I followed the documentation on https://getcomposer.org/doc/00-intro.md#globally to install composer globally on arch linux. When I do composer self-update, I g
this might be the case if you have downloaded composer.phar directly ,
but not by running php composer-setup.php
make composer.phar executable with following command before moving it to /usr/local/bin/composer or after moving
sudo chmod 755 composer.phar
composer-setup.php will make this change for us by default