I ran the Symfony PHP Framework configuration check script in Fedora 15 and got the following error:
[[WARNING]] The posix_isatty() is available: FAILED
*** Install and enable the php_posix extension (used to colorized the CLI output) ***
To enable this extension, you should install php-process from Add/Remove Software or using yum.
su -c 'yum install php-process'
Run the check_configuration.php again and you should not see this warning again.
UPDATE: If you also see the following:
[[WARNING]] A PHP accelerator is installed: FAILED
*** Install a PHP accelerator like APC (highly recommended) ***
and want to have a PHP accelerator, you can install php-pecl-apc:
su -c 'yum install php-pecl-apc'