PHP

Add php repository sources

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

sudo dpkg -i /tmp/debsuryorg-archive-keyring.deb

sudo tee /etc/apt/sources.list.d/php.sources <<EOF
Types: deb
URIs: https://packages.sury.org/php/
Suites: $(lsb_release -sc)
Components: main
Signed-By: /usr/share/keyrings/debsuryorg-archive-keyring.gpg
EOF

sudo apt update

Install php and its Apache module

sudo apt install -y php8.5-cli libapache2-mod-php8.5

Install additional modules required by Pixelfed:

sudo apt install -y php8.5-{bcmath,ctype,curl,exif,gd,iconv,imagick,intl,mbstring,mysqli,redis,tokenizer,xml,zip}

At the time of writing this tutorial (april 2026), php latest version is 8.5; check if you need to migrate.
Your installed version is given running php -v:

PHP 8.5.5 (cli) (built: Apr 11 2026 06:53:33) (NTS)
Copyright (c) The PHP Group
Built by Debian
Zend Engine v4.5.5, Copyright (c) Zend Technologies
    with Zend OPcache v8.5.5, Copyright (c), by Zend Technologies

PHP-FPM

sudo apt install -y php8.5-fpm

Configure a pool

sudo cp /etc/php/8.5/fpm/pool.d/www.conf /etc/php/8.5/fpm/pool.d/pixelfed.conf

sudo nano /etc/php/8.5/fpm/pool.d/pixelfed.conf

Modify the uncommented lines

; pool name ('www' here)
[pixelfed]

; Unix user/group of the child processes
user = pixelfed
group = pixelfed

; The address on which to accept FastCGI requests.
listen = /run/php/pixelfed.sock

; Set permissions for unix socket, if one is used.
listen.owner = www-data
listen.group = www-data
listen.mode = 0660

; The number of child processes to be created when pm is set to 'static' and the
; maximum number of child processes when pm is set to 'dynamic' or 'ondemand'.
pm.max_children = 4

Edit php.ini file

sudo nano /etc/php/8.5/apache2/php.ini

Find and modify the values of those parameters

; Maximum execution time of each script, in seconds
max_execution_time = 120

; Maximum amount of time each script may spend parsing request data
max_input_time = 120

; Maximum amount of memory a script may consume
memory_limit = 1024M

; Maximum size of POST data that PHP will accept.
post_max_size = 256M

; Maximum allowed size for uploaded files.
upload_max_filesize = 256M

; Maximum number of files that can be uploaded via a single request
max_file_uploads = 500

Instagram imports

Instagram imports are affected by these settings. If you enable imports, you will want to raise post_max_size to the maximum size you expect an Instagram archive* to be, upload_max_filesize to the maximum size you expect individual Instagram photos to be, and max_file_uploads to the maximum number of photos (not posts) you'd expect an Instagram archive to contain.

Source: Pixelfed Docs

* the archive is the exported personal data file sent to you by Meta, usually as instagram-user_name-YYYY-MM-DD-hash.zip

Modify those same lines in PHP-FPM ini file

sudo nano /etc/php/8.5/fpm/php.ini

Restart PHP-FPM service

sudo systemctl restart php8.5-fpm.service

Composer

cd ~/

curl -sS https://getcomposer.org/installer -o /tmp/composer-setup.php

HASH=`curl -sS https://composer.github.io/installer.sig`

php -r "if (hash_file('SHA384', '/tmp/composer-setup.php') === '$HASH') { echo 'Installer verified'; } else { echo 'Installer corrupt'; unlink('composer-setup.php'); } echo PHP_EOL;"

If Installer verified is returned, install Composer:

sudo php /tmp/composer-setup.php --install-dir=/usr/local/bin --filename=composer