makes the server more visible to scans.

How do I undo everything and start over?
Run sudo ufw reset. It disables the firewall and removes every rule. Remember to re-add the SSH rule before re-enabling, especially on a remote server.

Conclusion #

ufw keeps firewall management readable: allow what you need, deny what you do not, and lean on the default policies to cover the rest. If you want step-by-step instructions for setting it up on a new server, see how to set up a firewall with UFW on Ubuntu 24.04 .