Troubleshooting

This is a list of common pitfalls on using Composer, and how to avoid them.

General

When facing any kind of problems using Composer, be sure to work with the latest version. See self-update for details.
Ensure you're installing vendors straight from your composer.json via rm -rf vendor && composer update -v when troubleshooting, excluding any possible interferences with existing vendor installations or composer.lock entries.

Double-check you don't have typos in your composer.json or repository branches and tag names.
Be sure to set the right minimum-stability. To get started or be sure this is no issue, set minimum-stability to "dev".
Packages not coming from Packagist should always be defined in the root package (the package depending on all vendors).
Use the same vendor and package name throughout all branches and tags of your repository, especially when maintaining a third party fork and using replace.

If composer shows memory errors on some commands:

PHP Fatal error:  Allowed memory size of XXXXXX bytes exhausted <...>

The memory_limit ini value should be increased.

Note: Composer internally increases the memory_limit to 512M. It is a good idea to create an issue for composer if you get memory errors.

Get current value:

php -r "echo ini_get('memory_limit').PHP_EOL;"

Increase limit with php.ini for a CLI SAPI (ex. /etc/php5/cli/php.ini for Debian-like systems):

; Use -1 for unlimited or define explicit value like 512M
memory_limit = -1

Or with command line arguments:

php -d memory_limit=-1 composer.phar <...>