Composer fails with 'Allowed memory size exhausted'. How do I fix it?

Composer's dependency solver can use a lot of RAM, especially during update with many packages. Options, from simplest to most robust:

1. Lift the PHP limit for Composer only

COMPOSER_MEMORY_LIMIT=-1 composer update
# or
php -d memory_limit=-1 /usr/local/bin/composer update

If you see "Killed" with no PHP message, the Linux OOM killer ended the process because the machine itself is out of RAM; a PHP setting cannot fix that.

2. Add swap on small servers

sudo fallocate -l 2G /swapfile && sudo chmod 600 /swapfile
sudo mkswap /swapfile && sudo swapon /swapfile

Add it to /etc/fstab to keep it after reboot.

3. Do not run update on the server

Run composer update locally or in CI, commit composer.lock, and on the server run only:

composer install --no-dev --optimize-autoloader

install reads the lock file and needs little memory because it does no dependency solving.

4. Reduce what the solver has to consider

• Update a single package: composer update vendor/package --with-dependencies.
• Remove unused packages and * constraints.
• Use Composer 2 (composer self-update --2), which is much faster and lighter than version 1.
• Check the PHP binary used: composer diagnose, composer --version.

5. Prefer dist over source

Cloning git repositories uses memory and time. composer install --prefer-dist downloads zip archives. Install the zip and unzip tools so it does not fall back to git.

Pitfalls

• Memory problems in composer require for Laravel on shared hosting: do it on your machine and upload vendor/.
• Dev tools like PHPStan consume memory too but with a different setting (--memory-limit=1G).
• If Composer says the PHP version is too old for a package, check php -v for the CLI; it can differ from the web PHP version.