When configuring legacy PHP environments on Ubuntu Server and attempting to activate the mcrypt cryptographic module, administrators may encounter symlink collision warnings.

The Error Condition

After installing the extension packages:

sudo apt-get install mcrypt php5-mcrypt

Attempting to register the module via php5enmod produces the following error:

root@ubuntu:~# php5enmod mcrypt
WARNING: Not enabling the mcrypt module for apache2 SAPI since module symlink
WARNING: already exists in /etc/php5/apache2/conf.d with different content.
WARNING: Not enabling the mcrypt module for cli SAPI since module symlink
WARNING: already exists in /etc/php5/cli/conf.d with different content.

This error occurs when old or stale configuration symlinks pointing to prior configuration targets exist in the SAPI configuration directories (/etc/php5/apache2/conf.d/ and /etc/php5/cli/conf.d/), preventing the package manager from linking the canonical /etc/php5/mods-available/mcrypt.ini.

Resolution

  1. Remove the stale symlinks from the active SAPI configuration directories:
sudo unlink /etc/php5/apache2/conf.d/20-mcrypt.ini
sudo unlink /etc/php5/cli/conf.d/20-mcrypt.ini
  1. Re-enable the module cleanly across all SAPIs:
sudo php5enmod mcrypt
  1. Restart Apache to apply the module to the web runtime:
sudo service apache2 restart

Verify that mcrypt is loaded by querying the CLI runtime:

php -m | grep -i mcrypt