Install PHP 8.1 on Debian 13 / Debian 12

PHP 8.1 is not shipped in the default Debian 13 or Debian 12 repositories. Debian 13 defaults to PHP 8.4, and Debian 12 defaults to PHP 8.2. If your application specifically requires PHP 8.1 (WordPress plugins, Laravel 9.x, legacy codebases that haven’t been tested on newer versions), you need the Sury third-party repository to install it.

Original content from computingforgeeks.com - post 100

This guide covers installing PHP 8.1 from the Sury repository on both Debian 13 and Debian 12, along with common extensions, PHP-FPM configuration, and production tuning. Note that PHP 8.1 reached end of active support in November 2024 and receives security-only patches until December 2025. If your application supports it, PHP 8.4 is the recommended version for new deployments.

Tested March 2026 on Debian 13 (Trixie) with PHP 8.1.34 via Sury repository

Prerequisites

• Debian 13 (Trixie) or Debian 12 (Bookworm) with sudo access
• An active internet connection for package downloads

Update Your System

Start with a fully updated system:

sudo apt update && sudo apt -y upgrade

Reboot if the kernel was updated:

[ -e /var/run/reboot-required ] && sudo reboot

Add the Sury PHP Repository

The Sury PHP repository is maintained by Ondřej Surý, who is also the official Debian PHP package maintainer. It provides multiple PHP versions (8.1 through 8.4) for Debian releases that don’t ship them natively.

Install the prerequisite packages:

sudo apt install -y lsb-release ca-certificates curl

Download and install the Sury archive keyring, which sets up both the GPG signing key and the repository source:

curl -sSLo /tmp/debsuryorg-archive-keyring.deb https://packages.sury.org/debsuryorg-archive-keyring.deb
sudo dpkg -i /tmp/debsuryorg-archive-keyring.deb

Add the PHP repository to your sources list:

echo "deb [signed-by=/usr/share/keyrings/deb.sury.org-php.gpg] https://packages.sury.org/php/ $(lsb_release -sc) main" | sudo tee /etc/apt/sources.list.d/sury-php.list

Update the package index to pull in the new repository metadata:

sudo apt update

You should see the Sury repository listed in the update output, confirming it was added correctly.

Install PHP 8.1

With the Sury repository in place, install PHP 8.1:

sudo apt install -y php8.1

This installs the core PHP 8.1 packages including php8.1-cli, php8.1-common, php8.1-opcache, and libapache2-mod-php8.1 (Apache integration module).

Confirm the installed version:

php8.1 -v

The output confirms PHP 8.1.34 with OPcache enabled:

PHP 8.1.34 (cli) (built: Feb 13 2026 15:50:38) (NTS)
Copyright (c) The PHP Group
Zend Engine v4.1.34, Copyright (c) Zend Technologies
    with Zend OPcache v8.1.34, Copyright (c), by Zend Technologies

Install PHP 8.1 Extensions

Most web applications need extensions beyond the base install. Install the commonly required ones for frameworks like WordPress, Laravel, and Drupal:

sudo apt install -y php8.1-{fpm,xml,mysql,zip,intl,ldap,gd,cli,bz2,curl,mbstring,pgsql,opcache,soap,cgi}

The syntax php8.1-{fpm,xml,mysql,...} is a bash brace expansion that installs multiple packages in one command. Each extension maps to a separate Debian package.

Here is what each extension provides:

Extension	Purpose
fpm	FastCGI Process Manager for Nginx or Apache proxy_fcgi
mysql	MySQL/MariaDB driver (mysqli + PDO)
pgsql	PostgreSQL driver
gd	Image processing (JPEG, PNG, WebP, AVIF)
mbstring	Multi-byte string handling for UTF-8
xml	XML parsing (DOM, SimpleXML, XMLReader)
curl	HTTP client for API calls
zip	ZIP archive handling
intl	Internationalization (ICU library)
opcache	Bytecode caching for performance
ldap	LDAP/Active Directory authentication
soap	SOAP web services

Verify all extensions loaded correctly:

php8.1 --modules

The output lists every loaded module:

[PHP Modules]
bz2
calendar
Core
ctype
curl
date
dom
exif
FFI
fileinfo
filter
ftp
gd
gettext
hash
iconv
intl
json
ldap
libxml
mbstring
mysqli
mysqlnd
openssl
pcntl
pcre
PDO
pdo_mysql
pdo_pgsql
pgsql
Phar
posix
readline
Reflection
session
shmop
SimpleXML
soap
sockets
sodium
SPL
standard
sysvmsg
sysvsem
sysvshm
tokenizer
xml
xmlreader
xmlwriter
xsl
Zend OPcache
zip
zlib

[Zend Modules]
Zend OPcache

Configure PHP-FPM

PHP-FPM runs PHP as a separate service rather than embedding it inside Apache. This is the standard approach when using Nginx, and also works with Apache via proxy_fcgi.

Enable and start the PHP 8.1 FPM service:

sudo systemctl enable --now php8.1-fpm

Verify it is running:

sudo systemctl status php8.1-fpm

The output shows the FPM master process with idle worker pools:

● php8.1-fpm.service - The PHP 8.1 FastCGI Process Manager
     Loaded: loaded (/usr/lib/systemd/system/php8.1-fpm.service; enabled; preset: enabled)
     Active: active (running) since Thu 2026-03-26 09:22:26 UTC; 898ms ago
       Docs: man:php-fpm8.1(8)
   Main PID: 17500 (php-fpm8.1)
     Status: "Ready to handle connections"
      Tasks: 3 (limit: 4655)
     Memory: 13.5M (peak: 15.3M)
     CGroup: /system.slice/php8.1-fpm.service
             ├─17500 "php-fpm: master process (/etc/php/8.1/fpm/php-fpm.conf)"

PHP-FPM listens on a Unix socket at /run/php/php8.1-fpm.sock by default. Point your Nginx fastcgi_pass directive or Apache proxy_fcgi configuration to this socket. The pool configuration is at /etc/php/8.1/fpm/pool.d/www.conf.

Tune php.ini for Production

PHP ships with conservative defaults. For web applications, you will typically need to adjust memory limits and upload sizes. Edit the FPM php.ini:

sudo vi /etc/php/8.1/fpm/php.ini

Common settings to adjust:

memory_limit = 256M
upload_max_filesize = 64M
post_max_size = 64M
max_execution_time = 300
max_input_vars = 3000
date.timezone = UTC

Restart PHP-FPM to apply changes:

sudo systemctl restart php8.1-fpm

The CLI and FPM use separate php.ini files. Changes to /etc/php/8.1/fpm/php.ini only affect web requests. CLI scripts read from /etc/php/8.1/cli/php.ini.

PHP 8.1 Key Features

PHP 8.1, released November 2021, introduced several major language features:

• Enums – First-class enumerated types, replacing the constant-based workarounds
• Fibers – Lightweight concurrency primitives for async programming
• Readonly properties – Class properties that can only be written once (in the constructor)
• Intersection types – Combine multiple type constraints with &
• Never return type – Declare that a function never returns (throws exception or calls exit())
• array_is_list() – Built-in function to check if an array is a list (sequential integer keys starting from 0)

Going Further

• Set up a complete LAMP stack on Debian with Apache, MariaDB, and PHP
• Deploy WordPress with Nginx and PHP-FPM for better performance than mod_php
• Install MariaDB on Debian for the database backend
• Plan your migration to PHP 8.4 on Debian before 8.1 security support expires
• For Ubuntu servers, see Install PHP 8.4 on Ubuntu 24.04